Another VVR2 in a Ceriatone Liverpool

[kineteks]

Help! ...it howls at anything over 1/4 volume, I've obviously made a big mistake. Prior to the VVR installation I was in pretty good shape but that's history now....
I'm guessing the caps & resistors added at the volume pot & input jack are installed in an unacceptable manner? ...or the NFB wire is too close to the VVR mosfet? ...or?
Once again comments and observations are much appreciated.

[UR12]

The resistor/caps looks ok but you migh try chopsticking some of your wires, starting with the red one going to the 25w resistor. try moving it away from the power tubes and screens wire.

Does the howling you are hearing start at 1/4 vol on the volume control or with the VVR power control?

[kineteks]

Hi Dana...
VVR power control is on max.
Howl starts with volume pot at more than 1/4. The howl starts softly and quickly builds in volume.
I've chopsticked as many wires as will move with no noticeable effect. Tapping on the cap coming from the volume pot center lug gives a loud tapping sound but I can't find a wire or component that changes the way the howl starts & builds. The NFB wire is solid core and tough to make move any significant amount. I'll move the red wire as suggested. Do I need to look at any wire that gets near the mosfet? Could one of the new caps added at the input jack & volume pot be bad? I have more, is it worth changing them?

[kineteks]

Moved the red wire about as far away from the power tubes/screens wire no change at all. The howl/ringing tone builds slowly and likewise when I turn the volume back down it dies slowly, and sounds exactly like mike feedback. It really seems to start (very softly) with any volume at all.

[El_Martin]

Hi kineteks!

Did you install the VVR and the added R's/C's at the same time?

If so, I'd suggest to reset to usaual Liverpool layout and having the VVR as the only modification. Should be easier to track down the howl...

I had some trouble with my VVR too, but it was not a kit from Dana.
In fact, there is an oscillation around 70% Voltage. Haven't fixed it yet. Should be fixed w. some better PowerFets. (Rds/on might be too high on my current Fets).

Ciao
Martin

[ant]

Try swap the output trans primary wires on pin 3 around

[UR12]

With the VVR set to full it should effectively be out of the circuit so to speak. You can try to isolate the problem by removing the B+ in and B+ out from the board and temporarily soldering them together. This will completely remove the VVR from the circuit. If the osc is still there then the problem is in the amp and not the VVR. Have you tried a different tube in V1?

[kineteks]

I tried a couple of other tubes in V1, NOS GE & new J&J, I have more & will try them all later.

What is it telling me when the problem is much reduced without a guitar plugged in? Then I need to have VVR & volume at max, presence, bass & mid maxed and treble over 1/2 before it starts to squeal?

I'm thinking after trying all my 12AX7s in V1 I'll start by restoring the input jack to it's original config (remove the cap and reposition the resistor), then the volume pot ( remove the cap & resistor ), then jump the B+ in/out as Dana suggested & then start moving wires on the power tube sockets.

I did swap the order of diode to filter cap to standby switch from the standard Ceriatone layout as Dana suggested, could one of those wires be too close to something?

Will twisting any wire pairs besides the heaters be of any value?

[UR12]

I tried a couple of other tubes in V1, NOS GE & new J&J, I have more & will try them all later.

What is it telling me when the problem is much reduced without a guitar plugged in? Then I need to have VVR & volume at max, presence, bass & mid maxed and treble over 1/2 before it starts to squeal?

I'm thinking after trying all my 12AX7s in V1 I'll start by restoring the input jack to it's original config (remove the cap and reposition the resistor), then the volume pot ( remove the cap & resistor ), then jump the B+ in/out as Dana suggested & then start moving wires on the power tube sockets.

I did swap the order of diode to filter cap to standby switch from the standard Ceriatone layout as Dana suggested, could one of those wires be too close to something?

Will twisting any wire pairs besides the heaters be of any value?

The changes to the power supply wiring shouldn't be a problem. The Liverpool is a high gain amp and any changes you make can affect something else. One of the tests I use when building a new TW amp is something my brother Richie does to test for good tubes in V1. We take the amp and turn up all of the knobs to 10 without any guitar plugged into the amp. Turn the amp on and flip the standby switch. If the amp squeals and you know the OT leads are right then we start swapping different tubes into V1 until we find one that doesn't oscillate. then check it with a guitar to make sure it sounds good and is not just a weak dud tube. Sometimes you have to go through a dozen tubes or more just to find one that will work in V1 with out oscillating.

Twisting the wires to the pot might help but I doubt it. I think the most important thing is to start eliminating things, like the VVR. Sometimes it is better to have the caps and 1 meg resistors close to the tube socket but it should work the way you have it.

[Tubetwang]

Good info there Dana...

Thanks!!
Twang.

[kineteks]

Thanks Dana I will go through the pre-amp tubes I've got before changing anything else. I don't have dozens to try, more like 8... but 4 more are on the way

The cranked-volume hiss is quite a bit louder than the pre-VVR configuration. Dartanion's suggestion to stand up the grid & screen resistors and re-route the NFB wire got rid of a previous oscillation problem and dropped the hiss volume way down, it's now back to, or louder than it was before that change.

One step forward, two steps back. I love this amp though...

If I did move the caps/resistors down to the tube socket, where should I ground the resistors, the central star ground?

[kineteks]

double post

[kineteks]

Update...
Well I tried all of my 12AX7s including pulling 6 out of other amps, that makes 14. Although interesting 'cause I've never tried that many tubes back to back, they all howled with a guitar plugged in but 3 gave no howl with the guitar unplugged.
Removed the input jack cap & resistor and repositioned the 1 M resistor as it was... still howled.
Removed the volume pot cap & resistor and replaced the wire as before the mod.... still howled.
Completely removed the VVR2... big surprise (not) ...it still howled.
So... I've obviously moved some wire or component unintentionally during the VVR installation?
I've chopsticked the living hell out of everything I can move with no discernible (by me anyway) change. I'm getting ready to rip it all out and start over!
2 days ago this thing was sweet... now she's mad at me. Bad karma for trying to make her so I could play her more often?
I'll give her the night to cool off and see if she'll warm up to me tomorrow.
Sheesh! ..talk about in over your head.

[billyz]

Did you check the power tubes?

[lewilson]

Kinda grasping at straws but sometimes a speaker wire will cause something this .