A tale of two Vibro Champs

[matt h]

(deleted)

[xtian]

Matt, I would like to have this trick in my bag. I reviewed the plans at the bottom of this page:

http://www.geofex.com/Article_Folders/m ... tfolly.htm

Is that what you had in mind?

[matt h]

(deleted)

[epis]

Well done identifying the bad grid leak resistor!
But with a 1k cathode resistor, won't the cathode current and plate dissipation be rather different to Fender's design?

I put a 1K, 25W resistor between the recto and the first reservoir cap. It drops the plate down to 347vdc, the cat to 28.1, giving me 70% dissipation!

I don't see the relevance of 70% to a cathode bias SE amp? It seems likely to result in an over biased condition with consequent compromised performance, eg limited power output.

Hi Xtian, you overlooked pdf64's post. You should have 470 Ohms cathode resistor for 6V6, not 1k.
After you replace it all the voltages will be where it is supposed to be without circuit mods.
Cheers, Damir

[xtian]

These repairs are being paid by the seller, so he'll want cheapest.

[cbass]

Well done identifying the bad grid leak resistor!
But with a 1k cathode resistor, won't the cathode current and plate dissipation be rather different to Fender's design?

I put a 1K, 25W resistor between the recto and the first reservoir cap. It drops the plate down to 347vdc, the cat to 28.1, giving me 70% dissipation!

I don't see the relevance of 70% to a cathode bias SE amp? It seems likely to result in an over biased condition with consequent compromised performance, eg limited power output.

Hi Xtian, you overlooked pdf64's post. You should have 470 Ohms cathode resistor for 6V6, not 1k.
After you replace it all the voltages will be where it is supposed to be without circuit mods.
Cheers, Damir

Yes I was getting at that earlier .your voltage will come down with the stock 470 ohm cathode resistor . they will still be a little high cause of higher modern ac voltage. If you put in the stock rk and have 117 wall voltage it will be right in line with what's on the schem