# Updating Vintage Filter Caps: Make updates from Schematic?



## bcmatt (Aug 25, 2007)

My Bass player finally got a real tube bass amp to play instead of the silly modern high powered SS Markbass amp she has. She got an all original Traynor YBA3 off someone on this board from 1968. It sounds really great, but it is ALL Original aside from the 3 prong power cord. So, it is obviously time to update the filter caps. 

But here's the thing, it is the VERY first generation of the amp with none of the mods or changes that were made to the schematic over the first few years.

Right now, the filtering consists of using three 80uF caps, two 2x40uF cap cans and a couple 8 uF caps.

By the next year there was a 10 uF cap and then a second by the time a Master Volume was also added.

What would be the value of making updates that Pete would have made over the first couple years? I'm tempted to leave everything original seeing as it has survived in great sounding condition for 44 years with no changes... even has the original English Phillips 6Ca7 power tubes.

So, would there be any disadvantage to leaving the original values from the very first schematic and just replacing all electrolytics with the same values and adding nothing new?

I figure if she does ever need any super strong low end in a louder environment, she could use her MarkBass amp for extra power along with this one for the ultimate tone.


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## bcmatt (Aug 25, 2007)

This looks to be the exact generation of this one (69 some time):


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## WCGill (Mar 27, 2009)

I think you answered your own question. If the amp sounds good, doesn't hum and the caps aren't bulging, my preference would be to leave them be.


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## bcmatt (Aug 25, 2007)

WCGill said:


> I think you answered your own question. If the amp sounds good, doesn't hum and the caps aren't bulging, my preference would be to leave them be.


You are right. It appears that additional 10uF caps were later added in place of a choke to help with rippling. This one has a choke, sounds great, and is quiet. I'll replace the current electrolytics with similar values and be done with it so that she is good to go for another decade or two.


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## cbg1 (Mar 27, 2012)

glad it made the trip safely matt

ets


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## bcmatt (Aug 25, 2007)

Ya! Thanks Ets! It was here at the town post office waiting for us when we rolled in. It sounds great! Very cool amp!


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## Wild Bill (May 3, 2006)

bcmatt said:


> You are right. It appears that additional 10uF caps were later added in place of a choke to help with rippling. This one has a choke, sounds great, and is quiet. I'll replace the current electrolytics with similar values and be done with it so that she is good to go for another decade or two.


Actually Matt, the choke works FAR better for ripple! The real reason the choke got abandoned is because a choke costs FAR more than a couple of filters! And the filter method was "good enough for rock and roll"!

The choke was always overkill, at least for regular guitar amps, although I've always thought that the choke in the classic Plexi was responsible for a good bit of its amazing sound. However, when you have a powerful bass amp that you want to stay super clean it is never a bad idea.

Depends if your own needs justify the extra money, I guess.

Wild Bill/Busen Amps


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## bcmatt (Aug 25, 2007)

Thanks, Wild Bill. I hadn't noticed this rely until now. I am just awaiting the new Electrolytics to arrive so I can replace the originals. The amp sounds great and we've been using it in the meantime. Miked it up through the mains and it sounds great. NO need for her to supplement it with her MarkBass for more power since it sounds so awesome on it's own and the PA balances for the crowd. 
We played an outdoor show yesterday and this thing sounds great. Here's a pic of the other band (Shred Kelly) using it as well. I was so distracted by how great his bass town was. It's rare to oogle over bass tone for me, but I can't help it with this YBA-3!








and here it is indoors with my ampeg cab she uses it with:


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## loudtubeamps (Feb 2, 2012)

Hi bcmat.
If you have a moment, the next time you have your amp opened up, could you post the (stamped in white) numbers shown on the mains and o/p transformers.
Thanks.d


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## bcmatt (Aug 25, 2007)

loudtubeamps said:


> Hi bcmat.
> If you have a moment, the next time you have your amp opened up, could you post the (stamped in white) numbers shown on the mains and o/p transformers.
> Thanks.d


Sure. It should be soon. Are you trying to order some or something?


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## loudtubeamps (Feb 2, 2012)

bcmatt said:


> Sure. It should be soon. Are you trying to order some or something?


