transformer info..

[N2DTS]

Hello all,
I got an ebay bargan which included a power transformer.
Its marked EDO 06722
Acme T-14034

2850 vct
scratch70 ma.

Its square, solder sealed, grey in color.

I want to use it for a seperate modulator supply (811a's) for the 3 x 4D32 rig.
I wonder if anyone has any info on the current rating, its 170 ma (light) or 270 ma
which would be ok for 811 modulators.

The scratch is right over the important number.
i looked through old fair radio catalogs with no luck...

Brett
N2DTS

[WBear2GCR]

I'd suggest testing it with a suitable resistor as a load and see what the V drop is...
10% drop is a very conservative rating. Of course you'll be looking at the ohms law relationship to determine the current. Modulators rarely have a high duty cycle requirement, so you'll be able to get by with a good filter section and somewhat less than a CCS current capability...

             _-_-bear

[Opcom]

Sometimes the T- numbers are a 'sort of' part number for components made by various manufacturers of military gear. Not the NSN but often the same meaning from the component point of view. Bear's suggestion is a great way to get close, I use it myself.

[WD5JKO]

Brett,

   I'd measure the volume and weight of that transformer, and then look at some old transformer books relating CCS and ICAS VA ratings based upon weight and volume of a 60 hz iron core transformer. Also measure the DC resistance of the windings.

I did find this info pasted below:

http://www.tpub.com/content/logistics/59/50/211/00-645-1591.htm

EDO CORPORATION
DIV DEFENSE SYSTEMS
1500 NEW HORIZONS BOULEVARD
NORTH AMITYVILLE
NY
11701
631-630-4122

Reference Numbers (Part Numbers)

06722

Required Categories

TERMINAL TYPE AND QUANTITY
(NON-CORE DATA) WINDING TAP LOCATION
WINDING OPERAT

Required Description

5 STANDOFF INSULATOR
CENTER TAP SINGLE COMPONENT SINGLE SECONDARY
117.00 AC VO

[N2DTS]

Thanks for the info.
I did find the little bit of info on the web, its not much help...

I am a bit shy of putting a load on it and checking the regulation, at those voltages!

The trans weighs 12.6 pounds, and to compare, I weighed an old DX100 hv trans, also 12.6 pounds!

The DX100 trans does 900 volts @ 400ma, or 360 watts.
The other does 1425 volts, that is 242 watts at 170 ma, or 384 watts at 270 ma....

Would the oil filled solder sealed bit improve the power rating as well as the breakdown voltage?
The heathkit trans is potted...not a good way to get rid of heat...

Brett
N2DTS

[KE6DF]

If it is a military sealed unit, then the specs would likely be lower than DX-100 transformer of similar weight as the military spec units are conservatively rated and Heath would rate for amateur use. So that would argue for the scratch covering 170 ma rather than 270 ma.

But, that said, for a ham transmitter, a mil spec unit would probably work fine at higher than it's military rating as you probably don't run your transmitter in a un-airconditioned shack in Iraq in 115 degree weather 24 / 7. 

[N2DTS]

Well, I build to last, so if its 170 ma I wont use it for the modulator.
Yes, I know the duty cycle comes into play, but 170 ma is just to light for something that could pull 340ma.
I would rather go too big than too small.....

Brett
N2DTS

[KE6DF]

Well I wouldn't want to recommend you use it and then find I led you wrong, but my thought was that it might just work fine.

The idle current for a 2x811a modulator in class B is maybe 50-60 ma. Only the instantanious peak gets up to 350 ma.

So with a big output capacitor to supply the peak current (e.g., 50 uf +) it probably would work OK.

I think someone on this thread sugested seeing how the voltage holds up under load and that was a good suggestion.

If you up a 350 ma load on the transformer and the voltage doesn't drop much, then that would be a good sign that it would work supplying a class B modulator.

I'll be interested in seeing what other people with experience buildling modulators in this power class think.

It probably depends on what you have in your junk box. If you have a beefier transformer, it might be better. And if you have the bucks to spend to buy something bigger, then great. But I'm thinking you could make do with this transformer.

Dave

[KM1H]

If you decide to go with just a fat cap for the filter the unloaded DC will be 2kV which is a tad too much for some 811A's but OK for 572B's or a number of other tubes.

At your magic number of 340W that is about 550W input at a typical 60% Class B efficiency, So at 2000V that means a peak current of 275ma.  With a typical Class B duty cycle of 35% that leaves a bit of overhead for the transformer IF it is a mil-spec 170 ma.

As a comparison a Heath SB-200 transformer is 18.5 # and can run the 572B's all day in a SSB contest at 600-700W output plus it has a 8A filament winding.

Class B is the same in SSB as in a modulator for working with the E & I calculations.

One thing to keep in mind when using a fat cap filter is the secondary winding DC resistance. If its too high there will be excessive core heating as well as poor regulation. There is detailed information on that subject in the Bill Orr Radio Handbooks.

That transformer with a low resistance choke input and a fat cap will result in only 1283VDC at no load, Certainly not sufficient for 811's to get over about 300W on a good day and with a tail wind. Youre also 430 ma on peaks; not so good. Add in some audio processing and that 35% is now 50%+.

I prefer to overbuild, be it a modulator or amp for SSB or AM. Having a few hundred ma of reserve in the transformer resulting in tight regulation makes for a much better sounding end product.

Carl
KM1H

[N2DTS]

The 3x4d32 rig runs 360 watts input, for 300 out, that would be 180 watts of audio plus transformer losses, and I like to have 2x the audio power needed, that would be about what a pair of 811a's could do.

As it is, I have a variac on the common supply, and might variac the modulator supply so I could run 1500 volts on it.
I used to run 1500 or more volts on a modulator for a pair of 812a's, zero bias, the little extra resting current did not seem to hurt anything.
 I have other transformers I can use, but they are much bigger.
A good swinging choke is hard to find though...


