[AMPS] tube anode cap, etc.

[Jon Ogden]

>
>Isn't it nice? The way a mailing list ought to be....
>This reflector is much like tuning across 20 meters sometimes. I suppose
>that's good, but it sure is difficult to find time to filter through when
>ya gotta work for money.

Yeah, you're right.  I've just been on other reflectors that would tend 
to hiccup and some folks would not get any messages.
>
>
>>- --------------------------------------------------------------------------

>
>Contact Reid Brandon at CPI/Eimac for the answer, and maybe suggestions on
>getting a cap thing.

Reid could probably help but since Eimac doesn't support the tube anymore 
wouldn't it be better to call Triton since they are the ones who now make 
the old firebottle?

> It is very important to have the heat sink cap on the
>tube if you plan anode dissipation! It's part of the heat exchanger from
>the structure inside to the outside air.

Oh, I'd agree.  The 4-1000 plate fins tend to get quite orange and 
getting that heat out would be critical, IMHO.

------------------------------------------------
>
>I believe that you are speaking about the low RF (cold) side of the RFC,
>right, Jon?

Yes, the cold side.  I don't think putting bypass caps on the hot side 
would work too well. HI!

> At HF, in a kW level amplifier, you will pick up a little bit
>of RF on the wire, but it's not enough to consider adding more Cap to gnd
>to compensate, if your bypass cap is already there and capable of shorting
>out most of the conducted RF that got past your RFC.

This was my main concern.  How much pickup.  In higher frequency aps, my 
plan would be a no-no.  But I figured I could get away with it especially 
if I shielded the thing.

> It is my experience
>that you don't want a foot of wire in the PA compartment to the B+ feed or
>the bypass, it can couple magnetic fields like a loop if oriented in the
>worst way to the RF currents in the walls and the tube. A few inches is
>nothing though.

I am probably talking close to 6 to 8 inches.  Too much?  That was why I 
thought about shielding it and clamping the shield to the floor of the RF 
compartment.  It could be significantly less that that though depending 
how I arrange and orientate my glitch resistor.

> It hardly warrants a shielded cable unless you really want
>to go to the trouble, it certainly would be the ultimate approach to do
>that. I have used shield braid pulled over a silicone HV wire 

I was just going to use plain old RG-8.  I've used RG-8 without the 
shield to carry HV in the past and figured that this would be the easiest 
way to do it.  Bad idea?  RG-8 seems like it would handle 6 KV.
>
>In the 100 KW 2.8 MHZ amp that I just finished, the plate RFC is back in a
>corner, pointed out parallel to one wall, then a wire leads over
>perpendicular to the anode of the TH555A tetrode. It is about 6 inches
>long, but it already at the high RF potential being a shunt fed DC
>connection. I tend to put the loose wire in the high RF, and keep the cold
>end close to the bypass feedthru cap, in my case it was a 20 KV Draloric
>ceramic cap  that looks like a small mortar shell. Its 3000 pF and then I
>have an added Matroc/Unilator 5000 pF disk in parallel at the feedthru,
>that looks like a small Frisbee saucer.
>
I've got the B+ coming in through the back wall of the RF deck.  On that 
back wall right next to the feed I have mounted 2 20 KV .004 uF doorknobs 
I got from Fair Radio and 2 500 pf 30 KV doorknobs (original bypass in 
the amp).  I'd like to put the RFC right in that same area but I just 
don't have room due to the length of my load capacitor.  I figure that 
this is enough bypassing.
>
>Finally, I would like to post JPEG photos of my 2 x 100KW pushpull
>amplifier layout, if anyone is interested. But where to put them? Anyone
>have server space for this?

Sure.  Put it on my FTP site:  ftp.qsl.net  path: /pub/ke9na/incoming  
                          OR:  ftp.enteract.com path: /users/jono/amps

73,

Jon
KE9NA




--------------------------------------------------------------------------
Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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