The AM Forum

Hello all,
I finally got my Valiant II on the air last night on 3885 and got great reports.
Unfortunatly after a long winded QSO the unit pegged the plate meter.
After a little poking around, I found that C39 a big 350Pf mica cap on the back end of the bandswitch had shorted out.
Anybody have one of these that you would like to part with?
Thanks for reading this,
Don W9BHI

Don,

Replace it with a modern mica cap.  If you put one in of the same age, it may short again.  What's the voltage rating on the old cap??

Fred

Hello Fred,
The voltage rating is 2500vdc.
I can't find anything that value anywhere.
Not at Mouser,Allied or RF parts.
Thanks,
Don W9BHI

Can you post a photo?  I have lots of transmitting caps, maybe what you need.

73DG

Don,

I'm sure you'll get more replies from someone that has had the same problem.  You're probably not going to find 2500V micas.  I have some of those old high voltage mica caps, but wouldn't think of using any.  You can use a small doorknob cap.  Plenty of those around.  Look on eBay you should find them.

Do you know what circuit this cap is in??  Plate blocking? Loading? What??

Fred

Here is a picture of the cap.

Are you sure it's a 2500V cap??  What circuit is the cap in??  I see there is a second cap, maybe they're loading caps.  If you have a schematic you should be able to tell what the cap is use for.

Fred

Das' a baby one.  I have hundreds of those.  PM me and I'll set you up.

73DG

The cap is in parallell with the plate tune cap.
The capacitor next to it has a voltage rating stamped on it for 2500 volts working, 5000 volts test.
So I assume they both have the same rating.
Thanks,
Don W9BHI

Don.

Plate tuning, you need high voltage caps.  Maybe W7TFO has them.  I would replace them with high voltage "doorknobs".  Even 2500 volts is not enough for a plate modulated rig.

Fred

Hi Don,

The reason I asked is you never know just what is lurking in some transmitters....

BTW, that is an 866A in the socket for perspective. 8)

73DG

I have had the same problem three times, The peak RF at this point is very high. The doorknob seems to be the only thing that works. I have tried 4000V silver micas and they still went. This is a common problem with the VALIANT's or it seems like it is.

John W9BFO

You can have this one if it looks like it would work.
400pf "Meaty"  PM me with ur addy and I'll post it
Monday AM from CLE.

/Dan

Between you and me, he'll have a festoon of the things... :D

73DG

Hey Dennis,

     I had to google that, You wordsmith you.

/Dan

I'm just a product of the public schools system. :)

73DG

School?  Who went to school?  Don't confuse me.

Fred, your verisimilitude proves you are no flibbertigibbet. 

Perhaps it is just a matter of gender.  I'd as lief not go there. :D

All for the sake of some silly silver mica!

Electronic alliteration not valid in Nebraska.

73DG

I thought this was a family G rated forum.  Good thing I keep a dictionary handy.

I said not to confuse me.

Fred

I said not to confuse me.

Fred
[/quote]

10-4, good buddy.  I'll shift those gears now.

 ;D

Recieved the caps from Dan.
The Viking is alive again.
Thanks to all who offered advice and caps.
This is a GREAT forum.
Don W9BHI