Questions on ARRL 813 Rig

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Carl WA1KPD:
I have the caucus of the 5 band 813 rig from the early 50s ARRL Handbook. (Schematic atached in .doc format)It is designed for 80 to 10 meters. I want to change it to 160 to 40 rig. I also have a hefty PS and parts for a pair of 811A to be used as a modulator

The VFO seems fairly simple to me, change it from 3.5 to 4 mhz to 1.75 to 2 with some additional inductance and possible capacitance. I assume I then tune the rig as a doubler for 80, but how do I handle 40 with a minimum of circuit designs changes?

Also, how do I add to the tank circuit of the 813 so it will also work on 160?

Any thoughts or help is appreciated

Tnx and 73

Carl /KPD

N3DRB The Derb:
as a very rough measure, double yer tank coil L and double yer capacitance, I would use fixed micas that are switched in and out on your plate tuning and loading cap as you switch to 160. grid dip meter would work wonderz here. One of the gangsters here can give you a mo technical answer.  :D look to see if you can get rid of the 20-15 10 part of the tank coil and switch in both additional L and C to give you what you need.

don't forget the driver tuning. work from the low level stages up, not from the final back. Get yer vfo working first then your buffer then on up the chain.

Pete, WA2CWA:
FYI:
I also have one of these transmitters and so does W2ZM.
All the articles for this rig are listed and available on the ARRL AM web site (Three Control Six-Band 813 Transmitter)
http://www.remote.arrl.org/tis/info/am.html
    * QST, Jan 1954, pp. 11-16, 112, 114, 116 (1,087,092 bytes, PDF file)
    * QST, Jun 1954, pp. 37-39, 118 (475,128 bytes, PDF file)
    * QST October 1956, pp. 33-38 (626,007 bytes, PDF file)
    * ARRL Handbook 1957, pp.192-197 (720,163 bytes, PDF file)

Great transmitter!

KB2WIG:
w2icq runs the "Chambers" rig ....  maybee try him...............  klc

W3SLK:
Carl, I can help you with the tank circuit for the final. I did the samething to my HN-500. Most of those designs were around a Pi-network. Essentially a BW-850A. You can do one of two things here. 1)See if you can find the ever elusive B&W-850-160 coil set. I bought one of the last ones they made over ten years ago and I'm not dissapointed. 2) Place an extra coil in there with a relay to switch it in. For practical purposes, I would mount the coil vertical to prevent any mutual coupling from going on between the two. You will need some extra C for the load & tuning. I think I have about 500 uuf @ 4kv and 2800 uuf broadcast jobber I got from (un)Fair Radio. The voltage isn't critical there. I would make sure you have a RFC going from your antenna center conductor to ground. In the advent you have an arc or something happens that B+ winds on your line out, you can short it to ground. It also serves as a shunt for static build up on your aerial. Good Luck.

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