1973 Princeton Reverb question

[Michael1]

Hi everybody-i have a 1973 Princeton Reverb im working on for a friend (recapping etc.) Im not sure what circuit this is as it is not written on the tube chart. It seems to be missing a couple of 25/25 cathode bypass caps-it has 4 total. All the schematics ive seen have 6. The ones missing are pin 8 V2 and pin 3 V4. Is this normal for this amp (solder joints look original). Should i add them? Thanx in advance for you help!


                                                                                                                        Michael

[smackoj]

hi; how did you date the amp?  did the owner say whether adding stuff to the circuit is ok?  might want to hold off until you are sure you have the right scheme for the amplifier. 

 

[stratele52]

Yes you need these cap if you want original. Can work well without , another tone

Schematic is there;

ampwares.com/schematics/princeton_reverb_aa1164.pdf

More infos

ampwares.com/amplifiers/fender-silverface-princeton-reverb/

[sluckey]

Is it possible that two of the caps are actually double caps in one case (similar to the attached pic)? That would make for a total of 6 caps.

EDIT... added another pic. BTW, I just saw a couple SFPRs with only 4 cathode bypass caps. Don't know which circuit though.

[HotBluePlates]

Yeah, if you have any "3-legged critters" in the preamp, they are dual 25uF caps with a common negative lead.

[Michael1]

Thank you all for the reply's! I dated it by the numbers on the trannys-output reads 606-3-29. Power reads 606-3-45. There were no double 25/25 caps-all were singles. It has the 5u4 rectifier tube (also says 5u4 on the tube chart). I was surprised to see 2 less 25/25 caps in there-i havent been inside a princeton before-quite a few other fenders though. I thought that maybe someone removed them for some reason-the solder joints look factory.  I have replaced the capcan-bias cap-and the 4 25/25s. The amp is quiet-reverb and trem work-it sounds just ok-it has a 12" fender utah speaker in it(I would change that). Ill put them in and see how it sounds. Thanx a million everybody for the help! Any advice from you guys is much appreciated!


                                                                                                                                      Michael

[HotBluePlates]

The era your Princeton was made probably precludes the brown-wrapped Mallory caps Sluckey pictured, and likely the black dual-25uF's too.

Are yours the white Mallory 25uF caps? If so, there were probably others in there before that maybe someone took out. The PRinceton is one of the amps Fender never really changed during the transition form blackface to silverface.

[stratele52]

I see an 1 watt BURN looking  resistor close to the quad filter cap can. 

[LooseChange]

Probably removed because someone thought it broke up too easily.

[phsyconoodler]

  

it has a 12" fender utah speaker in it(I would change that).

Why? Utah speakers seem to get a bad rep for some unknown reason.I have them in two amps and have used them in many others and they are great.
 My two amps,a 68 Pro Reverb and 77 Vibrolux are both the best sounding amps I've heard lately.
Both have the original Utah speakers.

In your case I would look at an AA1164 Princeton Reverb circuit and add the bypass caps where they are missing.I bet it will perk it up quite a bit.

I see an 1 watt BURN looking  resistor close to the quad filter cap can.

That's Sluckeys picture,not the OP's.

.

[eleventeen]

Me, I would date that am to 1968 judging by the chassis ink-stamp.

[stratele52]

Dating the pots will say too.

IMO  Power Transformer is not the originald

[daven]

yours might not be a later pull-boost model, but it might already reflect some of the changes that occurred with it, notably the reverb drive circuit.  fender changed the common cathode resistor on V2 to 680 ohms, and dropped the cap.  that circuit only has five 25uF caps, and the fifth one was moved to the back of the chassis.  I've included pictures of my '78 SFPR, and you can see the fifth one attached to V4.

[DummyLoad]

also, in the 70's fender started using the 5U4GB in the PR and upped the PT sec. from 325V to 340V to compensate.

--DL

[HotBluePlates]

My '67 Princeton Reverb used a 5U4GB, and had that indicated on the tube chart.

[Michael1]

Thanx again guys for the replys! I forgot about the 25/25 on the back of the amp-that makes 5. The 25/25's were the white ones. And also-no push pull. It had a 1k 1 watt resister fried pretty bad-close to the cap can. I put in a 3 watt there-also put in 3 watt 18k's. I dont know about the Utah speaker-ive never owned one-just was reading some things about them not being the best lol. I'll let the owner decide on that-he might like it. Thanx again everybody!

[plexi50]

Thanx again guys for the replys! I forgot about the 25/25 on the back of the amp-that makes 5. The 25/25's were the white ones. And also-no push pull. It had a 1k 1 watt resister fried pretty bad-close to the cap can. I put in a 3 watt there-also put in 3 watt 18k's. I dont know about the Utah speaker-ive never owned one-just was reading some things about them not being the best lol. I'll let the owner decide on that-he might like it. Thanx again everybody!

It had a 1k 1 watt resister fried pretty bad-close to the cap can

Is the cap can good? Has the PS cap can been changed since? I actually have a princeton reverb cap can from 1977 that is still good and quiet. It's on the shelf. It might come in handy one of these days

[HotBluePlates]

It had a 1k 1 watt resister fried pretty bad-close to the cap can

Is the cap can good?

That was just a picture Sluckey posted to show examples of dual cathode bypass caps. NOT the amp Michael is working on.

[plexi50]

It had a 1k 1 watt resister fried pretty bad-close to the cap can

Is the cap can good?

That was just a picture Sluckey posted to show examples of dual cathode bypass caps. NOT the amp Michael is working on.

Whoops!