NAD... 1965 Fender Princeton Reverb

slider313

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Nice! Yeah, the tube chart stating AA764 was a printing error. There were no Princeton Reverb's in July of 1964; only the non reverb Princeton AA964. I see you have what looks like a GZ34 rectifier in it. The AA1164 calls for a 5U4GB. Did your tech say the B+ voltage was higher than expected?
 
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Torren61

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Nice! Yeah, the tube chart stating AA764 was a printing error. There were no Princeton Reverb's in July of 1964; only the non reverb Princeton AA764. I see you have what looks like a GZ34 rectifier in it. The AA1164 calls for a 5U4GB. Did your tech say the B+ voltage was higher than expected?

He didn't say. That was my error with the GZ34. I have several 5U4GBs. Good catch! I was in a bit of a rush to get her reassembled so I could play. I didn't even take any gut shots. I'll sort it on Sunday.
 

gridlock

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My biggest amp regret is selling my near mint 1966 Princeton Reverb with the original Jensen C10N speaker.

Congratulations and jealous! Super nice amp.
 

72_Custom

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There are a lot of rumors and legends surrounding the mythical AA764 Princeton Reverb. Supposedly, it had a couple of minor changes from the AA1164, the most notable being a GZ34 rectifier.
 

slider313

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There are a lot of rumors and legends surrounding the mythical AA764 Princeton Reverb. Supposedly, it had a couple of minor changes from the AA1164, the most notable being a GZ34 rectifier.

The first Princeton Reverb design was the AA1164, or November of 1964. The two letter code on the schematic shows K-FD. All pre-CBS schematics have a three letter production code, which is when the amp was actually put into production. CBS/Fender used the AA764 designation for some later amps but there was never a true AA764 Princeton Reverb, only the non reverb AA964; drawn up in September and actually went into production in December of 1964, or a month after the reverb model. The previous non reverb model was the tuxedo 6G2. The AA764 was actually a Champ/Vibro-Champ.
 

King Fan

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Even with Uncle Doug, trust but verify. As @slider313 says, there never was an AA764 PR *built or drawn by Fender*, but early PRs did come with a (factory goofed) tube chart saying AA764. Note the ND (Apr '64) stamp on this one, and recall the amps didn't show up until say November (AA 11/64).

upload_2021-6-30_10-57-4.png

Despite the nonexistence of the amp, it's spawned a ton of internet chatter and even analysis of how it musta worked.

For those who didn't follow the Uncle Doug saga, he was taken in (for a while) by an innocent hobbyist in Germany, who photoshopped up a 'faux' AA764 schematic, apparently for fun. When the hobbyist saw what he had done, he shared this clarified version (note inset) but by then it was too late.

faked_PR_aa764 copy.png


But wait.... *The GZ34 thing is even more complex.* Almost all PRs up until 1971 had the Schumacher 022772 PT, which could not support the 5U4's 3A heaters. (The later PR 010020 had 3A filament windings). Our PR-sensei friend @muchxs said, "Do not use a 5U4G rectifier in a pre-1970 Bronco, Champ, Vibro Champ, Princeton or Princeton Reverb amp with a stock Schumacher 022772 PT. When in doubt use a 5V4 or even a 5Y3 for lack of a 5V4." A GZ34 will work, of course, on the heaters, but it's lesser voltage drop will hot up your B+ even more -- which muchxs did not favor in an amp that as he said Leo apparently designed to overwork its output tubes. But, if your tech installed the GZ34, you could ask him about the B+ and run nice sturdy 6V6s -- the amp might sound great.

Side note: The AA764 tube-chart type-shop snafu may have happened, as muchxs also pointed out, because Fender seemed to be rushing a bunch of amps (AA764 Champ, late-arriving AB763 DR, and AA1164 PR) out the door before he sold to CBS in early '65.
 
