Viking 500 update

[WQ9E]

A few days ago I had posted in another Viking 500 thread about intermittent arcing in my 500 when the PTT is released.  In brief, RY-302 in the 500 power supply/modulator section supplies receiver muting, switched 115 VAC for an external antenna relay, and a part of the control circuit of RY-303 which is the plate supply relay.  RY-302 is referred to as a mechanical slow release relay and the intention is for the plate relay to drop quickly while RY-302 delays slightly before antenna changeover and receiver "un-mute" occurs.  The coils for the two relays are powered by the bias supply and are activated when the PTT connection is grounded, effectively the two coils are in parallel whenever RY-302 is activated through grounding the PTT line.

Since the mechanical delay appears to have disappeared with age I added an electrical delay by placing a 10 uf capacitor in parallel with the coil of RY-302 (positive end to end of coil normally grounded by PTT switch).  To prevent the capacitor from also discharging through the plate relay control,  I inserted a blocking diode (cathode end connected to RY-302 coil) in the wire connecting RY-302 coil to RY-303 coil.  This provides a very slight delay on PTT release for RY-302 while the capacitor discharges; RY-303 still drops the plate supply instantly and the arcing problem is gone.  Apparently this has been a problem with the "mechanical slow release relay" on other Viking 500's and I wonder if some of the complaints about those HV interconnects between the modulator/power supply and the RF unit are the result of "hot switching" the antenna relay with the protective gap inside the RF cage set too wide.

I hope this helps someone else with their Viking 500 problems.

Rodger WQ9E

[John K5PRO]

Thanks Roger, good work fixing that. Whenever I get mine finished, I have a HB power supply, modulator which has a DC relay in the place of that one, to accomplish the same function you are doing.

73
John

[W1ATR]

Excellent Rodger. I just got in a manual for the v500 from Ken, WB8CPW (www.radioreprints.com), with a nice clear skizmatic as mine was unreadable. With any luck, I'll get to dig in later this week.

On a side note, I found something odd now that I have the correct manual with clear pics. In the v500 manual, I noticed in one of the pics that the plate tranny doesn't look anything like mine, so I looked a little closer, the part number isn't for the v500(T-302, 22.1267), it's actually the plate tranny for the thunderbolt amp, pn 22.1466. The thunderbolt amp ran a pair of 4x4's, versus the v500s' single tube. I'll have to dig out the HV probe and take a look at the plate voltage as this is going to be stuck to my brain now until I check it. I think the thunderbolt amp ran 2200 vs the v500s' 2000, but we'll find out later.

[WQ9E]

Hi Jared,

I recall reading that there was a problem with the plate transformers failing on early production 500s and that changes were made.  Perhaps Johnson did switch to the same transformer that they use in the T-bolt as the voltages are pretty close (specified at 2000-2300 VDC in the T-bolt and 2000 VDC in the 500, both loaded to rated power).  I know that somewhere in the many articles about the 500 is a note that Johnson had "approval" from RCA to run the 811A modulators at a higher than rated plate voltage.  I have a T-bolt also but I have never compared the plate transformers.  Certainly the T-bolt and the 500 power supply/modulator are equally unwieldy to move about!

73, Rodger WQ9E

[W1ATR]

I have to agree with that one Rodger, my v500 doesn't have the factory mod iron anymore either, but there's a larger than life mod tranny in there that sticks out thru the side. I'm not sure what the hell it came out of, but I think it might have been a t-368. I can't make out the print on it, so be it. Between the giant mod iron and plate iron, that damn ps/modder has to weight around a 'buck seventy-five'

The t-bolt plate is physically larger than the v500 factory iron and it's mounted horizontally vs the vertical orientation of the factory iron. When I dig in, I'll take a closer look at this.

I have the ps for an invader 2000 along with the high power deck (pair 4x4's) hanging out in the junk room, (not even a junk box anymore), I wonder what that has in it for iron. It was originally an upgrade kit someone bought to upgrade the invader 200 to 2000 version and I'm pretty sure it was never used, so I definitely wouldn't tear it apart, but it might be interesting to see whats in there for iron.

Got more junque around here than I can catch up to. I keep telling the YL she's gonna have one hell of an estate sale one day.

sk

[John K5PRO]

I thought the Invader was really an SSB transmitter, with AM as a freebie, not high level AM design. As such, I would expect the transformer to be run lower duty factor compared to high level AM in a 500, or even a T'bolt. I think SNC in Oshkosh, WI was a source for big iron for Johnson back in those days. They make mostly wall warts now.

[W1ATR]

Rodger. Thanks for the quick fix. Just got around to it now, and that took care of the arcing problem right off the bat. Makes a nice little click-click now when coming off transmit.

Just to test it out, I closed the gaps (RF side, and PS side) up pretty close and no arcing at all, either modulating or not. I don't know exactly 'what' wears out on RY-302 to make it drop faster as I dont see anything else in the circuit either, but hey, the cap and diode took care of it. I didn't have a 10uF, but I had a 15, so thats what I put in there. Little longer on the drop-out, but that's ok.

John, I figured the same thing as far as the invader 2000 ps goes. Besides, the guts on the RF deck don't exactly look up to the task of AM. Maybe at a lower input, but things look awfully light for a pair of 4x4's.

[WQ9E]

Hi Jared,

I am glad the relay fix worked out for you.  It is nice to be able to use my 500 without having to fear releasing the PTT!

73, Rodger WQ9E