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From: N1BUG <paul@n1bug.com>
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Message-ID: <470ea500-3fb1-75c1-4c1f-4c2f1538f673@n1bug.com>
Date: Mon, 9 Apr 2018 11:28:27 -0400
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Subject: Re: LF: W1VD amp help - more waveforms
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Reply-To: rsgb_lf_group@blacksheep.org

Jay,

I appreciate your help with this. See below.

> I seem to recall you posted a link to a pix of your amplifier last week ... but it must already have 
> been deleted here since I can't find it. Please send the link again so I can have a critical look.

Forget that rather poor picture. Here are better ones.

Overall view #1:

http://www.n1bug.com/vd-amp1.jpg

Overall view #2:

http://www.n1bug.com/vd-amp3.jpg

Have a critical look at the primary winding on the transformer in
this one if you would please. The winding is held tightly against
the secondary by a Delrin spacer inside the core, but as you can see
the primary is not tight on the outside of the core, I had a devil
of a time with this and finally gave up trying to better it:

http://www.n1bug.com/vd-amp2.jpg

The wire I had was just too stiff to control! I tried speaker wire
similar to what Chris uses but the insulation melted all to crap
when I tried to solder it.

> It was hard to tell from your scope display ... I'd suggest moving the 
> traces so they share the same baseline ... essentially on top of each other ... to better see what's 
> going on at the trasnition.

Try this:

http://www.n1bug.com/drains2-wdv13.jpg

> What are you using for the bypass cap at the center tap of the transformer?

10 x 0.1 uf 1825 size ceramic chip caps. You can see them in the
above pictures. I can dig up a manufacturer part number if it might
help. Perhaps I didn't use caps of high enough quality?

> My unregulated HV supply (xfmr, rectifier and big filter caps) is on a powerstat which is convenient 
> for testing ... key the transmitter and dial up the powerstat while watching the drain waveform. Any 
> abnormality in the waveform (including excessive ringing) will likely be spotted before it becomes a 
> problem.

That is of course very preferable to my string of 12V supplies which
gives fixed steps of 12.5, 25, 37.5, 50V. I simply can't afford a
variable supply this year.

> After seeing the pix I may have more comments. BTW, I might have a spare driver PC board if you're 
> interested. Can't remember if I have any left. Was going to order another batch, but like too many 
> other things, I never got around to it.

I assumed as much when I didn't hear back from you about the planned
order last summer. If you do have a board, I am interested.

Paul