What project for 5E3 transformers?

[polymolly]

Hey there! (my first post over here!)

I have a PT and a OT from a 5E3 that I got real cheap for a scratch build, but I ended up getting a kit, so these been hangin around ever since. So I've been thinking what use to give them for a long time. I really want tremolo and reverb. Well, at least tremolo
One easy way out was to build a 5F11 (it has nice tremolo). Then I thought I should take the blackface route, since the tweed territory is covered with the 5E3. So I started looking into the vibro-champ (forgot to say: looking for smaller amps) and trying to find a way to make it a 2x 6V6, because I really like the preamp bias modulation tremolo of the vibro champ. But, truth is, I'm no electronic genius, and would probably mess it all up, so I put that idea aside.

So, I will probably end up building a blackface princeton.
But in the meantime, while looking at the circuit diagrams and transformers specs, I ended up confused with this:

Why does the princeton reverb (with 7 tubes) use the same power transformer as a small single ended amp like the champ (with 3 tubes in it)?!?!?!??! and why is, apparently, a 5E3 transformer (capable of delivering the juice to the deluxe's 5 tubes) not enough to feed the princeton reverb?

BTW, here are the specs for my transformer:

Primary: 230VAC/50Hz
Secondary: 325-0-325@70mA; 6.3v, 2A; 5v, 2A

I'd love to hear your opinions on this one!

Thanks!

[Chuck H]

There are some really fundamental misconceptions here. First... The original Princeton was a small single ended amp. You may be confusing the PT allocation on this basis. AFAIK the Princeton Reverb uses a different PT than a Champ. Second, the "juice" supplied by the PT is allocated to dedicated windings and taps that include, but are not limeted to, HV secondary, rectifier tube 5V, power and preamp filament 6.3V, bias voltage,etc. The capability of each winding may dictate any particular PT's suitabilty for a given amp design. In the case of the 5e3 PT not being able to support a Princeton Reverb, it's a matter of mA rating, HV voltage and a bias tap. The 5e3 PT has a lower HV than the Princeton Reverb PT. The output of the Princeton Reverb is marginally higher than a 5e3 and therefor needs a higher nominal current rating. The Princeton Reverb is fixed bias, and uses a "bias tap" from the PT to derrive this bias voltage. The 5e3 is cathode biased and therefor has no bias tap. They are different amps.

Asking questions is the right thing to do. If you want to build a specific amp design you will need to meet that amps design criteria to do it. If you mean to build an amp with the parts you have then you must either build an amp for which the parts are made or design a new circuit that fits into parmeters the parts you have can accomplish.

[JoeM]

... You may be confusing the PT allocation on this basis. AFAIK the Princeton Reverb uses a different PT than a Champ...

Chuck the BF versions of the Champ and Princeton (reverb or non reverb) use the same PT. Also no separate bias tap.



http://www.webphix.com/schematic%20h...z34_aa1164.pdf

http://www.webphix.com/schematic%20h...a764_schem.pdf

[Chuck H]

Thanks Joe. I should have looked it up first. But it is interesting to note that on the Princeton Reverb schem the PT is indicated as a 340-0-340 HV secondary and on the Champ schem it's a 315-0-315...?

Also, after looking it up, the Princeton Reverb and the tweed Deluxe have the same mA rating on the HV secondary.

Anyhoo... You can use a PT with a higher current rating than is needed in an amp with no problems. But you can't go the other way.

And to be more accurate at this point... You CAN build a Princeton Reverb type circuit with the Deluxe PT, BUT, you'll have low Vp and you'll stress the heater winding a tad.

Thanks for keeping me honest.

[JoeM]

Yeah, Fender shows a different Champ with even yet another HV spec. I think the 340 seems about right based on my Princeton and a friends I'm working on. They run hot. Several replacements have the secondary at 100ma rather than the 70ma, so if I was doing a build I'd definitely go with the higher spec PT.

[Chuck H]

+1 to the higher spec PT. Plenty of sag in tube amps, especially with a rectifier tube and/or cathode bias. No advantage to running your PT into the ground. And, as to the PT spec., I reworked a Vibro Champ for a friend (replaced the vib circuit with an extra preamp stage and cathode follower and adjusted the gain structure). It had 428Vp! In a single ended 6V6 amp?!? The burn in, which included me cranking the amp and playing the bejeesus out of it, blew up the onld RCA 6V6 that was in it. I plugged in an EH and it was biased just fine and lived through the torture test. The guy loves his amp now and since (maybe seven years ago).