# Unexplained Hi pitch Feedback comming out of 80's Superchamp



## urko99 (Mar 30, 2009)

Gentlemen;

I have never experienced this before, but I'm have a high Pitch feedback coming out of my Superchamp(1983 Rivera), while it is on with my guitar is plugged in. It kinda comes and goes, but goes away when I turn the amp on and off. But then it comes back. All pedals are off.

Could this be a Tube issue? The tube lineup according to the tube chart is 2, 6V6 Power tubes, 6C10, 12AT7, 7025.
What I have in the amp is 2, 6V6, a* "6D10" *, *"12AU7A", and a "12AX7EH"*. It looks like some of these tubes are not the correct ones according to the chart. Could this be part of my problem?
Otherwise, I'm very happy with the Tone of the amp, (besides the feedback of corse). I'll be the first to admit, I'm Illiterate when it come to tube amps requirements, tube interchageability, or reading schematics so I'm seeking some advice from the amp techs in this great Forum. I am concerned about loosing the tone if I switch the tubes to exactly what the tube chart says. I drive the amp pretty hard with the Volume on 10, and the Master on 7. I do not use the lead channel at all. Need help and advise!
Thanks in advance.


----------



## WCGill (Mar 27, 2009)

Tap your preamp tubes with a finger and see if you can make them ring or feedback. If so, then it's a microphonic tube and should be replaced. Definitely put a 12AT7 in where it belongs.


----------



## Sneaky (Feb 14, 2006)

Could be microphonic tubes. I would start by putting the correct pre amp tubes in there. A 6C10 can be hard to find, and expensive, but you can often find used ones on E bay. Same with a 7025, which I think is just a low noise version of a 12AX7. In fact I'd try a different 12AX7 in that slot first to see if the noise goes away.


----------



## washburned (Oct 13, 2006)

I'm thinking the 12au7 is the problem. IIRC it is hotter than a 12at7. the 6d10 should be ok as it is less powerful than the reccomended tube.


----------



## dtsaudio (Apr 15, 2009)

Neither the 6D10 nor the 12AU7 are running correctly. These should be replaced with the correct ones. 
Tube Depot has 6C10 ($34.95 ouch). It will make a difference in your sound though, as the correct tubes are going to add significant gain. The 12AX7 is fine. A 7025 is just a military spec'd 12AX7


----------



## urko99 (Mar 30, 2009)

Gentlemen, thank you so much for your replies. I have 3 spare 6C10's I picked up a while back, and I'm on the hunt fo a 12AT7. I will post a reply on the results. Thanks Again!


----------



## Astroman86 (May 6, 2010)

what does microphonic mean?


----------



## washburned (Oct 13, 2006)

Astroman86 said:


> what does microphonic mean?


means that the tube components behave like the cartridge in a microphone and transmit any vibrations etc to the amplifier circuit.


----------

