[600MRG] WD2XSH/6 transmitter failure advice please

[Edward R Cole]

I bought a couple sheets from McMaster-Carr over a year ago for a 6m 
QRO LP filter that I am building (from QST article).

73, Ed - KL7UW

At 08:21 AM 9/7/2013, Brian, WA1ZMS wrote:
>I often buy Teflon sheets from McMaster-Carr. Not as cheap as a 
>popsicle stick. hi....hi..... But worth it for HV.
>
>Another option is to try and cover any metal support bars with Kapton tape.
>That adds a kV or so to the arc-over voltage.
>
>Just ideas.....
>
>-Brian, WA1ZMS/4
>
>
>On Sep 7, 2013, at 12:15 PM, "Pat Hamel" <pehamel at cableone.net> wrote:
>
> > Dave and all,
> > I laid out the amp for a "pretty" front panel so the four 
> push-pull-parallel
> > tubes glow through a hardware-cloth screen. That, the three-inch-diameter
> > plate coil, and the oil-filled tuning caps make space tight.
> > There were two caps that failed. The variable and one of the two blocking
> > caps (one blocking cap feeds each of the 811 grids so I can individually
> > meter them).
> > One Cardwell variable has arced before a few years ago, which is why I put
> > the disk blocking caps in series with them.
> > The arcing is not directly between the plates, but apparently on or in the
> > insulating bars (not ceramic) that hold it together.
> > They are about 3/8 inch by 3/16 inch by 2 inches long.
> >
> > So - now comes the question that I should have asked last time it 
> happened:
> >
> > Given that the bars are small, straight, and rigid, I should be able to
> > duplicate and replace the insulating bars easily.
> >
> > Given: Here on the humid gulf coast, I don't think that varnished Popsicle
> > stick is a good idea for 1250 volts DC.
> >
> > Given: When I was a kid, in the 1950's K8DHN rebuilt a capacitor 
> for me. The
> > first time he used the wrong plastic which broke down, then he found the
> > right plastic which lasted until the amp was disassembled.
> > I never did know the correct plastic type.
> >
> > TO find: Recommended plastic or ????
> > This group always has a good answer.
> >
> > Till then, I will put the parallel power supply back to the exciter and 4
> > watts ERP tonight.
> >
> > Thanks and 73,
> > Pat /6
> >
> >
> >
> >
> > -----Original Message-----
> > From: 600MRG [mailto:600mrg-bounces at w7ekb.com] On Behalf Of dave.riley3
> > Sent: Saturday, September 07, 2013 9:52 AM
> > To: 600mrg at w7ekb.com
> > Subject: Re: [600MRG] WD2XSH/6 transmitter failure
> >
> > add:
> >
> > RG8 is about 17 pf per foot ( styrene type ), so pre figure length and
> > then some, connect, then clip to tune ( with power OFF fer sure )...
> > Use both connections at one end, other ends open, not connected for EZ
> > cut...
> >
> > With power off, tune final tuning cap with good load on final to see
> > minimum final grid current change...
> > Yes, driver connected and hot, final HV OFF, this will let you tune
> > neutralization real fine in safety...
> > SNIP
> >
> >
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>
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73, Ed - KL7UW
http://www.kl7uw.com
dubususa at gmail.com
"Kits made by KL7UW"