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AA1164 vs AA764 re BFPR

Monroe

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Joined
Mar 11, 2008
Messages
1,139
A while back I had a thread about a very early black face princeton reverb.
The FEI tube chart indicated AA764, but there was some doubt raised that an AA764 schematic ever existed.
Well, in case anyone is interested, I think I actually figured it out.

There's a cat that goes by Uncle Doug on Youtube that appears to have found one.
It may or may not be authentic, but if not, it is drawn with the changes that differentiate it from an AA1164 schematic.
In the video below, he explains the few differences.
He has a link to the download in his description in case anyone wants one.

 

Don

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Dec 1, 2001
Messages
5,732
If you go to the site that the schematic is on, it now says on it that it was photoshopped.
 

Wally

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Feb 27, 2003
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3,535
I am listening to the Uncle Doug video there. Fwiw, about the tube chart....Fender is well known for using tube charts that have nothing to do with the amp into which they place them...even to the point of incorrect tube compliments. Here are two examples of near mint Fenders that had tube chart anomalies...extreme anomalies.
I owned a near mint '57 Champ that had a 5F6A Bassman tube chart in it....original chart. I also had a blackline SF Dual Showman that had an AB165 Bassman tube chart in it. I don't put much stock in a tube chart. IF the circuit is unmolested, then that will tell a person what circuit is in the amp.
Among the '65 and later Bassman amps, the aB165 tube charts are known to have been used as late as 1969.......regardless that the circuits started changing in the summer of 1968..... Tube charts??? Don't rely on them is my advice.
AS for the difference in the GZ34 and the 5U4....Uncle Doug makes a good point about the current draw. A GZ34/5AR4 is easier on a PT. He doesn't mention the voltage. But then, the PT in a BF and early SF Prin Rev is walking a tightrope anyway. It is the same PT as in the Champ. (8^O The later PT is better suited to the demands of the circuit.) I have seen quite a few BF and early SF Princeton Reverbs that have weathered the storms as is. Others have seen a lot of PT failures. Proper maintenance might account for those failures as surely as the 'undersized' PT.
Imho, IT would have been of interest if that '67 Princeton, which IS an AA1164 circuit---ime,
had been subjected to comparisons of the voltages that a 5U4 and a GZ34 yielded in the circuit. ( I say that the '67 BF Prin REv is built on the AA1164 schematic because I have never witnessed Fender building an older circuit after a new schematic has been introduced. The AA1164 schematic calls for 410vdc on the plates. With modern wall voltage, that would be higher. IF one installs a GZ34, the B+ would be significantly higher than with a 5U4.....what...maybe 450-460vdc??? That is getting up there for a 6V6. The same problem exists in Deluxe Reverbs. That is why before modern production 6V6's construction was changed to deal with those high voltages...think JJ 6V6's....we would use 6L6's just to be safe...not to raise output...but to be as safe as one could be IF the owner did not want to pay up for NOS U.S. 6V6's. The Russian 6V6 tubes back in the '90's would not stand up to the demands.
I compared that AA764 schematic to the AA1164. There are exactly 3 differences.....there is a 5 volt difference in the plate voltage for the reverb driver tube, and the resistor and the cap in the bias supply are very lightly different....27K versus 32K in the AA1194 and 25mfd/50V cap in the 1164 drawing versus the 50mfd/50V cap in the 764 drawing.
Both schematics show B+ of 420vdc. It would be of interest to note the difference in the B+ with each of those two rectifiers in the amp, would it not?
Fender tube charts can cause a lot of confusion..... The AA1164 post-dates the July drawing, and I believe that any Prin Rev amp built after November, 1964 will be built on the AA1164 schematic....until the next schematic came out in December, 1970.
Fwiw and ime, he errs on the analysis of that schematic code. The AA indicates the first drawing. IF there is a revision, the schematic will be an 'AB'. Example......AA165 and AB165 Bassman. I have never seen a BF/SF schematic that has only an 'A' prefix. I have never seen an AA568 or AB568 Bassman....but the first new circuit for SF Bassman amps is labeled AC568....third revision, May 1968.
back in the tweed days, the revision indicator was a suffix...ex: 5F6 BAssman with the 83 rectifier and 5F6A with the GZ34/5AR4 rectifier. The Blonde/Brown era did the same.....6G6 Bassman, 6G6A Bassman and 6G6B Bassman....three versions of the circuit.
 

lare65

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Feb 18, 2017
Messages
110
I have two Princeton reverbs. One -64(dec.) and one -66(nov.) It says AA764 on both tube charts and they have GZ34´s. The -64 have 423 VDC on the plates and the -66 have 424 VDC on the plates.
 

sonar

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Jan 10, 2003
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I have two Princeton reverbs. One -64(dec.) and one -66(nov.) It says AA764 on both tube charts and they have GZ34´s. The -64 have 423 VDC on the plates and the -66 have 424 VDC on the plates.

Nice. Right in the sweet spot.

My first OT in my clone had a little over 500V on the plates. :wow
 

Wally

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Feb 27, 2003
Messages
3,535
Nice. Right in the sweet spot.

My first OT in my clone had a little over 500V on the plates. :wow

FWIW and for general information, OT's do not create voltage. The PT..power transformer.... is what was placing that voltage on the circuit.
 
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