New power transformer?

[chuckb]

Hey enzo, I did just as Tom suggested and the fuse blew. Only things connected were the primaries. So I guess the new Hammond replacement is blown as well.If I get another replacement ,I'll do as you suggested and hook up only the primary wires first ,then connect the secondary wires a set at a time until I find where it is the problem is coming from.

Chuck.

[bob p]

I think you would be well advised to build the current limiter. It will pay for itself with fuses that don't blow.

Now that you know your PT is bad, it's time to ask why your brand transformer is bad. It could be that the first one failed because it had a fault, and second one failed because it was wired improperly. But it's also possible that your two PT blowing up are the symptom of another problem and the PT are not the main problem in your amp. That's why I linked you to a list of differential diagnoses. That list will help you to find other problems that could blow a PT. Rule out everything on the list. You need to figure out WHY the two PT got ruined before you put in a third one; otherwise you'll just find yourself in an endless loop of sticking in new ones.

[eschertron]

Hey enzo, I did just as Tom suggested and the fuse blew. Only things connected were the primaries. So I guess the new Hammond replacement is blown as well.If I get another replacement ,I'll do as you suggested and hook up only the primary wires first ,then connect the secondary wires a set at a time until I find where it is the problem is coming from.

Chuck.

Once the PT is out of the chassis, put it on the bench and test it for clues: winding-to-winding shorts on the secondaries, short-to-ground, that sort of thing. One last test might be to power up the PT on the bench (fused, of course!) and verify that the problem doesn't misteriously disappear when the chassis wiring is taken out of the equation. I've seen more than a few threads where someone spent big $$ on big iron only to discover that the trannys weren't the problem at all. Be thorough, and very careful to ensure that the test results reflect the actual thing that you're checking. Good luck!

[chuckb]

Hey Bob, thanks for all the info,it's been a learning curve for me. I will build that current limiter, it'll save me on fuses for sure. I really don't know if the power trannys are gone for sure. Seems to unlikely for two to fail in such short order.I will investigate it further going through the list of things that you suggested and probably remove the board as well and resolder it. I'm looking to put all new caps in it anyways. In doing so I may just find something wrong that I'm not seeing right now. Thanks to all the guys who shared their knowledge and pointers ,it is very much appreciated. I'll chime in when I have the amp up and running again to give an update.

Chuck.

[Tom Phillips]

... and probably remove the board as well and resolder it. I'm looking to put all new caps in it anyways....

Chuck,

It saddens me to think of that amp being given the shotgun treatment. What do you see that suggests removing and re-soldering the board is needed. Those original blue tubular caps hardly ever go bad. Think about why you want to replace them. The electrolytic bypass caps yes, but not the blue tubulars. At this rate all that will be left of the original amp will be the chassis and the OT.

Sorry if that sounds harsh but I prefer to troubleshoot and isolate the problem and then replace the bad component / repair the bad whatever. Especially in 50+ year old Fender amps.

Tom

[chuckb]

Hey tom, your right, I don't know what I was thinking, frustration I guess. I'll be patient and find the problem and leave the amp as original as possible. It's not everyday you get one of these that is all original.

Chuck.

[bob p]

Chuck, I feel your pain. When things don't make sense it's easy to get frustrated and to want to just rip everything apart. Rather than doing that, I'd recommend being very methodical and running through the checklist to see where the problem might lie. By running through that checklist you'll accomplish the same thing as if you gutted the amp and started from scratch, but you'd avoid gutting the amp in the process.

Some of those items on the checklist involve pretty detailed test procedures. for example, verifying that the OT is good and isn't causing your problems can be a pretty involved process, but it's definitely worth taking it slowly, and running through each step on the list to isolate the problem. The key to success is to follow a methodical plan and to be patient. It may take some time, but you will find the answer.

R.G.'s troubleshooting guide is actually quite thorough and quite helpful. Another text that you might want to consider is Jack Darr's book on tube amp repair. It has a very practical section on troubleshooting power supply problems. If you google for it, you should find that someone has scanned it so that it's available for download as a PDF from one of the guitar sites (can't remember which).

I'm with Tom on the coupling caps. Unless you can demonstrate that one of them is out of spec or leaking DC, it's better to leave them be.

good luck!

[bob p]

Jack Darr's book was originally published in the 1970s and had been out of print for a long time. for as long as I remember you had to hunt through the used book stores to find one. Because the book was in such demand, somebody scanned it and posted the relevant chapters on the web. I can't remember where.

I googled for the book, and I found that you can buy used copies of the 1977 edition for as little as $20:

Amazon.com: Buying Choices: Electric Guitar Amplifier: Handbook

The really good news is that the book is back in print and you can buy a brand new one for less than $30:

Amazon.com: Buying Choices: Electric Guitar Amplifier Handbook

[chuckb]

Hey Bob, ya, it's time to stand back and take a deep breath, let the frustration go and concentrate on the checks I need to do. Thanks for the info on the troubleshooting guides, i'll see if i can track them down. Thanks again for your help, very much appreciated.

Chuck.

[Tom Phillips]

I understand the frustration. It will evaporate when you find and correct the problem.
There are some other things you can read up on and try before you jump into buying a new PT.
I add the following to the info posted by Bob P and eschertron above.

Make sure the amp is unplugged and the filter cap is totally discharged. With the pilot light bulb and all the tubes removed and the PT secondaries still all disconnected use your ohmmeter to measure the resistance between the points where the secondary wires were connected. That is connect the probes across where the two yellow wires were connected, where the two red wires were connected and where the two yellow wires were connected. They should all read very very high / over range resistance. Next measure the resistance from each individual connection point to chassis ground. Again the reading should be very high / over range with the following exceptions:

1. One of the green wires was connected to the chassis so that side of the green wire connection doesn’t get checked.
2. You may initially get a lower reading at pin 8 of the 5Y3 socket because that point is also connected to the filter cap. The resistance reading should drift up to a very high value. If it does not then it indicates that the filter cap is bad / shorted.

Please do those tests and report your findings.

Attached for fun is a gut shot of your amp's cousin. A 1963 6G2 Princeton.


Cheers,
Tom

[bob p]

That's a really good photo. Nice diffused lighting.

[Tom Phillips]

That's a really good photo. Nice diffused lighting.

Taken outside on an overcast day. Works great!

[Tom Phillips]

Hey Chuck,
At the beginning of the Princeton production run Fender used a PT with a pretty small core and it ran really hot. I'm trying to determine when/if Fender upgraded from the 125P1A to the 125P1B.
Can you post the Fender part number and Code number that was stamped on the end bell of the original transformer that was installed in your 64 Princeton 6G2?
Thanks,
Tom

[Enzo]

Seemed to me there were scans of the Darr book online. I don't condone stealing a guy's book, but if it is out of print and from 40 years ago, I'd have to think it was getting into the public domain.

A quick look found:
Some chapters from Jack Darr's classic book

[bob p]

When I made my posts about the book, I thought it was still out of print. It's back in print now, and I feel like a heel for promoting IP theft. So instead of stealing the online version, I decided to order a print copy for my library. I bought a brand-new copy of the 2006 edition for $27.95 + $3.99 shipping. Sounded like a good deal for $32.00, considering that it's a print copy that's easier to read. It's also got some schematics in it that you won't find in the online version. Should arrive here on monday.