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Post subject: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 6:14 am
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I have a 79 Princeton Reverb that hasn't been turned on in 20 years...it blew a fuse and hasn't been turned on since. Crazy I know. I feel like I should go to confession.
Since then I've lost the cap for the fuse so ordered that this morning. I was told to take the 2 6V6 tubes out and turn it on. If it doesn't blow the fuse, then those tubes are the culprit and need replaced. However, if it does blow the fuse, it could be something else....I heard the capacitor might need replaced since they can dry up...hopefully that's something I can do myself.
I don't have a good amp shop near me so I need to figure out what to do myself...any help on replacing parts/diagnosis would be very helpful. Anything I should do regardless, now is probably the time to do it as well.
Thanks!


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 9:42 am
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Your 5U4GB rectifier tube may be shorted -- such a situation will cause those exact same symptoms.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 11:27 am
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when you say could be 'shorted', do you mean just replace the tube itself or do you mean there is a short in the connection to that tube?


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 12:26 pm
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truffulaseeds write;
I was told to take the 2 6V6 tubes out and turn it on. If it doesn't blow the fuse, then those tubes are the culprit and need replaced.

Yes , first thing to do , do you do it ? I guess not , it's so easy.

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Fuse holder ( caps) can be order from an electrionic dealer , Busman an LittleFuse made fuse hoder like you have in your amp. Faster to buy complete fuse holder from the shelf

Fuse blow can be many thing , but first thing just remove your 6L6's and try it with new fuse. These tubes are often defectives (or bias too hot) before any other parts.

1- More often ; 6L6

2- If fuse Blow ; remove 5U4 and try again
Fuse holder could be defective and have bad contacts = fuse blow
Old fuse could blow for nothing, just too old, tired.

3- Also defective contacts on 6L6's socket.
4- Output transformer short

Dry cap make hum and /or less punch , rarely fuse blow .


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 2:46 pm
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" 79 Princeton Reverb that hasn't been turned on in 20 years. "

All of the above are good strategies. The one thing you may want to try, with an amp that hasn't been plugged-in; in 20 years --- good contact cleaner in the sockets, switches. & fuse holder.

It's amazing how many "fixes" occur with GOOD cleaner (even funky light switches & whatever around the house or in your vintage hot-rod). :D

I like CAIG De-Oxit D5 or GN-5 for general purposes.

BTW... I usually start with pulling ALL tubes. Replace fuse (proper amperage, slow-blow type). Have speaker plugged in. Zero volume. No input. Turn on. Fuse pops? Look at Power Tranny or wiring around PT or main switch.

No popped fuse? Insert rectifier. Repeat process. Popped fuse? Look at rectifier or wiring or socket of the rectifier.

No popped fuse? Insert 6V6GT's (with rectifier in). "Rinse and repeat" process. Popped fuse? Check BIAS POWER SUPPLY . Power supply filter stage (cap can). Wiring to output stage. Output tube sockets.

These are the Usual Suspects. Keep us posted. Good luck!

BYW #2.. wasn't "Usual Suspects" some kinda movie? Check for "Kobayashi" printed on any tubes. :mrgreen:


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Fri Oct 19, 2012 5:51 pm
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at your amp's age, the filter capacitor can needs to be replaced and that may be part of the issue. Won't change the tone, but will rule out problems.

http://www.blueguitar.org/new/text/tq-40w.pdf

This was a helpful article when I got my '77 Princeton Reverb; I ended up matching up the phase inverter better, adding a Deluxe Reverb output transformer, and adding a Weber 10" speaker to replace a very tired Oxford. The later Princeton reverb cabinets aren't anything to write home about; jamming a 12" in there wasn't practical, but I did pick up a closed 1x12 extension cab on eBay someone built in the same dimensions as the amp. The Princeton also sings when my 2x12 Bandmaster cab is hooked up...

Oh, and no need to remove the pull-boost circuit - just don't pull it out (sounds horrid).

Congratulations, and I'm sure you'll be able to get the amp

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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Tue Oct 23, 2012 9:04 am
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thanks for all the replies...I actually got really lucky! I replaced the fuse holder, stuck in a fuse and it blew....stuck in a new 5U4GB and she sang!!! sounds beautiful.


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Tue Oct 23, 2012 11:03 am
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Retroverbial wrote:
Your 5U4GB rectifier tube may be shorted -- such a situation will cause those exact same symptoms.

Arjay



+10000000000 right on Retroverbial


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Post subject: Re: 1979 Princeton Reverb Silverface trouble
Posted: Tue Oct 23, 2012 7:18 pm
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I had the exact same calamity befall my '80 non-verb Princeton on the day it arrived from the Ebay vendor I bought it from. A new recto and I was back in the game in no time.

Arjay

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