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Author Topic: Johnson 500 Power Supply  (Read 4396 times)
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n2len
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« on: September 17, 2020, 09:40:33 PM »

Hello all,
I am beginning to go through a 500 power supply.
The 866’s were removed and a diode setup was
installed under the cabinet. Also, the HV supply
is not original. It was replaced with a transformer
which was too tall for the top cover to close properly.
To accommodate the larger transformer, the floor of the cabinet
was cut out to allow the transformer to sit lower
down in the chassis. I believe the piece of metal that was cut out
is now attached to the bottom of the plate transformer.
Then very thin metal brackets and a ton of washers (spacers)were poorly
used to support the transformer mounts. The plate
transformer is loose and sitting slanted in the cabinet.
I plan to repair that.
I believe the replacement transformer used should provide
the adequate plate voltage for the 4-400?
Would anyone care to offer any information from the pictures seen
what type of diodes are are being used for the 866 sub?
Also, looking at the diagram on the plate supply, is it a keeper?

All I have done so far is a wipe down of all the dirt, grime,
& mold from the top of the chassis.


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n2len
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« Reply #1 on: September 17, 2020, 09:42:44 PM »

more pics!
Thanks!


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Pete, WA2CWA
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« Reply #2 on: September 17, 2020, 11:32:35 PM »

Depending on when the diodes were installed in the past, but, most likely, they probably came from K2AW's Silicon Alley, Westbury, NY He advertised almost every month in QST and CQ, and maybe even Ham Radio and 73, for years and years.
More info: http://amfone.net/Amforum/index.php?topic=37658.0
And, more info: https://forums.qrz.com/index.php?threads/re-k2aw-14-1-high-voltage-diodes.382028/
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
n2len
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« Reply #3 on: September 17, 2020, 11:40:45 PM »

Thanks Pete for your reply.
I did come across K2AW’s info during a quick initial search online,
but I was unable to find out any information on what
they actually looked like or specs. I did find some info on QRZ about
his and someone suggested these diode packs for microwave ovens that were
similar.
What I was hoping to find out if what is installed is sufficient.
A pair for each side... Smiley

Again thanks!


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Pete, WA2CWA
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« Reply #4 on: September 18, 2020, 01:10:52 AM »

https://forums.qrz.com/index.php?threads/need-spec-on-k2aw-rectifier-stack.305172/

I may even have one of Frank's sales handouts somewhere around here.
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w4bfs
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« Reply #5 on: September 18, 2020, 09:33:42 AM »

congrats on finding a mod/hv supply.... I have a 500 rf deck but no mod/hv supply ... I suppose that they are top heavy and tricky to handle

as I recall there is nothing tricky about this unit except one of the relays has a magnetic bias actuation delay that sets up the sequencing from rx to tx.  I don't recall if a discussion of this is in the manual.  If the relay is not working correctly you could have some nasty arcs and possible destruction of the mod xfmr which are essentially considered unobtanium.  as well if you need to replace the 811's in this xmtr they are running at 2kv already and if your new hv xfmr makes high b+ they will see it too...consider 572bs... Tim wrote up a very good update for this rig here in Amfone sometime back and it should be printed and included in your manual.

I just looked at your hv tranny .... if I understand what I see that xfmr is only rated to be used with the center tap at or near ground and NOT for use with a full wave bridge (the 1500 wV spec) ... use of a full wave bridge could exceed that rating .... there is a way out if you really want to use that xfmr and that is to use a center tap grounded full wave doubler into your filter inductor, etc ...
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
n2len
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« Reply #6 on: September 19, 2020, 12:38:23 AM »

Hi John,
Thanks for the reply.
Yes, the power supply is quite heavy and definitely needs some support
especially when working on the bottom of the chassis.
I have my son’s do all the necessary lifting.😂
I appreciate the input regarding the relay and will check. First I need to build a complete cable set to power it. Then I can really begin going through it.
The existing supply that you see in the pictures is wired up. No prior history of the unit on how well it was or wasn’t working.
I have been looking at a possible Peter Dahl replacement if necessary.
Another ham contacted me directly who owns 2 JK500’s and had a plate transformer built for a good price. That may be another router to choose if needed.
I do have a NOS 1998 Peter Dahl Thunderbolt Amplifier plate transformer, it may be the perfect substitute for the JK500. But I haven’t been able to match up the specs/weight even with using “Wayback” archives with Dahls older catalogs. From what see on the transformer, no model or part number. I have to get it on the bench and test it.

I appreciate the suggestion of swapping out the 811a’s with some good ole Cetron 572’s.


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WBear2GCR
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« Reply #7 on: September 19, 2020, 11:34:19 AM »

<snip>
I just looked at your hv tranny .... if I understand what I see that xfmr is only rated to be used with the center tap at or near ground and NOT for use with a full wave bridge (the 1500 wV spec) ... use of a full wave bridge could exceed that rating .... there is a way out if you really want to use that xfmr and that is to use a center tap grounded full wave doubler into your filter inductor, etc ...

