What to do with 10K OT?

[Phil_S]

So, my latest bargain-priced eBait acquisition is on OT that was supposedly in a Fisher 20-C. I can't find anything on that model. Bench test for turns ratio shows this item is either 10K: 16z/8z or 5K : 8z/4z. Size-wise it is consistent with your typical 15-20W OT. Secondary wires are black, green (16 or 8z), and yellow (8 or 4). 5K primary makes less sense than 10K primary, so that's what I think it must be.

If you had a 10K OT, what would you do with it? It seems 6V6 or EL84 PP is what to do with it. Tonally, what do you think is the affect on your typical circuit that calls for an 8K primary? What circuit might be a good candidate for a 10K primary?

[davent]

I've got a 10k OT here as well and someday going to use it with one of the pairs of 6AQ5's that i also have. http://www.tubebooks.org/tubedata/HB-3/ ... 6AQ5-A.PDF

dave

[mlp-mx6]

I built a 5F6-A circuit using 6V6s w/ a 10K OT. Sounds fabulous.

Allen Amps has a great little Champ-sized chassis just perfect for this type of build.

[tubeswell]

Besides running it at 5k with 2 x 6L6s, you could also use it with 2 x 6V6s. I built a 5G9 clone using a largish 5k OT and it sounds amazing. (The plate voltages of the 6V6s sit around 370 IIRC).

At 10k you could also use it with 6V6s, 6BM8s or EL84s.

[Phil_S]

Great suggestions all around. I was hoping someone would comment about using 6L6's as they are not the obvious choice. I've got a dozen cheaper than cheap Russian 6P3C (not the 6P3C-N heavy duty version) that are burning a hole in my pocket. I have been wondering about running a pair of these at 5K. The spec sheet says for AB1, Va = 360, load between 3800 and 6600 gives Pout = 18-26.5W. I'm thinking this is just about right.

Thanks for the comments. More ideas are welcome. I probably won't build whatever it is for a couple of months yet.

[FUCHSAUDIO]

Old hi fi iron sounds very good in guitar amps. I used Dyna's A-470's in early EL-34 50-W ODS's and they were terrific. Fear not the Fishers, Scotts, and so forth.

[Phil_S]

Hi Andy,
Yes, I've made a few amps with hi-fi iron. Generally, great stuff that can be had quite cheap if you have patience. Thanks.

So, this one struck me as a little odd-ball. Any idea how to know if it is 5K or 10K? Does it really matter?

Phil

[rp]

Good question, I've always wondered that too. You're lucky you can use it at 8/4 at 5K. I wouldn't even bother worrying about what's best for 10K unless you really need 16 ohms. Bet it kills in a 6V6 or lower V 6L6 amp, maybe a pair of coke bottle 6L6Gs?

Fischer was tops with Marantz and MacIntosh - bigger company but Cadillac all the way, so that's probably really fine iron.

I've sadly destroyed many Fishers and Scotts in the past when they could be had for $25. It's cheaper to just use new iron now, maybe that's for the better. Hope I don't burn in hell for the perfectly working 500C I mauled - But you gotta start putzing around somewhere.

It'd be nice to know what the orig tubes were and build something unique around them. Maybe you can try searching randomly with 30-C, 40-C, 20-A, 20-B etc and see if it gets you close. Try ebay, if not in a hurry put it in favorite searches and wait a few months. Try asking on the DIYaudio forum.

Maybe email this guy: http://www.fisherdoctor.com/

I checked through his site but no 20C. He's been around for decades on Staten Island, I believe he's the authority on old NY audio companies, not just Fischer. No idea if he's the helpful type or not.

[Alexo]

6AQ5's all the way!!!

[20to20]

That may be a tranny from an Electro-Voice A20C. Potted, light color paint?

If so, it used 6v6 tubes, PP.

[gary sanders]

I have an old one myself that reads in the 10s.First I thought I was checking wrong till I had someone else do it and sure enough it was right.Glad this was brought up.

[Alexo]

In my limited experience with old hifi iron, you get a lot of oddball loads.

Like a couple 10K OT's I pulled from 6V6 and EL84 amps. You can run those tubes at 10K, but 8K is sort of the standard..

But the weirdest were the 13K2 OT's I pulled out of a Fisher 400 running 7868's, all the datasheets call for 6K6, but they doubled it!

[Cliff Schecht]

We had a bit of discussion here about the Stancor A3311, a 25W 10k, 70mA output transformer. Funkmeblue and I seemed to stumble on ours at about the same time. Not sure what he did with his unit, but mine went immediately into my 6V6/6L6 5C3 Deluxe and has been a permanent fixture since. The amp sounds great and I think it was a choice transformer for any PP 6V6 build. Only problem with that amp is it really needs DC heaters on the preamp tubes, it hums like a sumbitch when cranked!

[Phil_S]

6AQ5's all the way!!!

LOL Yeah, I've got about 50 6AQ5's, so I guess you could say I like that tube. Whether I choose it may have to do with what PT I select and the circuit.

[passfan]

I too have run 6L6's in PP using one of these type transformers and it was the sweetest sounding amp. Trouble was it was my prototype for a 6sl7 rocket and I built it out using an Emcor from RJ and , while it sounded better than the stock Rocke t, it lacked something that the prototype had. Unfortunately , before I figured out what it was , the amp sold.