# Traynor Guitar Mate Winter Project



## ook ook (Jun 3, 2021)

Hi all, I bought a '67-'68 YGM-1 several months ago now and I've had some time to get to know the amp. I've also become much more knowledgeable in terms of amp circuitry since then and I have the confidence to go in there myself and try some things out to maybe get the amp more suited to my preferences. December's coming up and I should have some free time then. I do apologize for the essay I'm about to write, but I have a lot to say.

The amp sounds really great clean. Really beautiful, pristine, bright, but not piercing cleans. Great clean sound, get the reverb going and it's really wonderful, but, and there's always a "but," I don't primarily play clean. The amp has a decent overdriven sound already, but it could be much better to my ears. This is a different amp than the more common YGM-3, but it has a lot of common features. This YGM-1 does not follow the official schematic from '66 or w/e, it has quite a few changes leaning towards the YGM-3. Below is the schematic I drew up for the amp and as you can see, it has the YGM-3 phase inverter and feedback loop which means it has the dreaded presence cap in place. It also has the large first coupling cap (0.1uF) in place which people like to swap out. 










I currently have the negative feedback on a switch, and it does make me smile, but with it switched off, the amp gets a little bit flubby. 

Here's what I hope to accomplish:
1. I want to get a little bit more drive out of the amp
2. Keep the low end in check when the amp is cranked up
3. Keep the high end in check when the amp is cranked up
4. Maybe bring out a more British voice in the amp? I am partial to British amps and speakers

I have done a lot of reading on how people like to mod their YGMs and I'm familiar with the common mod of clipping the presence cap and swapping the 1st coupling cap. I imagine this will be my first order of business. I also stumbled upon a thread about modding a YGM-2 in which there were several suggestions that would apply to my amp and that sound rather appealing.

The amp has the original RSC-made Jensen C12R which sounds great until I put a treble booster in front of the amp and then it sounds horrible. I'm looking into G12H-30 55hz styled speakers, I think that would really fit here, but I'm not set on a speaker swap just yet.

Here are the things that I'm considering playing around with:
1. 1st coupling cap down to .022 or .01
2. Remove presence cap
3. Swap 1st triode plate resistor to 220k for some extra gain 
4. Tone stack adjustments (slope resistor, bass cap)
5. Clip bright cap
6. Speaker swap
7. Power supply resistors (upping that 12ohm after the first filter cap, lowering that 56k after the 2nd filter cap)
8. Screen resistors for the EL84s
9. Adjust filtering. I've read that Mr. Parkhead likes to raise the first filter cap above the recommended value and lower the rest of them because, and I quote,
"this lower pre amp filtering will make most modern amps sound vintage
and make most vintage amps sound RIGHT"
Sounds like a pretty good deal in my books.

Anyways, I'm looking for opinions from people who are more experienced than I am that could maybe guide me in the right direction. If something from the above list a really stupid idea (or actually a really good idea), please let me know.

Thanks everyone


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## player99 (Sep 5, 2019)

All I can say is good ook!


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## Paul Running (Apr 12, 2020)

That's quite the work order, you're doing well.
Depending on the condition of your speaker, you may wish to focus on that, first; a speaker swap can make a huge difference.
Number one will reduce the bass response, a good choice for lead tones.
Number two is a quick and easy experiment.
Number three would be a wise choice because the tube is already biased symmetrically for a 220KΩ plate-resistor.
Number four, tone stacks can become complicated. You can experiment with Duncan's program...his tone stack calculator TSC
Number five, you may wish to try different values too...I would go lower into the sub-1000pfd region, like 330pfd, again a personal choice.
Number six would be my first change.
Number seven, I would replace the 12Ω resistor with an inductor (10H, 50mA). Add an additional supply decoupling section to the filter network, to evenly distribute power supply decoupling.
Number eight could save a few EL84s in the life of the amp...I would go with 470 Ω, 3 watters.
Number nine is a controversial subject. I personally prefer tube rectifiers so, my opinion would be biased. Increasing capacitance is a last resort and even then, I do not recommend.


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## Jerome (Dec 4, 2015)

You sure the rev driver tube grid resistor is 56 K , not 560 K . Putting a 25u cap across the second triode cathode resistor will up the gain quita bit .


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## loudtubeamps (Feb 2, 2012)

You're on the right track with your to do list.
Put a pot in place of the 100 slope resistor, play and sweep and find your sweet spot.
Try raising the 470's in the phase inverter to 1 meg and lower the value of the .02 cap to .005.
More headroom achieved by a fixed bias circuit for the output section.

Nice work on the schematic...BTW


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## ook ook (Jun 3, 2021)

Paul Running said:


> Number three would be a wise choice because the tube is *already biased symmetrically for a 220KΩ plate-resistor.*


I appreciate the suggestions, I'll probably try a couple of bright cap values before just clipping it out entirely and I agree that a speaker swap would probably be the most substantial change. I'm probably gonna stay away from the inductor route and stick with a resistor there, but could you explain how you know that the tube is biased for a 220k plate resistor? Feel free to get theoretical if that's where the explanation goes



Jerome said:


> You sure the rev driver tube grid resistor is 56 K , not 560 K . Putting a 25u cap across the second triode cathode resistor will up the gain quita bit .


