Amp Squil at hi Volume

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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DaveWell
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Amp Squil at hi Volume

Post by DaveWell »

Hi,
I just Finish a new Express...
The Squil Hi frequency at volume cranked over 9...

I replace every tube, and still the same probleme..

Neep Help and Advive here Please
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pompeiisneaks
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Re: Amp Squil at hi Volume

Post by pompeiisneaks »

Sounds like you need to swap the output transformer leads on the output tubes. Your negative feedback is out of phase and causing positive feedback. Or at least that's where I'd start.

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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

At low volume every things ok, until the is crank full clockwise
Last edited by DaveWell on Sat Jun 17, 2017 1:31 am, edited 3 times in total.
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xtian
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Re: Amp Squil at hi Volume

Post by xtian »

Can't fault your lead dress--beautiful!

Try moving your OT primary wires away from OT secondaries.

Try totally disconnecting the gNFB, just as a test.
I build and repair tube amps. http://amps.monkeymatic.com
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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

Before weld the output wire, i test it with alligator clip, and switch the purple and green wire position caus it was noisy as hell...
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geetarpicker
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Re: Amp Squil at hi Volume

Post by geetarpicker »

On my original '89 Express it would ocassioanally do this when it was new. The fix was a small piece of foam rubber to keep the OT primary wires coming off the tubes tucked down tight against the chassis right as they went under the power supply board. On your amp these same wires are longer and looped back to the back panel and are elevated. Perhaps try shortening these for more of a straight shot over to the OT, and route them down against the chassis instead of having them go over other wires. I also note you shielded the signal wire going to the 2nd stage, where on an original this is left unshielded. On an original the only shielded wire is off the input jack. Oddly I've sometimes seen shielded wire actually cause issues, so it might be worth a shot investigating that too. Perhaps rigging up a buss bar on the pots would help, though with those pots (can't solder to stainless cans) you may need to elevate it on eyelets off the shafts. A grid stopper or two may be needed, but I would leave that as a last resort. In the end though you should be able to fully dime the amp (including the tone knobs) without any stability issues as long as he tubes aren't too microphonic. Hope that helps! GK
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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

Thanks All For the Help...
But I still have the same problem...

I Have put a 68K at Pin 7 V1 and a 820R at pin 2...

I move the OT primary wires away from OT secondaries, short wire and as close as possible to the chasis.

Still the same Problem.... Loud squile high frequency volume cracked a 8.5... ( on 0 to 10)
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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

The Amp is Fix !!!

A forgotten ground... Damn !

No more Squil !

The Amp Sound Awsome !

Thanks All for your Help And Advise !

Sorry for that NOOB Mistake !! lol
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xtian
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Re: Amp Squil at hi Volume

Post by xtian »

What?!? You forgot to ground the filter caps, and the amp even worked at all?
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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

Yep... The amp was sounding but nothing caompare after the filter cap grounded...

Weird hein !
Last edited by DaveWell on Sat Jun 17, 2017 6:47 pm, edited 1 time in total.
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sonicmojo
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Re: Amp Squil at hi Volume

Post by sonicmojo »

I think you mean the presence pot wasn't grounded. I could see that causing the problem.
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DaveWell
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Re: Amp Squil at hi Volume

Post by DaveWell »

No , the presence pot is grounded on his own post.

that was the 2 20uF filter cap
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Re: Amp Squil at hi Volume

Post by sonicmojo »

Ok, I was confused by the new black wire, it looks to me like you have the caps grounded in two places now. Why not just a single common ground point for them all?
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xtian
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Re: Amp Squil at hi Volume

Post by xtian »

sonicmojo wrote: Sat Jun 17, 2017 8:25 pm Ok, I was confused by the new black wire, it looks to me like you have the caps grounded in two places now. Why not just a single common ground point for them all?
Because grounding the reservoir cap(s) at the PT CT or nearby, and grounding the preamp filter caps at the input jack or nearby, is a proven grounding scheme to reduce hum.
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Re: Amp Squil at hi Volume

Post by RJ Guitars »

Thanks for posting this up and sharing the experience including the lessons learned. No doubt somebody in the future will experience something similar and maybe benefit from your work. Can't wait for the sounds check...
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