Crackling Peavey Triple XXX

[twangin6]

Got a Triple xxx on a trade that made noise and replaced the power tubes and set the bias. As I was talking to a tech at Peavey about the noise I was hearing the amp started to hum loudly and the two left power tubes were glowing cherry red. I shut the amp down. I swapped the position of the tubes per the tech and powered the amp back up. Now no sound.... any suggestions. Going to check the screen resistors.

[The Dude]

Schematic here:

https://www.thetubestore.com/lib/the...-Schematic.pdf

You may have an open HT fuse. Check F1. Sadly these days, new tubes does not always mean good tubes. After you get power back up, I'd leave the output tubes removed and check voltages at the tube sockets. Make sure you have screen voltage and bias on all tubes. Then reinsert the tubes one at a time and see if one causes problems.

[Enzo]

Agree, the red plating tubes probably blew the HV fuse.

[twangin6]

Agree, the red plating tubes probably blew the HV fuse.

I thought I would put the old tubes in before getting too far into it and it powered up and had output. I thought I would check the bias before running it thought its paces and I get no reading on the bias......??

[Enzo]

Putting old tubes back in it will not "heal" a blown high voltage fuse.

Welcome to the forum, but I have to nit pick. The only time you get "no reading" on the meter is when the meter is turned off. Zero volts or infinite resistance or whatever are still readings.

If your high voltage fuse is blown there will be no high voltage for the tube to make current with.

[twangin6]

Turned out the 6L6's were defective. Had three bad ones out 6 tubes. I had a new set of EL34 on hand that I put in. Amp is working good but I am still getting some frying and crackling noise. Should I be replacing the screen grid resistors? If so what is recommended for the value? I have read different things online.

[tedmich]

I only replace the SGR if they read zero ohms (they do commonly blow) and I usually replace them with 1k 5W versions.
I just did a XXX with 45F1K0E from Ohmite ($1.79 va Mouser)
Even PV "saw the light" and used 750 ohm SGRs in the later JSX version amp. 100 Ohms is just too low for modern tubes IMHO.

[Enzo]

I only replace the SGR if they read zero ohms

Does you perhaps mean infinite ohms, as in open?

In many PV amps, you will typically find the 100 ohms BETWEEN two tubes on a side. The 100 ohms are there to separate the two tubes to prevent interaction, not as typical screen resistors. They then made that four resistors instead of two. FInally they went all the way.

[tedmich]

oops, good catch enzo,! yah open
a lot of ohms!