[R-390] The second 390A

[Barry]

A VTVM like the HP 410B, etc, typically has an input impedance much higher (the 410B is spec'd at 122M).  Since you're not seeing voltage at that point on either radio but they both seem to work, I'm guessing the meter is loading the circuit due to too low of an input impedance.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "dog" <agfa at hughes.net>
> To: r-390 at mailman.qth.net
> Sent: Thursday, July 18, 2019 8:50:15 AM
> Subject: Re: [R-390] The second 390A
> 
> I've been using a Fluke 189 or an old HP427A FETVM, both 10MΩ or more
> input. I'll have to do some further inspections and also get the SA/sig
> gen going. A bit of signal tracing back from the IF input should be easy
> enough to do. Not sure how much I'll get done today, but maybe I can get
> the first one looked at about the high voltage on E209 also.
> 
> The power cord was so old on #2 the innards were so brittle it just fell
> apart. Luckily I found it right away. I'd like to find that mod for the
> new AC filter input.
> 
> This was the first trial in a long time of the PS on #2, it originally
> had the diodes installed and the tube sockets crimped shut. I replaced
> the sockets, re-wired everything and someone sent me a couple new
> rectifier tubes. It fired up just fine. The radio had been sitting
> around for maybe 20 years here and I was swapping modules out of it with
> #1 to get all the mods done I wanted. Mostly just the pertinent black
> beauties and coupling caps plus re-capping the audio/PS sections with
> filter caps under the deck. Also on #2 I had to rebuild all the
> mechanical filters. That took a year or more.
> 
> I've been thinking about re-painting the front panel on #2, it's got
> some holes drilled in it for the DB meter adjust that I removed. Looks
> like I may need a few small knobs too, like the ant trim. But get it
> working first, I kinda remember it worked to some degree 20 years ago
> when I got it. I think I gave maybe $50-80 for it at one of the local
> hamfests. I had 3 of them but loaned one out (the best one) and never
> got it back. I don't think I ever gave more than $80 for any of them.
> Why I needed 3 is beyond anyone's imagination?
> 
> 
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