Yep, it is definitely a 56k. The standard YGM-1 schematic calls for a 1M and later YGM-3s call for a 220k, but I found this schematic of a '69 YGM-3 that calls for the 56k we see here. I am considering a bypass cap on that 2nd triode, but I don't want to over do it with too much gain and introduce instabilities. I imagine it would be fine as it is present in the YGM-3 but I plan on taking it slow




loudtubeamps said:


> You're on the right track with your to do list.
> Put a pot in place of the 100 slope resistor, play and sweep and find your sweet spot.
> Try raising the 470's in the phase inverter to 1 meg and lower the value of the .02 cap to .005.
> More headroom achieved by a fixed bias circuit for the output section.
> ...


Thanks! 
I'm gonna keep it cathode biased, at least for now, but I was initially considering raising those 470ks. Might still do that but it's not on my #1 list of priorities


Also, a couple questions. 
The amp has several caps labelled ".01 P 1kV" which are found in place of where the original schematic calls for both 0.022uF and 0.01uF caps. Can I just assume these are .01uF? It would be really strange to me if they put .01pF caps there, so that's what I'm going with right now. 
Another thing is that voltages seem a little bit high. I've only taken two voltage measurements at this point, but I'll definitely be doing a lot more of that before I start changing anything. At the first filter cap I was reading 423-424V and for the tube filaments I was getting 6.72-6.74V. YGM schematics I've looked at call for 400V B+ and obviously 6.73 is a decent bit larger than 6.3. I'm getting ~125V from the wall which is higher than what the amp would have originally run at. Are these voltages anything to even worry about or is it mostly a non-issue? I did take these measurements with the tubes pulled so maybe that's why they seem high?


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## Paul Running (Apr 12, 2020)

ook ook said:


> I appreciate the suggestions, I'll probably try a couple of bright cap values before just clipping it out entirely and I agree that a speaker swap would probably be the most substantial change. I'm probably gonna stay away from the inductor route and stick with a resistor there, but could you explain how you know that the tube is biased for a 220k plate resistor? Feel free to get theoretical if that's where the explanation goes


There's 2 options for this: a chart or you can determine the values, using a load-line. I now just use the chart however, it doesn't hurt to learn or re-hash the theory. Here's the chart that I use and attached is the theory:


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## jb welder (Sep 14, 2010)

ook ook said:


> Yep, it is definitely a 56k. The standard YGM-1 schematic calls for a 1M and later YGM-3s call for a 220k, but I found this schematic of a '69 YGM-3 that calls for the 56k we see here.


That schematic is a 'fake'. (edit: no it isn't. My error, please disregard the rest of this post and move on to post #9) And I say that because the person who re-drew it labelled it as "original schmatic redrawn" when they should have said 'original schematic redrawn to show mods'.
It's not an official Traynor document.
I'm not suggesting anything nefarious, just the person wasn't clear about it with their labelling, and they should have also identified themself somehow.
Even the re-issues have the 220K there.


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## ook ook (Jun 3, 2021)

jb welder said:


> That schematic is a 'fake'. And I say that because the person who re-drew it labelled it as "original schmatic redrawn" when they should have said 'original schematic redrawn to show mods'.
> It's not an official Traynor document.
> I'm not suggesting anything nefarious, just the person wasn't clear about it with their labelling, and they should have also identified themself somehow.
> Even the re-issues have the 220K there.
> ...


Admittedly, I didn't look very closely at it, but I saw a schematic earlier that confirms the same thing. The 56k in there looks stock and, looking at the schematic below, I have no reason to believe that it isn't.

EDIT: Regarding cap values, looking at official schematics, the caps in question are in place of .01uF and .022uF caps. Issue is that it's the same one used in both positions.


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## jb welder (Sep 14, 2010)

ook ook said:


> Admittedly, I didn't look very closely at it, but I saw a schematic earlier that confirms the same thing. The 56k in there looks stock and, looking at the schematic below, I have no reason to believe that it isn't.


Big mistake on my part, sorry. Thanks very much for posting the original factory version of that schematic. I was unable to find an official copy of that particular re-vision anywhere else, so incorrectly assumed that 56K value was altered.
I will point out however that the cathode resistor for V5 on that original is shown as 68ohms.
That is bizarre. I think Traynor realized and changed to 220K and 470 pretty quick. As mentioned earlier that is what they used for the re-issue.


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## ook ook (Jun 3, 2021)

jb welder said:


> Big mistake on my part, sorry. Thanks very much for posting the original factory version of that schematic. I was unable to find an official copy of that particular re-vision anywhere else, so incorrectly assumed that 56K value was altered.
> I will point out however that the cathode resistor for V5 on that original is shown as 68ohms.
> That is bizarre. I think Traynor realized and changed to 220K and 470 pretty quick. As mentioned earlier that is what they used for the re-issue.


