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Post subject: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 5:23 am
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This amp plays very well. The only problem I have encountered is when you turn up the reverb control, it starts a very loud screaming ear peircing noise beginning at 5 and gets worse as you turn it up more.
Has all new pre amp tubes but that didn't stop the scream.
Anyone have any idea on what to check? this is a AB868 circuit. All original except for new
pre-amp tubes.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 6:10 am
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Look you may have a microphonic tube , but you said you try new one ?

1- Did he play well before ?
2- What is the story of this amp ? Any mods , repair ? Need some clean up in the wiring , some lead dress...


Tap gently on tubes V3 and V4 . Ear the noise ? Yes replace tube
No noise ;

Is the reverb tank is in a Tolex bag ? Put the reverb tank away from the speaker as long you can with the wire
Bad tank ?


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 9:24 am
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Is the reverb tank original to the amp -- ie: is it the correct tank for a Deluxe Reverb?

If it's a replacement, it may not have the correct input and output impedances for the send and receive circuits. That may be the source of your symptoms.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 10:00 am
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Okay, here we go....
Owner brought it in...everything hooked up, tubes, speakers and verb tank.
It would start the scream even with the tubes that were in it.
Having tested those 6 tubes, 7025-3, 12AX7-1 and 12AT7-2 on my
TV& D/U tester there were a couple well below min. Customer wanted all new preamp tubes.
So I ordered from my C.E. Dist. 3-TAD-7025, 1-JJ 12AX7(ECC803S long plate) and 2-JJ-12AT7's
The amp is all original and no mods or signs of any work being done. Owner bought it new.
There are a few resistors and caps in that reverb circuit. I have tested the resistors but not the caps yet. The power supply caps are original and are cardboard/paper wound, of course that isn't the problem.
Could it be one of the caps... .003 and a 10pf?
Thanks much for the questions and suggestions.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 10:39 am
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The 12AT7 reverb driver has a 500 pico-farad ceramic cap feeding its control grids. You could try the old wooden chopstick on it. This cap is on the main circuit board, paralleling two 25mfd/25VDC cathode bypass caps. The disc is connected to pins 2 & 7 of the 12AT7 reverb driver.


Also, may want to try tapping the tank, itself. Connectors, metal case, the transducers. Tap all components in the reverb circuit. And then, all components on the circuit board, sockets, caps on the pots. Etc.

Should help you find the culprit. Good luck! Keep us informed.

http://bmamps.com/Schematics/fender/del ... _schem.pdf


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri May 30, 2014 11:44 am
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tube dude wrote:

Having tested those 6 tubes, 7025-3, 12AX7-1 and 12AT7-2 on my
TV& D/U tester there were a couple well below min. Customer wanted all new preamp tubes.

Don't trust tube testers , they operate tubes at "idle " not at amp working condition

Thanks much for the questions and suggestions.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat May 31, 2014 5:31 am
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Okay, I failed to say without the verb tank even hooked up, the scream is still there.
The caps in that circuit is where I am heading. I let you know how this goes.

Stratele52, sorry you see tube testers in a bad way, but not to argue, we all have opinions about everything and anything...I am that way as well. My opinion of amps today is there are only a few amps out there today since 70's of being close to how well built the originals were from Leo Fender, John Soundholm, James Marshall, etc.
I have serviced/repaired 2-1939 Epiphone amps, identical to those Charley Christian used in the 30's-40's, a couple of 1960 Gibson's, 76', 72' SVT's, late 60's and 70's Ampeg guitar amps, many BF Fenders, older Marshall's, many with the original power and pre amp tubes. Wow they performed great......also of tubes being made today, only a few manufacturers produce good reliable tubes...and there are only a few tube manufacturers, not made by the names printed on them, of course some obsolescence is built into most every thing we buy .
That's my opinion...everyone has one...from what's good toilet paper to people....
This TV7 has never let me down on the testing of tubes, I trust it and I use it to first test tubes before digging into an amp.
I test tubes for free and in my ads ask folks, test the tubes before buying new ones thinking that is the problem with their amps.
Anyway that's from an older dude having played and worked on amps since the mid 60's.
This reverb scream is the first one I have ever encountered like this.
Anyway I will keep all informed on how this turns out.
Take care you guys and grateful thanks to all your replies!
tube dude going on 68!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat May 31, 2014 5:51 am
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I'm no technical guy when it comes to amps... when I got my Vibrolux Reverb it had a very strong reverb and would start acting crazy when you turn it up. It turned out to be the reverb pot. IIRC it had a 1 meg pot instead of 100k. Worth checking out if you're sure it's not a tube issue.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat May 31, 2014 5:54 am
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Ceaderblues...very good point. ...That has been my thought as well and I do plan to remove the pot and check it out.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat May 31, 2014 12:55 pm
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Tube dude ,

It is my experience with tubes tester . I have 3 of them , I sell one , the fourth , 4 year ago .

Gerald Weber on one of his book write about that . You probably don't know Gerald Weber or you don't have any of his book .

I test tubes on the amp with signal generator and scope .


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 3:14 am
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Tube Dude, have you tried the old wooden chopstick test on the amp? You maybe to locate the problem within the reverb circuit, tank, pots, whatever.

Sounds like it might be a tank issue.

BTW... I like my Hickok to compare a stash of similar tube types. To find strongest signal tube. This TT is only good for testing for gassy, shorted output tubes. As it doesn't test these tubes at plate voltage or cathode current levels of an amp.

Do you know anyone with an Amplitex tester? Those seem pretty nice.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 3:19 am
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BMW2002Ti wrote:


Do you know anyone with an Amplitex tester? Those seem pretty nice.



Pretty nice price too at $2,600

I could buy more tubes than I need for all my life


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 6:19 am
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There was one on Ebay, last month, for $1500. Seemed in good condition.

My Hickok is fine enough. As old as my amps. They relate to each other.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 9:16 am
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BMW2002Ti wrote:
Sounds like it might be a tank issue.


Negative -- the symptom manifests even with the tank disconnected (see the OP's previous post).

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 12:40 pm
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OK. Didn't see the "no tank" part of original post. Still, the wooden chopstick maybe the best method to find the issue(s).


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