Updating Vintage YBA3

[bcmatt]

So, I have influenced my bass player too much in our little 3-piece Bluesy Garage-Rock Band and she is about to pull the trigger on an early 70s YBA3 Bass head because we bug her about embarrassing us with her modern transistor Markbass amp and ruining our street cred (as if we had any). Well, the Markbass is great for power and light as a feather, but the YBA3 seemed like a decent deal, and I've always loved their tones (and she is often looking for more grit in her sound). I realize this isn't the huge 300 watt "Super Custom Special" version that blew away the competition when it came out, but rather it's 120W predecessor known as just the "Custom Special" (probably more useful for our size of gigs anyways).

Anyways, it seems like it is all original aside from the 3-prong cord... so in order to get it ready/safe for regular use, I figure I will need to update it a bit.
I actually haven't ever restored something old yet, I am realizing, so this is my first time making these decisions.

Any advice on replacing these guys? Cap Cans or do you think it would be better to just put all axial lead caps on a new board and mount it in there?

I'm assuming the three big dynamite sticks are probably the 80uF 450V caps on the schematic, and the 2 cap cans are probably each 40/40 cans.
I'm not finding any 40uF caps for sale at AES, aside from those crazy expensive CE cap cans.

Should I just unattach those external cap cans and keep them mounted for appearance sake? Or, should I try dropping in a JJ 32/32 ($8.50) with a clamp in each? Or perhaps a 50/50 JJ ($8.75)?

It looks like on the schem that each of the 40/40 cans are wired together parallel and then in series with an 80 to make a single High powered 40uF cap. So, if I use a 50/50, that makes it 100 uf before in series with the 80... then with the 80 it is down to about 45uF. Using the 32/32 would make it about 37ish? Is one better than the other?

Or should I just get some 47uF axials and mount them with 80s on a board?

Also, which resisters should be replaced? All the 2W carbon comps in the power section, or just the 2 on the power tube grids?

Thanks guys. I guess there are a few ways to go about this, but I'd like to have it go smoothly being my first time, and I know many of you do this daily...

[billyz]

I would use a single section 100uf/500v can to replace the dual 40/40 cans. you will probably need to mount a can clamp as well. I would not change any resistors unless they are way off or blown.

I would change out the bias caps though.

[Gaz]

Side note: Is that the actual amp in the pic? If so. it has the original Mullards. I bought one years ago, and it did as well. they tested good and I sold them on Ebay for $300 Hmmm, mine had a fan though, which helped tube life I'm sure.

Those sound great for bass, not so much for guitar.

[bcmatt]

Ok, so is it safe to assume that the 2 sections weren't used in order to get higher voltage handling? I figured it wouldn't be since they are used with an 80uF 450V in series anyways...

So, I could just forget about the 2 40uFs and replace with an 80uF or 100uF as long as it is rated for about 500V?
Maybe it would be more economical and convenient to just order 5x 80uF 500V axial caps then instead of the 4x 40 and 3x 80.
Also, I was thinking I would just replace all electrolytics. Is that not just the standard?

[bcmatt]

Side note: Is that the actual amp in the pic? If so. it has the original Mullards. I bought one years ago, and it did as well. they tested good and I sold them on Ebay for $300 Hmmm, mine had a fan though, which helped tube life I'm sure.

Those sound great for bass, not so much for guitar.

That is the actual amp. The fan is in the side of the head cab. You can see the wire that goes to it.

I'm not sure if it is the tubes currently in it or not. It may be an older picture and he may have replaced the tube since then... not sure. But since he did send these pics, I'm assuming it is the current state.

[Gaz]

Side note: Is that the actual amp in the pic? If so. it has the original Mullards. I bought one years ago, and it did as well. they tested good and I sold them on Ebay for $300 Hmmm, mine had a fan though, which helped tube life I'm sure.

Those sound great for bass, not so much for guitar.

That is the actual amp. The fan is in the side of the head cab. You can see the wire that goes to it.

I'm not sure if it is the tubes currently in it or not. It may be an older picture and he may have replaced the tube since then... not sure. But since he did send these pics, I'm assuming it is the current state.

Ah, of course, I've seen one like that as well. There's two different YBA3 circuits, one with a Plexi-like preamp, and the other with that is a little more unique and better suited for bass (the one I was thinking of. Both would be great. I can see now that those tubes are the original Phillips, not Mullard. Still, really nice tubes if you get them.

[bcmatt]

Ah, of course, I've seen one like that as well. There's two different YBA3 circuits, one with a Plexi-like preamp, and the other with that is a little more unique and better suited for bass (the one I was thinking of. Both would be great. I can see now that those tubes are the original Phillips, not Mullard. Still, really nice tubes if you get them.