All good. I have to agree that the values are really strange. I guess there's a reason they changed em


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## loudtubeamps (Feb 2, 2012)

As @Jerome suggested...cathode bypass caps in certain situations can be an easy way to add gain.
I will often use values to enhance certain frequencies .02 - 1 and 2.2u are good for top end through mid boost while 10 - 22u for boosting all the above and into the low end.
I use 2.2u alot.
I always put a 10 k pot in series to ground with the cap and play and sweep for a sweet spot. I often end up with 1 to 2 k resistor in line with the cap for a nice boost while taming the very high frequencies that a cap direct to ground will amplify.
Easy to do and well worth the effort.
Fine tuning cathode caps in a circuit where there may be several ( each being subtle ) can have a dramatic effect overall.


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## Jerome (Dec 4, 2015)

Interesting . Your hand drawn schematic is not the same as the factory schematic , for what it's worth . The tone controls are in a different spot , the rev signal bypasses the EQ in your drawing .


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## dtsaudio (Apr 15, 2009)

The 56k grid resistor on the reverb driver tube will set the low frequency limit for the driver. It's a pretty high limit. Making it bigger will give more bottom end to the reverb. It might raise the overall level simply because it is do small it's loading down feed from the previous stage.
The 68 ohm cathode resistor sets the operating point of the tube. It's running pretty hot with that value. The bypass cap across it will have minimal effect simply because that resistor is so small. Raising it to what the later models have (470 ohm), will definitely need the bypass cap.
Are you sure that power supply diode arrangement is right? It looks like an attempt to make a center tap from two diodes. Never seen that done.


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## ook ook (Jun 3, 2021)

Jerome said:


> Interesting . Your hand drawn schematic is not the same as the factory schematic , for what it's worth . The tone controls are in a different spot , the rev signal bypasses the EQ in your drawing .


Yes, it differs from the factory schematics. I thought I was mistaken when I first drew it and compared with the factory, but it seems like that's how my amp is wired



dtsaudio said:


> Are you sure that power supply diode arrangement is right? It looks like an attempt to make a center tap from two diodes. Never seen that done.


That's exactly what it is. Somebody did that at some point before I got the amp. Definitely not stock. From the factory it had the standard YGM-1 power supply

EDIT: It's a conversion to a full wave bridge rectifier due to the absence of a center tab on the PT


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## dtsaudio (Apr 15, 2009)

You might want to consider putting in the proper transformer. All current from the supply runs through those diodes. If one fails, a lot of smoke will be the result.
I just bought one from Hammond, I believe it was about $90.00


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## ook ook (Jun 3, 2021)

Took some voltage measurements today. 

Before you ask, yes, there really seems to be a 25V discrepancy between the el84 plates. That's what the meter read. I'm not really sure if I trust it so I might be taking that measurement again later today or tomorrow. That's what it was after measuring and re-measuring. The output transformer does have a discrepancy in the resistance to either plate from the centre tap but I don't think it would cause that much of a difference?

Seems like I could raise the preamp voltage a smidge and I might want to look into reducing the screen voltage on the el84s. Actually, thinking about it now, if I'm going to replace that 100k plate resistor with a 220k, I might want to raise the preamp voltages by a decent amount. Seems like that 56k in the power supply is gonna have to go

Thoughts?


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## Paul Running (Apr 12, 2020)

ook ook said:


> the resistance to either plate from the centre tap but I don't think it would cause that much of a difference?


Unless the primary is inter-woven wound, the DC resistance will be different one side to the next, remember most audio TFMs for guitar are continuously wound...as the coils approach the end winding, the length per wind will be longer thus the higher resistance for the outer winding.


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## Paul Running (Apr 12, 2020)

ook ook said:


> reducing the screen voltage on the el84s


Unless you want reduced headroom, don't go to high in resistance here. The voltage to the screens will control the break-up headroom...by varying the voltage to the screens you will vary the point at which break-up will occur as shown in the curve below: (note the difference in grid voltage from a 210V screen to a 250V screen (same plate voltage) to the overload point, an area where accelerated compression begins.


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## ook ook (Jun 3, 2021)

Paul Running said:


> Unless the primary is inter-woven wound, the DC resistance will be different one side to the next, remember most audio TFMs for guitar are continuously wound...as the coils approach the end winding, the length per wind will be longer thus the higher resistance for the outer winding.


I fully expected the two windings to have a different resistance, but I didn't expect such a voltage difference to the two plates. One sees 372.5V and the other 397V? That part seems abnormal and maybe concerning to me. 



Paul Running said:


> Unless you want reduced headroom, don't go to high in resistance here. The voltage to the screens will control the break-up headroom...by varying the voltage to the screens you will vary the point at which break-up will occur as shown in the curve below: (note the difference in grid voltage from a 210V screen to a 250V screen (same plate voltage) to the overload point, an area where accelerated compression begins.
> View attachment 389094


I'm not super worried about headroom. Not to say I don't want any headroom, but I'm cool with sacrificing some headroom for tube life, although I don't plan on dropping the voltage by any crazy amount. 400V just seems a little high


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## Paul Running (Apr 12, 2020)

ook ook said:


> One sees 372.5V and the other 397V


Most likely, one tube is drawing more plate current than the other; check the plate current for each tube.


