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Post subject: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb!!!
Posted: Wed May 08, 2013 11:42 am
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So I just got this 1970 Fender Dual Showman Reverb and everything seems to be working fine except the reverb. I cleaned the tube sockets, pots, etc. and tried troubleshooting the obvious (reverb tank, audio wires) but I am still unable to figure out what is wrong with it. When I turn the reverb knob I hear a slight change of sound, almost like an increase in treble, and if I move the reverb tank the springs do give a sound through the speaker. When I'm playing guitar however, I'm not getting any reverb which makes me think it must be something in the circuit.

Any suggestions would be greatly appreciated! Also, I'm referencing to an AA768 schematic, is that the right one?
Thank you!

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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 2:28 pm
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Have you tried a different 12AT7 (reverb driver) and 12AX7 (recovery) tube? Do you have another reverb tank to try in the amp? Footswitch ok?


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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 2:58 pm
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I'd look to the reverb tank itself first. Check it for continuity with a DVM -- a DCR of 81 to 255 ohms is considered nominal for a vintage Gibbs/Hammond tank. If your meter sees an "open" then it's likely that one or more of the transducers that transmit the electronic signal through the springs then re-convert it to audio are damaged.

Arjay

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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 3:05 pm
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Thank you for the reply. I have a working fender blues deville, I'll test the reverb tank from the dual showman on the deville and vice versa to rule out the tank. I'll let you know my findings.
Thank you!


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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 4:12 pm
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mydeadblues wrote:
Thank you for the reply. I have a working fender blues deville, I'll test the reverb tank from the dual showman on the deville and vice versa to rule out the tank. I'll let you know my findings.
Thank you!


Might want to try different tubes first. That would be a lot easier than swapping tanks between amps. Why risk potentially damaging the Deville tank before ruling out the tubes? :wink:

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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 5:12 pm
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Thanks for the reply I forgot to mention that I tested the tubes and also put in the correct 12AT7s instead of the 12AX7s that were in the 3rd and 6th sockets.


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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 5:42 pm
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I just spent a couple weeks on a early 70's BMR-new filter and e caps and tracking down a popping sound on power up. There are two 100K 1watt resistors for each channel and the reverb-six in all. From the first picture, the 100K on the left looks suspect. I replaced all six and what a difference. The amp came alive. I've also connected the braided wires from the tank to the rca inputs on the chassis backwards-same symptoms.


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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Wed May 08, 2013 11:28 pm
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Just my 2 cents. If you get the crash when jostling the amp head and no reverb signal through the amp, the problem is on the input side or a leaky cap goofing up the bias on the driver or recovery tube. JMHO Art

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Post subject: Re: 1970 Fender Dual Showman Reverb TFL5000D HELP fix Reverb
Posted: Sun May 12, 2013 7:21 am
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mydeadblues, prolly time to whip out the old DVM and take some VDC measurements around that 12AT7 reverb driver amd 12AX7 recovery tube.

Good luck with that!

http://www.webphix.com/schematic%20heav ... _schem.pdf


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