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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 5:25 pm
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Is one of your tilt-back legs stamped with a serial number?

Both legs were pretty well rust coated, there looks to be an illegible number etched on one of the legs at the top above the retaining screw maybe(I don't see to good, I'd have to remove it again to put it under the mag-light to tell for sure) . But nothing that was stamped other than the FENDER, logo F and Pat Pend at the bottoms.

The electrolytics arrived via mail this afternoon also.


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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 5:35 pm
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If your legs were serialed, you'd see something like this......

Image

The 19-inch legs (as used on the Super Reverb and Showman) would be prefaced by an "L" rather than the "M" seen in this photo.

Arjay

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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 7:13 pm
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Very cool, what years did they stamp the serial #'s?


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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 7:38 pm
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The serial numbers were used right from the inception of the legs themselves in 1960. These ID #'s served no purpose that I can discern other than to date them as historical artifacts and they appeared in tandem with the "PATENT PENDING" inscription. Sometime shortly after the 1970 model year the S/N's and the patent info was phased out but their end dates do not precisely coincide with each other. I've been trying to track down a more precise timeline but all I've learned for certain is that the serial usage ended first.

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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 11:17 pm
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Interesting, I would have thought from piggy backs to the end of the blackface era. Maybe up to the start where CBS started fuddling with the amplifiers in general. But at first thought I said that looks like a date code w/ a part ID in front.

Thanks for dropping the knowledge. :mrgreen:


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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 11:28 pm
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My late 1968 SR (42nd week) --- only has the "PAT. PEND." stamp.

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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 03, 2017 11:55 pm
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Documented variations continue to surface. From what I've surmised, initially only one leg of a matched pair installed on an amp had a serial. But beginning with the silverface era, I've seen rare instances where *both* legs were serialed and also where *neither* were so marked. But both were still stamped with the patent data. However I've yet to see any Fender amp made after 1972 with legs marked with anything other than the corporate "F" and the Fender lettering. Thus for the moment, that seems to be the cut-off date.

Steve, my '68 Pro Reverb's legs (with a build date of April) are marked just as those of your Super Reverb.

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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 8:10 am
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Well here is some more data for you Arjay...
'66 Bassman cab has the numbers with the "M" Prefix (Medium I presume) on one side the other just has the Patent Pending.
'69 Bantam Bass Amp legs just say Patent Pending on both.
'69 Bantam Bass Amp legs just say Patent Pending on both.
'65 Super Reverb has Patent Pending on both legs, no numbers.
'72 Super Reverb had Patent Pending on both legs no numbers.

It would seem the Bassman fits in with the info you posted. I know the Super Reverb is all original, can't imagine the legs were changed later when EVERYTHING else was bone stock on the amp. The Bantams appear consistent, but with so few runs made, who knows. Interesting to say the least.

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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 10:54 am
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Yeah, the leg serials were all prefaced with "S" (small), "M" (medium), and "L" (large). Interesting note about your '65 Super Reverb. Perhaps there's another '65 Super Reverb out there with serials on *both* legs (I've seen that happen too).

Arjay

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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 4:26 pm
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Replaced all but the two 80uf x 450 electrolytic cans, need a little room to replace the resistors.
I decided not to re-wire/route all the below the board wiring that the previous owner/tech decided to run above board. It just makes it easier to test diagnose, being new to me. I did move one of the 25x25 cans back to the board that was previously re-located to the back wall of the chassis.

I removed the 47ufx100 that was attached from a bal-pot lug to a PT ground lug(it was run paralleled w/a 100x100), I will probably have to re-install that to get a good bias reading of -44vdc from the bias board but will wait and see what the new 100ufx100 supplies.


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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 6:57 pm
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That's a bit low for the AB763 revision, Erik. The original bias supply voltage should -52 VDC.

Arjay

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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 7:48 pm
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That's a bit low for the AB763 revision, Eric. The original bias supply voltage should -52 VDC.

Yup, good catch again. Those numbers are for the balance pot AA1069 vs the bias pot AB763.


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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 8:10 pm
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sfceric64 wrote:
I removed the 47ufx100 that was attached from a bal-pot lug to a PT ground lug(it was run paralleled w/a 100x100), I will probably have to re-install that to get a good bias reading of -44vdc from the bias board but will wait and see what the new 100ufx100 supplies.


The 100mfd/100VDC should be fine. Place this cap closer to the bias supply diode, on the separate board with the drop-down resistor and bias supply diode. Place the 47mfd/100VDC onto the pot (to chassis connection). Like this photo of a Vibrolux Reverb with balance style pot:

WATCH THE POLARITY of these caps. Photos are nice, prior to any fixes. :)

Image


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Post subject: Re: 1971 Super Reverb
Posted: Tue Jul 04, 2017 10:21 pm
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BMW2002Ti wrote:
WATCH THE POLARITY of these caps.


+1!

That's critical if you expect the amp to pass the "smoke test".

:mrgreen:

Arjay

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Post subject: Re: 1971 Super Reverb
Posted: Wed Jul 05, 2017 1:35 pm
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What was the purpose of the extra can in the bias supply(stability/smoothness), I have seen were it is referenced as an AD1269 circuit. I understand it this way; two cans in parallel have the same supply voltage but share the capacitance(the sum of the two) in this case 100uf + 47uf = 147uf. In the AB763 schematic the bias calls for just 25uf x 50v, while the AA1069 calls for 50uf x 70v on the separate board.

So when modding back to AB763, I should keep the AD1269 added cap(.47uf parallel) but move it to the same lug(3rd/Left) as the bias mod calls for?


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