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## Paul Running (Apr 12, 2020)

ook ook said:


> 400V just seems a little high


Yeah, I would change out that 12Ω resistor before too long.


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## ook ook (Jun 3, 2021)

Paul Running said:


> Most likely, one tube is drawing more plate current than the other; check the plate current for each tube.


Looks like I gonna have to open it back up and do some more measurements soon... I did notice that when I switched the two tube positions, the 372.5V went up to 375V. I don't remember what the other tube read but it dropped a volt or two. Should've written it down... 

I'm gonna try with another set of tubes as well at some point



Paul Running said:


> Yeah, I would change out that 12Ω resistor before too long.


It's on my list


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## jb welder (Sep 14, 2010)

The 12ohm dropper between plate and screen supply nodes looks to be taken from the cathode biased YGM1 circuit. The YGM3 used 470R there, and the re-ish used 1K8. Either value will be a big improvement in reliability and longevity of the power tubes.

The tube with the 'good' plate voltage looks to be around 35mA. That's still a lot for 6BQ5. The 'bad' one is running around 150mA by calculation. Is it red-plating? Check it's grid voltage, maybe there is a leaky coupling cap from the PI. Both power tube grids should be zero volts.
A bad intensity pot could cause the issue, but should be the same for both tubes if that is the case.

Could also be some kind of measurement induced oscillation, any excess plate current must show up at the cathode, and it is not there. Cathode voltage shows 30mA (for 500ohm) should be flowing, which would be a cool 15mA per tube.
Instead of measuring plate to ground, measure each plate to center-tap. See if that works better.


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## ook ook (Jun 3, 2021)

dtsaudio said:


> You might want to consider putting in the proper transformer. All current from the supply runs through those diodes. If one fails, a lot of smoke will be the result.
> I just bought one from Hammond, I believe it was about $90.00


I'm considering this line of thought more. You're referring to the Hammond 290TRB, correct? That's the one they list as a replacement for the YBA-2B, replacing the original part number of A-1314. I believe this is what would have come in my amp as well, although I'm not positive since I got it with a non-original transformer. 
Would using one of these modern repro transformers drop the voltages at all? Looking at the YGM-3 reissue service manual, the included schematic (not positive it is the official schematic) shows a lower B+ voltage of 372V vs. 400V found on original schematics.



jb welder said:


> The 12ohm dropper between plate and screen supply nodes looks to be taken from the cathode biased YGM1 circuit. The YGM3 used 470R there, and the re-ish used 1K8. Either value will be a big improvement in reliability and longevity of the power tubes.
> 
> The tube with the 'good' plate voltage looks to be around 35mA. That's still a lot for 6BQ5. The 'bad' one is running around 150mA by calculation. Is it red-plating? Check it's grid voltage, maybe there is a leaky coupling cap from the PI. Both power tube grids should be zero volts.
> A bad intensity pot could cause the issue, but should be the same for both tubes if that is the case.
> ...


Seeing as my amp _is_ a cathode biased YGM-1, yes, the 12ohm is from the YGM-1 circuit. The 56k that follows it as well. I'm planning on going for the reissue-style larger resistor. Something around 2k. I'd have to back off on that 56k as well to keep the voltages up in the preamp.

The "bad" tube is not red plating. It is actually dimmer than the other. I'm not sure what's going on. Could be a trem-related issue. The tremolo is always on very slightly, even with the pot all the way off. You can hear it in the idle hum. Maybe I'll hook up footswitches and shut off the reverb/trem next time I take measurements.

The cathode resistor measures 299 ohms, so it would be more like 50mA, or 25mA per tube, assuming they draw the same current. I'm looking at my drawing now and I see how you could mistake that "3" for a "5"
Sorry about that!


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## dtsaudio (Apr 15, 2009)

ook ook said:


> I'm considering this line of thought more. You're referring to the Hammond 290TRB, correct? That's the one they list as a replacement for the YBA-2B, replacing the original part number of A-1314. I believe this is what would have come in my amp as well, although I'm not positive since I got it with a non-original transformer.
> Would using one of these modern repro transformers drop the voltages at all? Looking at the YGM-3 reissue service manual, the included schematic (not positive it is the official schematic) shows a lower B+ voltage of 372V vs. 400V found on original schematics.


That looks to be the transformer. Just make sure it physically fits. A couple of those are horizontal mount I think.
I'm not sure what voltage you'll get fully loaded. It should be about right though. I do remember that the voltage unloaded was dead on spec for the data sheet.
Don't forget to take out those two extra diodes that form that "center tap"


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## Paul Running (Apr 12, 2020)

The output tubes are biased on the cold side for audio...-15VDC is in the Class B region, if you prefer Class B, I'd use fixed-bias. 150Ω is a common resistance for 2 × EL84. Here's an excerpt from the EL84 data sheet:


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## Paul Running (Apr 12, 2020)

This curve will provide some insight into the bias condition. The screen voltage is only 250VDC so, you will need to extrapolate for your value however, you will note that at -15VDC with 400VDC plate, the tube is close to cut-off...it will be different at 400VDC screen which is too high. The EL84 is spec'd at a max. of 300VDC, as indicated in the previous data posted (high-lighted in red).


