Amp diagnosis please. Give a listen

nevusofota

nevusofota

Well-known member
Bogner Shiva 20th. This began after having the amp on standby for about 10 minutes without a speaker cable connected. I strummed a couple chords before realizing the overlook. Now this happens. It sounds fine until you wait for the notes to trail, then it breaks up and cuts in and out. I’m fully aware of the damage this can do to the transformer but this sounds like a tube issue. I’m thinking power tube because turning the presence knob seems to make it worse.

 
As long as you did not flip the amp off of standby you did not damage the amp.

If you did flip the amp off of standby and then caught the fact that you did not have the speaker(load) on the output transformer then you may have damaged the power tubes, stressed the screen grid resistors, stressed the HT fuse it it did not blow. I doubt you did any transformer damage, from your description I would say you damaged the power tubes, I would start there first then work you way backwards.
 
Thanks for the responses!

I did flip off of standby, strummed a couple chords, then realized the mistake pretty quickly. I haven't had a power tube go bad in any of my amps in a long time but I seem to remember it sounding something like this.
 
Could be preamp as well. Try different channels or plug into the loop return and see if it cuts out
 
I think it's a preamp tube, too. You can tell because if you let the chord ring out, it does not cut out on volume, but creates weird fragments and the gain structure breaks apart while you can still hear it on the same output level if that makes any sense.
A power amp tube would most likely cause it to go whacky from loud to silent and inbetween, at least that's what my amps did when a power tube was KIA.

:rock:
 
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