# Traynor bassmate ybm 2 a/b and a question for those that have worked on a YRM traynor.



## orlando.rigueira (10 mo ago)

I have a number of old Traynor amps that I have re-capped and updated over the years. I love that they all are different in various ways some subtle changes others more drastic. I currently have on my bench a YBM 2 a/b that I am re-capping and changing the power supply to add a choke and a thermistor to the AC as it does not have a standby switch. I removed the 1K 5W resistor between the 1st cap node and the second as that is where the choke is now located. from the second node I wired it to the screens using 2W 1.5 K individual resistors for each tube. I have also added adjustable bias pot. My question has to do with the arrangement of the first two gain stages before the tone controls. This revision of the bassmate is the only one with this arrangement. The others as well as my guitar mates all have a gain stage, volume, tone and next gain stage. This allows you to play with gain stage bypass values as well as plate and cathode resistors. With this amp if you mess with the two cascaded gain stages you could wind up with fixed clipping stages as there is no volume between them. If I leave it like it is I would not try to increase gain and the amp does sound great for both bass and guitar. I just think the earlier YBM 2 A design looks nicer as far as being able to play with the first two gain stages. Also this amp (YBM 2A/B) has no negative feedback to the phase inverter like the others do. Has anyone played around with one of these YBM 2 A/B amps? A second question has to do with the design of the YRM series amps. Unlike the YBA style amps with cathode follower designs the YRM is more like a fender blackface amp. The sound of the YRM with the master dimed and they control volume thru the volume control is just great, but if you want to overdrive the preamp and turn down the master and turn up the volume you start to lose the high end. This issues seems to be common to them. I noticed that the 3rd gain stage has a 1 meg plate resistor and a 5.6k cathode resistor. I reduced the plate resistor with a resistor box while running a sine wave thru the amp and the output of the 3rd stage increases with the lowering of the plate resistor but I was not sure why those original values were chosen as I am sure the designers knew a hell of a lot more than I do. I changed it to 500K and put it back together to make sure it did not screw up the reverb which is right before that stage. Has anyone played around with the 3rd stage of a YRM before? Any sugestions? The high end drop off was also improved with the reduction of the plate resistor to 500K but not gone. I will next try 220K. and report back.


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## diyfabtone (Mar 9, 2016)

Is there a grid stop resistor between the MV and next grid? If not try putting one in, the higher the better (up to 100k) to limit the tone-suck that happens when the MV is dialed down low. This actually reduces treble response over all, but it does even out the tone as MV is reduced - you'd have to try it and hear if the slight compromise between full MV tone without grid-stop and with, balanced against the benefit of less tone-suck works for you?

I haven't tried modifying the circuit values of a Bassmate (either version) but I can see that version 1 above is designed to give you plenty of clean gain with some high frequency emphasis (from the un-bypassed 5k6 cathode resistors) and it works because a chunk of that gain is used up when driving the EQ load - Traynor knew what he was doing! You could play with those cathode resistor values but at some point you may have to add a series resistor between the coupling cap and grid-leak (a voltage divider), and/or lower the grid-leak value to keep the gain from overdriving stage 2?


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## orlando.rigueira (10 mo ago)

Thanks for the response. I did add a 120K resistor after the MV in yhr YRM but I could not hear any difference. The only improvement to that was lowering the 1M plate resistor to 500k. Plate voltage went from about 60 volts at idle to around 90 volts.(on the 3rd gain stage) On the bassmate because of the 2 stages cascaded with no voltage divider if I was to lower cathode resistor or bypass one it may result in the second gain stage always clipping as volume and tone stack is after it. I will probably leave well enough alone. It has served me well as a bass amp and I have a open G tuned guitar for stones stuff and it sounds killer with that amp with the volume up. I guess the only distortion is coming from either the PI or EL84's.


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## diyfabtone (Mar 9, 2016)

You could try a London Power Scaling kit? That might preserve your cranked MV tone with reduced volume.


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## Paul Running (Apr 12, 2020)

orlando.rigueira said:


> the 3rd gain stage has a 1 meg plate resistor and a 5.6k cathode resistor.


When operating a 12AX7 (Ebb=270VDC) with a 500KΩ plate-resistor, if you wish to center-bias the tube, you may want to consider reducing the cathode resistor to 3.3KΩ.


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## orlando.rigueira (10 mo ago)

I am away till 4/10 but will check the value of what it is currently at. I do not think I changed it but not sure. Thanks for that suggestion as i plan to go lower on the plate value as well so I will need to lower Rk..


