Weak tremolo due to low grid voltage off tremolo tube?

[slidincharlie (Carlo P)]

I am overhauling a Silvertone 1472 amp. It's very similar to the more common 1482 with just less volume (maybe due to lower voltages in the power supply section?).
This amp has a weak tremolo: I can barely hear it even with the strength pot set at 12. Also, there is a 4-5 seconds delay when I turn the strength pot to max before I can hear the effect.
Voltages are in specs all over the chassis, EXCEPT on pin 6 (grid 2), where I have 42 instead of 75 VDC.
Can this explain the weak tremolo? What can cause such lower-than-expected voltage? I have tried a different NOS 6AU6 to no avail.
I have also replaced all the components around pin 6 (R30, R31, R32, C14 and C15).Schematic is attached.
TIA,
Carlo

[tubeswell]

Voltages are in specs all over the chassis, EXCEPT on pin 6 (grid 2), where I have 42 instead of 75 VDC.

A leaky cap can throw off grid voltage. Test those other caps for DC

[slidincharlie (Carlo P)]

A leaky cap can throw off grid voltage. Test those other caps for DC

Do you mean those C10 and C11 caps in the oscillator circuit? And also that .0068 cap maybe?
I have already replaced C14 (leaky) and C12 (with a smaller cap for speeder trem rate).
Carlo

[tubeswell]

Do you mean those C10 and C11 caps in the oscillator circuit? And also that .0068 cap maybe?

Well I'd look at C10, and possibly 11 and 12 if the speed pot was scratchy

[Enzo]

How old is this thing? Pretty old, right? You have alreasdy had to replace some caps, so REPLACE THEM ALL.

Your trem doesn;t wake up instantly - that means it is not oscillating. C10,11,12 need to be new. And if all those needed to go, why wouldn't we expect C13,14,15,16 needed to be replaced? Actually C13 is likely the only one in there that is OK.

Pin 6 voltage? What are the resistances of R31,R32? You got the 250v B+ up at the top of R31, R30?

How far off have R26,27,29 drifted from their value?

Turn the trem strength to zero, not measure the voltage at the grids of hte 6V6s - pins 5. Is there any positive voltage there at all? That would be leakage voltage coming through C7,C8. WHich brings me back to have you replaced all the caps yet?

[slidincharlie (Carlo P)]

I replaced the caps that I hadn't replaced before... Now the tremolo is strong and bold as it can be...
I had already replaced a few drifted resistors.
Thank you!

[powen]

I am experiencing the same problems with my 1482.
extremely faint tremolo.
What caps need to be replaced?
I am new to tube amps and would like to take this on as a project-
so any information would be appreciated.

thanks!

[tubeswell]

1st - you should really post in a new thread - these old ones rarely get read past their 'use-by' date.

2nd - always the first thing to resort to with a tube amp is to change the tubes.

3rd - after that then look at the voltages and if they are no good

4th - then change the filter caps and sometimes the other caps as well (and possibly even old resistors - but less likely to be an issue).

[Enzo]

Welcome to the forum. I agree with Tubeswell, best to start a new thread for your amp.

Most of the time I don;t worry about drifting resistor values, although the ones on the power tubes and in the power supply I pay more attention to.

Your electrolytic caps are OLD, and probably dried out inside, and ought to be replaced. The rest of the caps are either getting leaky or they could be OK. If a couple of them are leaky, then replace them all, they all probably need it.

Leaky doesn't mean stuff oozing out, it means electrically leaky, in that they let DC voltage come through. Although if you do see something oozing out of any cap, it is not good. SOme amps that age were made with caps that have lasted, you might be lucky.