Mod Iron ? ID

[KB3DKS]

  I have been trying to catalog my Iron and have this old potted block that appears to be a mod tranny. I also have the unfinished chassis it was mounted on that had sockets and wiring for possibly 4 807s or 814s (same socket and plate cap).
 
 It's a medium size, possibly 100-150 watt or better class at 20 lbs and appears to be prewar from the style and type of terminals and black phenolic, possibly RCA with the # XT-1933 ( RCA used XT #s)

The dim. are 6-1/2 X4 with a 1/4 inch mounting flange, and 5 inches high.

Terminals 1-2-3 measure 221 ohms DCR, 1-3, with a very ballanced center tap,2.
Terminals 4-5 are 774 ohms DCR.
A 1 volt RMS 400cy input to the full primary shows 1.74 volts out of the unloaded secondary .
Frequency response is pretty flat 50-10kc sourced from 600 ohms full or 1/2 primary to a 10 K load on the secondary.

Measurements indicate a step up? Not your usual mod ratio.

 A power tranny would not have a center tapped primary and the numbering protocall indicates otherwise anyway.

What could this have been used for? Any one seen this type before.

Bill KB3DKS in 1 Land

[WZ1M]

I have worked on many pwer transformers with center tap primarys.
Regards,
Gary

[W9GT]

I have a HV power transformer that looks just like that (very similar).  The terminals are labeled, however, with primary and sec (HV).  I think it is somewhere around 1750V each side of CT @ 200 mA or so.  I think it has 6 terminals.  I'll have to dig it out and look at it again.  I believe it does have a tapped primary as well.

73,  Jack, W9GT

[KM1H]

That style xfmr were all over Radio Row in NYC in the 50's. A variety of different terminals were available but the markings looked identical to yours.  It could be a step down transformer if you reversed leads. It may even have been used in something entirely alien to ham thinking.

Id start with a variac on the 2 wire "primary" and see what happens with a 100W lightbulb load on the CT secondary. If it starts buzzing consider it possibly a 400 Hz unit.

Carl
KM1H

[Opcom]

I have something of that style but a bit larger and with screw terminals. It appears to be for a frequency changer. push pull tubes to 120VAC. 

But to your transformer, what would use:

four 807's can do (110/160W to 1850/3400 Ohms CT @ 400V/600V) and make a 1:3 step up in impedance to 5550/10200 Ohms?

four 814's seems a bit too much since one pair will do 160W @ 1000V.

as for modulating:
What "load of the day" ran like a 5550 Ohm class C load with 220W DC input being modulated by 110W of four 807's? It does not make much sense that way. The terminals are not very well insulated such as for a higher voltage (1000V?).

Could there be another 5-pin tube of ye olde lower-power type that would have fit the sockets and pushed that transformer in class B?

four 46's = 40W @ Eb=400V
four 47's = about like the 46

Also, the old transformers were what we today consider physically oversize compared to power rating. I have a similar one about that size rated 50W for four 6L6G's.

Is a filament transformer present?

[KB3DKS]

  OK, I put 120vac to the "primary" terminals 1-3 and got 210vac out of 4-5.
Reversed that and got 68vac out of 1-3. No noticable current draw showing with either hookup. I did not try any loading altho at that ratio I would expect to see an appropriate reflection of any current draw.

 Pat,
  I looked at the chassis. It is an unfinished homebrew with a UTC LS10 for input, 1 octal preamp and 1 single ended driver for a UTC HA-106 interstage to the parallel PP grids of 4 807 based tubes. Power supplies were external. 3/4 of the wiring is done but the B+ lines and filters were never wired. The plate caps were just tied to terminal strips. Nicely done old buzzard cloth wire. The transformer was not mounted when I got it but the matching mounting and terminal holes were done. The transformer had been sanded and repainted metalic silver as had the Bud chassis.

 The terminals don't seem H.V. but have seen similiar old pieces like this that used just the phenolic without any insulators.

