[600MRG] Thank You WD2XSH/6 transmitter failure advice

[Pat Hamel]

Thank you Brian and all !
If I replace the metal mounting screws with nylon and add tape to the metal
mounting tabs, that should be the quickest and simplest method.
There is always a solution on this mailing list !
73,
Pat

 

-----Original Message-----
From: Brian, WA1ZMS [mailto:wa1zms at att.net] 
Sent: Saturday, September 07, 2013 11:21 AM
To: Pat Hamel
Cc: dave.riley3; <600mrg at w7ekb.com>
Subject: Re: [600MRG] WD2XSH/6 transmitter failure advice please

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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