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## orlando.rigueira (10 mo ago)

I am back and just checked the YRM schematic I marked up. The wiper of the master volume goes thru a 120K resistor before the coupling cap. Other changes were 1st gain stage .68uf bypass cap on rk. Tone stack 250PF, .022, .022 and a 150pf boost cap. I also changed the el34 to EH 6ca7. The 3rd gain stage is now 500k instead of 1Meg and the rk is the stock 5.6k. I will try updating RP and Rk next. The only change that made a difference was the reduction of the 3rd stage plate resistor.


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## orlando.rigueira (10 mo ago)

Finished the bassmate. left the preamp alone but added adjustable bias, added a choke to replace the 1k dropping resistor but added individual 1.5k 2w screen resistors. replaced all electrolytics and disc caps with mallory 150's. It gets about 14.8 volts clean into a 9 ohm resistive load which is around 24 watts and when pushed to clipping clips very symmetrical. Going to assemble it and try it. This amp always worked fine as a bass amp and also sounds great with a guitar. I am not a fan with the preamp design of this one but it sure seems to work just fine.


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## orlando.rigueira (10 mo ago)

max clean output.


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## orlando.rigueira (10 mo ago)

Now that the bassmate is done back to the yrm. I went back and looked at Kevin Oconnors book about adding a resistor in series with the wiper of the master volume. I did that thinking it may help the lackluster tone when preamp volume is high and master is low. But in his book he states that that type of master volume kills the low end and What I am hearing is the loss of sparkle when doing that. If I dime the master and raise the preamp it sounds fine but I'm not really pushing the volume as it gets too loud. Today I am going to use the dummy load and signal generator to run 1K and 10K sine waves thru it and check eash stage seeing if I see anything strange going on. I did check Rk on the 3rd stage and it was a 3.3k reisitor not a 5.6. It is very hard to read the schematic. Any sugestions are welcomed or questions on any values.of the preamp.


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## Paul Running (Apr 12, 2020)

When you perform the frequency response, record your measurements and then plot them on a graph; this should provide a visual representation. I find that I interpret response graphs more effectively, when I wish to alter the amp's response.


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## dtsaudio (Apr 15, 2009)

What I believe you are experiencing is Miller Effect. The impedance preceding the phase splitter is reacting with the tubes grid capacitance to form a filter.
I see you've put a 120k resistor in series with the pot. Make it much smaller. No more than 10k.
The pot itself will increase miller effect as you move toward higher volume as the tube see higher and higher resistance. 
The other thing you might try is replace the plate resistor of the preceding stage. Not only is that resistor dropping a ton of voltage, but at the extremely low current that tube is running at, the output impedance is very high.
This will also contribute to Miller Effect and reduce yours high end considerably. It will change your gain though.


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## orlando.rigueira (10 mo ago)

I don't know how to do that. I am home sick so I go up and play with it for about a half hour at a time. The 1K then 10K testing did not work out so instead of going from *100 to *1000 and then readjusting the time base, I just rotate the signal generator dial from about 500Hz to 5000Hz. What I am seeing is the amplititude of the sine wave at 5K is much larger than 500K and with the boost switch it is double. I had changed the plate resistor on the 3rd gain stage from the original 1M to 500K and that has increased the signal out of the 3rd stage so that if volume is up it starts clipping quickly. I will take some pics and post them. There are a few schematics floating and for the SC version they do not have a cathode bypass cap on the 3rd gain stage. I was thinking of removing the 1st bypass cap and test then put it back and remove the 3rd stage bypass cap to allow more headroom. Still have a lot of test info to collect.


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## orlando.rigueira (10 mo ago)

few mistakes in my post. The SC schematic has no Rk cap. Dan thanks for the info I will look into the miller effect. When you say the preceeding tube that is the 3rd gain stage and yes changing the plate from 1m to 500 K made an improvement it how it sounded but still does not work well with preamp vol up and master down. With the master full volume and just using preamp volume the amp does not have that loss of sound quality but its way too loud to try playing for any length of time. I am trying to get it to have a good crunch with using preamp volume to dial in the crunch and master to tame it down. The three gain stages and fender style tone stack make it look like a super reverb type amp. Its not at all like the YBA traynors with the cathode follower driven tone stack.


