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Re: [TCML] Custom GU-81M Vacuum Tube Socket

Greetings Gentlemen,

You are correct about the trace width. I miscalculated the requirement for 12A (maximum filament current, according to the datasheet). As designed it might be able to handle around 7A assuming a ~40C temperature increase (ouch!). I think I may have done my calculations based on 2oz/ft^2 copper, but I only ended up using 1oz. 

With my limited knowledge of these tubes, I'm not terribly concerned about the clearance between parts. They are calculated for >1kV peak between them, if I remember correctly, and these are not particularly high voltage connections. What does concern me is the creepage distance between them, if the PCB is not perfectly clean and dry. Provided everything is clean, however, this is probably a non-issue.

I am sure there will be a Rev 2 of this board at some point. The more I think about it, the more I think it'll be a good idea.

Matt, Fairlee VT

-----Original Message-----
From: Carl Bradley via Tesla <tesla@xxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Mon, Mar 11, 2019 5:34 am
Subject: Re: [TCML] Custom GU-81M Vacuum Tube Socket

As already mentioned, at 123 watts, you might want to double up on the trace.  Looks nice and professional, really.  In sixty years of soldering, the only two problems I've ever seen are solder shorting something out, or a cold solder job.  Yours looks fine. 

Sent from Yahoo Mail on Android 
  On Mon, Mar 11, 2019 at 12:50 AM, Chris Reeland<chrisreeland@xxxxxxxxx> wrote:  Hi Matt, the first one, with the Russian tube :-)

Been busy lately and I have not even been lurking much here, but catching
up tonight. Also I can see it has been kinda of quiet on the list overall.

So I just wanted to say nice looking work for a solution.

So a few comments now.

I had to go online and look at some specs of the tube and also look at the
original socket. I knew they are kinda of strange and I forgot how odd they
really are...and why for the cut out. The big glass slot on the tube.

I see that it has a 126W filament.
Just as a note, my 304's are a 125W filament.

I know you already are considering a thicker PCB. If you do, since there is
not much room for a wider trace, because of the final blade terminal
connections, you may want to double side the traces of the
filaments/cathode because of the current requirements.

But what you have currently, may be just fine, just a slight concern.

That said also, I am a bit concerned about all the final blade connections
and the closeness of them.

Again could be fine, but again a bit concerned.

Also looking at your pictures, you said your slightly embarrassed about
your solder "blobs". Not completely a bad thing here. I personally think a
healthy amount of solder on both sides of the board is a good thing. Of
course not big overly rounded blobs, but plenty of solder "coverage".

I see this has been posted for a while and no real responses yet.

I would like to hear some others chime in on all these things I mentioned.
Would be interested in their opinions and I don't mind if I am wrong on
some things.

Chris Reeland
Ladd, Illinois, USA

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