 Seems to be a nice piece of Iron  but what can I do with it?? Could try a heising style hookup to be careful about the voltage rating or suppose I could just sub it in a suitable audio amp and determine the sweet spot of output loading.
 Maybe finishing the chassis wiring & trying out a quad of 807s might be just as easy.

 Was hoping that someone might recognize it so as to minimise the time spent fiddeling with it if it doesn't proove to be useful.

Bill, KB3DKS in 1 Land

 

 

[KM1H]

That phenolic will handle several KV at that spacing. Ive seen commercial iron running 4kv CT without any ceramic feedthrus.

One of the ones I picked up in the mid 50's was marked as 850VCT @200 ma so I figured it would be fine for a couple of 6L6's running easy on 80/40 CW. I had previously toasted my VOM so was flying blind. Hooked it up, threw the switch, keyed the TX and watched the plates head for orange. Next thing I heard was a loud hiss and just got the power off before the filters blew. Come to find out the iron was 1700VCT so it was rebuild time with a 829B and series filters....and another cheap secondhand VOM.

Those were the fun days of learning. Blow something up and head to Radio Row for more cheap parts.

Carl
KM1H

[k4kyv]

That phenolic will handle several KV at that spacing. Ive seen commercial iron running 4kv CT without any ceramic feedthrus.

Early UTC transformers, even HV plate and modulation iron, used a sheet of bakelite for a terminal board, with feedthrough terminals made of black thermoplastic.  At first I thought they were phenolic until I saw an old transformer with an overheated, deformed terminal.  Later, they changed to white ceramic feedthroughs.

[k4kyv]

Those were the fun days of learning. Blow something up and head to Radio Row for more cheap parts. 

Radio Row was destroyed in vain.  They tore it down to build the WTC.

[KD6VXI]

Those were the fun days of learning. Blow something up and head to Radio Row for more cheap parts. 

Radio Row was destroyed in vain.  They tore it down to build the WTC.

Shortly thereafter, they paved paradise, and put up a parking lot

Mmmmm BOpBOp

--Shane

[Steve - WB3HUZ]

And the tore something esle down to build Radio Row. And so it goes.

[Opcom]

Ah so there are plate caps - proof..

So back to the question then, with four 807's making 100-150 watts, what kind of 200-300 watt DC input, class C load would present 5000-10,000 ohms (depending on 807 plate volts) to that modulator?

I hate assuming, but to take straight from the RCA manuals, and citing the low and high CCS modulator specs for four 807's, 

the modulated RF stage parameters between some reasonable extremes would be:
1.) a 200mA load with 1000V on the plate. 5K load to modulator. (807;'s at 400V)
2.) a 120mA load with 2500V on the plate. 10K load to modulator (807's at 600V)

a couple of 811's (808's are almost the same):
1000V plate
115mA per tube
88 watts out (carrier) per tube
load to modulator 8330 ohms

a pair of 814's
1000V plate
120mA per tube
87 watts out per tube
load to modulator 8333 ohms

or a pair of 813's?
1250V
150mA (total)
140W carrier
load to modulator 8300 ohms

anyway just trying to help by throwing some possible RF stages out there that would present a reasonable load. Or am I mixed up on this entirely?

[KB3DKS]

Pat,
 Now that is the info I'm interested in !

I have 803s, 813s, 814s, even several 4-125s. A couple 811s but need those for rebuilding a Meissner 150B mod deck.
 The only thing that I don't have is the time to put everything together.
 Have been struggling with finding work and health issues for the last couple years.
But I really need to get something on the air while I still can.
 Even have a couple potential one or two tube RF finals and really just need to build up a "universal" supply/modulator and maybe can get a 200-250 watt rig on the air this summer using what I already have. Got a great stash of radiorector set pieces to start with.

Thanks for your input. The transformer is a keeper for sure.
 
Bill, KB3DKS in 1 Land