'66 BF Princeton Reverb - Player or Collector?

Discussion in 'Amp Central Station' started by LittleSonny, Apr 26, 2019.

  1. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    I'd get the service done ASAP.

    That multi-section can filter capacitor appears to be original. Many techs avoided changing them for many years for a couple of reasons - 1) they were thought to be a pain in the a**, and 2) for a long time replacements were poor quality.

    But they are not that hard to replace, and several companies such as F&T & JJ (among many others) make replacements - and it's also easy to simply bypass the can and install individual caps on the chassis (this wasn't common when everyone was using huge Sprague Atoms, but those are now overpriced and lesser quality).

    If that can is original and a section blows you could lose *another* power transformer. I always recommend that newly purchased Fender tube amps over 20 years old go directly to a tech. Virtually every one I see has old parts that are past their service life - most being filter caps.

    Sadly, most are brought to me because something has blown in a players "new amp".

    Please - take it to a tech.
     
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  2. LittleSonny

    LittleSonny TDPRI Member

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    The mention of the 5U4G was in reference to a different amp. This PR has a GZ34 and that is what I intended to stay with, albeit with something else, when I can find what I want, instead of this MIJ Lindal.

    I'm not remotely knowledgeable about electronics other than having an idea of gain from various preamp tubes and my experience with different brands, which to my ears do have differences.

    I also hold the view that although I can understand the reasoning for speaker swaps and other mods to make an amp more useful for the players needs, my default position is to keep things as stock and original as possible. What people fell in love with in vintage amps and guitars is the way they sounded were when they discovered them. Not after some modification or another. There are exceptions, I've done the occasional speaker swap or bought an amp where it had already been done and the amp was the better for it, especially with amps that were originally designed for a budget market. So in that light, I'll leave it for a few days until the new rectifier gets here, replace the Russian preamp tubes and then take it in to be checked over and anything amiss put right.

    It had crossed my mind to look for a year correct PT to replace the replacement. Though not original to the amp would that mitigate some of the decrease in value or is that a pointless exercise at this point???

    I like discussing and learning about vintage amps so I'm already getting a lot of fun out of the PR. I look forward to it inspiring me in my refocusing on guitar. You can't buy talent but you can buy things that inspire you to be a better player. Some of that comes from guitars and amps that have a tone and a responsiveness that just makes you want to play more. The more you play the better you get.

    BTW, just for giggles here's a list of my small vintage collection:

    mid-60s Kalamazoo Model 1
    1955 Danelectro Commando
    1961 Gibson GA6 Lancer
    1965 Deluxe non-reverb
    1966 Princetion-Reverb
    Maxi Mouse (A fantastic little battery powered busking amp I believe is from the 80s.)

    There are others that harmonica players would find interesting but others perhaps not so much. I've had loads go through my hands but these are what I own now. They've all been bought for a specific purpose.
     
    Last edited: Apr 29, 2019
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  3. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    I'm going by the schematics. Princeton-Reverb-AA1164.JPG

    I was looking at the BF PR AA1164 and the BF PR AB1270 schematics, both of which show a 5U4 rectifier tube.

    The Fender Guru says the BF PR used a 5U4, and that "circuit changes where the 5U4GB was replaced by a GZ34" and later "The 5U4 rectifier tube was changed to a GZ34 in AA764. GZ34 has noticably less sag than a 5U4. So if you want the sag (compression effect) of a pre-CBS blackface PR, go down to 5U4."

    Now, if the schematic shows a 5U4 and they actually used a GZ34, will, I can't do anything about that.

    Ryan Sobb at Reverb.com says,

    "The rectifier tube used in the original pre–CBS AA1164 circuit was a 5AR4. This tube is also found in the ‘65 reissues. Where things get interesting is with the AB1270 and AA764 Blackface circuits.

    "The AA764 configuration used a GZ34, which would eventually make its way into the Silverface AB1270. The AA1270 Blackface circuit, however, would use a 5U4."
     
  4. Snfoilhat

    Snfoilhat Tele-Afflicted

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    This thread would take a big leap upward in usefulness if someone would kindly socket a GZ34 and then a 5U4GB into their PR and take some measurements of B+ and power tube bias. Extra points for adjusting one to have the same cathode current as the other and then comparing B+.

    A lot of today's references/resources/received wisdom appear to be made not from direct observations but by reasoning things out from other sources, which is subject to some tail-chasing, especially once some of the supporting materials are found to be suspect.

    I notice that the B+ on the Princeton Reverb schematics is given as +420 VDC whether the schematic shows 5U4GB or GZ34. Where is the difference in voltage drop? Sure, the schematics are plus-minus 20% even when they haven't been photoshopped, but does that explain it? An idling PR even with a factory-cool bias is still pulling a decent amount of current (for a PR). The rectifier difference should show up if it is real. The 5U4GB data sheet claims 50V drop but it also indicates 275 mA current, an amount a PR can never come close to as I understand it.
     
