Source for HV Keying Relays?

[WA1LBK]

Made some substancial progress on my Johnson Viking II restoration over the long holiday weekend.    Replacing the open interstage transformer & R13 finally got the modulator working, but listening to it on a monitor receiver, the audio quality sounded absolutely horrid   - loads of distortion.    Installed new larger filter caps for the modulator, but still no change; got to wondering if it was the mic I was using, an old Shure controlled reluctance job that dated back to my early days as a Tech licensee on 6M AM in the early 70s.    Then I noticed that the audio still sounded noisy even if the mic was disconnected & the mic gain turned down to 0.    - Started to suspect a possible RF chain issue at that point.  Replaced the original 6146's (which may actually have been original equipment - they had identical 1956 date codes!) with a pair of matched 6146B's - no change in the audio quality, but power output went up 120 watts on 75 M.    Decided to start tube swapping beginning with the 6AU6 crystal oscillator - & VOILA!  CLEAN AUDIO!!!  My voice now sounded natural on the monitor receiver, & virtually all the background noise disappeared.  Using the "Signal Suite" AF generator app on my iPhone 4 (feeding the headphone output of the iPhone into the mic jack), a "quick-&-dirty" audio frequency response check showed usable audio from @ 60 Hz. on the low end to @ 4.7 ~ 5 KHz. on the high end.  

At this point, I'm starting to get ready to actually put it on the air.  At least for the time being, I'm going to use RF sampled from an ICOM IC-706MKIIG set to QRP into a small dummy load to feed the VFO input through a variable cap, to both block DC & adjust coupling into the Viking II.  I also have to start thinking about T/R switching, thinking of homebrewing a sequencer.  Primary receiver I'll be using with the V II is a Collins R-388, which has its own internal muting relay (12 V. coil).  I also have a coax antenna relay which is also has a 12 volt DC coil to handle the RF switching from RX to TX.  One mod I found in the Viking II as I acquired it was cabling connected to the plate switch & brought outside the cabinet into a round military-style multi-contact plug; I initially had thought this was to tap power for an external VFO & had planned to remove it, not wanting HV outside the transmitter case   ; but I now suspect the mod's purpose may have been to connect to an external HV keying relay.  What I'm looking for at this point is a source of a suitable relay, something with a 12 VDC coil, but capable of switching the 800 volts or so of plate DC safely  (I also plan to wire RC arc suppressors across the HV relay contacts).  I might build most of the sequencer inside the Viking II's cabinet to keep the HV entirely inside, only bringing out 12 volt keying lines for the antenna relay & the R-388's muting relay.  Any suggestions as to a suitable source for such a relay (preferably reasonably priced!   )?  Tom WA1LBK

[DMOD]

I would recommend against hot switching the HV.

Suggest you place your relay contacts across SW1 and SW2.

Phil - AC0OB

[K1JJ]

If you ever need HV vacuum relays, Allen Bond at MaxGain is a great source.
He deals in a lot of surplus stuff and has an impeccable reputation.

I've bought lots of stuff from him and he always takes an occasional return back with a smile.

http://www.mgs4u.com/index.html

T

[WA1LBK]

OK, had to pull the PDF schematic I got online up to see what you were talking about, Phil; hadn't particularly paid attention to where the "PLATE" switch actually was connected to this point, had been more focused on just getting the rig actually working.     Looks like SW2 is it; in that case its actually switching 110 VAC   rather than the HV, which I agree IS safer.  Can't see relay switching SW1, though, as that looks as though it would cut the filament power as well.    That should actually make finding a relay MUCH easier; should be able to find a 12 V. relay with 110 V. - capable contacts without much difficulty (might even have something suitable already kicking around in the junk box).  

Been doing a bit more thinking on how to design the sequencer - if all the relays have 12 volt coils, I might be able to drive them directly with 555 timers, adjustable to give the appropriate switching times I want.  (For the record, I've built many 555 relay drivers   for model railroad applications).  It did occur to me though, that installing IC relay drivers inside the high RF environment of the Viking II's cabinet   may have unintended consequences   (especially when I start MODULATING that RF!); think the wisest approach may to build the sequencer in its own shielded enclosure, with only the relay doing the plate circuit switching across SW2 actually inside the V II cabinet (& with bypass caps from the relay coil leads to ground as well).  Planned T/R sequence is (1) mute the R-388 by grounding one end of its 12 V. muting relay coil; (2) energize the coax relay coil to switch the antenna from receive to transmit; (3) ground the PTT line of the IC-706MKIIG "VFO" to supply RF drive to the Viking II's VFO input; & (4), energize the relay which will switch on the V II's HV supply.  Things would be done in reverse order going back from TX to RX; (1) drop the V II's high voltage supply; (2) unkey the IC-706MKIIG; (3) de-energize the antenna relay from TX back to RX; & (4) open the R-388's muting relay.  

Oh, & K1IJ, thanks for that link to the Max Gain site; even if I don't wind up needing a HV-specific relay, looks like he has lots of interesting "stuff"!    Tom WA1LBK

[N2DTS]

Yes, you key the 120 volts to the HV  transformer.
I do not think they had any sequencing when that rig was built....it all happened at the same time.
Push to talk keys the 110 which works the T/R relay which mutes the receiver.