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[DIY] Amp Squeals!

4/1/1998 8:57 PM
[DIY] Amp Squeals!
First of all, thank for all reply.  
(Steve, Bruce) I found fender tweed  
deluxe schematic in ampage and built it!  
(I am not an expert. It's my first work!)  
But now, whenever I turn the volume and  
tone knob, it screams and squeals. I read  
the article by Brucee and change the output  
transformer input line polarity. But nothing  
specific happens.  
What can I do?  
Thank you very much!
4/2/1998 2:13 AM
Dave H

Make sure you have one side of the output transformer secondary connected to chassis. They can squeal if you donít do that.  
4/2/1998 4:37 AM

Kim -  
Well done on the DIY project. I'm sure you'll get there in the end, and be very happy with it when you do. Can you get any playable sound out of it before the squeals and screams begin?  
I too built a DIY Tweed Deluxe from the Ampage schematic (using an old Newcomb phonograph as the basis), and mine squeals - but only when tone is turned up near full with any significant volume on Channel 2 (even with no input signal).  
This hasn't been a real problem because that channel doesn't sound great with tone up high anyway, and I can play Channel 1 (the one connected more directly pre-tone) on 10 with no trouble at all - and great, FIERCE, rich, warm tone. But I'll try what Dave H suggests and see if that solves the squealing.  
Anyway - one thing that DOES puzzle me, and I'd be curious to know if yours is the same if you get a chance to play it without the squealing - is that my Channel 1 goes from no sound at volume 0 to near full-blast at 1 (what you'd expect at about 4-5 on a Deluxe Reverb) then some increase in distortion and compression from 1-6, and no significant change after that (just, again, some increase in compression - as I'd expect).  
The 1 meg pot I used in Vol 1 was new from Mouser, but could it be that's the trouble?  
Any help greatly appreciated.  
4/2/1998 8:52 AM
Make sure you construct the amp  
using the original fender layout.  
Also, in Gerald Weber's most recent  
book there is some information on  
preventing oscillation in these amps  
by moving a capacitor.
4/2/1998 9:59 AM

Thanks, Dave -  
When you say "using the original Fender layout" do you mean that's a slightly different schematic from the one on the Ampage shematics page?  
I've got the Tube Amp Book. Would one of those Tweed Deluxe Fender shemes do the job? If so, I'll compare and make changes - but your recommendation would help.  
Also, I haven't got access to Gerald Weber's book (a delayed and costly mailing job to me here in London, I fear).  
Can you say briefly what that cap change/move would be? It would be a big help.  
Thanks again.  
4/2/1998 4:51 PM

Dear Dave,  
When I say you should copy the layout,  
I mean the pictorial representation  
of the inside of the amp.This diagram  
will show where all the components  
should be placed for optimal circuit  
operation.There are several different  
Tweed Deluxe Model Numbers.The most  
desirable is supposed to be model numbber  
5E3.This layout is pictured in Weber's  
Desktop Reference of Guitar Amps and  
Dave Funk's Tube Amp Book.The coupling  
capacitor that feeds the power tube grid can  
be unsoldered on top and moved 90 degrees.  
This value is .1 at 400 volts.This tip  
is in Weber's latest book.If you can't  
find a pictorial layout in England,  
e-mail for further information.
4/4/1998 8:10 AM

Thanks, Dave -  
Yeah, I see what you mean by layout now (should have understood you in the first place).  
I'll check whether I've got one here (haven't got many books, and I don't recall whether there's one in Pittman's book). If not I'll e-mail you as you very kindly offer.  
I'm kind of stuck with a lot of aspects of my layout because everything is squeezed into the chassis of this 1961 Newcomb tube record player that I converted, with a chassis probably only 1/2 or 2/3 the size of the Deluxe, but I can probably at least get an idea for what should be where relatively speaking.  
Also, I'll take a look at that coupling cap when I get some free time in a couple days and see if moving it helps. I had wondered before if this squeal might be due to some internal feedback from components just too close together.  
The fact that it only happens with tone up high and Vol 2 up to midway or beyond implies this might be the case - but this fact also means it's not a big problem, because I'm usually playing through Vol 1 anyway.  
Thanks again. I'll look into these things and get back to you.  
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