What to build? (salvage iron)

[Phil_S]

sell the two, small, scott transformers as a pair. plenty of hifi guys who'd want them. then, buy exactly what you want. took me a long time to figure that out for myself.

When I saw this post, I thought, yes, that's the ticket. However, looking at completed listings on eBait, I think a pair of OT's will go for $80-$100. There is one recent "basket case" model 222C with no PT that went for $160. I imagine $200 with PT? It seems the item is worth more left as-is than any other way. There are guys who want to rebuild it, I guess. But what can you buy for $200? Is there another market besides eBay?

[Phil_S]

i like the choke input idea phil! i dont use standby anyway and i have these big (i think) chokes that are ~14H, this one i pulled out says it tested at 16H but by who/where/how i have no idea...

do you think this can handle the current?

IMO 14H is plenty of inductance. 5H would be more than adequate (see Aiken, below). The problem is current rating. mA rating is determined by wire gauge and the size of the window. I'm no expert on this topic. Chances are that an old pull was between the plate and screen nodes and not up to the job. One time I bought a choke for a Vox AC30 rated at 150mA on eBait for cheap. You might look there.

I found this here: http://www.diyaudio.com/forums/tubes-va ... ltage.html
Inductance is not so easy to measure. The problem is that on a power choke inductance goes down as current goes up. The iron saturates. Your meter completely ignores this because it uses very little current. We are not taking about a few percent error either. Your meter is giving you "best case inductanc which you will never see in use.

I don't understand your voltage rating test. voltage on a choke is just the point the insulation fails. You don't want to test that, estimate it then don't go close. Once it fails the choke is junk and you'd have to rewind it with new wire.

Current is different. You can estimat that from the size of the wire and comparing to other chokes and then test it with 1/2 your estimate and then move up slowly.
You need a test curcuit that can load the choke with varying amounts the DC curent and on top of that a 120Hz AC component. So in a series you place a transformer secondary, the choke and your DC current source. This will place DC throught the choke and also the transformer, so make sure the transformer can handle it., Next place an AC source in the transformer primary.

Next get out the DMM and measure the drop on AC volts and in DC volts. From this you compute the reactance of the choke and them solve for inductance.

Next turn the DC current up and measure reactance again. it should be less. With enough current yu could drive it to zero, But the choke will get warm well before that. When it is just slightly warm and temperature remains stable for, 20 minutes or an hour use that current as the rating and then measure reactance, that is the chokes "minimum inductance that you can use for power supply design

Then you've got more fun here: http://www.angelfire.com/electronic/fun ... lyzer.html

Finally, Aiken has some wisdom: http://www.aikenamps.com/index.php/chokes-explained

Here is a choke for a Dynaco ST70. According to the schematic, that was a choke input design for PP EL34. Cheap. Seems appropriate. Maybe yours is similar? http://www.ebay.com/itm/Dynaco-Choke-Co ... 2ed2f0f005

[eniam rognab]

great info, thanks phil!! lotsa thinking about stuff and learning lots.

thanks to everybody!

[eniam rognab]

whelp, i pulled em. PT has 2 1/2 inches of laminations, about three inches wide. just over four inches tall. just about 3-4 1/2 inches all around, this is bigger than my HAM-ROCK build, although that was only designed for two marked on tx "TP-77 883431"

OTs have 4/8/16 ohm taps, leads are a little short all around... gonna need more heatshrink! haha

pulled the bias or whatever board when i removed the PT. nice little piece of stripboard for future products, or cut them down for fuzz pedals.

gawd i love this stuff, LOUDER!!!

[dorrisant]

A Gibson 79RVT would be a great preamp to try...

Tony

[eniam rognab]

A Gibson 79RVT would be a great preamp to try...

thanks Tony! or is it "Tone-y" hahaha

will check it out, thanks