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Post subject: 1967 Super Reverb: Ringing at about 3kHz when D chord played
Posted: Wed Jan 29, 2014 10:36 am
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[b][/b]Hi Folks -New to the forum here and proud recent owner of 3 Blackface Fender amps in great condition: A 1965 Champ; 1966 Princeton Reverb and 1967 Super Reverb!

All the amps sound amazing in their own right, and the Super Reverb is truly awesome, however: it has a ringing resonance when I play certain chords, like D, and it is in the 3kHz range.

I am positive it's coming from the amp through the speakers, and not sympathetic vibration. Also, it's not the guitar, because it doesn't happen on the other amps. I swapped ALL the tubes out one by one including the rectifier, to no avail. The big power filter capacitors were all recently changed to Spragues. I'm thinking it's a small signal capacitor or something?

Does anyone have any insight in regards to this phenomenon?

Thanks

Westeagle


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 11:19 am
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Try running it into an extension cab with the amp's internals disconnected, correct imp. of course and see if it still happens.


Last edited by upnorth on Wed Jan 29, 2014 3:58 pm, edited 1 time in total.

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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 2:26 pm
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westeagle wrote:
[b][/b]All the amps sound amazing in their own right, and the Super Reverb is truly awesome, however: it has a ringing resonance when I play certain chords, like D, and it is in the 3kHz range.

Thanks

Westeagle


Welcome to the Forum! :D

First, try cleaning the pins and sockets of all tubes with a good contact cleaner. I like DeOxit D5 or GN5. Really work the cleaner into the socket connections, by inserting and removing each tube a couple of times.

If you still get this oddball resonance, you prolly have a microphonic tube. Try rotating the 12AX7 and 12AT7 between the various appropriate sockets. See if this changes the resulting tone. Isolate the tube with the problem and replace with a known good tube.

Do you have some good 6L6GC's to try out?

Good luck! Tell us the results. :mrgreen:


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 2:31 pm
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BMW2002Ti wrote:
If you still get this oddball resonance, you prolly have a microphonic tube. Try rotating the 12AX7 and 12AT7 between the various appropriate sockets. See if this changes the resulting tone. Isolate the tube with the problem and replace with a known good tube.

Do you have some good 6L6GC's to try out?


westeagle wrote:
I swapped ALL the tubes out one by one including the rectifier, to no avail.


I think that train already left the station, Steve.

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: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 2:46 pm
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Gotta rule-out something microphonic in the amp. Chinese wooden chopstick test time! :D


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 4:02 pm
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Thanks for the suggestions. I will spray the tube sockets out.
Also, I flicked all the tubes with my fingernail while on and didn't get a tube acting up microphonically, although that is very much what this problem sounds like.
Is the "chopstick technique" tapping components in the open chassis? I shall try that also.


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 4:39 pm
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Make any difference if plugged into the "normal" or "vibrato" channel? Reverb on or off?

vinyl

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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 4:41 pm
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The last time I dealt with a situation like this was with a blackface Bassman head. The culprit turned out to be the mica disc cap tied to the bright switch in the amp's normal channel. Aging components can create some pretty novel issues at times.

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: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 5:28 pm
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It happens using both channels. Reverb switched on or off, or rev pot dialed up has no effect.


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Jan 29, 2014 7:52 pm
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Wooden chopstick test is tapping on the components of an amp (switches, jacks, resistors, capacitors, sockets, etc) -- to see if you have a noisy component. Hopefully, you find one noisy part that can easily be replaced.

"Wooden" because of the live circuit --- running many hundreds of volts. Use one hand, keep other in pocket. Don't hold the chassis. Best left to a tech, if you feel any bit nervous about this test.


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Thu Jan 30, 2014 2:24 am
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Replace bypass caps on each tubes . Those are 25 MFD 25 volts electrolytic. Put some Sprague or other good one .

You need 7 of these caps . 2 are for tremolo , you may want to keep original caps if you don't use tremolo and want to save few buck :lol:

Did you replace the bias circuit filter cap ? It is under rated voltage and dry like big
filter caps, I use 100 volts rated and 100 mfd is good too.


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Thu Jan 30, 2014 5:20 am
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Thanks for the suggestion on replacing the other caps. I actually did replace the bias filter cap, but with a 25/50v as spec'd. I have since read about the under-ratedness of those caps. Maybe I'll change that one to a 100/100v first and work from there.


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Thu Jan 30, 2014 5:34 am
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westeagle wrote:
Thanks for the suggestion on replacing the other caps. I actually did replace the bias filter cap, but with a 25/50v as spec'd. I have since read about the under-ratedness of those caps. Maybe I'll change that one to a 100/100v first and work from there.


Bias voltage on this cap often exceed 50 volts , best is to replace .

About other caps , 25 mfd bypass , trust me its worth the few dollars .


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Feb 05, 2014 8:03 am
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Hi friends

So I changed out the bias filter cap to a 100/100v, and the 7 original bypass caps on each of the tubes (all Spragues). Although the amp sounds a bit quieter now at idle, the resonance/ "ring" sound is still there, most pronounced when I play a D note on the B string.

Any other suggestions on how to further isolate sections of the circuit to hone in on this problem? (To reiterate: I changed out all tubes; it happens in both channels; reverb vol is down).

ALternately, maybe this is just part of the "Bell like" sound of a blackface super?

Cheers

Wes


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Post subject: Re: 1967 Super Reverb: Ringing at about 3kHz when D chord pl
Posted: Wed Feb 05, 2014 8:44 am
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Take amp out of cab. Connect to speakers. Try tapping all components in the amp's circuit with a wooden chopstick. Can you get a component to make the offending noise? It could be any cap, resistor, socket, pot, wahtever on the tagboard. Or a loose tranny or choke.

No? Then, plug in guitar. Tap the pickup and bridge. The controls. Get the noise now? It could very well be a guitar issue. Have another guitar you can try in the amp?


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