 Thanks for getting in touch..
No to the ordering. I have a few old Hammond transformers and I am curious to see if any of my numbers match yours. 
I can't seem to find out very much in the way of reference material/specs. for these guys.
Thanks d


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## Wild Bill (May 3, 2006)

loudtubeamps said:


> Thanks for getting in touch..
> No to the ordering. I have a few old Hammond transformers and I am curious to see if any of my numbers match yours.
> I can't seem to find out very much in the way of reference material/specs. for these guys.
> Thanks d


And you won't, LTA! Those are not Hammond numbers but Traynor numbers. It is common practice in the electronic manufacturing industry to have a custom part marked with their own inventory number. That way, they could order from a number of different part makers and get the same thing, marked with their inventory number.

The kicker is that to Hammond, the part number and the information about the transformer is proprietary - Traynor owns it! It is not a catalog number for the whole world to see, along with all the specs. What if a competitor wanted to know that info? Why should Traynor want to make it easier for them? Why should they order ever again from Hammond if they gave out that information?

That being said, if you know your theory it is easy to choose a replacement from the Hammond catalog with specs "close enough". Sometimes the mounting holes might not line up so you'd have to get out your drill. 

Hammond makes some replacement Fender, Marshall and also Traynor trannies under their catalog numbers. If you poke around at the Hammond website you will find them.

Wild Bill/Busen Amps


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## loudtubeamps (Feb 2, 2012)

Thanks for the info Bill.
These Hammonds are from Traynor amps. I was told when they were given to me that they came out of Bassmaster MKII's ,YBA 1's etc.
A couple of the transformers(especially the mains) are massive and would be something you would see in a Traynor 4 valve. 
I wonder if they would have used the same mains trans. in 2 and 4 valve models at some point in time? The pic. of the YBA3 got me thinking?
If you or anyone else has some reference material on these, I'll post the numbers I have on these trannies, shortly.
cheers, d


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## loudtubeamps (Feb 2, 2012)

So..... these ones are 2 valve iron.(pretty sure... from reference numbers found in Traynor schematics)

mains:Hammond 112002.no secondary b+ c.t,no bias tap.
choke 68347
O.P. Hammond 92105 

a small O.P . ..YBA1 I believe, but very small. Not like Traynor to use something this small to light up a pair of 6CA7's
hammond 112003/OP A1323

and the monster
mains:78632 H (inside a circle) 
stamp on top#2745
has C.T. at b+ secondary and CT on filament tap.

Thanks in advance for any info.
cheers, d


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## bcmatt (Aug 25, 2007)

Pulled this thing open just now, because I am finally changing the caps....

PT - 79691
OT - 79692
Choke - 68347

so, it looks like you have the same choke... I guess that would have been a safe assumption anyways... but the big iron; not the same.


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## bcmatt (Aug 25, 2007)

So, I have a quick question.
I wanted to make sure things are safe once I got the new caps in, so I thought I would make sure there was no bias adjustments needed.

The YBA-3 Schematic says to adjust the 10kL trimpot to allow 8VDC drop across the 1K 20W Screen Resister. Right now (before changing anything), it reads at 10.5VDC drop. Adjusting to 8 VDC drop really seems to make little or no difference in tone or volume. I imagine the state it is in already is safe, if it has been running on all original parts/tubes for about 44 years, but I'm a bit confused... which is actually safer for the tubes/circuit, a larger or a smaller voltage drop across that screen resister?


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## bcmatt (Aug 25, 2007)

Finished the Cap-Exchange. All the old ones were Mallory, and all the new ones are easily noticed because they are all black... JJ cap cans, F&T, and Sprague.
Before:









After:

















So,
Switching caps did seem to alter the voltage drop across that 20W 1K Screen Resister, so I went with what Pete Traynor's Schematic suggests and set it to about -8VDC, by turning the trimpot pretty much all the way to the left... Any thoughts on whether this is fine?


