Problem with my Bogner Shiva

[Rampage]

Well, I have a problem with my Shiva and figured I might swing it by you guys to see if anyone has any ideas about what it could be.

The first time I fired up the Shiva it was perfect. The next couple times I began experiencing problems. The first problem was a high pitched squeal that would start up after a little while of playing. I dealt with it a couple times, then a few days ago when I fired it up the volume was squashed. The channel and master volumes basically did nothing so I started checking tubes. Turns out two preamp tubes were totally shot. I figured it would be a good idea to just buy a full retube and see if that would fix it all (by the way, Doug's Tubes is incredibly fast when it comes to shipping! ).

I replaced the tubes last night and fired her up. Not a problem so I was very happy . I should mention that while I played the Shiva, I left the back cover off the amp.

Well, today I replaced the back panel and fired the Shiva up (I always wait about 30 seconds between going from Standby to Play). After about 20 minutes of Shiva goodness, the original annoying high pitched squeal came back. The squeal doesn't sound like a whistling microphonic squeal. It is like a loud, high pitched hum. The tone will go from being perfect to having the faint squeal, then the squeal gets very loud very quickly and stays at that volume. The squeal sits at a steady volume and frequency after that. When I switch from Play to Standby, the squeal decays like the normal tone, but you can still somewhat hear a similar squealing sound (frequency, speed) coming from the amp (not speakers: from the amp itself) while it is in standby

Needless to say, I was not too happy .

I took everything out of the signal path outside of my guitar, cable, amp, speaker cable, and cabinet. Squeal was still there. I tested my cables and guitar through my practice amp and they all worked perfectly.

This then got me to thinking: Could the Shiva just be overheating? I have the Trafficgreen2+ revision Shiva (Bright switches/Variable boost) which lacks the fan. Coupled with the high plate voltages of the EL-34s in the Shiva and the poor ventilation with the back panel, could the heat be doing a job on the amp?

I moved the amp and cab away from the wall a bit further than it was though, and after playing for 7 minutes (yeah, I clocked it ) the annoying squeal was there. I have still yet to try taking the back panel back off the Shiva (need to let the tubes cool again), but I guess this may throw off my theory.

I was also wondering if this could be related to speakers. I wired up the cabinet myself with some Reinhardt R65s for 4 ohms. I think I did pretty well with the soldering, but I am wondering if the soldering or something else might be bad from my description. I don't think thats the problem, but you never know.

One more thing I should mention: I live in an apartment so the power here might not be the cleanest, could that have anything to do with it?

I really don't want to have to take this to a tech, so I am wondering if anyone has any insight as to what this might be. If I need to take it to a tech though, there is a Guitar Electronics out here so if worst comes to worst, I can do that.

 

['63-Strat]

Did you change your power tubes, and if so, did you bias the amp? What made you think the two preamp tubes were "shot"?

 

[Rampage]

I replaced all the tubes, however I did not rebias the Shiva. I'm not sure if thats the problem though, because the problem also existed with the stock power tubes.

I rotated a good 12AX7 through the amp to check the preamp tubes and found two of the 12AX7s to be problems. One of the bad preamp tubes muffles the tone significantly while it is in the amp and the other is very microphonic (something is rattling around in there like crazy).

 

[Rampage]

Well, I tried it out a bit more. I took the back panel off of the Shiva, let it warm up for a few minutes, then I started playing through it. I was on the OD channel for a while and that was fine. After a few minutes I switched to the clean channel and that damn squealing came back right away. When I switched to the OD channel it was still there. I am starting to think that something might be screwed up with the amp when switching from OD to clean. Switching between normal OD and Boost is fine so maybe there is something flawed within the switching or clean channel circuitry that is causing it. I am going to let it cool back down again then try switching it with the pot on the back of the amp instead of the footswitch.

 

[hunter]

Maybe you just had bad luck and received again a bad preamp tube. Shit happens....

I would check the cab with a multimeter and make sure the amp ohm match the cab ohm.

I have the same Shiva as you, it gets hot but not that hot, in fact my Budda becomes much much hotter than the Shiva, I don't think that's the issue.

Try again all preamp tubes and if nothing works, there is only the possibility to get it over to Bogner or a specialist who can fix it.

 

[Rampage]

Well, I figured I would go over everything one more time yesterday, but nothing worked.

- I swapped around all the tubes with more known good tubes from my buddy's amp. Noise still occured.
- I tightened tube sockets and cleaned them with Caig Deoxit. Noise still occured.
- I cleaned all input and output jacks. Noise still occured.
- I resoldered the speaker cabinet. Noise still occured.
- I took everything out of the signal chain. Noise still occured.

I am going to try the Shiva out on a different cabinet this week and make sure that the cabinet isn't the problem. If the noise is still there, I think I am just going to take it to Gary Lowe at Guitar Electronics. I am thinking though that it is something that has to do with heat as the problem only comes up after playing for about 7-10 minutes which is sufficient time for the tubes to start getting hot. Maybe a faulty tube socket or cold solder joint.

 

[Rampage]

I thought I should update this thread. I took the Shiva in to get serviced and there was a microphonic component. So after all that hassle, all it needed was a tech to look at it and replace a $ .50 part. Oh well!