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## ook ook (Jun 3, 2021)

dtsaudio said:


> That looks to be the transformer. Just make sure it physically fits. A couple of those are horizontal mount I think.
> I'm not sure what voltage you'll get fully loaded. It should be about right though. I do remember that the voltage unloaded was dead on spec for the data sheet.
> Don't forget to take out those two extra diodes that form that "center tap"


Yeah, I was just wondering why the reissue has a lower B+. These images are taken from the datasheet, I just don't know why the voltages are different. 




















Paul Running said:


> The output tubes are biased on the cold side for audio...-15VDC is in the Class B region, if you prefer Class B, I'd use fixed-bias. 150Ω is a common resistance for 2 × EL84. Here's an excerpt from the EL84 data sheet:
> View attachment 389374


Appreciating the info. I'm not super well-read on tubes. They don't exactly teach that stuff in school these days


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## ook ook (Jun 3, 2021)

Paul Running said:


> The output tubes are biased on the cold side for audio...-15VDC is in the Class B region, if you prefer Class B, I'd use fixed-bias. 150Ω is a common resistance for 2 × EL84. Here's an excerpt from the EL84 data sheet:
> View attachment 389374


Also, the original schematic shows a 250 ohm cathode resistor rather than the 300 that's in there. Might swap that out back to 250 once I've addressed the voltage issues


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## Paul Running (Apr 12, 2020)

I would place more confidence in the data sheet...it will produce about 295 × 1.414 ≈ 415V peak.
Depending on your plate voltage that cathode resistor could be decreased further.


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## dtsaudio (Apr 15, 2009)

ook ook said:


> Yeah, I was just wondering why the reissue has a lower B+. These images are taken from the datasheet, I just don't know why the voltages are different.


That's interesting. When I measured the one I bought it was smack on 620V


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## jb welder (Sep 14, 2010)

Paul Running said:


> The output tubes are biased on the cold side for audio...-15VDC is in the Class B region


He has 15V across a 300R resistor, that is 50mA, or 25mA per tube. At near 400volts at the plate that is approx. 10W per 6BQ5, which is pretty hot.


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## Paul Running (Apr 12, 2020)

ook ook said:


> Yeah, I was just wondering why the reissue has a lower B+. These images are taken from the datasheet, I just don't know why the voltages are different.
> View attachment 389389
> View attachment 389391
> 
> ...


It would appear that that is not a unique appearance, many of the other models have the same discrepancies from data sheet to schematic.


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## ook ook (Jun 3, 2021)

Paul Running said:


> It would appear that that is not a unique appearance, many of the other models have the same discrepancies from data sheet to schematic.


Really strange. Maybe I'll email them and ask about that


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## ook ook (Jun 3, 2021)

So I emailed Hammond and Traynor for some answers and I didn't really get anywhere. Hammond said they have no information regarding the YGM-3 reissue since they didn't make the transformers for this amp. I don't think that's right but w/e. They said the 290TRB is their replacement for the YGM transformer and that the 589.9V on the data sheet is a mistake. Traynor said that the amp is designed purposely to have high voltages and they are not detrimental, but the opposite! I said I'm not on a quest for tone improvement, but one of increasing tube life but haven't heard anything else.


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## jb welder (Sep 14, 2010)

ook ook said:


> Hammond said they have no information regarding the YGM-3 reissue since they didn't make the transformers for this amp. I don't think that's right but w/e. They said the 290TRB is their replacement for the YGM transformer and that the 589.9V on the data sheet is a mistake.


Maybe he was thinking of the YCV's. You can throw the attached back at them, it's from the Yorkville website parts lookup.  Definitely a Hammond product, and A1314 is the number from the YGM re-issue service manual. Looks pretty much the same as the 290TRB. They may not be allowed to comment on OEM parts though.
Yes, the 589.9V on the datasheet did not look right to me either. 620V is supposed to be the loaded voltage. Therefore unloaded voltage must be higher, not lower.
Still not sure how they got lower voltage numbers on that re-issue schematic.

As far as the tube life goes, idle dissipation is more important than high voltage. There are lots of designs using plate voltages higher than norm, as long as they are not biased hot they do ok.
So agree it's nice to run lower if you can, but don't worry about it too much, bias as cool as you can without having too much of a negative impact on the tone.


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## ook ook (Jun 3, 2021)

jb welder said:


> Maybe he was thinking of the YCV's. You can throw the attached back at them, it's from the Yorkville website parts lookup.  Definitely a Hammond product, and A1314 is the number from the YGM re-issue service manual. Looks pretty much the same as the 290TRB. They may not be allowed to comment on OEM parts though.
> Yes, the 589.9V on the datasheet did not look right to me either. 620V is supposed to be the loaded voltage. Therefore unloaded voltage must be higher, not lower.
> Still not sure how they got lower voltage numbers on that re-issue schematic.
> 
> ...


Yeah, the reissue schematic voltages still elude me. I'm more so concerned about the screen voltages, which is a relatively easy fix.

