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Author Topic: 3-500 Filament Problem with Henry 2K Classic X  (Read 24621 times)
W1QJ
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Posts: 2966




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« Reply #45 on: March 19, 2014, 06:15:53 PM »

Jack, the Henry amp does not use a Zener diode for operating bias.  It uses a "block" diode which is basically about 10 regular 1N5408's in series.  When a string of diodes are used in plae of a real Zener it is wired in reverse.  SO if you stay with the Henry block diode then leave it as it is.  If you change to a real Zener then put it in the opposite way.  I would remove he leveling choke as you won't need it now. 
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W8KR
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Posts: 28




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« Reply #46 on: March 19, 2014, 06:49:21 PM »

W1QJ  Lou... Thanks, that solves the mystery of the backward Zener!  But how's a guy to know that, since D1 in the circuit parts list is labeled "Zener, 1.2 amps, 10VDC, Semtech SS-5534"?  That's very misleading, as are many other things in this manual, I've discovered.  But, If you think it's okay to leave it in there, vs putting in a real zener, I'll leave it. 

Now, when I take out the leveling choke, there is no direct bias connection to the filament pins on the socket.  That would appear to be alright, since there is a connection through the filament transformer center tap, which is how the W4NFR circuit works.  Would you agree, or should I run a connection directly to the filament pins, as well?

73,

Jack
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W1QJ
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« Reply #47 on: March 19, 2014, 07:43:59 PM »

The bias gets applied in series with the filament transformer CT., then comes the diode stack (in reverse) then comes the cut off bias resistor in series with B-.  The resistor gets cut out in transmit.
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W8KR
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« Reply #48 on: March 20, 2014, 07:58:10 AM »

W1QJ  Lou... Yes that's how the circuit looks, except that they insert the leveling choke (L7) between the bias resistor and the filaments of the tubes.  So I will take out L7 and the wiring to the tube sockets.  Now that I understand the bias circuit, I can start having some fun putting it all back together.

Thanks again,

73,

Jack
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W8JI
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« Reply #49 on: March 20, 2014, 11:54:01 AM »

W1QJ  Lou... Yes that's how the circuit looks, except that they insert the leveling choke (L7) between the bias resistor and the filaments of the tubes.  So I will take out L7 and the wiring to the tube sockets.  Now that I understand the bias circuit, I can start having some fun putting it all back together.

Thanks again,

73,

Jack

Bias goes on the CT jack, and the bias has to return to the power supply negative rail.

http://www.w8ji.com/metering_amplifier.htm
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W8KR
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« Reply #50 on: March 21, 2014, 06:14:24 PM »

Thanks Tom; got it!  Wiring it this weekend.
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W8KR
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« Reply #51 on: March 24, 2014, 11:55:03 AM »

Here's a new wrinkle: Most of the schematics I'm looking at (most notably Eimac's suggested schematic in their old 3-500 spec sheet),  call for .01mf, mica, 1000 V. capacitors, as RF input feed-throughs.  I didn't give that a second thought until I looked all over Minneapolis this morning and learned that you can't find micas locally.  The closest I came is a roll of 25 capacitors from Digi Key, which is a possibility, except that I only need two caps!

Henry did not use micas for this purpose and neither does Ameritron in the AL 82, so I'm thinking .01 ceramics would be acceptable.

Any ideas?

Alternately, does anyone have a couple of .01, 1000 volt micas they would part with?

p.s. On another subject, I found a completely unsoldered connection on a mica capacitor in the ALC circuit. As a CW op, I'm planning to disconnect this circuit, anyway, but I would never have seen it had I not unsoldered the other end of that capacitor from the filament pin.

W8KR
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W1QJ
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« Reply #52 on: March 24, 2014, 01:28:50 PM »

a .01uf ceramic 1kv disc is fine.  everybody uses them.  A standard item from Mouser, Digi key etc.
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W8KR
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« Reply #53 on: March 24, 2014, 01:34:31 PM »

Thanks Lou... I have a parts drawer full of .01 ceramics!  I also have some brand new .015s, with nice long leads, which it seems to me would be OK.  Do you agree?

 Jack
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