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 Post subject: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 7:49 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
I won't to replace the 866a rectifiers in a Johnson Valiant with solid state diodes. The HV is around 680v with 450ma plate current at full smoke. I don't intend to run the rig at 450ma more like 300-350ma was thinking of using 1N5408 in a string of two or three on each leg of each tube for a total of six diodes per tube does this sound right or over kill?


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 8:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 35421
Location: Livermore, CA
Hi

Diodes are rated 1000PIV and 3 amps. Current is enough. Under certain conditions 866A is rated @ 10,000PIV.

What is high voltage out of the transformer? Figure you need more than 2.8 times half the transformer voltage without load. Your 680 volts may be after a choke input filter and full load? Three diodes for each 866A will give you 3000PIV.

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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 4:17 pm 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
Norm Leal wrote:
Hi

Diodes are rated 1000PIV and 3 amps. Current is enough. Under certain conditions 866A is rated @ 10,000PIV.

What is high voltage out of the transformer? Figure you need more than 2.8 times half the transformer voltage without load. Your 680 volts may be after a choke input filter and full load? Three diodes for each 866A will give you 3000PIV.


I measured 725v (680v was a typo) on the output of the 866's I think pin 4 with transmitter in standby. 10,000PIV for 866a that's a lot of diodes hooked together maybe I should rethink this idea and go with 3B28 tubes. I'm trying to take some load off the LV transformer the 866's use a 10a tap off the LV transformer.


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 4:34 pm 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
Of course there's these "Licorice Sticks" 1N2637 plugin units probably impossible to find at a reasonable price.


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 4:53 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 35421
Location: Livermore, CA
3B28 is a nice tube but has the same filament current as 866A, 5 amps each.

1N2637 is rated 10,400 PIV and 750 ma.

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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 5:02 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 8827
Location: Santa Rosa, CA
The licorice sticks are old technology and a bad choice.

1N5408 are cheap. For your application, I wouldn't worry about trying to achieve the full 10KV capability of the 866, but might put about 5 diodes in series for each segment of the 866 circuit.

If you are going to run them at nearly half an amp, they will get warm.

http://www.mouser.com/ds/2/149/1N5408-888344.pdf

The rating of the diode is based on using a 3/8" long lead (9mm) and having that lead attached to something substantial, like a square inch of copper circuit board foil.

Like this:

Image

NOT like this:

Image

Rich


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 9:49 pm 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
I like that PCB layout with all the diodes in line I might be able to produce some thing like that.


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Wed 21, 2016 11:44 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 8827
Location: Santa Rosa, CA
You can buy pre-made boards from suppliers like FAR Circuits:

http://www.farcircuits.net/SB220%20RECT ... D%20V4.pdf

Also:
Quote:
RECTIFIER BOARD FOR 2000 VOLT POWER SUPPLY

ARRL HB 88-94 CHP 27 FIG 72

Description: The board for this project mounts the diodes, and equalization capacitors and resistors in a full wave bridge configuration for a 2000V, 1 amp power supply. Five diodes are used in each leg of the bridge.


http://www.farcircuits.net/power2.htm

Note, you still have to buy and solder-in the diodes.

Rich


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Thu 22, 2016 9:01 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 775
Location: Roslyn,Pa 19001
I did 3 or 4 1N5408's in series for each 866 tube. My filament winding went open else I would have just kept the 866's. This was one of many failures in my Valiant. I traded it for a nice NC-100X receiver.
https://www.flickr.com/photos/42774321@ ... ateposted/


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Fri 23, 2016 12:11 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
Radioroslyn wrote:
I did 3 or 4 1N5408's in series for each 866 tube. My filament winding went open else I would have just kept the 866's. This was one of many failures in my Valiant. I traded it for a nice NC-100X receiver.
https://www.flickr.com/photos/42774321@ ... ateposted/



Yes I understand seems the Valiant is pledged with all sorts of failure points its really to bad. My Valiant is a factory made unit and appears to have never been run at least not very much anyway. All the parts that normally show signs of over heating, wear are pristine as though right off the shelf. So I've been doing all the mods people have learned the hard way to try and prolong the Valiant's demise I'm not ready to give up yet.