I'm looking into a voltage regulator or variac to drop my line voltage by several volts but it seems like it's a pretty expensive route for not that much difference.

I'm probably not gonna be too concerned with dropping the voltages going forward


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## Paul Running (Apr 12, 2020)

Here's a simple circuit that will provide a variable voltage to the screens:


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## jb welder (Sep 14, 2010)

ook ook said:


> I'm looking into a voltage regulator or variac to drop my line voltage by several volts but it seems like it's a pretty expensive route for not that much difference.


It may have been mentioned in the thread already, but bucking transformers are cheaper and fairly non-invasive. A 12V bucker would drop your primary voltage from 123 to 111V for example.
It can be internal or external: Vintage Voltage Adapter


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## dtsaudio (Apr 15, 2009)

I think you are seriously over thinking this. A screen regulator is all well and good, but not necessary when a simple resistor change will get you close enough safely. Also using the correct power transformer, and wiring properly will get you close to original voltages. 
The amp I had on the bench recently matched the values in this schematic pretty close, including the voltage out of the new Hammond transformer. The one bug here, is that when these amps were designed, tubes were more rugged. Many manufacturers exceeded ratings and got away with it. 
As for today's EL84's they should be able to handle the extra plate voltage as long as you stay well below rated plate dissipation. Most tubes can. If in doubt, get some 7189 tubes instead. They have a 400V plate. However you may have to add some resistance to the screen to get it down.
If you still want to use a screen regulator, Paul's schematic will work, but make sure you heatsink the mosfet and isolate it from the chassis.


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## ook ook (Jun 3, 2021)

Paul Running said:


> Here's a simple circuit that will provide a variable voltage to the screens:
> View attachment 390607


Yeah I don't think I'll be going this route



jb welder said:


> It may have been mentioned in the thread already, but bucking transformers are cheaper and fairly non-invasive. A 12V bucker would drop your primary voltage from 123 to 111V for example.
> It can be internal or external: Vintage Voltage Adapter


I have looked into bucking transformers and I might do something like that at some point



dtsaudio said:


> I think you are seriously over thinking this. A screen regulator is all well and good, but not necessary when a simple resistor change will get you close enough safely. Also using the correct power transformer, and wiring properly will get you close to original voltages.
> The amp I had on the bench recently matched the values in this schematic pretty close, including the voltage out of the new Hammond transformer. The one bug here, is that when these amps were designed, tubes were more rugged. Many manufacturers exceeded ratings and got away with it.
> As for today's EL84's they should be able to handle the extra plate voltage as long as you stay well below rated plate dissipation. Most tubes can. If in doubt, get some 7189 tubes instead. They have a 400V plate. However you may have to add some resistance to the screen to get it down.
> If you still want to use a screen regulator, Paul's schematic will work, but make sure you heatsink the mosfet and isolate it from the chassis.


I agree with this. I wanted to drop voltages mainly to protect modern tubes and get the filament voltage closer to 6.3V, but I think I might just get the Hammond replacement transformer, replace that 12ohm resistor and maybe add some screen resistors and call it a day in that respect

EDIT: not going the new transformer route right now


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## ook ook (Jun 3, 2021)

I was re-reading the thread and noticed I may have given some misinformation. The diode arrangement is a conversion to a bridge rectifier due to the lack of a centre tap on the transformer that's currently in there. It can be thought of like this:


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## ook ook (Jun 3, 2021)

While taking the voltage measurements the first time around, I noticed that the amp was acting a little funny. I've now taken a 2nd batch of measurements with no funny business and I think these are more representative of the amp than the previous batch. I think there's something strange going on in the output section, but I still haven't figured it out. Updated readings here:









That one tube is still having issues. I measured the voltage drop from the OT CT to the plates and found that the reading on V3 is out of whack. Taking the measurement from the CT, the voltage reading fluctuates between -10V and -13V, even though the voltage w.r.t. ground tells us we should be seeing a ~25V drop. Even still, the -10V to -13V range implies a plate current of between 50mA and 66mA which is too much (not even going to mention the plate voltage with a 25V drop...)

Somebody previously suggested checking the voltages at the power tube grids at pin 2, and they are both at essentially 0V


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## jb welder (Sep 14, 2010)

All plate current must also go through the cathode to ground. Your cathode voltage means there is only a total of 29mA for the two tubes (14.55V/500R). At least while you are not measuring at the plates.
So there are 2 possibilities, one is that the 22uF cathode cap is leaky. That would mean the net cathode resistance is really something less than 500 ohms.
Easy to check, lift one end of the cap and recheck cathode voltage. If the cathode voltage stays the same, the cap should be ok. If voltage changes, replace the cap.

The other possibility is there is oscillation induced by the measurement conditions. Try removing the phase splitter tube and see if the plate voltages change.


