Thordarson Iron (Tru-Fidelity) Specs/Update

[W9ZSL]

Just got info off these two pieces before shelving them. The Mod XFMR T-4M51 has no serial number.  Has 9K Ohm primary. 4 terminals, top two labeled P.  Bottom two B1 and B2. PUV style.
46db level, plus/minus .4 db from 30-12,000Hz.  Secondary has 3 terminals.  Top right labeled B2, left 2400.  Single on the bottom 3750.  Ratio listed as 6700-3750/2400. 7 terminals in all. Measures 12"w x 5 1/4"D x 6 7/8H.

Reactor is T8C82, labeled as Filter Reactor. 7500 test volts RMS. 5-16 HY at .75ADC. 9"W x 6 1/4D x 9"H. Any clues? As I said, these came from a Gates-equipped station. Also salvaged a Gates BC-1T. K2PG/Phil is assisting with info. Hope to build AM rig after getting license back. Tubes forever! Mike (ex-K9ZSL) Rhinelander, WI.  passagerecording@yahoo.com TNX/73. Anybody want these?  I'm using the Gates iron in my rig.  Gonna be modest.  250 watts of the best audio you ever heard.  After all, have a recording studio and all the processors will be tied in.  February 23?  Might as well go for the General class.  Step up from my old Conditional.  Now I'm dating myself. Pshaw!

[The Slab Bacon]

With specs like that the reactor is a swinging choke. Most likely the filter choke
from the plate supply. A mod reactor would have a much different rating. It would be a fixed value somewhere around 50Hy. Still a nice find! The transfoma also sounds like a nice piece of iron!!

                                                                         The Slab Bacon

[W9ZSL]

Mr. B,
Kind of figgured that which lead me to question what happened to the Mod reactor or was there one in the first place?  Since the secondary is labeled B2, it's possible that there was none (though unlikely if in fact this actually came from a BC xmtr) and the B+ for the finals of whatever this was used in went directly thru the sec to the PA. That's what makes this iron interesting.  In any case, it probably will end up as surplus because I have all the Gates iron and know it's complete history because I helped install the transmitter in the early 60's when I first started working for the station and was there when she died in the mid-90s. TNX!
 Mike

[John K5PRO]

The Tru-Fidelity line was available both for broadcast professionals and for amateur use. There were separate catalogs. I found a 1941 Tru-Fidely broadcast catalog 500-FX.

Thordarson of today wouldn't remember Thordarson products from 1941.

T8C82, as you noted already from the nameplate, is a swinging choke good for 3/4 amp DC. It is a swinger, so it is 5 Hy @ 3/4 amp, and it is 16 Hy at 0.1 Amp. 30 ohms DC resistance. It is used as the first choke in a power supply.

The mod transformer, T4M51, is a 60lb piece rated for 225 watts of audio, and 250 Watts of RF (DC load) on the secondary. The modulator is recommended to be push pull 805s, with 6700 ohms plate to plate. On the secondary, it is 3750/2400 ohms. Nothing said about DC current on the secondary, but they made reactors too, so I bet it wasn't specified to have the DC on the winding.

[k4kyv]

You can tell if it was designed to carry the DC by looking at the  laminations.  If there is a gap in the iron that extends the full length of the core, it was designed for DC.  If the laminations are  staggered, interlaced like a power transformer with no continuous gap, then it was designed for use with a reactor.  The gap will be filled with some kind of insulating material.  Usually varnish impregnated paper.