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Fri 23, 2016 12:20 am 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 2019
Location: Tucson, Arizona U.S.A.
Quote:
I don't intend to run the rig at 450ma more like 300-350ma

I would design it to handle the full power; it isn't that much harder. Full power will happen sooner or later whether you intend it or not.

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Jim Mueller


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Dec Fri 23, 2016 4:10 pm 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 132
Location: Livermore, CA
Jim Mueller wrote:
Quote:
I don't intend to run the rig at 450ma more like 300-350ma

I would design it to handle the full power; it isn't that much harder. Full power will happen sooner or later whether you intend it or not.


True especially if the unit is sold off and the next guy doesn't know to hold back on the power or I forget.


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Mon 09, 2017 1:48 am 
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Joined: Oct Thu 20, 2016 3:54 am
Posts: 29
Why reinvent the wheel? You can buy soild state replacement plug ins cheap. Thay plug in the 866 sockets and away you go. You cant buy the parts and build one for the cost of 2 replacements. 73s WA7OPY (this true for the 872 as well)


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Mon 09, 2017 4:51 am 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 8827
Location: Santa Rosa, CA
Five 1N4007s at 10 cents each.... pretty hard to beat 50 cents per tube!

Rich


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Tue 10, 2017 2:04 am 
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Joined: Mar Sat 08, 2008 3:21 am
Posts: 191
Location: hillsborough, nc
Don't forget the R and C in parallel with each diode!
WL


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Tue 10, 2017 2:27 am 
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Joined: May Fri 04, 2012 10:39 pm
Posts: 1089
Location: Hidden Valley, AZ
I'd send you a free set of 866A's just to stop the needless proliferation of silicon...


73DG

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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Thu 26, 2017 8:36 pm 
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Joined: Aug Mon 09, 2010 2:57 am
Posts: 279
Location: York PA.
I pulled the cover off my Valiant over the holidays in preparation for restoration.

I removed the 866's, but decided to go with a pair of 3B28's as the voltage drop is so low that I didn't think it was worth it to go solid state.

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73 Mark K3MSB
www.k3msb.com


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Thu 26, 2017 8:55 pm 
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Joined: Mar Sat 08, 2008 3:21 am
Posts: 191
Location: hillsborough, nc
Good thing, wrong reason.
866 has low drop, but the 3B28 does not make RF hash.
The hash may or not be a problem, depending upon your ant and transmission line.
Old schematics often show RF chokes in series with 866 plates.
And, of course, 866s occasionally arc, short and raise general hell with your transformer.
It's also fun to see the fire fly when your ancient filament transformer finally arcs and puts B+ to ground.
The second time that happens, you'll have a fuse in place.

The Si has its own problems, like massive current surge on startup, depending upon how much you have oversized the filter caps and a general increase of stress caused by the increase of B+.

Enjoy,
Wilson
W4BOH

And don't forget the CX contest this weekend and Tuesday. See classicexchange.org


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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Fri 27, 2017 2:06 am 
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Location: Somers, CT
infomet wrote:
Don't forget the R and C in parallel with each diode!
WL


Not really needed with modern diodes.

Pete

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 Post subject: Re: Solid diodes in place of 866a's
PostPosted: Jan Fri 27, 2017 5:22 am 
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Joined: Aug Mon 09, 2010 2:57 am
Posts: 279
Location: York PA.
infomet wrote:
Good thing, wrong reason.
866 has low drop, but the 3B28 does not make RF hash.

And, of course, 866s occasionally arc, short and raise general hell with your transformer.
It's also fun to see the fire fly when your ancient filament transformer finally arcs and puts B+ to ground.


I never considered using the 866's that I have on hand. I'm sure the glow is nice, but the continued existence of other parts in the radio is more important.

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73 Mark K3MSB
www.k3msb.com


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