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Post subject: '74 Twin - sustain at clean tone levels becomes distorted
Posted: Sat Feb 22, 2020 11:40 am
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Even when "cold" -- immediately after flipping the standby - at low volume levels, a sustained note or chord if left to ring will start to distort ... knob settings are all in the mid to low end of their range (guitar and amp.)

All original '74 Twin Reverb. No pedals... tested with Les Paul (humbuckers) and Strat (single-coils.)

The amp is seldom used, stored dry but chilly (South Oregon Coast.) Never frozen.

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Last edited by Bartimaeus on Sat Feb 22, 2020 1:53 pm, edited 2 times in total.

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Post subject: Re: '72 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Feb 22, 2020 12:25 pm
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When was the last time the amp was serviced?

Arjay

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Post subject: Re: '72 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Feb 22, 2020 1:24 pm
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Thanks Arjay.

Other than self-solving the tube issue with V1 a while ago, (See this post: https://forums.fender.com/viewtopic.php?t=106319) it's never been to a tech, that I know of. Nearest one to me that I trust is in Eugene (130mi.)

But! I noticed that the issue was common to both channels. Reading all over the inter-web on this ... example here: https://www.kcanostubes.com/content/fen ... mendations - discovered I could substitute a 12-ax7a in V6 - the inverter common to both channels...

In my collection: I just so happen to have a balanced 12-ax7a from a MESA 5/50 that I re-tubed a while back...

Tried it. Problem solved. Crisp & Clean.

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Post subject: Re: '72 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Feb 22, 2020 1:51 pm
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Actually it's a '74... I have '72 stuck in my head. Apologies ...


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Feb 22, 2020 3:34 pm
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Likely it's due for a re-cap (bias supply, cathode bypass, and filter array).

Arjay

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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Feb 22, 2020 4:24 pm
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Retroverbial wrote:
Likely it's due for a re-cap (bias supply, cathode bypass, and filter array).

Arjay


I expect you are correct. I'll see that it's done.

Since I'm scheduled to gig in Salem in a 3 weeks, I'll drop it off in Eugene on the way by. Getting it back will be another story.


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Feb 23, 2020 12:50 am
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I'm pretty certain that a '74 TR was factory-equipped with a grounded, 3-conductor power cable but if not, see that your amp tech installs one. Also, ditch the "death cap" and bypass the rear-panel polarity switch (you will no longer need it). Any resistors that appear "toasty" should be replaced, especially those soldered to the power-tube sockets and the voltage-divider network beneath the "dog house". Metal-oxide equivalents may be used in lieu of the original carbon-comp types.

Arjay

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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Feb 23, 2020 11:22 pm
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Retroverbial wrote:
I'm pretty certain that a '74 TR was factory-equipped with a grounded, 3-conductor power cable but if not, see that your amp tech installs one. Also, ditch the "death cap" and bypass the rear-panel polarity switch (you will no longer need it). Any resistors that appear "toasty" should be replaced, especially those soldered to the power-tube sockets and the voltage-divider network beneath the "dog house". Metal-oxide equivalents may be used in lieu of the original carbon-comp types.

Arjay


Apologies for the wait on a response. Sundays are busy days (musically/)

Yes: Confirm that the power cable is original and it's grounded, three-prong ...

The other stuff like "death cap" -- sounds serious, never heard that term. But I'm not well versed with this amp. Certainly will take your recommendations to thy fellow in Eugene (http://twisted-wires.com/)

Huge thanks, Arjay.


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Feb 23, 2020 11:31 pm
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Your amp tech should be familiar with everything I've mentioned.

I've owned a half dozen Twin Reverb amps over the years and still have two of them in my collection. Never had one fail on the job even after beating the hell out of them.

Arjay

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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Mar 01, 2020 10:19 am
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Quick followup - I played a 4H fundraiser last evening. Used the TR and my V-series Strat. Big space. We played mostly 40's & 50's country -- think "The Hanks." Anyway, people loved it and several local musicians with other bands came up during breaks and afterward to ask about my setup. Just the guitar and amp, boys.

Great experience.

BTW I also worked my Doerr SJ through a "vintage" Fender Acoustasonic Pro -- using various 'plain' effects (presets.) This got almost as many questions.

Love ya-all.


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Mar 01, 2020 10:55 am
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Congratulations.

Glad to hear that all went well!

Arjay

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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Mar 07, 2020 6:50 pm
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Cool amp ! I'm lusting after a twin reverb. I've never had one but want one !


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sat Mar 07, 2020 11:12 pm
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After lugging one of those ballbusting sonofabitches around for five or ten years it'll be interesting to contrast your observations then with those you've just opined.

:lol:
Arjay

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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Mar 08, 2020 5:56 am
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One of the few amps that gains enough momentum to quickly and efficiently shear off the shaft of a potentiometer.

UN


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Post subject: Re: '74 Twin - sustain at clean tone levels becomes distorte
Posted: Sun Mar 08, 2020 11:10 am
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upnorth2 wrote:
One of the few amps that gains enough momentum to quickly and efficiently shear off the shaft of a potentiometer.

Been there, done that.

:wink:
Arjay

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