Traynor YSR-1 mysterious electrolytic capacitor

[mlannoo]

I am replacing all the electrolytic capacitors in my YSR-1. The original schematic does not show C1 and C2 ... in fact, C3 is the first cap shown.

But in my amp, there is a 125uf/16v electrolytic parallel with R7 (see attached drawing please). I'm assuming this is C1 but just wondering why it isn't on the schematic. and where's C2?

Secondly, I noticed on different model Traynors from the same era they used a 250uf/16v for C1. How does this cap's size effect the sound of the amp? Can I safely experiment with other values? I don't have a 125uf/16v cap laying around but I do have a 500uf/50v I thought I might try.

Any thoughts? Thanks in advance.

[52 Bill]

That's a cathode bypass cap. In general terms will increase the signal gain of the stage. Larger values will add more low freq. boost, smaller values will add high freq. boost.

The standard Fender blackface value is 25uF. The original Fender tweed Bassman used a 250uF value. If you look at different schematics, you'll find values from as small as .47uF to as large as 250uF. Some designs will have a switchable bypass cap.

I'd suggest a smaller value than the 500uF that you have on hand.

[loudthud]

Traynor amps frequently don't match the included schematic exactly. Many times I have found amps that look original but don't match any published schematic I've ever seen.

[mlannoo]

That's a cathode bypass cap. In general terms will increase the signal gain of the stage. Larger values will add more low freq. boost, smaller values will add high freq. boost.

The standard Fender blackface value is 25uF. The original Fender tweed Bassman used a 250uF value. If you look at different schematics, you'll find values from as small as .47uF to as large as 250uF. Some designs will have a switchable bypass cap.

I'd suggest a smaller value than the 500uF that you have on hand.

do you have to also change the resistor if you change the cathode bypass cap value to keep things the same? i'm assuming if i change the cap value, that will change the amount of load on the plate correct? is it OK to do that without considering that resistor? it sounds like if i increase the cap's value i should decrease the resistor?

[52 Bill]

No leave the resistor as is and try different cap values. The bypass cap will only change the ac signal gain. Changing the resistor will change the dc load.

[Enzo]

And if you still don't know where C2 would have gone, I'd be guessing it went across R9, in the same fashion as C1 and R7.