some day figuring out PT output will be simple!

[deci belle]

The friendly neighborhood mad scientist unloaded a stash of old military and hi-fi equipment from Los Alamos Lab employees on me. Out of these, only one had a 5v rectifier in its circuit. (one was a 70lb submarine reciever!)

It's a Stromberg-Carlson 220-c stereo amp. The schematic on the chassis says the PT is a 290-0-290. There is a 5v tap for a 5AR4, and it says 350v comes out of the rectifier tube.

It used four 7408 power tubes, two 7199 and three 6EU7 tubes.

Aside from the separate 6.3 taps which confuses me a little bit (and sets of wires coming out of it that aren't on the schematic), I don't understand how to determine the current output for the PT.

I know to add up the heater filament current requirements for each tube. Is that all I do? It seems I need to figure out the mA rating for the 290v windings too, somehow.

Also, I may not be writing the math figures correctly; or not knowing enough when I consult the tube datasheets.

I'm just too unfamiliar with these things still.

Could someone please help me learn what to be aware of to calculate the current values accurately?

[bob p]

It's a great score when you get to receive the local mad-scientist's private stash of gear!

Figuring out the current ratings for the transformer windings is difficult if you don't have any specs to work with. Most of the time it's easiest to work backwards using the tube compliment and the tube data sheets. If you don't know the tube compliment, then determining the output rating can become an exercise in load testing. Looking up the answer is much easier if you can pull numbers from the chassis or the transformer itself.

So the easiest way to find the answer would be:
1. Looking up the T1 spec sheet
2. Reverse-engineering the specs from the application's tube compliment and operating class
3. Reverse-engineering by load testing.

You mention that it was a Stromberg-Carlson 220-c stereo amp. Is the actual model number "ASR-220c"? If so, then this might help you:

T1:
SC Part Number: 161000-232
117 VAC @ 1A
580 VCT @ 200mA DC
5V @ 1.9A
6.3V @ 2.5A
6.3V @ 2.8A

[bob p]

T1:
SC Part Number: 161000-232
117 VAC @ 1A
580 VCT @ 200mA DC
5V @ 1.9A
6.3V @ 2.5A
6.3V @ 2.8A

That's some nice iron you've got there.

[deci belle]

Wow!! Thank you, Bob! Yes, I did score— Yay!

I got the 5v tap ok @ 1.9A. And 290v x 2 is 580vct so that makes sense to me as well. And I understand where the 6.3v figures come from.

If I reverse-engineer the 200mA value you sleuthed, using the tube compliment and the operating class as you state …that is what I should figure out still, just so I know how to arrive close to the figure you so easily provided me with from the transformer data.

The amp's power tubes are in dual pairs of cathode biased 7408 tubes @ 345v, so under what category do I look in the tube datasheet when I already have plate voltage and operating class figures to enable me to estimate the PT's mA rating?

Until I realize how to figure out that part myself, I thank you for the numbers for the PT, Bob!!

[bob p]

based upon your excitement, I'm guessing that your amp's correct model number is ASC-220c, right? need a definite yes/no on this to know if some other info that I have will help you.

regarding the tube data sheets: take a look at the specifications for the relevant topology, operating class and voltage. then look at the maximum plate current numbers (at idle and under load) and the maximum screen current numbers (at idle and under load). add up those numbers. that will tell you how much current each tube will draw under maximally loaded conditions in a worst case scenario. add up those numbers for all of the tubes. the total should not exceed your PT's HV current rating.

it gets tough to ferret out the right answer when you have an amp that runs the tubes outside of the design center values listed on the datasheet.

[deci belle]

Hi Bob, ya it must be obvious~ haha! Yes it is a Model ASR 220 C Output: 12w each channel Input 130w. A GZ34 powers three 6EU7, two 7199 drivers and four 7408 output tubes.

I'd already decided my next amp would be a quad-6v6 based on a 5F8 chassis/head cab I already have, so this PT is pretty dope for that! I won't be able to use the OTs for this project, but they're huge!

Thank you for the further instructions, Bob. That's gonna be real helpful because I have the answer to check my math— I just have to see how to work it out from the data sheets now and note how to do it for when I don't have the answer next time!

[bob p]

too bad you don't need a little 18W stereo amp. here's the information you'd need for restoring it: Sam's Photofact.

http://www.audiophool.com/Schem_A/ASR-220C.pdf

[deci belle]

Oh I remember that! I saw it while I was first searching for the amp data before I gave up and asked how to do it myself here! I wasn't successful on my own I guess because I didn't include the "ASR" designation!! I just googled Stromberg-Carlson 220c.

Obviously, I'm not adept at popular guitar amp designs yet— or spec-ing components for that matter… I've never even considered building or restoring audiophile equipment!

I came across one forum where a man asked about the 220c, and he got a gnarly response from somebody who said SC just used guitar amp transformers in it… meeoowww!!! haha!!

[bob p]

Gutiar amp transformers? That makes no sense.

If you're looking for anything about Stromberg Carlson gear, check out the Made in Rochester site. I think that's where I found the link to the 220c info.

[deci belle]

That's where you found it?!! ok, I did stumble onto that site… I'll look around some more.

That guy was being an audio fanatic on some level, calling the S-C iron guitar transformers~ but that suites me just fine!!

The stereo output is rated at 12w per channel, so those OTs must be able to handle more than that …I wonder how much!!

[bob p]

They're about 8K, which is going to limit what kind of tubes you can hook up to them. As a general rule, in guitar applications people get away with driving a full-bandwidth hi-fi type OT with double the rated power. So you could safely push a pair of 6V6 as hard as you want to.

[deci belle]

8k is as Tweedy/6V6 as an OT can get, so that is very cool. Double the power—! I'm in scratch-build heaven, Bob! Thank you for your helpful tip on describing how ratings for hi-fi type OT characteristics apply to limited frequency guitar amps!

[deci belle]

I got the PT back from the Transformer factory. Baaad news after all.

The secondary taps measured as follows:

390-0-390v @ 150ma What do I do with that?
56v @ 100ma
6.3v @ 6a
5v@ 3a

Dang. So i just ordered a retail PT with 315v… dang!

[tubeswell]

I got the PT back from the Transformer factory. ...

The secondary taps measured as follows:

390-0-390v @ 150ma What do I do with that?
56v @ 100ma
6.3v @ 6a
5v@ 3a

Good enough for a pair of 6L6s and 4 or 5 dual triodes (all driven by a 5U4GB for a B+ of around 460-470) I'd say. Separate bias winding too - bonus.

[olddawg]

Los Alamos, wow..... My cousin still owns property along the a Trinity fence. I have a picture of my older sister sitting inside the A Bomb casing. You could just walk there from his house in the 50s at the time, no fence. When I visited in the 60s as a kid, every fence post along the road in front of his house had a nose cone from a test rocket on it. He told me he got money from the government from metal falling out of the sky and and killing his cows. Went through his roof once. My uncle, his father died of leukemia in the early 50s. They are mentioned in the book, "The Day the Sun Rose Twice". The A Bomb blast turned many of his cows white on one side. The Feds bought them...Trippy place. I guess they only allow people at the Trinity Site once a year now. And I guess they buried all of the Trinitite somewhere.