Choosing a Princeton Reverb Transformer

Mongo Park

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I always read Muchxs with great interest and care, he does have experience you don’t have to go his way but if you do you can’t go wrong. As mentioned tone is subjective, Leo was forced by economic to put in the minimum and I don’t think you are under the same pressure That’s the beauty of DYI, considering other options.
You should also consider Matt at Musical Power Supply.

https://www.musicalpowersupplies.com/products/

He has great transformers and you can get both pt and op in one shipment
Nice thread lots of information and options which is always good.
 

nest

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I haven't changed out the power transformer yet but here is the amp with my son playing two guitars through it. It has a celestion blue in it right now.

 
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Drorangedrop

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Im sorry to hijack this thread (or resurrect it) but wondering if you guys could offer me advice on a power transformer I have lying around and want to use?

I'm basically trying to make a Princeton reverb turn into a small portable lower wattage version of my favourite BF Super Reverb.

The circuit I'm trying to use is a Princeton Reverb PCB but with these intended changes:

* Solid State Rectifier
* Long Tail Phase Inverter (like a deluxe or super)
* No Tremelo
* Master Volume inserted.
* No pilot lamp

Im intending to absolutely max out the volume for distortion and use the master volume for lower actual loudness

The PT I have lying around has 325-0-325 at 100ma and 6.3v at 2A.

I guess I then have two questions:

1) Given Im using a SS rectifier which i understand sends a very high voltage down the B+ line, will my 325-0-325 @100ma HT be workable? Will I need to lower the b+ resistors to bring it down? Im wondering if the plate voltages will be too high for the 6v6's to handle if I dont?

2) Given a pair of 6v6's use 900ma for filaments and four 12ax7/12at7's use 1.2A for a total of 2.1A, will this be a problem if my filament winding is only rated to 2A? Would that 100ma difference cause the amp to become BBQ?


Thanks!
 
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Drorangedrop

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Hi guys, just a humble bump in the hope someone could offer me a bit of help answering my post above.

Thank you:)
 

Paul-T

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Others will know more than me, but in case they don't turn up, my theoretical take on the loading of the PT (I'll leave the B+ question to others).

1: many folks use a 75mA 325V PT and that's fine, although of course higher capacity gives more reliability. So your extra 25mA means you're about 8W under capacity.
2: The 100mA difference in your 6V TAP represents around 1/2W over capacity.



So while that extra draw on the low voltage tap might mean you're producing 1/2W more heat than your PT likes, you're still 7.5W under on the whole thing. That suggests the PT shouldn't overheat.I don't know what your PT is, how rugged and how generous the manufacters specs are, but my take would be it looks ok.

Obviously, monitor the temp carefully when you fire it up the first few times, and run it hard while monitoring .
 
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Uncle Daddy

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Just seen this, while I'm thinking of doing another PR build, and kit available in the UK comes with the Hammond 291BEX, with 330v/ 138mA on the secondary. Would this be OK, with the regular GZ34 and 6V6s?

bex.JPG
 

King Fan

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The PT I have lying around has 325-0-325 at 100ma and 6.3v at 2A.
I guess I then have two questions:
1) Given Im using a SS rectifier which i understand sends a very high voltage down the B+ line, will my 325-0-325 @100ma HT be workable? Will I need to lower the b+ resistors to bring it down? Im wondering if the plate voltages will be too high for the 6v6's to handle if I dont?
2) Given a pair of 6v6's use 900ma for filaments and four 12ax7/12at7's use 1.2A for a total of 2.1A, will this be a problem if my filament winding is only rated to 2A? Would that 100ma difference cause the amp to become BBQ?

My guess is you will be pushing the tubes on B+ voltage and maybe the PT a bit on heater current draw. Here's a tool I use a lot:

https://thesubjectmatter.com/calcptcurrent.html

If I'm entering your numbers right, it tells me this:

upload_2021-3-12_8-16-10.png


BTW, welcome to TDPRI. :) If you want a fuller discussion, I'd suggest you just start a new thread with your question in the title. Lots of folks smarter than me, but old threads don't attract as many eyeballs.
 

2L man

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Ungle Daddy!

Yes it would. High voltage comes bit high for 6V6 but lots of them are built using 330VAC PT.

Installing current limiter resistors to rectifier anodes lowers the output voltage, improves filtering and lengthen rectifier life. You can still improve filtering and lower voltage installing another RC filter if chassis has room for it.
 
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Uncle Daddy

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Ungle Daddy!

Yes it would. High voltage comes bit high for 6V6 but lots of them are built using 330VAC PT.

Installing current limiter resistors to rectifier anodes lowers the output voltage, improves filtering and lengthen rectifier life. You can still improve filtering and lower voltage installing another RC filter if chassis has room for it.

Thanks. I guess the 3A feed for the rectifier makes it better for tube choice too, something like a 5U4 to drop a few volts.
 

Jason McG

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adding some data based on my actuals:

built a RobRob Princeton Reverb Delete AA1164D, and used the Hammond 272BX. GZ34 rectifier.

Biased at just under 70%
B+1:379 VDC
B+2: 366 VDC
B+3: 275 VDC
B+4: 186 VDC

Can't use a 5U4 with it, because of the 2A rectifier section. Not a concern for me, that tube is too tall to fit in my head anyway.

Its a stand-up style transformer as well, so great for a smaller chassis size, and no need for a cutout.

image.jpg
C4885282-F3B3-45D1-B416-B19423AF39B1.jpeg
6429A04F-8DC0-4EC5-9B95-8769B120108E.jpeg
E72EC60A-C3A0-450C-81EC-2AEFA90081E5.jpeg
CA564D99-577B-4948-821E-0F3ECA50C478.jpeg
 

BenTobith

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adding some data based on my actuals:

built a RobRob Princeton Reverb Delete AA1164D, and used the Hammond 272BX. GZ34 rectifier.

Biased at just under 70%
B+1:379 VDC
B+2: 366 VDC
B+3: 275 VDC
B+4: 186 VDC

Can't use a 5U4 with it, because of the 2A rectifier section. Not a concern for me, that tube is too tall to fit in my head anyway.

Its a stand-up style transformer as well, so great for a smaller chassis size, and no need for a cutout.
Unless I’m mistaken, it seems like that might fit mounting holes in a standard Princeton chassis? Would it support 6L6s?

Perhaps a dumb question, but is the 125VAC meant for the stronger home power we get in the US? My wall voltages are always closer to 125VAC than 120.
 

Jason McG

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I think the footprint is a bit different, but you can see the exact dimensions on the hammond website and compare. Yes, the 125v hook up is for that reason, if your wall voltage is higher. Can't say on the 6L6's, but theres more that factors into that determination than just the PT. RobRob's site gives you some steer on how to go about that.
 




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