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## loudtubeamps (Feb 2, 2012)

Thanks for the trannie info bcmatt.
Without getting into alot of detail, with regard to your bias concern: if you are comfortable with the high voltage stuff going on in your amp, the only way that I know for sure what the tubes are doing is to measure what they are drawing at idle.
This method is commly referred to as the "Transformer Shunt" method.
I have been using this method since I got into this stuff. Again, this is my preference and I do not recommend it unless you are comfortable and careful with high voltage. It is a quick and accurate way to measure what your tubes are doing.
The amps I make are fitted with a 10% -1 ohm cathode resistor and separate bias trim pots on the fixed bias supply and is a much safer way to go when you are making amps for the consumer.
Here is a link to detailed info on both methods.
Bias FAQ
cheers and thanks again. Doug


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## bcmatt (Aug 25, 2007)

Thanks Doug,
I usually use the Cathode resister method mentioned in the article you included with 1 ohm resisters. I guess I was feeling too lazy to install some on this one, since Traynor's schematic seemed to be suggesting a much simpler process. I would think that I should be wary of any method not requiring me to measure plate voltage, but these are the original tubes as well, and if they have been fine these last 44 years... I'm thinking I shouldn't be too concerned because the assumptions made about them back then should still apply when only the caps are updated... I've heard these old Traynors are designed well in a way that is not too hard on tubes (as this amp seems to be an example of)...
But, I've heard that new production tubes are not nearly as rugged as ones from those days... so should I need to replace these, I think I'm in for a whole new ball-game and more careful measurements... Thoughts? 
Of course, thus far in this whole process, I have not thought through exactly how a tube works with any understanding and applied it to the biasing of this amp.... It would be a good exercise... but I am feeling lazy...


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## jb welder (Sep 14, 2010)

Matt: Screen current increases along with cathode current, but is much less. So more screen current will give a larger voltage drop across the resistor, indicating hotter bias. Your 10V across the resistor means it was biased hotter than the factory 8 volts.
Back when these amps were in production, the tube tolerances were probably tight enough that you could get away with biasing according to screen current.
For best results with modern tubes, I would recommend using cathode current measurement. (Or shunt method or plate current if you play real safe.)


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## bcmatt (Aug 25, 2007)

jb welder said:


> Matt: Screen current increases along with cathode current, but is much less. So more screen current will give a larger voltage drop across the resistor, indicating hotter bias. Your 10V across the resistor means it was biased hotter than the factory 8 volts.
> Back when these amps were in production, the tube tolerances were probably tight enough that you could get away with biasing according to screen current.
> For best results with modern tubes, I would recommend using cathode current measurement. (Or shunt method or plate current if you play real safe.)


Thanks very much JB! That's exactly what I was wondering. I appreciate the response.


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## WCGill (Mar 27, 2009)

Correct me if I'm wrong but wouldn't a larger voltage drop across the screen resistor limit the screen current more than a smaller voltage drop thus resulting in colder bias?

I don't quite understand screen bias per se. I always use transformer shunt to measure plate dissipation, 70% is my benchmark. Screen dissipation I can understand but like the JB man says, "it ain't what it used to be."


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## jb welder (Sep 14, 2010)

WCGill said:


> wouldn't a larger voltage drop across the screen resistor limit the screen current more than a smaller voltage drop thus resulting in colder bias?


With the value of the screen resistor remaining constant, a larger voltage drop across the resistor can only be due to increased screen current. Screen current increases with cathode current so more screen current = bigger voltage drop across screen resistor = hotter bias.
I think what you mentioned would be the result of increasing the value of the screen resistor, but in this case the screen resistor value is constant, we are just using it as a measurement point.


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## Wild Bill (May 3, 2006)

The screen resistors don't have enough effect to actually control the bias, WCGILL. They are there to try to offer some protection to keep the screens from burning out under a catastrophic failure. Actually, they tend to protect the power supply if the tube shorts internally.

However, since the screen current will change according to the cathode current it can at least make a good measuring point for the idle current.


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## WCGill (Mar 27, 2009)

Actually I thought screen resistors were something you put on your storm door.


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## Wild Bill (May 3, 2006)

WCGill said:


> Actually I thought screen resistors were something you put on your storm door.


I should put some on my German Shepherd, Fred! He's hard on screens! :bullbeg:


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