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## ook ook (Jun 3, 2021)

jb welder said:


> All plate current must also go through the cathode to ground. Your cathode voltage means there is only a total of 29mA for the two tubes (14.55V/500R). At least while you are not measuring at the plates.
> So there are 2 possibilities, one is that the 22uF cathode cap is leaky. That would mean the net cathode resistance is really something less than 500 ohms.
> Easy to check, lift one end of the cap and recheck cathode voltage. If the cathode voltage stays the same, the cap should be ok. If voltage changes, replace the cap.
> 
> The other possibility is there is oscillation induced by the measurement conditions. Try removing the phase splitter tube and see if the plate voltages change.


The cathode resistor is 300 ohms (actually 299) so there's about 48.7mA between the two tubes. I'll check with the phase inverter tube pulled the next time I open up the amp, and I'll check the cap when I bust the soldering iron out


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## jb welder (Sep 14, 2010)

ook ook said:


> The cathode resistor is 300 ohms


I can't believe I did that twice. Doh! 
Anyway, the approx. 150mA you are measuring at the plates is not showing up at the cathode, so it seems it is only there when you have your probe on the plates.
Or the 'real' cathode resistance is approx. 100 ohms.


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## jb welder (Sep 14, 2010)

If pulling the PI tube straightens out the issue, it's likely that the OT phase is reversed, which turns the negative feedback loop into positive feedback.
In that case, the cure would be to swap the OT primary wires at the power tube sockets.


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## dtsaudio (Apr 15, 2009)

jb may be right. Something is affecting the readings. Your numbers don't make sense.
I don't think it is a positive feedback situation though, as that should affect both tubes. It would also be present all the time. In which case V3 would probably red plate.
As mentioned pull the PI tube. That should stop oscillation. Or short both EL84 grids to ground. Then check your measurements. 
You did swap V3 and V4 didn't you? To see if the problem followed tbe tube.
The other thing I see is the dc resistance from ct to plate on the OT. A 22 ohm difference seems high, and since your readings are not steady, you may have a problem there.


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## ook ook (Jun 3, 2021)

jb welder said:


> If pulling the PI tube straightens out the issue, it's likely that the OT phase is reversed, which turns the negative feedback loop into positive feedback.
> In that case, the cure would be to swap the OT primary wires at the power tube sockets.


I don't think that's gonna be the case here. The OT wires match the circuit schematic (many schematics have the wire colour labelled), and the negative feedback loop is negative feedback. I have the nfb loop on a switch and when the loop is active, the output drops.


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## ook ook (Jun 3, 2021)

dtsaudio said:


> jb may be right. Something is affecting the readings. Your numbers don't make sense.
> I don't think it is a positive feedback situation though, as that should affect both tubes. It would also be present all the time. In which case V3 would probably red plate.
> As mentioned pull the PI tube. That should stop oscillation. Or short both EL84 grids to ground. Then check your measurements.
> You did swap V3 and V4 didn't you? To see if the problem followed tbe tube.
> The other thing I see is the dc resistance from ct to plate on the OT. A 22 ohm difference seems high, and since your readings are not steady, you may have a problem there.


I have swapped the two tubes. I forgot to mention this, but in one configuration, while measuring the voltage from the CT, the V3 plate voltage reading was +1.991V, indicating an increase in voltage from the CT, while V4 was at -3.704V. The voltages with respect to ground were the same, however. That +1.991V was unstable and took a long time to land on.


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## Paul Running (Apr 12, 2020)

ook ook said:


> the amp was acting a little funny


You are beginning to discover the reasons why Mr. Traynor decided to go with fixed-bias for the -3 and -4 models. Note that he decreased the cathode resistor to 250Ω for the -2 model and he still was not satisfied with it's performance. You can operate EL84s with 500+VDC on the plates and obtain acceptable performance however, use fixed-bias and pay careful attention to your screen voltages...cathode bias was primarily conceived for class A operation, it will produce the best results in this class...take a look at the Vox-AC15.


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## ook ook (Jun 3, 2021)

I've gotten my hands on all the parts now other than a new speaker which is unfortunate. I'm planning on getting started this week or the week after. Still hunting for g12h 55hz style speakers...


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## ook ook (Jun 3, 2021)

Well this project's not dead in the water, but has been delayed a bit, as you can probably tell. I had some stuff come up which changed my schedule around. Gonna just wait at this point until I have a speaker to do everything at once. Could be two weeks from now, could be six weeks from now, not sure. I guess we'll have to wait and see...


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## diyfabtone (Mar 9, 2016)

A related question: If the original circuit card, wires, pots and jacks are removed from a Traynor amp but untouched otherwise and offered for sale with the modified amp would there be value in that approach? I'm asking cause I like love the originals but can't stand the hum related noise caused by the random chassis grounds, 2-prong plugs, and poor layout of AC wiring so I do some extensive mods which make them sound the way I like but compromise the resale value.


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## ook ook (Jun 3, 2021)

Hi everyone, iteration one is now done. 

Here's a list of changes. I'll maybe get an updated schematic up in the next few days.

