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scutterflux 27th December 2010 03:57 PM

3 Caps parallel to series vs ??? Sonic Performance?
OK, I have an old Traynor yba-1a That's needing the power/filter caps replaced as the noise floor is quite audible. This is an old tube amp based on a fender bassman/marshal circut, with a few twists. In the output section the caps according to the schematics run 2 parallel 40uf into 1 in series 80uf, however this has been modified into 1 80uf in series with another 80uf, so the overall value has always been 40uf. I'm just trying to understand the benefits to doing it one way or another, as I will be using this amp primarily as a bass amp, a nice rhythmic response would be desired. I would guess that's why there is an array of caps that would give a greater "reserve" of power while maintaining the desired value. What's the best way to do this? Would there be any benefit to running 4 20's into an 80, or 4 20's into 4 20's or maybe an 80 into 2 40's, I'm confusing myself, please help?

Also I was thinking of going with F&T's unless there's anything juicier?

jeffreybehr 27th December 2010 05:30 PM

Does "In the output section..." mean in the powersupply? Got a schematic you can post?

scutterflux 27th December 2010 06:13 PM

This looks pretty close to mine, The schematic groups 2 40/450's in Parallel, where my amp currently has a single 80/450. Is there any benefit to doing it one way or another?

VictoriaGuy 27th December 2010 06:29 PM

Not the 'whole answer' to your questions but the series-connected caps (and the balancing 100k-2W resistors) in the power supply are to manage the HV (535v DC) using 450v-rated caps.


benb 27th December 2010 07:07 PM

No, and using the two 40's and an 80 like that seems a little bizarre. I can only guess they had a bunch of both 40's and 80's in stock and they wanted to use them all up. It would only make sense to use all 40's or all 80's, and stock one part.

After another moment's thought, I'm guessing the 40's are in a metal can with the negative connection going to the can, and the 80's are in fully insulated cases. Keep in mind even the negative terminal of the 80uF caps at C15 and C18 are 250V above ground, and need to be electrically insulated from the chassis, as well as from random things that might touch them such as fingers.

I googled for some pics and this thread has several:
Traynor YBA-1A ?'s (Pics added) - The Gear Page
The 40's are in the silver cans by the power cord in the second pic, post #3, and the 80's are the three large brown (insulated) cylinders inside the chassis in the later pics.

You may want to use the dual 40/450 metal cans in addition to the 80's in the chassis just to make it look original.

As far as the "noise floor" you say you hear - is this a power-line-related hum, or a hiss? Decades-old electrolytics might as well be replaced on principle, but replacing them will (may) fix a hum, but probably not a a hiss.

scutterflux 28th December 2010 02:34 AM

After looking at Hiwatt and Ampeg schematics, they both had similar idea's with paralleling two smaller values closer to ground than the larger cap. Mmmmm? Somehow would this increase bass response? Seems to be a common trait among (older?) common bass amp designs.

Anyway, amp has hiss and hum, hiss only when cranking treble on the bright channel, otherwise hum, is always there.

So Thanks for the help, if there's no reason for it one way or the other, I might as well just put all 80/450's, but I'll probably go bigger than that.

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