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Uses for old output transformers

I've just found an old pair of Transcendar transformers I put aside a number of years ago.

There's some slight rust around the perimeter of the transformers - what would be the best cleaning agent?

Here are the specifications:

5K to 8 ohms, Frequency Response 20 Hz to 90 kHz, Maximum DC Bias Current: 90 mA, Primary DC Resistance: 370 ohm, Primary Inductance: 40 H, Part Number TT-012-OT

Any suggestions for a simple PCB based tube amplifier that would be suitable for a shed/workshop style set up?
 
Good thinking - I've read a little about the TubeLab gear, I'll have a look on the sub-forum to see if it will work.

On inspecting the transformers the rust is worse than I thought.

See attached pics, does anyone know of a good cleaning method?

There's a power transformer I had stashed away as well, which hasn't suffered any rust whatsoever despite being stored in exactly the same location!! The power transformer has some kind of protection resin or coating on it. Datasheet attached as well, will this have enough juice for a pair of 300B tubes?
 

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The power transformer looks quite a bit too small for a 300B amp, looks more like somtehing that could be used for a preamp or a small guitar amp IMHO.

The output transformers look like they have seen better days but unless the windings have been ruined by corrosion they should be functional. A rotary wire brush would be my weapon of choice to clean up the laminations, then I would remove the end bells and have them sand blasted.
 
Yes, but the HV winding is nowhere near what you usually see in 300B amps. By the way, is it 190-0-55-190V 120mA (top of the picture) or 550Vac center-tapped @ 100mA (bottom)?
Depending on your budget and level of ambition, this power transformer may still be useful but it's not a very good match for 300B tubes.
You can probably build something nice with the transformers you have (perhaps with EL34, 6L6 or some other similar-sized indirectly heated pentode) but if you decide to cash up for 300Bs, you might want to buy a more suitable power transformer too.
 
Hi This is worth a read.
https://www.mercurymagnetics.com/transformer-rust-friend-or-foe/
Quote from the above link
If you are still bothered by the cosmetic aspect of rust, never scrape off the rust to the point of exposing bare metal because you will bring back those nasty eddy currents. Instead, brush off the loose particles and re-paint the area with varnish.
At one time in history rust was used as the insulation between the laminations, iron oxide is a good insulator (try striking an ark with a stick welder on rusty steel). I would wipe the loose rust off the laminations with some turpentine on a rag and pant with an oil based anti rust paint. The bell ends can have whatever treatment you desire.
Ken_K
 
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I would design it by myself and build it PTP wired. This really isn't an overly complex affair. I'm not aware of kits, but maybe googling will disclose some?

Be aware, however, that you might be in need for an additional PS choke, as with any SE design, to get rid of the immanent hum.

Best regards!
 
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Hi This is worth a read.
https://www.mercurymagnetics.com/transformer-rust-friend-or-foe/
Quote from the above link
If you are still bothered by the cosmetic aspect of rust, never scrape off the rust to the point of exposing bare metal because you will bring back those nasty eddy currents. Instead, brush off the loose particles and re-paint the area with varnish.
At one time in history rust was used as the insulation between the laminations, iron oxide is a good insulator (try striking an ark with a stick welder on rusty steel). I would wipe the loose rust off the laminations with some turpentine on a rag and pant with an oil based anti rust paint. The bell ends can have whatever treatment you desire.
Ken_K

I reached out to a friend of mine, Jack Elliano (formerly of Electra Print audio), who gave the following advice for cleaning/servicing rusty output transformers:

"The transcendar’s rust means they did not varnish them why? I have no idea!!
Rust is just another oxide on the lams will not hurt anything in the transformer,
Just paint them with a dark grey paint (DO NOT SAND OFF THE RUST!!)
That will alter the low frequency due to removing the original oxide on them will make the lams metal contact themselves!!
Just paint over the rust. And paint the bell ends too, those you can sand if needed.
The laminations are each an individual oxide covered lamination!!
That is why they work. Notice no one used just a block of steel!!! Because it will not work at all!!!
The frequency response indicated is not correct, should have its sloop limit/s or -1db points.
1db is the least change you can hear. -3db is half power!!
Do not know about Transcendar fate if any, out of touch these days."
 
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I would design it by myself and build it PTP wired. This really isn't an overly complex affair. I'm not aware of kits, but maybe googling will disclose some?

Be aware, however, that you might be in need for an additional PS choke, as with any SE design, to get rid of the immanent hum.

Best regards!

I have never tried point-to-point but considering the state of these transformers and the limited juice in the power transformer now is a better time than any!!

Would would be the simplest point to point amplifier one could build using these transformers?
 
Just went through my collection of valves that might be suitable and came up with the following:

6S4A
12B4A
5686

I don't have any EL84 or 6V6 sadly but hopefully someone knows of a circuit using the above valves that might be suitable?

Perhaps something very simple such as this?

-464365198-769641826.jpg