Questions on ARRL 813 Rig

[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.  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.

[N3DRB The Derb]

Also, in all your HV supplies, consider the use of a "safety bleeder" running offa yer B+ bleeder resistor. In case the big bleeder opens up and you go in the rig to find out what is wrong, it could save your life. Something like a 2 meg 2 watt~3watt ( use ohms law here) to ground will slowly drain the voltage to ground without any effects. There's formula to figure out best values but I dont remember it. Use a decent margin of safety (double the wattage 'required' is my rule) because teh resistance is so high, you dont need much power handling.

[Carl WA1KPD]

Derb,
Thanks for the input. I planned to start with the VFO first and work my way up to the 6146.I only need 400V up to that point and am using a bench supply for that. Once I have that tamed and running I will build up the permanent supply and then go back and rebuild the HV supply I have courtesy of a local. Good idea on the extra bleeder. I'm more then a little concerned about the HV. I generally stay with rigs 100 watts or less for that reason

I have the parts for the modulator from 10 years of collecting- including the iron which I hope is good. For a speech amp I have a really buzzardly HB one from the 40s. It uses some 2A3s so I may convert it to 6L6s given the current cost of a 2A3.

Mike,
I'll keep an eye out for the B&W. If not when I get to that point I have a fair amount of stock some big caps and a good GDO. I appreciate the info.

Pete,
Appreciate the info. I had most of the articles except the particular HB one. It is nice because it calls out in more detail the parts locations. Would have gotten there anyway, just saves time.

Tnx all
KPD

[N3DRB The Derb]

6L6's make crap driver tubes for audio unless you bring the plate impedance way down. Triode connected they are teh ok. I used 2A3's in my HB rig and they just drive the hell out of almost any mod tube you will use. They could pin a 500ma meter on a whistle in my mod deck.

I think the chinese 2A3's are ok quality these days. I fixed the bias on mine at -62 volts with a zener. on of the few modern concessions I made on my HB rig. No 2 volt fil transformer, use 6B4G's, just like a 2a3 but with a 6 volt fil. maybe confusing it with a 9pin mini tube. PM a message to N3LHB and ask him what driver tubes he used on his HB rib when he lived in Carlisle PA. I have no reference material here, not even a arrl handbook.

use audio toobs fer audio. RF toobs fer RF. I sez.

of course, if you never step out of ab1 operation, it's not as important. But the second you deliver power onward up the chain and go into ab2 mode, the 6L6's will turn to crap.

[KL7OF]

6L6's will work very  well for your speech amp if you give them some neg feedback...... that will lower the output resistance....... look at the arrl 6L6 speech amp for the values of coupling cap and feedback resistor. It is in the handbooks from about 1947 on.  I have built several of them and they  work .  Very cool rig... good luck  I hope to hear you when you get it going..

[WBear2GCR]

Before you neuter the bandswitch - check to see if it has an extra contact! or a space for an extra contact!! Then just move the stop and add 160!

It's often possible to "borrow" a contact or two off unused contact positions on the switch, sometimes the mfr actually provides "unused" contacts intended to have the rivet drilled, and the contact used for field repair - or you can scare up another switch with a suitable contact and add it in.

You could consider adding in the 160m positions by pulling the 10m contacts for now, and moving them to the 160 position if that is applicable in your situation - go back and fix the 10m spot later when the contacts appear at NEARFEST or someplace like that.

By the way, REALLLY nice find!

         _-_-bear

[W3RSW]

Here's a nice coil calculator, Q, Z's, turns, etc.  I think it was already referred by this site.

 I'm referencing his pi net page but you can back into his other Java calculators.
I used it on my 813's and came out pretty darn close.
http://www.qsl.net/wa2whv/radiocalcs.shtml

[WA1GFZ]

a two watt resistor is good for maybe 500 volts I would not use one over 1kv
A lot safer to series up a bunch. Also use your final volt meter as an additional path so you can see the voltage decay. If the time changes you have a problem.

[W3RSW]

Correct.
In my HV meter string, I used 6 each 1 meg. 3 watt resistors (IRC thickfilm 5%, Mouser P/N 66-GS31001004JLF, rated 1kv each) with a final 1k resistor to ground. The 500 micro-amp meter being picked off right above the 1k resistor.  So the HV circuit is always to ground through reasonably safe 6.001 meg. string.  Same wiring for the screen circuit and hot switchable on the 1k pick-off. Found both to be in circuit continually.  Frank, your the catalyst that's clarified my thinking yet again; this time for an extra added attraction, Safety.

  Note that I'm not too concerned about absolute accuracy, just relative and watching the rate of charge/discharge.  Pretty neat watching the HV drop faster than the screen due to the relatively smaller filter cap. in the HV string, diff. time constants, etc.