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## orlando.rigueira (10 mo ago)

Still wrong, sc version has no Rk cap on V1. Sorry I'm suffering from bronchitis and just started Antibiotics but not really with it yet. 
Orlando


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## orlando.rigueira (10 mo ago)

I did some digging into the miller effect and also re-read the Kevin O'Connor ultimate tone section 5 where he talks about the resistor in series with the pot wiper. The effect he was trying to fix was the opposite of what I thought it was for. While he did not mention the miller effect, he said the high impedance of the EQ before the MV and the stray capacitances cause a variable filter (as volume is moved) killing low end as the volume is reduced. I guess that's why I could not hear any difference with it installed. I am trying to decide if I should remove it as My YRM EQ is after the first stage. O'Connors example has a cathode follower driven tone stack before MV to the PI. Anyway I took some scope pics of the amp the way it was with the 3rd stage Ra = 500k and Rk =3.3K with a 25uf bypass cap at max clean volume (around 5-6) and clipped. Then today I decided after checking that the reverb and trem would not be affected by changing values I use the trainwreck express cold clipper design for the 3rd stage so now its Ra = 100k, Rk = 10K no bypass cap. To my surprise it still clips the top of the signal when cranking up the volume. I would have thought that cold biasing would have clipped the bottom of the sign wave. looking at the signal at the dummy load it appears like a nice asymmetrical clipped signal when preamp is clipping. Before I do anything else I will play it and see what it sounds like then take more pics. I also had a choke to put in this amp the last time I was recapping and first going thru it but did not do it as it was not going to be easy to mount but may do it now. Here are the pictures I took, the first two are before modding the 3rd gain stage both clean and clipping, the last two are the cold clipper with volume up, and the last picture is the output at the dummy load. the top 3 traces are always the sine wave generator, first stage, second stage.


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## Paul Running (Apr 12, 2020)

On the last scope trace, the positive peaks have a softer and slower pinch-off than the negative peaks. I have encountered that before. It could be screen-grid related. If you switch positions with the output tubes, does it change the waveform?


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## orlando.rigueira (10 mo ago)

Paul that is because the volume (preamp) is causing the cold clipper to clip. If I back it off till its not clipping then raise the master it will clip symmetrically. I also thought it was lacking volume but I spent about an hour with it and the scope and would get around 22V RMS into 9 ohms so it is outputting 45 watts clean before starting to clip. Also I played it and the original issue with master low losing the sparkle is now fixed and with the cold clipper and unbypassed cathode on the 3rd stage I can run volume up to 3/4 of the range before clipping. I will take some scope traces and post them when I get more time to show the 3rd and output traces clean and clipped. I was confused as to why a cold clipper does not clip on the negative side but looking at some trainwreck express scope traces it looks just like mine on the output of the cold clipper, the positive side is clipped while the negative side is not clipped.


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## orlando.rigueira (10 mo ago)

Some more progress, I've played it with a master volume 47pf bypass cap jumpered in and it worked well when master dialed down, so I added it. Amp sounds great but to get it loud the preamp needs to be cranked and the master set pretty high. I think the unbypassed 10K cathode resistor limits the gain and even though witth a 400mv sine wave thru it the cold clipper clips asymmetrically, With a guitar overall the amp is very clean and has that fender sparkle that was missing originally. Today I jumpered a 2.2k resistor and 25uf coup;ling cap across the 10k cathode resistor of the third gain stage and wow what a gigantic jump in volume. It now can get dirty with preamp at anything over 4 and its very loud and sounds killer with higher preamp settings and master volume turned down. With the 10k cold clipper the amp with both volumes dimed was loud but fairly clean. I checked the output and it was at 46 watts clean before clipping. I have not checked it out with the extra resistor cap on the third stage but it is loud and had thunderous bass. I'm going to go with a 1.5/25uf cathode resistor Which makes this a lot like a super reverb vibrato channel. With the 2.2/25uf jumpered and volume up it does get the infinite sustain/feedback I was trying top get with the cold clipper like a trainwreck but I think the master volume pot which is a 100k pot (so acting like a 100k grid leak) may have been killing the signal to the phase inverter a bit. The trainwreck express has no master volume.


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## Paul Running (Apr 12, 2020)

Keep experimenting, you're on a roll...it's fun, eh?


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## orlando.rigueira (10 mo ago)

It is fun but now even better that I have gotten it to sound better. I want to get some scope traces comparing the 3rd stage output with the cold clipper then with the resistor/bypass cap jumped in to see if I get symmetrical clipping with the regular cathode bias values.


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