1. Swapped speaker from RSC Jensen to Mojotone G12H30 copy
2. Removed presence cap from the feedback loop
3. Adjusted power supply resistor values
4. Added 3W 470 ohm screen resistors to the power tubes
5. Swapped the first coupling cap to 0.022 uF (might experiment with 0.01)
6. Swapped first plate resistor to 220k 
7. Added bypass cap to 2nd triode

I think that's all

Possible future experiments (non-exhaustive):
1. Bass cap in the tone stack from 0.1 to 0.022
2. First coupling cap to 0.01 
3. Further adjust power supply resistors to fine tune preamp voltages
4. Swap 300 ohm power tube cathode resistor to a lower value (250? 200?)
5. Swap speaker again (if I find a speaker than better fits what I was looking for or just want to try something new)

Loving the speaker on first impressions, and I'm loving the removal of the presence cap. When fully cranked up, it gets a little woofy and bass-heavy, which is a useable sound in itself, not exactly complaining. The cleans when turned down are nice and bright due to the treble cap on the volume (which I didn't remove and don't really have plans to anymore). 

The amp sounds so damn cool with a treble booster in the front now. Before the mods and with the old speaker, it had this really terrible nasally compressed sound with a treble booster, but now it sounds so great. Fixes the woofiness 100% and pushes the amp over the edge. Sounds crazy cool.


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## ook ook (Jun 3, 2021)

Never got around to taking voltage measurements after doing the mods, but I did take some measurements in the power supply. In any event, here's the schematic as it stands now. My mods are highlighted:










I have other issues with the amp which I'm seeking to address, namely a very harsh, nasally, not pleasing distortion when the gain is too high. Swapping a 12AU7 into the PI remedies the issue for a short period. This distortion comes on suddenly once a certain gain threshold is reached. When switching off the nfb loop and turning the volume all the way up, it appears, and when using a boost in front of the amp and pushing the treble/volume too high, it also appears.

I think it may be blocking distortion, but I've never actually heard what that sounds like so I can't be sure. I know that the grids of the power tubes (pin 2) both measure between 0 and 2 mV unloaded so I'm thinking that it isn't a leaky coupling cap there. Could it be the coupling cap into the phase inverter leaking? I'm considering increasing the grid stopper resistors up to 8.2k like on a marshall 18w to see if there's any difference and maybe dropping the coupling caps to .047 or .022 uF. 

I'm not sure if it would be more appropriate to make a new thread for this or continue this one, but I have a video which somewhat captures the sound I'm referring to. The video doesn't fully capture the sound I hear in the room, it actually sounds more nasally and unpleasant in person. It goes away if I drop the volume.






Help and suggestions would be much appreciated


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## Paul Running (Apr 12, 2020)

ook ook said:


> I think it may be blocking distortion, but I've never actually heard what that sounds like so I can't be sure.


You would recognize it by displaying it on a scope. It could be cross-over distortion, too; I believe that the output tubes are biased on the cold-side, with 300Ω for both cathodes. I would refer to the datasheet for the EL84 and verify the correct bias for the voltages that you have measured on the pins of your output tubes.


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## ook ook (Jun 3, 2021)

Paul Running said:


> You would recognize it by displaying it on a scope. It could be cross-over distortion, too; I believe that the output tubes are biased on the cold-side, with 300Ω for both cathodes. I would refer to the datasheet for the EL84 and verify the correct bias for the voltages that you have measured on the pins of your output tubes.


Yeah, the bias is another factor I'm considering. Next gen guitars, which is where I got all of my parts from, only has 250 ohm 10 watt resistors so I might need to go elsewhere for that if I want a lower value.

I also don't have a dummy load which I can use in place of a speaker, but I guess I could still check out the waveform going to the speaker for crossover distortion.


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## ook ook (Jun 3, 2021)

Tested the amp at 1kHz. I don't have a good quality scope or wave generator, but I think it got the job done. Here are some scope readings:




































Looks like some cathode resistor experimentation might be in my future

Measured with nfb loop switched off. None of these measurements were taken at full volume, the highest one is roughly 80% on the volume knob


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## Jerome (Dec 4, 2015)

Top image shows crossover distotion . Lowering the value of the output tubes cathode resistor should remedy this . 125 ohms seems to be about right , depending on the plate voltage .


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## ook ook (Jun 3, 2021)

Jerome said:


> Top image shows crossover distotion . Lowering the value of the output tubes cathode resistor should remedy this . 125 ohms seems to be about right , depending on the plate voltage .


Plate voltage was around 400 V last I measured


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## ook ook (Jun 3, 2021)

Adjusted the bias to be very close to 100% on the power tubes. The plate voltages are also now within 1V of each other. The horrible distortion sounds continue. 

Today I'm gonna take more waveform measurements and swap out my grid stoppers. Hope that solves my problem


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## ook ook (Jun 3, 2021)

Swapped the power tube grid stoppers to 8.2k and looked at the waveform. Good news is that the bias adjustment from last night eliminated the crossover distortion, the bad news is that the 8.2k grid stoppers did very little, if anything, to correct the ugly distortion sound.

I think the phase inverter is the problem area so I'm off to do research on LTP phase inverters

Edit: actually the crossover distortion is still occurring even at ~100% max dissipation, I just didn't use a strong enough signal. I'm gonna try the coupling caps and the 220k grid leaks at the power tubes. YGM-3 schematics have 100k there


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