AC30 screen and grid resistor values

[allstonma]

Hi All
Have a 1964 AC30/6 on the bench for servicing.

Watched the psionic audio YouTube clip on servicing a similar amp (link below) and he recommends raising screen resistors to 1k (from 100) and Grid resistors to 3k (from 1.5, probably use 2.7k s) to account for the lower quality of current tubes. Anyone got any thoughts on this ?

Also the amp has a non stock output transformer, a Stancor A-8053 which seems to have fairly similar specs. Been in there for years and my guy hasn't had any complaints about it so Im inclined to leave it in unless this is a really bad idea.

Many thanks
TH

[PRR]

Is it working now? Good?

I'm not keen on change for the sake of change.

What could be wrong on a Stancor of the right specs?

[HotBluePlates]

Hi All
Have a 1964 AC30/6 on the bench for servicing.

Watched the psionic audio YouTube clip on servicing a similar amp (link below) and he recommends raising screen resistors to 1k (from 100) and Grid resistors to 3k (from 1.5, probably use 2.7k s) to account for the lower quality of current tubes. Anyone got any thoughts on this ?

Do what you like.

I own a 1964 Domino Super Reverb, a 1963 AC30 Bass, a 1964 AC30 Top Boost, a 1964 AC30 Super Twin, and a 1965 AC10 Twin.  Where screen resistors are present, I leave the original 100Ω resistors.

I think the risk/need is vastly overstated.

[allstonma]

Is it working now? Good?

I'm not keen on change for the sake of change.

What could be wrong on a Stancor of the right specs?

Working ? Well, yes, in the sense that it made sound, but it was pretty anemic probably because it arrived with two blown out screen resistors which got me thinking about this. So not change for the sake of change, just something to do if it's a good idea...
As to the Stancor, dont know anything about them. From your response Im guessing they are regarded as solid ?

Anyway thanks for responding.
TH

[pdf64]

With a full compliment of functioning valves, what’s the mains and heater VAC, and the HT VDC, at the reservoir cap?
The design puts the EL84 dissipation really high. If the mains voltage is higher than intended (using the heater voltage as a guide for this) then the EL84 take a hammering, and screen grid shorts become more likely.
I suppose altering the screen grid resistors might help to accommodate that scenario, but it seems better to try to address the root cause.

[tubeswell]

Another vote for leaving the Stancor where it is. Very good xformers.


(On the other hand, if your customer wants it removed, send it my way and I’ll dispose of it free of charge).