# Help with Peavey 6505 problem



## reco46 (Jan 11, 2008)

My sons Peavey 6505 is somehow screwed up. The problem is this: on the lead chanel only when you turn the pre gain up past 6 the amplifier just whistles loudly, a very high pitched sound. It does this even when nothing is plugged into the amp! Also the rythym chanel works just fine. We tried everything we could think of - changing cables - changing power outlets but have come to the conclusion it is internal. 

The head is only 4 months old and has had no problems at all.

The only thing that comes up is he did a gig on Friday and after the show he told me when he touched the mike, he got a mild shock which was also felt in his guitar strings. The soundman told him it was probably something with your amp. However the amp performed without a prob during the show.

Anyways after this show - that is when the amp started this prob. I dont know, could that have fried a capcitor or tube or anything internal?

We are taking it in to have it serviced,(thankfully its under warranty) I just hope the service guy wouldnt detect anything not covered under warranty.

Thanks for any reply's!


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## Wild Bill (May 3, 2006)

reco46 said:


> My sons Peavey 6505 is somehow screwed up. The problem is this: on the lead chanel only when you turn the pre gain up past 6 the amplifier just whistles loudly, a very high pitched sound. It does this even when nothing is plugged into the amp! Also the rythym chanel works just fine. We tried everything we could think of - changing cables - changing power outlets but have come to the conclusion it is internal.
> 
> The head is only 4 months old and has had no problems at all.
> 
> ...


I doubt if the shock problem caused any internal harm or is in anyway related to your original problem.

My first suspect would be the very first 12AX7, V!. Some brands of 12AX7's have a bit more gain than the published spec's today. Also, some amps set their circuit up to flog the tubes for way more gain than they were designed to put out. What often happens (I've had a lot of this problem with MESAs and CARVINs) is that the first 12AX7 can actually have too much gain and the circuit goes unstable when cranked up.

It's not that any particular brand of 12AX7 is "bad". It's just that too much is being asked. It's hard for some players to understand that they have a problem using a TungSol 12AX7 which has such a great reputation. It IS a good tube, in a PROPER circuit!

Why do manufacturers do this? Because it's cheaper to try to get extra from one tube stage than to put in 2 stages, with the cost of an extra tube, socket, caps/resistors and space on the chassis.

How do you check it out? Easy. Get yourself a Sovtek 12AX7WA. This is a regular gain tube. Plug it in and see if the problem goes away.

Boogie themselves advise their techs in a service bulletin about this problem. They don't make their own tubes but buy other makes and re-brand them. They make sure to avoid hyper-gain tubes in their amps when they leave the factory.

It's also possible that one or more 12AX7's has simply gone "bad" in becoming microphonic, which means sensitive to vibration. The support parts inside the tube can get loose, allowing the grids or plate to pick up vibration which actually gets amplified by the circuit! Again, some "over clocked" circuits just beg for this to happen. Usually you can identify a microphonic tube by cranking up the gain until it's just starting to act up and tapping the tubes with a pencil. A microphonic tube will pick up the tap like a microphone. The ringing gets caused by actual acoustic feedback from the loose elements in the tube, just like putting a vocal mike in front of the speaker.

Hope this helps.

Wild Bill

:food-smiley-004:


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## Isaac Galindo (Aug 29, 2011)

I have the same problem only at volumes higher than 3. Ive had certified techs from Peavy say that I'm not using the amp right, Ive also had others tell me its a design flaw. I would like to know what you were told and what actions you took to correct this problem.


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