Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on March 04, 2012, 02:39:48 pm
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Hi guys,
I have the need for a small, portable fender with reverb, and my favorite in terms of sound as always been the princeton reverb. However I do have a set vibrolux reverb transformers hanging around, this will automatically make the amp heavier, but my question is how much will it change the overall tone of the amp, if I use the same schematic as the princeton?
The OT is 4000ohms primary but it has several secondary taps, so I intended to still use 6V6s and compensate the ratio by pluging the amp into a 8ohms speaker using the 16ohm tap.
Your thoughts are welcome, I don't really want this to sound like a deluxe reverb or a bigger amp. Should I go through or just get smaller transformers?
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it probably will sound a bit "bigger"/cleaner, but i think a lot of the princeton character will still be there just because of the cathodyne p.i. and no choke as well. rh
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The OT is 4000ohms primary but it has several secondary taps, so I intended to still use 6V6s and compensate the ratio by pluging the amp into a 8ohms speaker using the 16ohm tap.
You'll need to apply 8 ohms to the 4 ohm tap to reflect 8k to the primary, but you probably just mis-typed that.
Let's assume your transformers are spot-on replicas of the original Vibrolux Reverb transformers. The blackface Princeton Reverb had a 340-0-340v PT and a 5U4 rectifier, where the Vibrolux Reverb had a 315-0-315v PT and a GZ34 rectifier.
Assuming US voltages, 315/110 = 2.864 * 120v = 343.7v. So happily, applying modern wall voltage to an accurate Vibrolux PT results in old-style secondary voltage perfectly suited for a Princeton Reverb. Though you might see some variation on the proper rectifier for the PR, I always used a 5U4 in mine; my first tube amp was a '67 Princeton Reverb, and that was the specified rectifier in that amp.
I agree with 6BQ5 that much of the Princeton character will be retained by the power supply and phase inverter style. And original blackface Princeton's used a Jensen C10Q speaker. Don't use a "too-good" speaker that has a bigger, clearer sound than the original, and you'll be fine. I haven't done a speaker shoot-out, but the reissue Jensen C10Q sounded reasonably close to originals to me, after some break-in. I've used maybe 3 C10Q's in the past. They're not 100% the same, but a new speaker will have a hard time matching a 40-yr old original. And you can't beat the price of the reissues.
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Thank you 6bd5 and hotblueplates,
Yes the secondary tap was a mistake I meant 8 ohms in the 4 ohms tap.
I intend to keep everything the same even the 10" speaker, I think the C10Q is the best speaker the current jensen reissues have going on, but even their alnico ones sound good once they're broken in.
The transformers I have are vibrolux reproductions sold by mojo, I suppose these are made by heyboer. I will try and do the princeton with these than, that will save me some money.
Thanks guys
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Also, you might like 6L6's in there. Worth a try.
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run it with 2 pair of 6V6. switch out a pair if not needed and double the speaker load.
--DL