Stupid ART-13 Tricks

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WU2D:
AM and closet CW fans.

Well I did it again. I got out the soldering iron before looking at the schematic.

Here was my problem. The ART-13 sounds like a hammer when it is keyed in CW mode. It scares XYLs, cats and small children. To fix this, I have been keying my ART-13 on a circuit suggested by the good old CQ Surplus Conversion Handbook. It basically adds grid blocked keying to the final. Now grid block keying an 813 takes some fairly high negative voltage. They suggested -400 VDC. Anyway, the circuit used some caps resistors and a choke to shape the waveform and I used a small relay to do the HV keying.
By the way, the other contacts of the relay key the sidetone oscillator. The regular keying relay (big kerplunk) gets keyed by a timer circuit which keeps it activated all the time you are keying. That had a retriggering effect as you key and it can be set from just under 1 second to 5 seconds for the release.
It keys like a Marauder or any modern radio.

In this way the oscillator is always running as you are keying just the final. This circuit has been running for upwards of 15 years without a hitch.

Here is the problem. Backwave. The 813 is not neutralized and killing just the final does not eliminate the signal completely. I figure it is putting out somewhere around 200 mW key up! This is a little bothersome to the listener.

Neutralization would help and I will try that, but I thought I would try keying the stage ahead of the final, the last 1625 along with the final. This should be good for another 30 dB or so of isolation.

I was able to get in and lift the 100K grid resistor off ground, add a bypass and strap over the keyed -400 VDC no problem. Actually it was a B**** but I did it. It worked fine on 20M and on 40 M, killing the backwave but had no effect on 160M or 80M's backwave problem.

What stupid detail had I missed?

Mike WU2D

KB2WIG:
Without looking at the skizmatic, the 1625's are part of the osc. multiplyer(S)..   the 1st 1625 is the 2X,3X or 4X freq mult, the 2nd mult.  is a 3X....  which multiplier did you werk on? ... any freq greater than  about 6mc(?) both  the 1st and 2nd are utlized........  hope this helps.....  today a had my plate meter crap out compleetly....  that little 4k meter resistor turns black when the smoke goes byby....   klc

WU2D:
KLC,

Exactly!  I was grid block keying only the second multiplier stage. On lower bands, this stage was not even in the circuit! :(

So my great idea stopped working below the 6 MHz band. I suppose I could pop the lid again and do the same hookup to the first multiplier and see what happens keying all three tubes! I do fear some pulling on the oscillator keying the first multiplier though. There is no buffer and I do not regulate anything. I suppose that I could see how it sounds and If I run into trouble, I could try regulating the screen of the 837 PTO stage.

I suppose in hindsight that I should have tried differential keying the oscillator along with the final and not touched the multipliers. Now that would have been a classic approach. It would require adding a triode and a regulator tube I think.

Mike WU2D

KB2WIG:
Mike,
 In the June 65 issue of 73, it is suggested that a 50 ~ 100 uF 'litic cap be placed from the test key switch to gnd.. this sounds like a clip lead mod... I havn't tryed it with my ATC's, im just getting these squared away after thay sat in a barn for?? years.....   gud luck  klc

WU2D:
Yup,

That quiets down the relays when you are keying it stock.

Mike WU2D

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