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Author Topic: Is this really BTA-1R Mod Iron?  (Read 12567 times)
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WZ5Q
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« on: March 26, 2013, 04:12:16 PM »

Howdy Y'all,

I pulled the Mod Iron from my rig today to measure it's Turn Ratio. It has a label on it stating it is from a BTA-1R. I don't believe this is true as the Mod Iron from the BTA-1R should have an open core. This one is sealed and filled with oil, you can hear it sloshing around inside when you move it. Another thing is that its big and heavy, 90lbs worth of heavy. Plus it has a Tertiary Winding on the secondary. But someone marked the Top as "T501" which is the Schematic Number for the BTA-1R.

The transmitter it came from is a homebrew 4-1000A Modulated by a pair of 3-500z's. The Mod Iron was being used with a 40H, 600ma Reactor with a 1uf 7.5Kv coupling cap. I am basically using this transmitter for parts to build my own version with the same tube complement, albeit with allot more headroom, features, and improvements.

I have attached some pictures of the Mod Iron. below. If anyone has any information as to what Transmitter this actually came out of, I would appreciate it. I am curious.

The Transformer measures 13" high, 9" wide, and 6" deep.
The weight is exactly 90lbs.
It is Oil Filled.
The measured Turns Ratio is 1.25:1 Step Down.
Tertiary Turns Ratio is 100:1 Step Down.
The Impedance Ratio calculated to 1.56:1

Here are the pics...



* Mod Iron Pri.jpg (311.17 KB, 1500x1125 - viewed 745 times.)

* Mod Iron Sec.jpg (293.65 KB, 1500x1125 - viewed 724 times.)

* Mod Iron Side.jpg (296.51 KB, 1500x1125 - viewed 738 times.)
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Mike
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Ed-VA3ES
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« Reply #1 on: March 26, 2013, 06:18:33 PM »

It looks  very similar to the iron in both my RCA BTA1R3 and my BTA1S.    Your ID tag is  missing, but it would say "Electro Engineering Works", and various part and serial numbers.      The BTA1 series ran a pair of 4-400's modulating another pair.    I don't have immediate access to the rigs, or I'd go and positively ID the thing.
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« Reply #2 on: March 26, 2013, 09:52:29 PM »

Hi Mike,

Looks similar to the one in my 1R1.

73 Jack KZ5A
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73 Jack KZ5A
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« Reply #3 on: March 27, 2013, 08:47:03 AM »

Yepper!


* DSC03193.JPG (3817.17 KB, 3456x2592 - viewed 735 times.)
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WZ5Q
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« Reply #4 on: March 27, 2013, 10:55:43 AM »

Thank Y'all for the input, and I really appreciate the picture Phil. Now I have a Label.  Smiley

Looking at that label,
It states the Primary voltage is 2560v @ 250ma.
This got me to wondering...worrying...

The rig had previously been operating with 3kv on the Primary of the Mod Iron supplying a pair of 3-500z.
The Secondary had a 1uF 7.5Kv Coupling Capacitor between it's hot end and a 40H, 600ma Reactor which was supplying the RF Final with 3Kv (common Power Supply).
The cold end of the Secondary was tied directly to Ground.
The Mod Iron case was isolated from Chassis Ground.
I would think that in this configuration the windings would be at different voltage potentials and arc over could have been a real possibility.

This is how I am going to build it...

I plan on operating with around 3.6Kv on the Plates of the 3-500z's running in Class B on the Mod Iron Primary.
I will connect the Secondary hot end directly to the RF Deck Side of the Mod Reactor which will be supplying around 3Kv to the 4x1 in Full Strap mode.
The cold end of the Secondary will connect to the 1uF Cap, then the Cap to Ground.
The Mod Iron case will be isolated from Chassis Ground.
I will be using Spark Gaps.
I will also be using a Step Start on both the Modulator and RF Deck HV Supply's.
Variacs will be used for power control.

I think in this configuration arc over would be least likely to occur as the windings will be of similar potential. Even when there is a difference due to low power operation, it's better then having the cold end of the Secondary tied directly to Ground.

I know these transformers are way overrated, but do Y'all think this Mod Iron will survive or should I be looking for a much bigger "spare" for when it does fail me?
I am very interested in Y'alls thoughts.

Thanks,
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Mike
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« Reply #5 on: March 27, 2013, 05:52:12 PM »

The first thing I would do is hi pot it and hope it passes at least 2X what voltage you plan to use.

The 3-500Z is not listed for Class B, just AB2, and the idle current alone for a pair is 300ma at 3000V and the plate to plate load is 8600 Ohms. At 3600V you are pushing them too hard IMO.

Why not use them as the RF end with 4-400A modulators, they still all glow nice and at 3000V a 4x1 wont even show color, that aint even half strap, even the BC rigs ran 5KV.

I believe there is an article on here somewhere that gives an analysis of the various secondary configurations of the reactor and blocking cap.

Carl
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WZ5Q
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« Reply #6 on: March 28, 2013, 07:13:28 AM »

Howdy Carl,
Thanks for the response.