Brett
N2DTS

[Opcom]

well 2850's a fair bit of voltage, but if you were to JS it to a variac, pushbutton switch, and a resistor, a 15K and a 1K in series for 170mA, and a 10K and 1K for for 275mA, it would be a quick measurement and not necessary to have resistors rated for 100's of watts. Use the resistive divider network there to measure the voltage, so your DVM does not fry. Use a analog meter or DVM that responds quickly, and you need only hold the big red button for that long.

Another method a little safer assumes you have a junk 500-1000 watt screen grid amplifier laying around. Just JS it to the amp and use the amp's bias control to set the current appropriately, and note the AC voltage. srsly.

[WBear2GCR]

...check the darn thing with a load that is similar to the expected plate Z... see what the difference voltage is, figure the current, see whatcha got!

i don't think 2 x 811 will do 300watts. consider something like 838s or 805s?

Or 4 x 811?

          _-_-bear

[N2DTS]

Everything I look at says a pair of 811a's do 340 watts out in class B at 1500 volts.

I may JS the transformer into the modulator power supply on the big rig, it has a remote transformer, so the ac terminals, and HV terminals all come out on insulators, plus it is metered and has a variac on it, that should make for easy testing.

I suppose I can just adjust the bias on the modulator as a load on the transformer.

But what am I looking for?
What would be the difference between a 170 ma and a 270 ma trans?

Brett
 

[WBear2GCR]

Hey Brett,

I'm not sure what you mean about adjusting the bias on the modulator as a load on the transformer??

You want to use a resistor(s) for load testing the iron.

The difference between 170ma and 270ma iron is a fair amount if you need the current to make power. 1500v x 200ma = 300watts. But, that is total dissipation, not power output. You'd need to look at the efficiency of a class B modulator to see if that will give you 300watts continuous. Otoh, you don't need 300 watts continuous, you just need to be able to make voice peaks at the voltage level that is equal to 300 watts output. That means that if your filter section can provide the instantaneous current needed during peaks (ie. the B+ voltage does not drop on peaks) then you can use a "lower" current spec transformer. It's going to come down to a back of the napkin figuring and then an empirical test to see how it works out.

I'd personally test it with a suitable resistor, and if it looks plausible, put it into the circuit with clip leads or leave extra space on the chassis for a bigger bit of iron, if you need to pull it out for another one with more snot capability.

I suppose that you can slam 811s with 1500v B+, but they'll be running out on their hairy edge, probably no full power sinewave tests for any length of time... I don't have the "book" handy, so I don't know if RCA spec'd them for audio use at 1500v or not... if they did, then go for it for sure! 

                _-_-bear

[KM1H]

Everything I look at says a pair of 811a's do 340 watts out in class B at 1500 volts.

A. You dont have a solid 1500V available

B. Dont believe everything you read. Those ratings are with a sine wave under lab conditions.

C. I wouldnt try it with Chinese or Russian 811A's. OK with 572B's.

As has been repeated here on this forum and elsewhere over and over and over is that you dont want to run a modulator at the ragged edge and that you really need more than half the RF stage input of audio to do the job right. Many go for a 1:1 ratio or even more with iron to match so they dont wind up spinning their wheels and wasting time to find that, on paper, perfect match and power transfer.

I'm not sure what you mean about adjusting the bias on the modulator as a load on the transformer??

You want to use a resistor(s) for load testing the iron.

A combination of both will work if the resistors available arent enough but just resistors are preferred.

Set the 811 idle current so that the plates just barely show color, a muffin fan will help. Run the xfmr load in 50ma steps and watch the voltage drop while monitoring the DC current. If you graph it there will be a point when the slope steepens. Youve reached the steady state limit. If its really a 170ma mil grade xfmr and reaches the 250ma point OK then let it run while monitoring case temperature. If it is still comfortable to touch after 15-20 minutes it may be OK for 300 ma voice peaks, depending upon filter C but I wouldnt bet on it.

Carl
KM1H

[N2DTS]

Well, the modulator is running NOW at 1200 volts, and with the rf deck running at the same voltage, the 811a's modulate the rig very easy.

Now what plate voltage you run on tubes is an interesting subject, people run 811a's at 1750 volts, or even 2000 volts without problems.

The 4D32 is rated at 600 volts max plate voltage in AM service, and I have been running mine at 1200 volts for years, I have run 811a's at 1500 volts or more for years, no crap outs.
Even though I run the voltage up, I run well under the plate disapation ratings.


I always use choke input power supplies, never cap input, always use center tap, not bridge unless the voltage is under 100 volts.
I also use a minimum of 40uf in the power supplies.


I think the 811a modulating something like a pair of 812a's or 3 4d32's is a good setup, as the modulator power equals the RF input power roughly.
It is NOT pushing the modulator at all.

Brett
N2DTS

[Opcom]

I agree, 1500V is perfectly OK for a proper 811A. Ran them for a few years as a self rectifying oscillator in a tesla coil with a 2600V RMS transformer. No experience with the Chinese ones except at 900V.

Here are the audio and plate color specs. OK by me if they are lab conditions - they are in a TT-4 book by RCA, back when lying in specs would damage a company's reputation.

[KM1H]

Here are the audio and plate color specs. OK by me if they are lab conditions - they are in a TT-4 book by RCA, back when lying in specs would damage a company's reputation.

Thats good to get you started and I use that book for quick references. For an actual design I use the original full spec sheets with the engineering curves.

The JAN RCA and other USA brands are capable of a bit of excess ham abuse but finding NOS ones without gas is getting harder each year. Hams and audioholes are gobbling them up like a squirrel and acorns.

Carl
KM1H