Tranformer Selection for DIY Tube Amp

[punkin]

I'm considering building this little project http://www.tube-town.net/diy/tt-sam/tt-sam-en.html . The build looks simple enough and appears to be a nifty little platform for some mods and experimentation. As I am in the USA the power transformer needs to be different than what is shown. I'm looking for a cost effective and suitable replacement. That in mind, I'm having difficutly selecting an appropriate size as the schematics and information don't tell of the power consumption requirements. Anyone with a little more experience who might be willing to recommend a transformer?

Thanks a bunch in advance 

[petemoore]

  I'm sure Hammond has a nice affordable tranny for that, if a departure from the torroidal shown.
  I'd take a look at the Epi Valve Jr. also, though this amp seems to have more tubes, the heater Ma. is bound to be greater, lookup the data sheet on the tubes, figure out what voltage or voltages are required to power the heater filaments, add up the current draw[s, make sure the PT can output at least +10% that amount.
 

[mac]

Toroidal power transformer as my laney, cool.
This single ended EL84 is going to dissipate 10-15w most likely, 3w to the speaker, the rest to the air .
Any power transformer of the size shown in the pict can handle enough power. I have power trnasformers of the size of that output transformer rated at 100w.
If size and $$ are not an issue get a +50w PT.
Check Epi Valve Jr and ax84.com, they have similar power requirements.

mac

[punkin]

Thanks Gents,

My trouble seems to be matching the output voltages shown in the diagram. I can find transformers with the high voltage above and/or below the spec'd 200 volts but nothing exactly matching (so far).

[gmoon]

Antek makes some very affordable toroidals, including a 100VA, 200-0-200V job with two 6.3V filament secondaries:
http://www.antekinc.com/

You might also consider a higher voltage transformer, together with a VVR to dial the down the voltage as needed. Should be simple to used with a single-ended cathode biased output stage...

[punkin]

I thank you kind sir 

[sean k]

Theres a few tricks you can do to tailor an output voltage to the one you want. After using tube rectifiers, which drop a certain amount of voltage theres basically the idea of playing with caps and chokes. Cap input gives you 1.414 x the voltage and .707 x the current and a choke input is the other way round, given your using full wave CT. But you can kinda get anywhere in the middle of those two by using smaller caps before a choke and lager caps after a small choke.

An old trick of mine is to use a choke adequate for the job then put a small cap, anywhere from 100n to 1uf before the choke until the voltage rises beyond .707 to where I want it to be so it's basically a cap input followed by a choke but the cap size is tailored to only grab a portion of the rising voltage. I haven't done it but I would suppose that a smaller choke followed by big caps would do the same thing.

Plus it's always a good idea to have a choke on an SE build... so I'm told.

[punkin]

So, if I get what you're saying there, you're suggesting that perhaps say...by building in additional power supply filtering (post post rectifier), I might be able to drop voltage here-n-there to get me closer to the desired circuit requirements? I now recall seing this done in smaller regulated supplies where a diode is inserted in series on a DC line to drop a little voltage.

[JKowalski]

Plus it's always a good idea to have a choke on an SE build... so I'm told.

Thats because, unlike the push-pull format, the single ended output does not have any common mode rejection of power line ripple, I believe.  You need a better DC power supply so you don't get bad hum.