Quote
The first thing I would do is hi pot it and hope it passes at least 2X what voltage you plan to use.

Yes great advise, I plan on trying to find someone local to me to Hi Pot it as I do not have an adequate tester.


Quote
The 3-500Z is not listed for Class B, just AB2, and the idle current alone for a pair is 300ma at 3000V and the plate to plate load is 8600 Ohms. At 3600V you are pushing them too hard IMO.

The 1968 data sheet does give a listing for using the 3-500z as a pair of Modulators in Class B service.
http://www.shinjo.info/frank/sheets/088/3/3-500Z.pdf
I will have to run some bias since I will be over the 2.5kv Zero Bias Plate Voltage limit, so this should drop the idle current some. I think by juggling the tube parameters around it should play nicely at that Plate voltage. I believe the limiting factor will be the Mod Iron.


Quote
Why not use them as the RF end with 4-400A modulators, they still all glow nice and at 3000V a 4x1 wont even show color, that aint even half strap, even the BC rigs ran 5KV.

I don't care for Tetrodes in Audio Service, and I really want to play around with the 3-500z Triodes as Class B Modulators. My RF Deck Power Supply will be able to run the 4x1 at more then 4Kv+, but I fear the 3-500z's wouldn't have enough scrote to fully modulate that much of a carrier with ample Positive Peaks and reserve headroom. The 4x1 will be just Cadillac'in at the lower plate voltages for normal legal power limits. I will get plenty of glow & "light show" from the Modulator's 3-500's, 845's, 575A's, and the 866A's while modulating.  Smiley
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Mike
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Rick & "Roosevelt"


« Reply #7 on: March 28, 2013, 12:29:45 PM »

Before you hi-pot it, see if it will fit in your kitchen oven.  Uh, take out the flimsy racks or they'll be bent.  Run oven at 150 def. F, no more than 200, for several hours.  Send your wife shopping with her sister all day. Run fan in kitchen with all the doors open for a minimum of one hour before women return.  Plan on spending some alimony money.  Grin

Caution: some ovens can't take it. Fewer wives.
Remedy (only for oven): reinforce oven with 2x4's from floor to frame.
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« Reply #8 on: March 28, 2013, 02:49:17 PM »

Quote
Before you hi-pot it, see if it will fit in your kitchen oven.

I don't see a vent on that transformer? I personally wouldn't bake that sealed transformer.
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« Reply #9 on: March 28, 2013, 03:45:24 PM »

Quote
Before you hi-pot it, see if it will fit in your kitchen oven.

I don't see a vent on that transformer? I personally wouldn't bake that sealed transformer.

They develop vents on their own.
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« Reply #10 on: March 29, 2013, 01:19:22 AM »

I don't see the point of baking a potted transformer Huh.  Hi-potting, yes.  Baking, no.

The thing is sealed against moisture and such by design.

73DG
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« Reply #11 on: March 29, 2013, 03:31:48 AM »

Dont let a sealed transformer fool you. I have had plenty in the shop that were potted and when I opened them up, full of rust.
Drll a small vent hole in the top cornor.
Regards,
Gary
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WZ5Q
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« Reply #12 on: March 29, 2013, 07:27:28 AM »

Thanks Y'all,

I'm still chucklin,  Grin

It's a Sealed Oil Filled Unit. I am resistant to drilling a hole in it, so I don't believe I will put the Iron in my XYL's new oven and risk the Alimony Payments that would seriously hamper my Transmitter Build Fund.
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Mike
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« Reply #13 on: March 29, 2013, 08:42:12 AM »

In the interest of domestic tranquility, stay away from the oven.....
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« Reply #14 on: March 29, 2013, 10:06:51 AM »

In the interest of domestic tranquility, stay away from the oven.....

Or stick your head in it!  That is what I would have to do around here but I do have a oven at my camp that is never used and it's a men only man cave so we can do whatever we want to a point Cheesy Cheesy Cheesy i.e. smell bad, puke, fart. all the options.
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« Reply #15 on: March 29, 2013, 03:32:48 PM »

Here is the real Eimac 3-500Z, the last spec sheet released. That 1968 one isnt even an Eimac; built by Amperex as Eimac was having problems in production, specs are different in some areas also.

http://www.g8wrb.org/data/Eimac/3-500Z.pdf
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« Reply #16 on: March 29, 2013, 06:48:27 PM »

I use the Eimac 3-500zs in my HB modulator for for TMC GPT-750 A2, now a B2.

3KV on the modulator plates, and 4-400s in the final. Using about -10V of bias on the 3-500s, and they idle at about 30ma total. I'm using a modulation transformer and reactor out of a Gates 5kw broadcast transmitter and can easily modulate the transmitter to over 120% positive at 1KW DC input. The audio driver is a modified Eico 730 modulator, using a Hammond 1703 class B driver tranformer replacing the stock Eico modulation/driver transformer.

They make great modulator tubes for me.

Al VE3AJM
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« Reply #17 on: April 01, 2013, 03:39:51 AM »

Thanks for all the information and ideas Y'all,
I will play around with them and see what happens.
Take Care,
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Mike
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