New home-brew 40 meter RF deck

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W8ACR:
Hi Jim and N1BCG,

Thanks for the comments. Yes, a swinging link is always useful, but alas, I'm fresh out of jackbars and coils. I'm sure I could figure out how to homebrew one if my life depended on it, but this was easier, and I thought I'd give it a try. We'll see.

As I review the pictures, a couple of thoughts come to mind.

1. Maybe I should have mounted the tubes next to the tuning cap with the neutralizing caps on the other side. This would have allowed for shorter RF leads.

2. I could have mounted the grid coil on the top of the panel, in the horizontal midline behind a small metal shield. This would look nicer, and would allow for better symmetry, but the leads to the grid tuning cap would be much longer. I'm not sure if this might cause problems or not.

3. I wonder if it would be better to take the grid leads from the neut caps directly to the grid pins, rather than putting them on the other side of the parasitic suppressors?

I guess I'll find out soon enough if my design works. Just thinking out loud here. One nice thing about homebrewing - you know how it was put together, so you know how to change things if necessary. BTW Jim, could you draw a simple schematic of that series adjustable C? I assume it is in one leg of the output line.

Ron W8ACR

KB2WIG:


The cloth covered wire on your HB TVL 40 coil is strangely appealing, visually. I like the way you reduce strain on your plate caps -   wide conductor/braid....

Nice work, you make me jealous.

klc

W8ACR:
OK, so I applied power to the RF deck last night. Flipped the switch, no smoke after five minutes, good. Fixed bias showing -150VDC, good. No grid or plate current, good.

Applied RF at 7.250MHz, grid cap tuned for peak grid current, good. Adjusted the variable grid leak for 40mA to give -260VDC, good.

Applied Plate voltage, start with 500VDC, dip the current, good. Disconnect plate power supply and adjust the neut caps for minimum indication on the wave meter, good.

Increase plate voltage to 1000VDC, uh oh, plates are bright orange. With 1000V @ 250mA, I'm showing 125W output, so everything seems to be working except my fixed link plate tank coil not matching output impedance (my guess). Don't think it is a parasitic since plate current is not running away.

My solution - I'm building a home-brew swinging link output coil. Will update later.

73, Ron

W2PFY:
Quote

I'm building a home-brew swinging link output coil. Will update later.

Hi Ron, great to see you at it again! You really don't need a swinging link unless you want to maintain the old buzzard appearance. One one end of your link just install a variable capacitor in series to ground. That's what I have done in the past on my 610. I just purchased a PP T-55 triode amplifier on ePay and it has the swinging link and a series variable capacitor to ground. It looks like the cap on the T-55 rig is about 100 uuf. On the 610 I used a 500 uuf with a 1000 volt rating and it made it much much easier to adjust the proper tank plate current as compared to the variable link that is in 610 coils. So to recap, on the 610 I kept the link fully engaged all the time and made all my loading adjustments from the variable cap. On the T-55 I am going to use 610 coils and toss the swinging link.

WD5JKO:

Ron, 

   The setup shown by W2PFY has good illustrations. Here are some more that I found on the net:

http://www.antiqueradios.com/forums/viewtopic.php?f=15&t=228639

   I have a box of TVL & JVL coils. Most are in sad shape. I did pull out a salvageable 40m TVL, and the "T Jack Bar" with 5 banana jacks. I also have part of the swinging link which includes the bakelite piece with the side ways rod at the bottom. The "T Jack Bar" center banana if removed, and replaced with the link hardware (missing) would be close to W2PFY showed in his last post.

    You can have any of this for the cost of shipping. I attach a photo of what I described.

Jim
Wd5JKO

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