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slider313

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Even with Uncle Doug, trust but verify. As @slider313 says, there never was an AA764 PR *built or drawn by Fender*, but early PRs did come with a (factory goofed) tube chart saying AA764. Note the ND (Apr '64) stamp on this one, and recall the amps didn't show up until say November (AA 11/64).

I'm going to say that tube chart says "NL" not "ND"

As you can see, the scanned schematic does not have a three letter production code listed. CBS Fender made use of many pre-CBS schematics but those will show Fender Musical Instrument Co. at the bottom and not Fender Electric Instrument Co.

wtta0hmimvxcbsbeynkn.jpg
 
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King Fan

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Heh, yeah, for sure it could be NL, which would be December. :) I went for ND partly cuz the base of the letter is lighter/thinner on the chart above, while the top of the letter is heavier compared to your L -- the serif, for all you typesetters out there. I've also seen discussion of earlier 1964 date stamps on those charts, but I can't cite any sources.

No matter. April or December, it's the AA764 designation on the tube chart that created all the confusion. That and some (?later) schematics showing a 5U4....
 

slider313

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Heh, yeah, for sure it could be NL, which would be December. :) I went for ND partly cuz the base of the letter is lighter/thinner on the chart above, while the top of the letter is heavier compared to your L -- the serif, for all you typesetters out there. I've also seen discussion of earlier 1964 date stamps on those charts, but I can't cite any sources.

No matter. April or December, it's the AA764 designation on the tube chart that created all the confusion. That and some (?later) schematics showing a 5U4....

Well.....all AA1164 and B1270 Princeton Reverb amps should have a 5U4GB. The non reverb AA964 did have a GZ34.

The confusion is the AA764 showing a GZ34, where no such schematic exists. One should go with the 5R4GYB by default; it pulls 2 amps and will lower the B+ a bit more than the 5U4GB.

That Twin chart may be a repro.

https://thumbs.worthpoint.com/zoom/...abinet_1_f45745e902574de0e36979fcfa7ad789.jpg
 

72_Custom

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I think the transformer swap in early 70s was the missing link in my mind.

I know Fender tended to use charts with the wrong circuit designation on it (plenty of other examples out there), but usually not with the actual tubes being different!
 

schmee

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Very Nice. Replaced grill cloth I guess. They are just so toneful... The PR is a bit unique compared to other Fenders...
 

King Fan

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Sorry, @slider313 , I respect your knowledge but can't square what you say with what @muchxs said (above). FWIW, this is the AA1164 schematic I use, but yes, there's another, earlier, 99% identical, showing the 5U4. And of course after 1971, with the new PT, they went *back* to the 5U4 on the later schematic (Rev. D? the one that includes the export PT).

Fender AA1164 schematic GZ34  .jpg


But we gotta stop hijacking this great thread. In any case, @Torren61 knows what he's doing.
 
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Torren61

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Sorry, @slider313 , I respect your knowledge but can't square what you say with what @muchxs said (above). FWIW, this is the AA1164 schematic I use, but yes, there's another, earlier, 99% identical, showing the 5U4. And of course after 1971, with the new PT, they went *back* to the 5U4 on the later schematic (Rev. D? the one that includes the export PT).

View attachment 872648

But we gotta stop hijacking this great thread. In any case, @Torren61 knows what he's doing.
Oh no way! You’re not hijacking the thread at all. I love these discussions!
 

slider313

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Sorry, @slider313 , I respect your knowledge but can't square what you say with what @muchxs said (above). FWIW, this is the AA1164 schematic I use, but yes, there's another, earlier, 99% identical, showing the 5U4. And of course after 1971, with the new PT, they went *back* to the 5U4 on the later schematic (Rev. D? the one that includes the export PT).

View attachment 872648

But we gotta stop hijacking this great thread. In any case, @Torren61 knows what he's doing.

Ahh, but that schematic is a reprint and has been altered by CBS Fender. Look at the bottom of page: Fender Musical Instruments, Santa Ana. There was no Fender Musical Instruments in 1964 and they weren't in Santa Ana!
 




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