Power supply transformer selection

[k7mdo]

For the last few years I have been haunting the local recycler. In that time I have come across three relatively high voltage transformers that might be suitable for a project I have had in mind for some time.

I want to build an rf amplifier for my Eico 720/730 station.

The problem is the selection of amplifier tube/tubes and transformer that are compatible for the maximum "umph" from what I have on hand.

When I look into the transmitting tube manual I see tubes from 6146 to 813 and none of my proposed transformers seem like a good plate voltage fit.

I am attaching photos of all three showing the voltages.  They seem too much at full wave rectification for a 6146 and too small for the 813.  I am willing to go 811 or some such but none seem "ideally" suited based on my HV calculations for the supply. 

Which one (if any) might any of you readers with this experience pick?

Tom

[N2DTS]

What kind of power out do you want?

You need a big heavy duty amp to do AM.
None of those transformers will do much in an amplifier on AM.
Two would do 100 watts out, one for a pair of 6146's or a 4D32 modulated by something that will give you 100 watts of audio.

A pair of 6146's as amplifiers will give you 25 watts of carrier output, like all the old rigs did on AM.
Four would do 50 watts carrier, at 700 volts and about 400 ma.

Four 813's will get you about 200 watts out at 2500/3000 volts and a lot of current, like 700 ma on peaks.

Four 811a's want 1500 volts and a LOT of current, and might do 100 watts out.

[KA2DZT]

Tom,

You need a bigger xfmr for any amp worth building to increase your power out over the Eico station you now have.

Fred

[k7mdo]

Fred, I had pretty much come to that conclusion when looking at the plate requirements of tubes in the handbook. I was just hoping to be able to use one of the transformers rather than see them scrapped.

It makes me re-think where my project ampliifier idea might go. The Eico puts out 'maybe' 40 watts on AM. Will live with that for now.

For now they just continue to hold the house down .... can't throw them away.

Tom

[N2DTS]

You can give them away, sell then for a little, or ask a lot on ebay.

I have been giving away a lot of stuff I have no use for, to anyone who is building anything.
Not much left now, but I made a big dent in the stuff that was filling the basement.

I am younger then a lot of AM'ers, but I do not want to leave tons of old radio crap in the house after I keel over or have to move, I have had to help clean out peoples houses after they passed (family) and the excess worthless junk that filled the houses was a wake up call.

Those transformers would make a nice start for a 100 to 200 watt plate modulated rig, a nice audio amp, or maybe a replacement/upgrade for some vintage rig.

For an amplifier used for AM, you want a 220 volt outlet and a pair of 3-500Z's and a heavy duty power supply.

[KA2DZT]

Fred, I had pretty much come to that conclusion when looking at the plate requirements of tubes in the handbook. I was just hoping to be able to use one of the transformers rather than see them scrapped.

It makes me re-think where my project ampliifier idea might go. The Eico puts out 'maybe' 40 watts on AM. Will live with that for now.

For now they just continue to hold the house down .... can't throw them away.

Tom

Tom,

Not counting the some 150 xfmrs I scrapped about 20 years ago, I still have over 1000 xfmrs and chokes on hand (counting the small ones).

You have a long way to go in xfmr collecting

Fred

[k7mdo]

Fred, I see there is a potential problem with collecting transformers, possibly a disease?

I only have about 15 loose ones... pictured are my "BIG" ones...

My shack is on the second floor and I worry about the floor.

What I seem to be collecting also (heavy things) are numerous Viking II's, three so far (also from the scrap yard), and I probably should ressurect those before I tackle the big amplifier project anyway. They weigh quite a bit.

So little time.

73, Tom