Master at 6+ loud SQUEAL

[JohnnyCrash]

Got my 36w fired up today.

I had some cold solders, then the two EI Elites I bought were BOTH microphonic! Swapped them out, got it running... AND THEN:

I notice with the Volume dimed I can hear my guitar with the Master at zero. THEN when I try to turn the Master up past 6 or so, it starts squealing like a stuck pig!

1. Why the quiet volume at zero on the Master (it should have NO sound instead!)?

2. Why can't I crank the Master past 6?

Sounds great though! I'm not sure if I would ever need it past 6, but it would be nice to know I could dime it if ever needed

[tw001_tw]

JohnnyCrash -
This may or may not help - you might want to wait until an expert arrives. But
I had the same problem on an 18 watt. (volume coming out when volume knob was set to zero)

I replaced the resistor that is between V1/pin 6 and the high voltage, from the
recommended 100K to a 330K. I initially tried at 220K, and it improved it
dramatically, but the 330K got rid of the problem completely.

May or may not help, but good luck regardless.
-tw

forgot this - I can not comment on the squeel past 6 - I never took mine past
3 or 4 until I fixed it - it was too loud.

[playazinc]

I hate those EI elites they are ALWAYS microphonic. Try moving around your MV wiring, get it away from PI.

[JohnnyCrash]

JohnnyCrash - I had the same problem on an 18 watt. (volume coming out when volume knob was set to zero)

I replaced the resistor that is between V1/pin 6 and the high voltage, from the
recommended 100K to a 330K. I initially tried at 220K, and it improved it
dramatically, but the 330K got rid of the problem completely.

May or may not help, but good luck regardless.
-tw

forgot this - I can not comment on the squeel past 6 - I never took mine past
3 or 4 until I fixed it - it was too loud.

Thanks for the tip!

Yeah, it's only in my TMB channel, so I was thinking it was somewhere in the TMB's Volume and/or Tone Controls. I was checking for weak grounds in that area.

Pin 6 (one of V1's Plates) is where the TMB channel's Volume pot drops into the mix (via a 0.022uF cap ending at the 100k in question) - so your suggestion totally makes since even for the 38w version/build.

Could be the cheap 500k pots I'm using too

I got great pots all around, but the 500k ones were from a different order/batch and physically look different than the other pots

Perhaps swapping for a 1m on my Volume pots will help as well... I'll start troubleshooting in the morning. Thanks again!

[JohnnyCrash]

I swapped V1's Plate resistor at pin 6 with a 220k.

Still get nothing but squeal after 6 on the Master (with the TMB's channel volume on 10).

And like tw001_tw's suggestion, it didn't even make much of a difference IF any. The Master on zero still has some sound from the guitar...

I'll dig for a 300k+ resistor and we'll see how that works out... I'll be back with my results

The amp sounds great, but I'd like to be able to completely dime the thing, just to make sure it works 100% - and you never know, I just may play a GIANT outdoor show.

Besides, I'm building a new Attenuator, so I'd like to hear the amp dimed

[twangbanger]

could be a problem with lead dress or you need to use shielded wire for the MV! I also will never buy those EI 12ax7's have bought 3 and 2 were microphonic right out of the box and one went microphonic shortly after!However I do like their el84's.

[JohnnyCrash]

I moved some of the more likely locations for crosstalk and got a slight improvement.

I'm using shielded wire off of the Master's pot (both from the Treble pot, and to the board).

I'll look into rerouting more preamp wires to make sure I can clear it up... I could've used shorter wire for some spots too.

I have no 330k resistors, so crosstown traffic may be the best thing to avoid here.

[engels]

I have a squeal problem on one of my builds which I haven't solved yet, but I was questioning about it a lot and what people say is this must be a feedback from the output stage.
Possibly from the output tube(s) cathode(s) to the master pot.

Have you tried to remove the master pot just to test it?

[JohnnyCrash]

I'll do that as well.

Haven't had time to really do anything with it yet.

Thanks for the suggestion