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Post subject: 1969 Twin Reverb (Capacitor Identification)
Posted: Wed Jan 09, 2019 8:27 am
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I can't seem to find any information on the yellow caps in the photos below. Theres an eagle logo, and "American Radiant" on them. Anyone know anything about these? Were they ever original to Fender amps?

This amp doesn't sound bad, but it doesn't sound like a Twin should. It's almost like someone wanted it to sound more like a Marshall. I'm going to go through the entire thing and check component values, but I just thought I'd ask about these caps before I got started.

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sat Jan 12, 2019 12:46 pm
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Are those 40-watt "guaranteed for life" Radio Shack speakers I see?

If so, that may be part (or all) of your problem.

Arjay

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sat Jan 12, 2019 4:46 pm
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Looks like its been Blackfaced, not a bad thing. Probably needs a good cap job(poor sound quality) or if Arjay is right about the speakers, well find something better suited to a great high-powered clean sound.
As far as if that brand of caps were used originally, NO not Fender installed. Notice the Dates(1979) & solder joints, some look perfect well rounded- those are the original ones. Your caps/amp was probably modified in the early 80's. They look like American capacitor company caps.
The bypass caps are "illegible" in your pic but probably need to be replaced along w/ the power supply caps and negative bias cap.

If you can add more pics like the last one of the rest of the circuit other modifications would likely be spotted by members of the forum,


Last edited by sfceric64 on Sat Jan 12, 2019 9:42 pm, edited 1 time in total.

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sat Jan 12, 2019 6:50 pm
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Retroverbial wrote:
Are those 40-watt "guaranteed for life" Radio Shack speakers I see?

If so, that may be part (or all) of your problem.

LOL!
I built a 4x12 using the RS speakers with the chrome center caps.
Sounded just fine paired with my Peavey Deuce with the gain dimed.

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sat Jan 12, 2019 8:13 pm
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They may have sounded fine but they never sounded Fendery, at least to me. And with an SPL of around 80dB, they weren't very loud/efficient either.

Arjay

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sat Jan 12, 2019 11:06 pm
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Retroverbial wrote:
They may have sounded fine but they never sounded Fendery, at least to me. And with an SPL of around 80dB, they weren't very loud/efficient either.

Six 12" speakers running 120 watts cranked to sound like EVH from the first album... nope, not Fendery.

And yes, I'm pretty deaf by now.

But seriously... that cabinet was more furniture than anything. Mainly to get the 212 amp up off the floor. It worked nicely when I used it for "The Runaways" at Cal High, and they decided to put the band in the orchestra pit and NOT mic us through the PA :facepalm:

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sun Jan 13, 2019 12:03 am
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CB91710 wrote:
Six 12" speakers running 120 watts cranked to sound like EVH from the first album... nope, not Fendery.


Well that is the OP's issue -- his Fender amp doesn't sound like a Fender amp.

I'm trying to help him identify the cause. What are you doing?

Arjay

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Sun Jan 13, 2019 11:17 pm
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Those yellow coupling cap appear to by made 30th week, 1979. My guess they are sealed, polypropylene types, similar to the Mallory-150. These last forever.

Maybe, check to be sure they are leaking DC voltage.

:)


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 2:52 am
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Not original;

American Radiant cap
Tremolo photo cell / LDR
Bypass caps
Orange drop caps

Sound like a Marshall ! Check all bypass caps value ; report


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 5:46 am
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stratele52 wrote:
Not original;

American Radiant cap
Tremolo photo cell / LDR
Bypass caps
Orange drop caps

Sound like a Marshall ! Check all bypass caps value ; report


+1

Any tone-related caps I would replace with Jupiter's or Zoso's.

Arjay

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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 8:04 am
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BIAS POT, anode plate resistors on phase inverter, & grid-to-ground resistor all resemble an AB763-style retro fit.

Those American Radiant caps seemed to be replaced only a few years after the amp was made (1979 versus 1975). I suspect that is when all mods were done.

To the OP, how do you like the present tone?

:?:


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 8:07 am
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BMW2002Ti wrote:
BIAS POT, anode plate resistors on phase inverter, & grid-to-ground resistor all resemble an AB763-style retro fit.

Those American Radiant caps seemed to be replaced only a few years after the amp was made (1979 versus 1975). I suspect that is when all mods were done.

To the OP, how do you like the present tone?

OP write ;

" This amp doesn't sound bad, but it doesn't sound like a Twin should. It's almost like someone wanted it to sound more like a Marshall. "

I understand he don't like :?
:?:


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 8:23 am
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Then, I'd look to replace all coupling caps with Zoso or yellow Vintage Jupiter caps.

Prolly worth his while to measure voltages and be sure he is within 20-25% of schematic values (for an AB763 circuit).

Wonder if the OP will respond to these suggestions?

:mrgreen:


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 8:26 am
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BMW2002Ti wrote:
Then, I'd look to replace all coupling caps with Zoso or yellow Vintage Jupiter caps.

Prolly worth his while to measure voltages and be sure he is within 20-25% of schematic values (for an AB763 circuit).

Wonder if the OP will respond to these suggestions?

:mrgreen:


These caps are expensive, are they really better than Orange drop ?


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Post subject: Re: 1969 Twin Reverb (Capacitor Identification)
Posted: Tue Jan 15, 2019 8:37 am
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"Better" is a relative term. Better = longer life? Prolly not. OD last forever. Better = closer to original Fender tone, for the Twin Reverb? IME, yes.

Prolly best, to wait for OP's response. Hopefully, he is still looking at this thread.

:mrgreen:


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