.22 howling feedback

[jbal122819]

my .22 recently started howling sometimes when I hit a power chord. this is not on High Gain, it starts like a Santana feedback but just keeps going even if I turn the volume off !!!
I looked at the tubes and they're all glowing the same color - what do I check next ???

 

[Buddy]

I'd start swapping pre amp tubes .

 

[plumptone]

+1. Sounds like it's pre-amp tube related.

 

[stomper]

Is the reverb on? Turn it off and see what happens.

 

[jbal122819]

Reverb is ALWAYS off since it's maybe the Worst Reverb I've ever heard.
Fortunately I only use the amp in a studio.
I'm gonna try swapping out the preamp tubes in order - I think they are all 12AX7's . Does the brand matter all that much ?- oooops - bag that comment 'cause it's sure to start a Firestorm

 

[stomper]

Before you swap tubes, try tapping on them lightly with a Sharpie pen while the amp is running. You might hit the microphonic one and make it start to howl, saving time and trouble.

 

[jbal122819]

I changed the V2 tube and the howling stopped - also gave me more headroom on Clean settings!

Funny thing when I tried changing V1 with a 12AT7 I lost all my High Gain - it sounded cleaner than the clean.

I'd like to tame the High Gain a little but it doesn't sound like there's much of a middle ground between 12AX7 and 12AT7 in the V1 socket - any suggestions?

 

[V3]

Find a good NOS 5751 like an RCA, that should cut some gain without killing the od all together.

 

[stomper]

Find a good NOS 5751 like an RCA, that should cut some gain without killing the od all together.

Good call. They will lower the noise floor too.

12AT7 tubes are not good in gain stages. They can be microphonic when fed a lot of gain. They are basically two separate tubes in one bottle. 12AT7 is good for reverb and phase inverters. Stay with 12ax7, 7025, or 5751 in the gain stages.