I'm hoping this is the one better suited to bass. The controls seem to indicate so. I thought is was the YBA1 that was more plexi-like and that people love for guitar.
http://www.yorkville.com/products.asp?t ... =46&id=293

He said the fan is having trouble, so I'll probably need to replace it too.

[bcmatt]

Does anyone know what those white electrolytic caps are? Would they be original and in need of replacement?

I'm guessing they must be the two 10uF 400V caps, and assume they must be original since all the other caps look original. I just don't recognize the type... and they don't look as old....

[greekie]

My advice is to get some serious capacitance in that amp's primary reservoir! I would recommend at least 150uF or more in that spot. That is, if you want strong bass. I find that grit is better to get in the preamp, than in a power amp crapping out, when playing bass.

JJ sell a can cap at 500uF / 500V for just €11 at my supplier - that's around $15 a piece. Get two of those in series, with some splitters across.

Don't increase the screen supply, but make use a zener to get it down around 400V. 536V as the schematic suggests is simply too high for the EL34 screens.

Good luck with the project!

[Gaz]

Does anyone know what those white electrolytic caps are? Would they be original and in need of replacement?

I'm guessing they must be the two 10uF 400V caps, and assume they must be original since all the other caps look original. I just don't recognize the type... and they don't look as old....

I pretty sure those are two MOV type thingys across the plates for OT protection. One of those burnt out on mine for no good reason (maybe age and repeated stress from past tube failures?) There was a tech bulletin at one point by Traynor to remove them. I would just leave them, but if the amp starts to sound extremely constrained and weak, and the B+ falls dramatically, it's probably those. Of course, they may have failed for good reason. They could always be replaced with more modern MOVs.

And you're right about the YBA1 being the Plexi deal, but Kevin O'Connor says is The Ultimate Tone 3 there was two version. But yes, I think "yours" is the one with the James style tonestack, which is better for bass IMHO.

[bcmatt]

My advice is to get some serious capacitance in that amp's primary reservoir! I would recommend at least 150uF or more in that spot. That is, if you want strong bass. I find that grit is better to get in the preamp, than in a power amp crapping out, when playing bass.

JJ sell a can cap at 500uF / 500V for just €11 at my supplier - that's around $15 a piece. Get two of those in series, with some splitters across.

Don't increase the screen supply, but make use a zener to get it down around 400V. 536V as the schematic suggests is simply too high for the EL34 screens.

Good luck with the project!

Oh oh! You seem to be making a pretty good argument... but I am a very visual person and I'm afraid using zeners and such to alter voltages is beyond my experience. I think I would need to see an alteration of the schematic to understand exactly what you mean. Dramatically increasing capacitance seems like a scary venture to me. I feel like I was sternly warned about that in the past.

So, I take it that you would be in favour of me adding the master volume like the last generation of the YBA3 (page 5 of the schematics). I was considering that already.

[Gaz]

Don't be fooled by the high voltages. Crank one of these amps up to full shred and observe how the screens DO NOT glow like they do in most vintage amps with high screen supplies. This is because the B+ dips down (sags) significantly, which keeps screen dissipation in check. I've measured this a few times. Increasing the main resovior just for the sake of 'bigger bass' may not be advantageous since it would stiffen the supply and perhaps push the screens and plates into over max dissipation when cranked. However, this would probably not be a big deal if the amp was being operated cleanly for bass.

[bcmatt]

Does anyone know what those white electrolytic caps are? Would they be original and in need of replacement?

I'm guessing they must be the two 10uF 400V caps, and assume they must be original since all the other caps look original. I just don't recognize the type... and they don't look as old....

I pretty sure those are two MOV type thingys across the plates for OT protection. One of those burnt out on mine for no good reason (maybe age and repeated stress from past tube failures?) There was a tech bulletin at one point by Traynor to remove them. I would just leave them, but if the amp starts to sound extremely constrained and weak, and the B+ falls dramatically, it's probably those. Of course, they may have failed for good reason. They could always be replaced with more modern MOVs.


And you're right about the YBA1 being the Plexi deal, but Kevin O'Connor says is The Ultimate Tone 3 there was two version. But yes, I think "yours" is the one with the James style tonestack, which is better for bass IMHO.

Oh! OK Thanks! Well, I think it is becoming clear to me that I will need to wait until we have the amp in person before ordering any parts; 2 off-angle gutshots are not enough to go on. Perhaps the 10uF caps are contained in the cap-cans. Maybe they are 40/40/10. I guess I'll have to wait... or look for other peoples' gutshots online.

[Gaz]

And I had the version with the master. I don't really think it's necessary for bass since you probably have it all the way up anyway for max headroom. Depends on how much grit you want, and at what volume. But I'm guess this thing is gonna be considerably quieter than the Markbass, and seems more colored and gritty even at "clean" settings.

[Gaz]

Oh, and the top panel that lifts off will have the schematic glued to it.