Grounded caps in pin 8 of V1-V2 Fender

[chocopower]

Hello!

I recently bought a Guyatone GA-1050. Is like a Pro-Reverb, but with diode rectifier. (soo..... a 45 watt´s Twin Reverb )

Comparing whit the original one, i found:

1.-My amp don´t have the 820ohm/25uf grounded pair in V1-V2´s pin 8.
It just have a 1500ohn resistor grounding each pin 8.
Should i put it like original schematic?

2.-Most electrolitic caps who are 25uf in original, are 33uf in my amp.
Should i change it too?

3.- Bias cap, 25uf-50uf in original, is a 47uf in my amp...... again......should i change it?


Best regards from Spain...... and sorry for my bad inglish

[Rob Mercure]

If I understand you correctly the output tubes don't share a common cathode resistor and capacitor but instead have individual cathode resistors - if so and the amp works well then you don't need to change them. Sharing a resistor does kinda force the tubes to work in the same region and bypassing the resistor (s) with a cap will provide more gain.

Otherwise the cap size choices are just modern equivalents of older values that were once common - and since the older common values were specified as +/- 20%, or greater, there really isn't any difference.

Again, "if it ain't broke don't fix it."


Rob

[MWJB]

1 - This mod is often performed on Fenders. You don't say whether the 1500 ohm resistors have their own bypass caps, as tolex fenders have? To voice it like a Fender you could make sure that these bypass caps are 15uf, but as Rob says it doesn't "need" fixing.

2 - what Rob says.

3 - 47uf is fine, check the voltage rating, 100v would be good.

[chocopower]

1 - This mod is often performed on Fenders. You don't say whether the 1500 ohm resistors have their own bypass caps, as tolex fenders have? To voice it like a Fender you could make sure that these bypass caps are 15uf, but as Rob says it doesn't "need" fixing

Hi again, and thank!!

No bypass caps in those 1500ohm´s resistors.
Just the resistor to ground.

I´ll test a 15 or 25uf bypass cap in the Normal Channel. I´m modifying it to Bassman59 / Marshall specs (via a switchable tone-stack) and a little more gain will be cool....


best regards from Galicia (Spain)

[chocopower]

3 - 47uf is fine, check the voltage rating, 100v would be good.

I cheked it last night...... 144v.

Is it a problem?

[MWJB]

No, that's fine.