Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on July 13, 2010, 02:41:49 pm

Title: Replacing PT in Princeton (AA1164)
Post by: dude on July 13, 2010, 02:41:49 pm
Probably stupid question.

I'm replacing a fried PT in a 1971 Princeton Reverb for a friend. The amp has no voltages and the PT is melted (I'll check the power tubes). Doug has the replacement but:

What is a dual primary PT?  Is this a PT that can run off 120v or 240v? The old Fender PT has four wires on the primary side, I'm use to seeing two black primaries for 120v. I'm assuming that the old Fender PT was able to run on 120v or 240v and wired for 120v, therefore it's a dual primary PT?  All the schematics I find on that amp show just two black wires on the primary side. Was this common on 70's Princeton Reverbs?

I was a little confused about the wiring on the old PT, on the primary side they have the two black wires tied together to hot side of 120v and red/bk tied with yellow/bk to the neutral side. I'm assuming this is a dual primary PT wired for 120v operation?

So, I'd just wired the two black primaries to the hot and neutral, doesn't matter which to which...?

thanks, al

   
Title: Re: Replacing PT in Princeton (AA1164)
Post by: Fresh_Start on July 13, 2010, 03:01:17 pm
There's a link on Hoffman's transformer page to the Library.  From there you can find:
http://www.el34world.com/Transformers/fentrans.htm

No, no need (or way) to differentiate between the two primaries or the two secondaries for that matter.

Good safety practice is to have the HOT from your power cord go to the fuseholder tip, then side of fuseholder to power switch so you are switching the hot side.  Also, make sure that the green safety ground is longer than either the black or white so that it would be pulled out last (or use an IEC socket :wink:)

HTH

Chip
Title: Re: Replacing PT in Princeton (AA1164)
Post by: jjasilli on July 13, 2010, 03:34:46 pm
2¢:  Please be aware that a fried PT may be a faulty PT; but may be a symptom of some other problem which caused the old PT to fry.  If you simply swap-in a new PT, it may it fry too. 
Title: Re: Replacing PT in Princeton (AA1164)
Post by: Fresh_Start on July 13, 2010, 03:48:39 pm
Quote from: jjasilli on July 13, 2010, 03:34:46 pm
2¢:  Please be aware that a fried PT may be a faulty PT; but may be a symptom of some other problem which caused the old PT to fry.  If you simply swap-in a new PT, it may it fry too. 

Darn good point!  Search for "light bulb limiter", build one, and use it on initial power-up.  Might save you from frying a brand new PT.

Chip