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  5. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Oh, yeah, the schematic!!! I was going by one too. :)...

    princeton_aa1164_schematic.png

    Yours is earlier (Fullerton), and you've totally ID'd a powerful reason experts think the original PR needed a 5U4. But then those early PRs (through, what, 1971?) definitely had Champ transformers that supply only 2A to the heaters, and a 5U4 wants 3A, so MuchXS is also right. Heck, I don't know what Leo actually shipped in the BFPR. I do know that erroneous tube charts, undocumented corrections, and outdated / uncorrected schematics were pretty common with Fender.

    The other sources you cite, though, appear to have been misled by confusion about the "AA764" PR -- which never existed. The actual AA764 (Champ, VibroChamp) used the same transformer, but of course ran a 5Y3, with 2A heaters.
     
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  6. AlbertaGriff

    AlbertaGriff Tele-Holic

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    My early '68 Princeton Reverb came with its original tubes, and the rectifier is a Mullard GZ34.
     
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  7. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Good points. There must be lots of PRs with each rectifier out there. The poor little stock PTs are sturdy ponies; no doubt some, perhaps many, have survived 5U4 service. OTOH I suppose 5U4s might be a factor in the PT's well-known tendency to burn out after only 40-50 years. :D

    I've never run either a 5U4 or GZ34 -- I did what MuchXS suggested and run a 5V4. Lots more voltage drop than a GZ34, but perfectly happy on 2A heater current. (He also liked to upgrade PR PTs to provide more current -- as you say, it is pretty overworked in ordinary service.)

    Though it doesn't quite drop voltage to 5U4 levels (nominally ~25V vs. ~45-50V for a 5U4) it's perfectly happy on 2A and drops my Champ-transfomer PR B+ to 410VDC.
     
  8. AtlantaSpike

    AtlantaSpike TDPRI Member

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    I have an all original FEIC '65 I 've been using for a few years now - I changed the baffle too,and really dig it. I run a vintage C12N. I also use 5881 tubes and a solid state rectifier to stiffen up the bass and get more usable headroom before it starts to volume-distort.The result is sort of like a pocket Vibrolux. Plenty loud enough to gig with, and still lightweight, with glorious blackface tone. Both the vintage police and the amp police have gotten after me, but they are all reversible mods and it ain't blowed up yet. I have around a dozen bf and tweed amps to choose from, and that one goes out the door the most.
     
  9. PooTwang

    PooTwang Tele-Meister

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    I own a 66 PR it came with Better Coil brand transformers , I run the 5v4 it has the Jensen C 10N IMHO a 12 inch speaker is better served in a Ext.cab
     
  10. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    When I look at the Classic Tone PT schematic, they list the following, with 120VAC input:

    Secondary: 650VCT @ 70ma (325-0-325)
    Rectifier: 5V @ 3A

    MEASURED B+ VOLTAGES W/40µ CAPACITOR

    70mA
    5U4 - 383V
    5AR4 - 399V
    5Y3 - 391V

    45mA
    5U4 - 408V
    5AR4 - 422V
    5Y3 - 415V

    Since a BFDR pulls close to 70mA, I don't see any way to get 420VDC out of a 5U4, unless they're using a 680VCT PT. All of the PR PTs - ClassicTone, Magnetic Components, Marvel, Hammond - that I find use 650VCT and not 680VCT.

    I'm building one now, so we'll see.
     

    Attached Files:

  11. mherrcat

    mherrcat Tele-Holic

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    If the GZ34 has a seam in the top of the glass it may be a Japanese Mullard made in the Matsushita plant. The have various labels. Not a bad tube.
     
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  12. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    I fired up my build, tested it, and delivered it to the customer of Friday 5/17. His comments included phrases such as "amazing tone" and "tone for days." He gigged with it three times last weekend.

    Here are the voltages I recorded using a ClassicTone Princeton Reverb PT and a JJ 5U4 rectifier and 120.8VAC on the primary:
    • 664VAC at the 5U4
    • C1 392
    • C2 382
    • C3 323
    • C4 295
    These were very close to my pre-build targets.

    First gig w/the blonde amp:
    03-DontDoIt.JPG
     
  13. BobbyZ

    BobbyZ Doctor of Teleocity

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    The AA764 did exist from August 1964 the schematic date, till November 1964 when they changed the schematic to the AA1164. You can see the added in artificial center tap, two 100 ohm resistors drawn in off the pilot light and some other hand drawn changes.
    That change was because they changed the power transformer to one without a center tapped heater winding, they also went from the GZ34 to the cheaper 5u4 at that time.
    AA764s after that time are likely just left over tube charts, not uncommon for post Leo (1965) Fender CBS at all. The guy stuffing in tubes just grabed GZ34s. (wonder what he though went my 67 BFDR came by with a non verb BF Deluxe chart)
    Muchxs explained all this and all the different PTs used in the PRs several times, unfortunately he's no longer posting here.
    He also told me to swap out the still working PT in my 64 AA764, before it went up in smoke. I didn't listen thinking after the service it'd last for years, already went 50 and it did, about two years. :)
     
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  14. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    What's a good source (and brand/type) for a 5V4?
     
  15. King Fan

    King Fan Friend of Leo's Ad Free Member

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    I get mine from (gasp) eBay. And I haven't researched brands in depth. You can spend a lot on classic Dutch beauties, but I usually find late-50s 'best-brand' US (RCA etc.) without spending a fortune.
     
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