Old Stancor PT Wiring

[dorrisant]

Many thanks for these suggestions. I may have a Fender set in the works... HT will be a tad high but I have a good solution for that.

Phil, you got me wondering about those Antek PTs... Do you really think a 100VA PT will be sufficient current-wise? I know that their ratings seem a bit odd. I was actually looking at there stuff and got bogged down in the conversion from mAs to VAs again...

https://tubeamparchive.com/viewtopic.ph ... 80111d078e

You were in on that discussion... what do you think. I need 200mA on the HT.
So 700V x 0.2A = 140VA. Here I'm not calculating HT load but using 200mA from a suggested/equivalent PT for the circuit (Jim Kelly).
+ (4 x 12AX7 filament draw) 1.2A x 6.3V = 7.56VA
+ (4 x 6V6 filament draw) 1.8 x 6.3 = 11.34VA

140VA
+7.56VA
+11.34VA

=158.9VA

This needs to be over spec'ed so I was thinking 350-0-350 200VA if going with Antek. AS-2T350 looks like it will fit my needs, if my math is correct.

http://www.antekinc.com/as-2t350-200va- ... ansformer/

Does this sound right?

[Phil_S]

Tony,
I was looking at the spec sheet on the 100VA PT page. It shows parallel 350V secondaries and the test section shows 343V @ 220mA. I figured that one is OK. After looking at the 200VA PT, I am thinking the data sheet may be the wrong one for the 100VA PT as what's published seems a little bit off to me.

I believe the 200VA PT is more than adequate for what you describe. If you allow 19VA for the heaters, 4x 50mA = 200mA [Note 1] for the 6V6's (something for the screens, too), and 4x 4mA =16mA for the preamp tubes (more than generous), that's a total load of 235mA.

[Note 1] In a push pull amp, one pair is idle some of the time, probably less than 50% but I'd guess around 40% is right. This means you don't need 200mA. Something like 120mA is closer to the real demand most of the time, though it is possible that can be pushed closer to 200mA, but doubtful it will ever get there.

I'd ignore the 200VA rating. He says 290mA for the HT and 8A for the filaments. Both of those are well above whatever you might imagine you could possibly need for the amp you describe.

It occurs to me, you might write to John Ango at Antek. Describe the amp just like you did to me and ask him if the 100VA model is adequate. I think he'll respond honestly.

At that that price, I don't see how you can go wrong with the Antek, as long as you have room on the chassis. I have one build with an Antek, and it is just fine. I don't think there's any reason not to get it and it's in stock.

Good luck!

Phil

[dorrisant]

Thanks Phil, that's exactly what I needed as far as info. I was second guessing myself, and I appreciate that your approach is different yet gets roughly the same result. Thank you.

I will probably go ahead and get the set from Xtian that I mentioned earlier, but I still want to go the Antek route for more future builds. I built the Cornford Hurricane clone with one and was very pleased with it.

[lord preset]

I'm working on a second Antek based amp, the 1st and AC30 variant and now a 2-6L6GC build, both using 100VA transformers. I am inclined to trust the current ratings - in both cases the toroids run cool.