Rare PT Find - what to build?

[tedmich]

I was about to head out of my favorite electronics surplus store (R5D3 in Pdx) when I noticed this black brick on the floor. It was as Bob said "An interesting transformer, $10" Its a 7x7x4" black steel painted box, with a bakelite top bearing a US Navy anchor stamp and the following specs:


quite a beast, at 22lbs (~10kg) maybe 1000VA (?). I wonder what the HV taps are rated at? With 12A of heater current and 9A of rectifier current the HV tap must be >1A right?. Could I compare DC resistance and scale the current rating on the HV to match the 5/6.3v taps? I just ran across a Phaez Daisycutter that Randy said had a "300 watt" PS running 2xEL84 PP, and that this overkill made "a big difference" (hopefully not just in weight!)

I doubt I will run 50 EL84s off this baby but I WILL use it!

[Don Moose]

Hope you can find an OT that can keep up!

That thing looks like it could do SVT-like duty (6x 6550).

[Glasgow]

Why two 5V supplies?
Is that a clue to what this was used for?

Brian

[tedmich]

maybe a Battleship anchor? No idea really, can't find any mention on the WEB except an odd audio surplus web site which states it to be an RCA manufacture....and sells them for $179 each.

Thats a ton'o 5vac... maybe they needed 20 rectifiers?


Maybe I'll finally make my hexaphonic el84 PP amp to go with my hexaphonic pickup...6 Edcor XPP15-8-8K's would only be $120.06USD

[Glasgow]

I don't know what your needs/desires are, but if I came across this behemoth, I might consider building into a bench supply. Especially given it's weight.

Or, cool, electronics-related door stop for my shop!

Brian

[Enzo]

If I had to guess, I'd say one 5v@3A was for a single rectifier tube for one power supply, then the other 5v@6A was for a pair of rectifier tubes for a different supply. If you had for example a 500v and a 300v supply using 5U4 tubes, you could not run them off the same 5v.

And 12A of 6v? We are used to thinking in terms of guitar amps with a few 6L6s and a handful of 12AX7s. But think about a radio set or radar that has 35 small tubes and a couple power tubes. That is a lot of heaters to keep warm.

[Glasgow]

Ah!

Your powers of deduction are quite honed Enzo.
I'll bet you are on the mark.

Brian

[Steve Conner]

If I had to guess, I'd say one 5v@3A was for a single rectifier tube for one power supply, then the other 5v@6A was for a pair of rectifier tubes for a different supply. If you had for example a 500v and a 300v supply using 5U4 tubes, you could not run them off the same 5v.

That seems good, except the transformer only has one HT winding.

I also agree that it was probably to power some fridge-sized device with dozens and dozens of small tubes. If you wanted to power a SVT, you could change to a bridge rectifier and get 800V with 400V from the center tap.

[Enzo]

OK, then it uses the same winding but makes two same voltage B+ rails that for whatever reason need to be separate. In the sense that today we see circuits with two or more 5v rails, one for digital and one for analog.

There you go, make a tube synth with separate B+s for the audio and the oscillators.


My thinking based upon that in all my years of electronics, about the only thing that ever needed 5VAC was rectifier tubes.

[Glasgow]

My thinking based upon that in all my years of electronics, about the only thing that ever needed 5VAC was rectifier tubes.

Rectifiers and relays, but that would have to be a 'boat'-load of relays to justify 3A!

Brian

[Enzo]

I thought about relays, but seems to me that 5v relays are mostly more modern. Logic circuits make 5v supplies common, but in the day of that transformer, I think relays are more likely to have been 12 or 24v.

I have many years experience servicing pinball machines. Prior to 1976 they were all electromechanical - meaning relays. You want to see a boatload of relays in something, well there it is. Depending upon brand, those relays were all 24v or 50v. But there sure were a lot of them in the machines. 24v supplies were usually fused at 10-15 amps.

[imaradiostar]

maybe it's plates on one rectifier with a cap input filter and screens and other misc power req's from a second rectifier and swinging choke, as described by Bruce at one point.

I'm not a hifi dork but let's not forget the 300B is a 5 volt directly heated tube. Maybe they needed rectifer, 5 volt power tube and 6.3 volt everything else supplies.

I have a rather large collection of very moldy and dusty tubes all dated about '42. If I recall correctly there are some other random oddball 5 volt tubes in the lot, with JAN markings and leftover after the war.

jamie

[Enzo]

Certainly a possibility.


I just spotted Doylestown. Would you happen to know the Murrays?

[tedmich]

If you wanted to power a SVT, you could change to a bridge rectifier and get 800V with 400V from the center tap.

This! I will run EL84s at 400v, course they sound nice at 320v too, if only there were some way to downsize or "scale" the voltages and have both available...

[tedmich]

If you wanted to power a SVT, you could change to a bridge rectifier and get 800V with 400V from the center tap.

This! I will run EL84s at 400v, course they sound nice at 320v too, if only there were some way to downsize or "scale" the voltages and have both available...

and change the fixed bias too...