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Author Topic: Getting a large Modulation Transformer ready  (Read 9821 times)
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WX1WX
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« on: September 13, 2015, 11:01:30 AM »

Greetings gang-
I finally have a good Modulation Transformer for my BC-610-E restoration this winter,

and I have a few questions:

* What are some good things to do before putting this into service?
* How would you suggest drying it out? heat lamps? oven? how warm? how long?
* Is sending to a motor repair shop for vacuum re - lacquering a good idea or not?
* Suggestions for DIY  re-lacquering ?

I looked for a long time for this baby, and I want to do the right thing to keep it in good shape!
Thanks in advance !

Alex
de WX1WX
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de WX1WX
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« Reply #1 on: September 13, 2015, 12:43:59 PM »

* What are some good things to do before putting this into service?

good question .... I am convinced that the largest single danger to a properly applied modulation tranny is not adequately snubbing the end-of-transmission turn off generated voltage spike ...the old practice was to use a spark gap whjich sometimes works and sometimes doesn't

some rigs sequence the relays by various methods in an attempt to control this ... mostly undocumented in the owners manuals .... consider adding a proper relay controlled resistive snubber .... K1JJ detailed his own diagnostic journey down this path in the forum a while back ....good luck

n.b. this was one of the discussions
http://amfone.net/Amforum/index.php?topic=33816.msg261496#msg261496
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Beefus

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It would from many blunders free us.         Robert Burns
flintstone mop
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« Reply #2 on: September 13, 2015, 02:52:25 PM »

Make sure the wife is not going to freak out,,,,the oven at the lowest setting for about 6 or 7 hrs will be goodness

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Fred KC4MOP
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« Reply #3 on: September 13, 2015, 08:31:32 PM »




Are not the Mod transformers potted? If so, do we need to wait until the wife goes out and the oven is free?


klc
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PD0RTT
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« Reply #4 on: September 13, 2015, 09:28:32 PM »

Some modulation transformers have an isolation with tar.
I often see that also with HV transformers.
As an example the modulation transformer from the BC191, the modulation transformer from the BC610 I do not know.
In that case, the placement of the modulation transformer in an oven is not a good idea.
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N8ETQ
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Mort


« Reply #5 on: September 14, 2015, 08:05:10 AM »

Hey Alex,

   Is it a real 610E mod xfmr?  Later units were potted.
2 things you could do for testing.

   insulate from ground
   HV protect "ON"

   The 610 should work fine with "HV PROTECT" on but
not for long..

GL

/Dan



    As an afterthought, you could/should also adjust
the AC input to a level that will provide 6.3 vac to
the 6V6 or 807 as measured at the socket. I'm pretty sure
the 610's are expecting 110 VAC. although I can't find
anything in the TM 11-4057 that states it, I'm pretty
sure he's not expecting 120+ VAC..

"I just found it" TM-11-4057 pg 4, paragraph 3e.
"BC-610-E requires 117VAC".

    all the LV/FIL xfmr's have tapped primaries, insure they are
set to the highest input voltage.

Greetings gang-
I finally have a good Modulation Transformer for my BC-610-E restoration this winter,


Alex
de WX1WX

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WX1WX
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« Reply #6 on: September 14, 2015, 09:36:46 AM »

Thanks for the great suggestions gang!
Yep this is a really real BC-610-E Modulation Transformer, with the correct Hallicrafter's Part number from Stancor and everything.... and the DC resistance on the windings are correct to all documentation. Looks excaly like any I have eyeballed or seen photos of.

This is the earlier issued open frame with bell ends into which tar was poured from the access ports on the bottom sides of the bell ends.

Thus my questions in regards to oven treatment. I fear all I'll do is get the tar flowing out and that would be counter productive for a transfomer with a history of noise and talk back.

I did invest in a real honest to goodness 30 amp Variac to adjust input voltages and I like the idea of measureing at the filament at the socket.

