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FDP Forum / Fender Amps: Vintage (before 1985) / Repeated loss of bass response on B/F Showmans?

kart24
Contributing Member
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Vacaville CA

Runs with scissors !!
Feb 28th, 2017 10:07 PM   Edit   Profile   Print Topic   Search Topic

I have repeated loss of bass on both my old Showmans. Both on the normal and vibrato channels.

I give them to my amp tech. When I get them back they work fine about 9-12 months then fail again.

I have a new Showman 500 ( looks like an old one, only 15 lbs.) It just did the same thing on the vintage channel.( has tube pre-amp only)

What is the likely hood they would have the same fault?

ECS-3
Contributing Member
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USA / Virginia

Mar 1st, 2017 06:58 AM   Edit   Profile   Print Topic   Search Topic

I would find out from your amp tech what he did to fix them before, as the beginning step in understanding what is happening.

Hammond101
Contributing Member
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So. Cal. USA

Mar 1st, 2017 03:42 PM   Edit   Profile   Print Topic   Search Topic

Does the bass control not respond? See if the mid control is not working on those channels so equipped as well.

kart24
Contributing Member
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Vacaville CA

Runs with scissors !!
Mar 1st, 2017 06:41 PM   Edit   Profile   Print Topic   Search Topic

The mid range on both amps are working at this time.
Just poor tone response from the bass pot. There is some variance in tone. Just very little.

The amps I'm comparing in this post are '65 single and my '67 dual showmans. The newer Showman 500 "PR 2809"is at our practice space across town. With same issue.

(This message was last edited by kart24 at 08:42 PM, Mar 1st, 2017)

Hammond101
Contributing Member
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So. Cal. USA

Mar 2nd, 2017 09:41 AM   Edit   Profile   Print Topic   Search Topic

Clean all the pots with DeOxit D5. I've seem many Fender blackface style tone stacks where the treble pot gets shorted with some crud, dendrite or who knows what and that takes out the rest of the tone stack.

You should be able to test for this with a VOM. The wire that connects the treble pot to the wiper (middle terminal) of the bass pot on both channels in your case would show shorted to chassis.

If cleaning doesn't fix it and the short is evident you will have to replace the tone pot. I've always been successful with a good cleaning and to best of my knowledge the problem has not re-occurred when using DeOxit D5 cleaner w/lube.

It could be other things but try this first if you are comfortable with pulling the chassis, discharging the filter caps and cleaning the pots.

kart24
Contributing Member
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Vacaville CA

Runs with scissors !!
Mar 3rd, 2017 04:43 PM   Edit   Profile   Print Topic   Search Topic

Will do. thank you.


kart24
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Vacaville CA

Runs with scissors !!
Mar 8th, 2017 10:56 PM   Edit   Profile   Print Topic   Search Topic

My amp tech will be picking up both of my old B/F Showmans as well as my almost new Bassman 500.

He does excellent work and can do the warranty repair on my Bassman 500.

Meanwhile its back to my PF500 Ampeg for awhile.

Hammond101
Contributing Member
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So. Cal. USA

Mar 9th, 2017 10:22 AM   Edit   Profile   Print Topic   Search Topic

I'd be interested to know what your tech finds and what he does to correct it.

1958Bassman

USA

Mar 13th, 2017 02:19 PM   Edit   Profile   Print Topic   Search Topic

Does a loss of gain accompany the loss of bass? If so, I would have him check the cathode bypass cap on V1 and V2.

Hammond101
Contributing Member
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So. Cal. USA

Mar 13th, 2017 03:39 PM   Edit   Profile   Print Topic   Search Topic

There would be an inherent loss of gain in that the bass signal would not be contributing to the overall output of the stage. Agreed that bypass caps could be the issue but usually not cause a total loss of bass response at the control.

Interesting re-failure here.

amphead4

Cincinnati, USA

Mar 14th, 2017 07:23 AM   Edit   Profile   Print Topic   Search Topic

A mystery. I'm also interested in the outcome of this.

kart24
Contributing Member
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Vacaville CA

Runs with scissors !!
Mar 17th, 2017 11:21 PM   Edit   Profile   Print Topic   Search Topic

The "single" Showman is now out for repair.

FDP Forum / Fender Amps: Vintage (before 1985) / Repeated loss of bass response on B/F Showmans?




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