Assuming that the wiring as found is "correct" and it functions in theory, the CT is not connected when looking
at the image supplied. FYI.

The SS rectifiers ought to be ok. You may or may not need to install a "step start" or time delay relay
IF the B+ is supplied to the tube when the PS or rig is turned on. Putting full B+ on a tube when
the fils are not hot is usually not a great plan.

Do you have the other half of the pair? The rig itself??

Use a 10vac or so source to determine the voltage ratios on the Dahl transformer.
It likely has both a 120 and a 240 primary. 10vac makes it easiest to determine the other
voltages... of course 12.0vac might be better still as it is approximately line voltage divided
by 10...

Good luck with it...

                           _-_-
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_-_- bear WB2GCR                   http://www.bearlabs.com
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« Reply #8 on: September 19, 2020, 06:31:57 PM »

I believe this is what you want.  If not, let me know,  have a couple Dahl catalogs dating from the 80s to early 2000s.

Hope this helps.

--Shane
KD6VXI

Edit:  I dunno why it came out upside down....


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n2len
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« Reply #9 on: September 20, 2020, 12:37:57 PM »

Thanks Bear and Shane for your replies.

I appreciate you giving me some additional details on the wiring
If the transformer from the pictures. Yes, I do see that the center tap
is not connected and that the original piece that was cut out from the chassis
floor is being used as a support table for the larger transformer.
I would really want to remove this Plate Transformer and weld back the plate with a transformer that will correctly fit in the stock mounting spot.

Before I do anything, I need to make up a cable set. I checked eBay and see
the 9 pin octal connectors are available to purchase. I am also planning on swapping out the (3) HV connectors to BNC as seen on WOYVA’s website. It was also suggested by a ham who reached out to me directly via email.
Several other hams who reached out stated the Peter Dahl Thunderbolt Plate Transformer (4800vct)I have would be a direct swap. I would have to revert the rectifier back to full wave center tapped.

Shane, the pics you supplied and several archive Dahl Catalogs don’t list this transformer based on measurements and weight. (28.2 pounds) It seems a bit smaller then what is listed. Would you have any older catalogs that may have a Thunderbolt Plate Transformer listed around that weight. I can take measurements if needed.
I plan on testing it to confirm voltage specs using Bear’s suggestion.


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WD8KDG
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« Reply #10 on: September 20, 2020, 01:51:01 PM »

Hammond Transformer in Canada ended up with all of Peter Dahl's designs and can build Dahl's iron for you. Digi-Key is Hammond's US distributer.

Good iron, great design, new, last long time. Dig deep into pocket book.

Regards,
Craig
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w4bfs
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« Reply #11 on: September 20, 2020, 02:11:49 PM »

looks like things are getting better, getting better all the time ....  if you use the TBolt (via P Dahl) xfmr please be sure to keep that ct cons close to ground .... a long time ago I modded my TBolt to fw bridge with the ct floating ....I got away with it for a while ... it all depends on construction .... I have a junk TBolt hv xfmr  Shocked 
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
WBear2GCR
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« Reply #12 on: September 20, 2020, 03:20:10 PM »

Thanks Bear and Shane for your replies.

<snip>
I would really want to remove this Plate Transformer and weld back the plate with a transformer that will correctly fit in the stock mounting spot.
<snip>
<snip>
I plan on testing it to confirm voltage specs using Bear’s suggestion.

Len, I would use what is there first and determine how it functions before doing much more.
The series lightbulb is a good way to go.

A variac and ammeter in series is essential for working on old or new gear to make sure
there are no dead shorts before applying AC line.

With SS rectifiers, you can bring up the B+ very very slowly to reform the old electrolytics.
Few actually need replacement typically. Very very slowly is like a day...  
This is essential.

I make plug in SS tube replacements for gear that uses tube rectifiers for this purpose.

Welding? Nah. Not going to work. Gets way way too hot. Unless you were rebuilding from
scratch and had removed just about everything first...

But anyhow, a simple plate will suffice, and there is absolutely nothing wrong with the way
it was done, except I would use a better bit of metal and maybe better standoffs than a
10-32 screw alone, although that works ok too. (best if the plate is mounted under the
surface... if clearance is an issue.)

IF you use the Peter Dahl, then there is no reason whatsoever to "repair to stock" the
transformer mounting hole.

But notwithstanding your purchases, why not get on the air with a 100watt class rig first?
Easier and safer to work with... and more manageable overall. High power rigs require that
everything from the grounds, the power, the T/R system, the Ant switching, the feedlines and
the ant itself be able to really handle juice.

                   _-_-


EDIT: looking at the pix, why not just get on the air with the Valiant - with a proper antenna it is
really all you need for 96.78% of all situations... it's what I use everyday. Works fine for me.
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_-_- bear WB2GCR                   http://www.bearlabs.com
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