PLEASE any other suggestions! I also like the idea of the aggressive management of end of transmission voltage spikes. very  insightful. THANK you Hive Mind!

de WX1WX

 
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de WX1WX
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N8ETQ
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Mort


« Reply #7 on: September 14, 2015, 10:57:56 AM »


  Hey Alex,

      It's been my experience the majority of the talk back
comes from the overload relay, that can be cut back quite
a bit with a large value electrolytic across his coil.

      Once that is done you can hear the Mod Iron but
it sounds better than the relay!

BTW: consider the cap across the relay as "Sacrificial Lamb"
as a serious overload will blow the daylights out of it.

73

/Dan




Thus my questions in regards to oven treatment. I fear all I'll do is get the tar flowing out and that would be counter productive for a transfomer with a history of noise and talk back.

de WX1WX

 
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W7SOE
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« Reply #8 on: September 14, 2015, 01:49:19 PM »

Careful with the oven, my Valiant mod transformer puked all its potting at 170 degrees.  I think it was wax like...

Rich

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VE3AJM
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« Reply #9 on: September 14, 2015, 02:02:20 PM »

How about building up a bake box/enclosure with a non-combustible material and mount a couple of incandescent light bulbs not in any direct contact with the box material in it. Choose the wattage values based on the temps you get. 100F for few days should dry it up.

Other information here too:

http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=94119

Al VE3AJM
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WZ1M
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« Reply #10 on: September 14, 2015, 04:52:19 PM »

Just adding my two cents worth from years of experience. Potted transformers are not all that cracked up to be. After years the potting material breaks away from the transformer coil and creates a little air gap. Hence, running, not running, running has a tendency to collect moisture between the potting material and the coil. Not trying to throw a wet towel on your project but just adding my views from experience.
Regards,
TRS
Gary
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N8ETQ
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Mort


« Reply #11 on: September 14, 2015, 05:27:00 PM »


 Hey Gary,

       Yes I've seen that as well, Do you think the heating would
help to re-flow that goop? Perhaps if the iron was positioned in
the oven so as to not let the stuff leak out, like upside down?

Thanks

/Dan



Just adding my two cents worth from years of experience. Potted transformers are not all that cracked up to be. After years the potting material breaks away from the transformer coil and creates a little air gap. Hence, running, not running, running has a tendency to collect moisture between the potting material and the coil. Not trying to throw a wet towel on your project but just adding my views from experience.
Regards,
TRS
Gary
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WZ1M
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« Reply #12 on: September 15, 2015, 02:26:30 AM »

You would have to get that oven pretty hot to have the potting material re-flow. Let alone the smell it would cause in the kitchen. Doing this would also seal in any rust that mite have happened over the years. Rust and high voltage do not mix. What I have done in the past and it takes some time, is to carefully remove the end bells. Chip away at the potting material. Doesn't have to be clean but enough to expose the core. Do some hi-pot testing at 7kv or there a bouts. If it passes the hi-pot tests, toss it into the oven for a few hours at 150 degrees. Let it slowly cool down in the oven. Do the hi-pot test again and then submerge the transformer in varnish for half hour. While you are doing this, paint up the end bells, reassemble and you got a good working, looks new transformer.
Regards,
Gary
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Carl WA1KPD
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« Reply #13 on: September 16, 2015, 09:09:21 AM »

Gary,
Spar varnish OK?
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Carl

"Okay, gang are you ready to play radio? Are you ready to shuffle off the mortal coil of mediocrity? I am if you are." Shepherd
WZ1M
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« Reply #14 on: September 17, 2015, 04:16:37 AM »

Wouldnt want to lead you down the wrong path on the varnish but it should work just fine. I use Dolphs AC-1.
Regards,
Gary
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Patrick J. / KD5OEI
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« Reply #15 on: September 17, 2015, 09:31:40 AM »

a question: schemes to protect the mod transformer are for when the RF stage plate current flows through it, and a modulation reactor is not used. Right?

If a mod reactor is used, is there any need to protect it in a similar way?
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