Choosing Power Transformers

[acheld]

I am planning an amp that is aimed at experimenting with circuits mostly on the pre-amp side, but which also has the ability to use either 6V6 or 6L6 output tubes, in push-pull.  Not at the same time, I just want the ability to change circuits and only use the one power transformer. 

As I review the data sheets for both of these tubes, and what is available thru Allenamps, Mojo, etc, it seems like the transformer voltages as published don't line up with what I see on schematics.  In addition, the amperage required per the data sheet seems higher than what I see on purported "suitable" PTs.

I want the PT to provide adequate (but not too high) HT, and sufficient current to provide some flexibility. 

I'm assuming 5 12AX7's would draw only 10mA.   Plan SS rectification.   

So, if you were ordering power transformers for 6V6, what HT voltage would you choose?  How many mAs should be spec'd?

Same for 6L6s:  HT voltage? and amps?

No schematic as yet -- trying to get in front of Edcor . . . 

[shooter]

the best way to answer;
what amp "in the world " are you aiming to get close to?
so 5E3, what did fender do
Marshall 18W, what did.........
then we might help dial in closer

[tubeswell]

Whatever PT you get, the power supply load will decrease when you switch from 6L6s to 6V6s, which will affect all the voltages.


Also, due to the different bias requirements, the bias voltages will be different (which will affect the way the PI drives the output tubes) when you switch from 6L6s to 6V6s.


Also, an OT that is sized and power-rated to handle 6L6s will perform differently when you put 6V6s in (even if you ‘right-size’ the reflected load by switching speaker impedance).


If you find some xformers that enable compromise between the two, you may end up with something you’re not too fussed about either way. (Or you might not - hard make a call about someone else’s preferences).

[acheld]

Good questions.  I was not more specific because this is intended to be an experimental amp to try out various pre-amp configurations over time -- ie, not a production amp that would be static.

I thought this might be "doable" but also had a sinking feeling that I'd be asking too much from one PT.  I knew the OT would have to be configured differently.  So maybe an impractical idea.

OK, since I've built a bunch of 6V6 amps, why not then settle on a 6L6 amp push-pull, SS rectification, and then experiment off that platform?  Seems more sensible. So with that in mind, if you were to source a PT for such an amp, what HT would you look for?  How many mA on the HT circuit?  I would have no more than 5 12AX7s on the pre-amp side (they seem to have minimal draw in any event). 

[T Wilcox]

If what you are wanting is to only try different preamps then why not just build the preamp only?
I have been doing this myself. If any of your amps have an fx loop you are set!
I use 2u rackmount units to build my preamps in with Antek torroidal trannies and run them direct into the fx return of my other amp heads ( one at a time) with great results

[Backwoods Joe]

consider this: pick a PT 300-0-300 Volts that has windings for a rectifier with enough ma's for the 6L6's. Use a 8 pin socket for the rectifier. This way you have the option of using a solid state rectifier or tube rectifiers for different plate Voltages on the output tubes. Some where around 425V with solid state rectifier down to almost 100 volts less with a 5y3 (when using 6v6's).

[PharmRock]

I'm not sure if this might solve the problem with the voltages, but I built a Trinity Amps "Triwatt" last year that allows KT66 or 6V6.  The schematic calls for a DPDT switch that does 2 things...in 6V6 mode, it runs HT through an 18V Zener which drops voltage for 6V6 operation.  It also switches in an additional bias resistor in parallel to the 6V6 bias resistor for KT66 operation.  Of course, this doesn't solve the OT issues, but it seems like a potential solution for the power supply and bias. Maybe a variation of this approach might be something worth looking into?

[acheld]

Many thanks for these good ideas.   

LOL, now I have to crunch the real numbers before putting in my Edcor order . . .