opinions on what to do with a stancor a-3311

[funkmeblue]

I just aquired a stancor a-3311 25 watt output. I't's a 10k primary/70 ma /4, 8, 15, and 500 ohm secondary. My first thought was for a 2 hole liverpool. I was also wondering what if, I used it in a 6v6 express?

[Cliff Schecht]

No joke, I just acquired one of these myself! Mine is in brand spanking new condition too. Someone gave it to my dad who just had it sitting around forever. He kept saying he was going to use it in something but I can only let a good, usable transformer sit around for so long .

Anywho, as far as what to use it in, I've done quite a few power amp designs based around this transformer (just playing around with ideas really). Aside from the slight increase in distortion and decrease in output power, the transformer is a great candidate for either a two-tube rocket or something similar. Two 6V6's or EL84's are the perfect compliment for this transformer really. The higher primary resistance does allow you to go slightly higher on the B+ without pulling too much current, but I doubt you'll be able to get a true 25W out of this transformer with a 6V6/6BQ5 set.


I've already put mine to use in a 5C3 build. Before I had a Stancor A-3851 in there and was running 6L6's but the PT got fairly hot after an hour or so. Since it's ancient iron (the PT), I figured I would do the amp a favor and reduce the demand on the whole system. That and the fact that with 5 tubes in a 11"x6" chassis, things get pretty hot inside and I don't want to cook my carbon comps.

Let's see what others have to say too. I couldn't find a single guitar amp that uses a 10k primary (8.4k seemed to be the max). Something to note though is that some quad tube amps use a 5k transformer and, when two tubes are pulled, they end up with a 10k primary. This does change the sound, although I'm sure there is an argument somewhere over whether this change is good or bad..

[David Root]

When you crank a power tube with large signals, you get rectification effects that actually increase the primary impedance a bit, so you might be better off with 10K on a pair of 6V6 rather than 8K, to maintain as much output as possible, if you are a dimer!.

What that does to the tone I don't know. I bet it's in RDH4 though.

Look up the Radiotron 6V6GT in www.tubedata.org. There are two pages that show this effect on the plate curve nicely, printed in 1941 no less.

[Phil_S]

If you guys aren't sure what to do with those, send them to me. I'm sure I can think of something.

I recognize 70mA/25W gives you a lot to work with. Pair of 6V6 is what comes to mind for your typical guitar amp. I think it's wasted on a pair of EL84.

You might think about a concertina into a pair of 6SN7's (that's 4 sections). Done right, you'll get about 10W of pure clean tone. You can even introduce some preamp distortion if you feel the need. I'm talking about old USA 6SN7-GT, not current production, which I understand is hit and miss.

[funkmeblue]

ya, I'm leaning toward the 6v6 express

[Cliff Schecht]

Personally I think that's a waste of both a transformer and an Express build. 6V6's work well in an Express as is, why make one that can't be used normally (i.e. with EL34's as well)?

I don't think EL84's are a waste on this transformer. It seems like a great candidate for a Marshall 18W build or even a lower wattage Rocket. I was leaning the Rocket route myself, but I need to build a normal one first before I start tweaking on the circuit.

[Phil_S]

Cliff,
I think I didn't say it well when I said EL84's are a waste. I was thinking that it is a 25W OT and how very difficult it would be to get more than about 15-18W from a pair of EL84. OTOH, you can probably get 22W from a pair of 6V6 and not "waste" the capacity of the OT. Of course, I agree, it will make a perfectly wonderful EL84 OT.
Phil

[funkmeblue]

It really seems like this could be a great output for a 6v6 express. The express is an el34 amp that happens to be able to run 6v6's. Most seem to prefer the el34 to the 6v6 in a stock express. I built an all octal express with a 6.8k marshall style ouput (50 watts). This amp is too loud for most of my uses (blues player). Since I was 13 I've been playing through a 1966 deluxe reverb.....and a few boogies.....and I love 6v6's. So.....I'm going to stick it in there and see what happens. Thanks for all your help.