Bummer - sparks on V5 pin 7 - 18 watt

[Lindz]

I was quite proud of myself yesterday after installing a Ruby zener mod on my 18 watt - sounded great, got rid of the buzz I was chasing. I had played it for about an hour or so and just thought I would double check voltages since it seemed to be running hot (output tubes seemed quite bright (pins were glowing), smelled "hot" - not burning though).

brought it upstairs to my workshop, connected speaker, warmed it up, clicked it on and got my meter out. I went to measure voltage on pin 7/v5 and got a very noticeable spark on the pin and the meter immediately overloaded ..... shut amp off but the damage appears to be done - bummer

I am positive I did not touch anything except the pin so I don't think I shorted it by careless meter placement (I'm a noob and still pretty intimidated by DC voltage and am VERY careful) - I have a shitty meter but it was in the correct mode - DC high voltage setting with my leads on the correct inputs so I don't think it caused the short

I'm kind of perplexed but have a few questions about how to proceed

I'm assuming that because it was pin 7 on the EL84 it likely took out the OT (or the OT had the short) .... correct?

Should I risk a set of tubes and boot it back up as is in case it was a just bad tube, or are sparks as I describe not indicative of a bad tube? Is there a really simple way to detect a short on the OT?

If I drop in a new OT, what other components tend to go with a short like this? I might as well replace a few parts while I am in there to minimize the risk of blowing a new OT 5 seconds after I turn on the amp again.

Lastly, I am assuming that since I played the amp for an hour after installing the Ruby mod that the Ruby mod itself is not the immediate cause but does the modded amp run harder or much differently than stock? i.e. enough differently that I should have checked bias or changed resistor values elsewhere besides the mod itself? I just fired it up after the mod and started jamming - ha ha

I was playing through a Weber mass with the amp dimed as well. I've read that there can sometimes be impedance issues with attenuators (My Mass does not have an impedance adjustment and the docs say it does not need it). Perhaps me running it biased a little hot on the attenuator with the amp dimed I simply cooked the OT and it was just a coincidence that it did not crap out until I went to test the voltages...?

sorry for the Noob questions but any input would be appreciated

[Andy Le Blanc]

yank the tubes in the power side and visually inspect the tube sockets

arcing leaves a mess that will arc again

check the screen grid resistors, and wire dress around the sockets for any debris

with the tubes out measure circuit voltages, see if the opt, pt, or ps has issues no load..

with tubes in, do the same (with a load), use bench tubes, ones that are good but used
dont want to cook good tubes.

work your way from the power supply thru the power tubes on to the inverter
and see what you can find.

everyone has oh crap moments