K1KW 2 X 813 modulated by 2 X 572B's

(1/8) > >>

Chuck...K1KW:
Well, here is my attempt at an 813 rig.  Here were the design goals:

1) The whole rig including VFO/RF driver, modulator, HV PS, and final must fit into a nice 17 1/2" high rack cabinet I already had.

2) All hollow state except for power supplies, no switching supplies, just good old silicon rectifiers.

3) Completely self contained, just hook up a receiver, antenna, and a mic.

4) 1 KW input just like in the good old AM daze

5) Must run off 120 VAC @ 20 A  (This will be my bar rig!, no 220)

6) 160 to 10M frequency coverage.  WARC bands with XTAL OK


Here it is in the final stages of being built.  It already produces RF to spec but I need to work on the audio.  The mod transformer hasn't been installed yet nor the audio driver.

More pics later if anyone is interested.  A bit more cosmetic work is needed since the guy I used as my engraver of the brass has gone bankrupt last week so the temp labels.

K1JJ:
Bery, vely cool looking 813 rig, Chuck!

A one-of-a-kind. Very attractive front panel.

Did you use a plate-screen dropping resistor rather than a self-mod screen choke?  

It looks like the mod xfmr will sit on the upper chassis.  Will you be using a modulation reactor or unbalanced DC current?

Curious why the SO-239 coax connectors are recessed.   A Bird thru-line?

Yes, more detailed pictures!  A view of the bottom if possible.  

This is a perfect time since I'm still laying out my own 813 rig.

T  

Chuck...K1KW:
Hey Tom,

A few design notes:

Yes, a 20K screen dropping resistor using two 10K/100W resistors in series.  This gets rid of a screen supply and a choke!

There is no bias supply.  Not needed since I use a relay and its coil in series with the grid resistor that trips in at about 10 mA.

This relay controls the application of HV through the series Ruskie HV relay in series with the B+ supply so no B+ unless there is at least 10mA
of grid current.  BTW, a 24V relay with the spring relaxed a bit can be used here.  It will kick in at about 10 mA.  Test a few...interesting

Anyway, the mod transformer is from a GPT-750 I got from Tim.  I removed it from its hermetically sealed can, got rid of the PCB's, and will
mount it behind the 572B's.  I adjusted the gap spacer to handle about 400 mA before saturation, it took about two 0.015" spacers.  Still
has about 14H of inductance and is good to about 50 Hz.

The VFO is a Globe V-10 modified and the driver is a Globe HG 303 very heavily modified, I would say just about redone.  It had the low profile
I was looking for since the V-10 and the HG-303 would fit with a standard 5 1/4 " rack panel side by side.

The plate supply uses a Triad 3300VCT transformer rated at 650 mA and with the capacitor bank (6 X 1000 Mfd/450V) produces about 2300 VDC

The two SO-239's are from the internally mounted Dowkey relay.  You will see the top connector going up to the loading cap with a banana plug through a piece of coax.

One SO-239 goes to the antenna and the other to the receiver. A turn key rig was the goal here like the old Globe Kings...

More later....

Chuck

K1JJ:
Amazing rig, OM.

There's a lot to see when enlarging the pictures and carefully studying.

I like the big heatsink plate caps. Yours is a "no air" convection cooled rig which is exactly what I am doing with my 813s this time... quiet shack.

I wonder why the loading cap is raised an inch on metal spacers?

Cool on the 10mA grid current triggering the Ruskie HV relay. I can see the HV lead from the PS to the vac relay. So no need for protective fixed bias.

FB on the Globe VFO and driver. Self-contained.

Do you think there is any operational or linearity/ IMD difference between using a screen resistor vs: a screen choke?

I'm curious why you don't have  .001 bypass caps across the meters?  Is that just an old practice like TVI filters of the 50's?  I've never seen any difference without them, but still use them from habit.

That shade of blue for the cabinet is my favorite  - for all the rigs here.

I can see when you finally get the brass engraved panel labels it will be a real beauty. Wish I had the patience to attend to the finer details like that... ;D

T

w9jsw:
If like mine, loading cap raised to allow for right angle drives.

Navigation

[0] Message Index

[#] Next page