Princeton AA964

mjcyates

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Starting a build of a Princeton AA964. It is going into a vibrochamp chassis so rather than drill another hole in the chassis for the second 6V6 I plan to use the rectifier hole for that and use diodes instead of the GZ34 for the rectifier. Does this look like what I need to do?

tube rectifier to diode.png
 

SerpentRuss

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No, I don't think so. If you don't have a rectifier, you need to build a diode bridge. Look that up. Also not having a rectifier tube is going to boost your output voltage

Fullwave-Bridge-Rectifier.png
 

NTC

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Uh, not quite. If the PT wants to see a rectifer tube, you only need 2 diodes - D1 and D4 in SerpentRuss's diagram. The CT of the PT HV winding goes to ground. The bias tap, if there is one, should either bebused to power the bias circuit or be tied off. It should NOT go to the rectifier.
 

dan40

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As NTC stated, you can get by with a single diode on each one of the secondary wires but I often double them up as you did. Your diagram shows a full wave rectifier setup which is used with a PT that does have a centertap connected to ground. If your PT did not come with a centertap on the high voltage winding, the full wave bridge that "SerpentRuss" showed would be the correct option.

Does your PT have a bias tap or do you intend to tap it off of the high voltage winding like the original Princetons did? If you tap off the high voltage then your drawing would work fine. If your PT has a bias tap, you could use that instead but you would need to change the resistor value in the bias circuit.
 

peteb

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Starting a build of a Princeton AA964. It is going into a vibrochamp chassis so rather than drill another hole in the chassis for the second 6V6 I plan to use the rectifier hole for that and use diodes instead of the GZ34 for the rectifier. Does this look like what I need to do?
Your first drawing looks mostly right to me.

Except

your yellow PT wires are the rectifier tube 5VAC filiment heater, which won’t be needed, that you correctly did not use.

your red bias wire may be the 6.3VAC filiment heater, which is for all the other tubes, and can omitted from your drawing.
 

mjcyates

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Thanks for the responses so far. I am using the Hammond 290AX which does have a CT. This is the layout I am trying to complete.

AA964 Layout.png
 

dan40

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Your layout drawing is missing the bias circuit. Are you planning on copying the standard Fender Princeton bias circuit? I would go with one of Hoffman's versions that includes a bias adjustment pot if you haven't already built it.

 

Phrygian77

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No, I don't think so. If you don't have a rectifier, you need to build a diode bridge. Look that up. Also not having a rectifier tube is going to boost your output voltage

View attachment 945569

I would use a 4 amp rectifier bridge in solid state and heat sinkit


You cannot use a bridge rectifier here, not if you're using a Champ/Princeton PT. You also cannot run the negative bias supply off the same secondary, like the 6G2/AA964/AA1164, when using a full wave bridge. You either need a separate secondary or a cap coupled supply.
 

mjcyates

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The HT CT is red with yellow on a Hammond 290AX. It would attach to the reservoir cap negative side.
The Hammond 290AX does not have a bias tap. Your drawing in post #1 will work when the HT CT is connected.
Yes you are correct, I forgot to put that in. My layout has been updated. Thanks for your response.
 

mjcyates

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Your layout drawing is missing the bias circuit. Are you planning on copying the standard Fender Princeton bias circuit? I would go with one of Hoffman's versions that includes a bias adjustment pot if you haven't already built it.

Yes I haven't gotten to the bias circuit yet. I was intending to use the standard Fender Princeton bias circuit but I will take a look at Hoffman's. Thanks for your response.
 

King Fan

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Cool project, good ideas here. I would for sure design the bias circuit before I went any further. If you can tap into the HT voltage, here's my attempt to update Doug's elegant circuit but old dot-matrix drawing. Feel free to check against original, below...

Also, maybe more important, I can't quite tell from the above discussion if it is or isn't good to tap your diode rectifier for this current. SS rectification not my thing. But @dan40 and @Phrygian77 will be able to confirm.

Hoffman simple bias pot.jpeg


Hoffman bias.gif
 
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King Fan

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Oh and separate question. That 290AX has 275 and 325 HT options? If I'm thinking right (and I may not be -- diode rectification as I say isn't my thing) those values might get you B+ of around either ~375 or ~445, neither one exactly what I think of as Princeton territory. Again, others may be more helpful here.
 

King Fan

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Schematic shows B+ of 405 so if I can get in the ballpark I think it will be ok.

Right, I just wonder if people think 375 or 445 are in that ballpark? There are ways to drop high B+, of course. It's just... in my mind that 400-410 area is where BF Princeton happens.
 

dan40

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Your drawing looks good. The bias circuit wants to see AC voltage so you can tap your bias voltage from either one of the HT secondary wires right where they connect to the diodes.
 




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