I have completed restorations on two guitar amps in recent times.
Both had crackle and pop noise problems and in both cases it was necessary to change the output tubes to get rid of the noise. Yes - I changed the screen resistors etc first.
I now have a matched pair of black plate RCA 6L6 "pulls" which test at 95% of gm (from a Tiesco R12)
and a matched quad of 6L6GC STR "pulls" (labelled Mesa Engineering) which test at 100% gm (from a Fender Twin Reverb)
In both cases the noise is the only problem with them.
I believe that the noise is due to overstressed screens. Is there anything I can do about these tubes to try and recover them or is it a case of the screens are damaged so just trash them?
Any weird ideas like sticking them in an oven, .... etc entertained. These tubes a worth a few experiments to try to recover them and if I manage to destroy them in the process - well no real loss, I can't use them as they are.
BTW I have a tube tester on which I can pull stunts like hitting them with extra heater volts for a short period etc ( I found that that works sometimes to clear cathode leakage).
Cheers,
Ian
Both had crackle and pop noise problems and in both cases it was necessary to change the output tubes to get rid of the noise. Yes - I changed the screen resistors etc first.
I now have a matched pair of black plate RCA 6L6 "pulls" which test at 95% of gm (from a Tiesco R12)
and a matched quad of 6L6GC STR "pulls" (labelled Mesa Engineering) which test at 100% gm (from a Fender Twin Reverb)
In both cases the noise is the only problem with them.
I believe that the noise is due to overstressed screens. Is there anything I can do about these tubes to try and recover them or is it a case of the screens are damaged so just trash them?
Any weird ideas like sticking them in an oven, .... etc entertained. These tubes a worth a few experiments to try to recover them and if I manage to destroy them in the process - well no real loss, I can't use them as they are.
BTW I have a tube tester on which I can pull stunts like hitting them with extra heater volts for a short period etc ( I found that that works sometimes to clear cathode leakage).
Cheers,
Ian
Some tubes are just noisy. I have a 6GH8 or two that's downright crackley in Frankenhouse. Socket oxidation will also cause this. If adjecent components are okay (you replaced resistors, unlikely) and the socket is okay, then it's a good bet the tubes are worth replacing. Can't say I know what causes the noise though; possibly cathode wear? Might try heater at 120-150% rated for ten minutes to see if it changes anything. Probably will just shorten the life even more, so whatever.
Tim
Tim
One thing you might try is resoldering the pins.
Because guitar tubes are ususally mounted upside down (in combos anyway) sometimes the solder in the ends of the pins melts or gets crystallised causing an intermittent connection.
Just a thought...
Also melted screens you might be able to see with a bright light or something... If you definitely decided they were dead you could try putting voltage on the screen with no anode voltage, getting them to glow red so you can see em. Always fun
Because guitar tubes are ususally mounted upside down (in combos anyway) sometimes the solder in the ends of the pins melts or gets crystallised causing an intermittent connection.
Just a thought...
Also melted screens you might be able to see with a bright light or something... If you definitely decided they were dead you could try putting voltage on the screen with no anode voltage, getting them to glow red so you can see em. Always fun
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.