Mystery Freed transformers

I made a trek to visit the legendary "Andy" and his garage with CJ recently and got, among other goodies, two Freed transformers marked: "P/N 39811" on one side (presumably the part number) and ""52 8-69" on another which looks like a date code for August 1969. I can't find anything about them anywhere on the web.

These are in fully sealed metal cans about the size of the UTC A series--square cross section, but a little taller--maybe 3.25" (8cm). There are four mounting studs at the corners and eight eye-loop terminals. I forgot to take a photo--will post one later. I had a few minutes to spare last night so I did make some measurements. Here's what I found:

There are four independent windings. Apparently there is no internal shield connection brought out to a terminal and the can is isolated from all the terminals.

DCR:
1-3 8.6 ohm
2-4 10.8 ohm
5-7 32.7 ohm
6-8 32.4 ohm

Leakage C (all connections open):
1-2 170pF
1-5 211pF
1-6 208pF
2-5 420pF
2-6 580pF
5-6 320pF

Inductance (using cheap BelMerit digital LC meter)
1-3 0.633H
2-4 0.631H
5-7 1.96H
6-8 1.96H
1-4 with 2&3 strapped 2.4H
5-8 with 6&7 strapped 7.3H

I put 600 ohms in series with my generator and ran a sine into 1-3 with all other connections open (it was late and now I realize I should have used a lower series resistance ). Turns ratio relative to 1-3:

2-4 1
5-7 1.7
6-8 1.7

Did a quick sweep with a 10K load and it was fine up past 30kHz, but got a little grungy and lossy down at the low end. Then again, my input resistance was probably wrong and who knows about the load.

So it looks like two split coils with a 1:1.7 (or 1.7:1) ratio. Using PRR's rule of thumb about impedance and DCR it looks something like a ~100ohm Z for 1-3 and 2-4 and ~300ohm Z for 5-7 and 6-8. So, what is it? Input? Output? Repeat Coil? Any other measurements I should do to suss it out?

Thanks,
A P

sorry i do not have answers to your question
but also have 2 mysterious freed tx...
small cylinder size, sealed(military). 4 connections. came from collins radio gear....
here the ref and specs.
freed TF1A 11YY pot test 700v rms
150 _ 20khz
0db max
primary 82 ohm 50MA DC
sec 100K
any idea for use them?

audioforge

audioforge,

Did you check CJ's Freed data? Have you measured the DCR, L, and turns ratios yourself?

A P

Pretty simple, this one.

If it´s big, use it as 1.7:1 output, in a SRPP or white cathode follower. Look at NYDAVE circuits, the older, bigger ones, with a 12bh7 tube at the output. NOT the one bottle or two bottle.

If it´s small use it as a 1:1.7 mic input with a low noise discreet electronics, like a 990 or Forssell opamp.

1:1.7 could be ment for driving decently-high output level out from a circuit based on e.g. discrete opamps with limited powersupply voltage capability. The relatively low inductances points towards this trafo being designed to be driven from very-low output impedances, like an opamp output.

Stuff like older NTP often does this.

Jakob E.

Or a melcor/api 1731/2520 clone.

Thanks, guys. The can is 1-7/8"x1-3/4"x2-5/8" (4.7x4.3x6.6cm) which could probably fit a 2503 sized E-I core. Weight is 15.8oz (448g). Let me try sweeping it with a low impedance driver (I've got some 1731 clones lying around) and a 600ohm load and see what it does. I'll also check inductances with my ESI bridge for another set of data points.

Maybe I can use them for outputs on a DOA makeup gain stage in some passive EQs I'm looking at building. I don't seem to have any of NYDave's earlier schematics. Time for a search.

:thumb:
A P

I think Rafa is referring to this amp:

http://electronicdave.myhosting.net/miscimages/nydave_lineamp1.gif

Couple of tips: the heater circuit should be "elevated" on a DC bias since the cathode of the upper triode in the White cathode follower is sitting at ~+135V. Also, the schematic shows 1K grid stoppers but you may not need that much--try 220 ohms to start.

Freed transformers were manufactured in my old hometown :thumb:.
I wish I had more Freeds in my collection; I only have a couple of the little 600:600 cans.

Thanks, Dave. I know that Andy has one other Freed (same can size, different markings) and probably more. I won't be able to check it out for a few months, though, as he's traveling. The only other Freed I have is a pulse transformer. Lemme know if you're looking for something specific and I'll check when he returns.

:guinness:
A P

Yes, that was the circuit. I guess this one can drive the high impedance side with good FR.

Also, there was a variation with a gain control (multiple feedback Rs , with lots more of max gain) that could be used as a mic pre if you use a suitable transformer.