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Re: [Amps] Heat Dissapating 8877 HV Plate Caps

To: (Amps), "Fern Rivard" <>
Subject: Re: [Amps] Heat Dissapating 8877 HV Plate Caps
Date: Sat, 25 Aug 2007 05:45:36 +0000
List-post: <>
All those tubes you mention can be called bottles.  Anodes inside a glass 
envelope.  The cooling from these tubes involved air passing around the glass 
envelope.  And yes they use a plate cap with horizontal fins which also served 
as an attachment point to the PLATE of the tube.  (BTW, I have seen anode caps 
with vertical fins, though rare.)  They help reduce the temperature of the 
metal plate conductor and glass envelope.  With heat cycles it is importanmt to 
ensure a somewhat parallel coefficient of expansion of the glass and metal to 
ensure the vaccuum seal is not damaged.

With an 8877 and similar tubes with an EXTENAL ANODE (plate) the cooloiig is by 
passing air through the fins of the external anode.  Most connections to the 
anode are by a strap of some type that goes completely around the anode.  (No 
blockage of air flow.)

It might be a handy connection to have the heat dissapation caps that W2 CQM 
has for sale but I have NEVER seen any reference to such in EIMAC data.

As someone stated, remove that cap and you will find a pinched-off tube which 
was used during creation of a vccuum in the tube. The tube just looks nicer 
with the cap. (the plate cap has nothing to do with the cooling of an 8877). 
Check out the EIMAC Y-503, 8755, 8767, 8847A, ML8538/8933/8538B,Y-540, Y-654 
for examples of the pich-off tube process (thas just a few of the TETRODES).  
If you really want a plate/anode cooling fin look at the 3X600/Y-872.

For the 8877/3CX1500A7 use conventional cooling with air directed through the 
fins of the external anode (use the amount of air recommended by EIMAC), and NO 
additional cooling is required.


My opinion, nice looking caps, BUT NOT NEEDED, so save the $$ for other items 
(a bigger/faster relay for TX/RX switching).

As far as I can see, W2CQM sell parts from older  good amps (this plate cap is 
a new twist).  I think he feeds someone who modifies older amps  to work on 6M. 
 However I believe a lot of newer hams would love to get their hands on an 
SB-220, L4B, or similar amp to use on HF instead of buying the newer $4000.00+ 

Example, I just picked up an SB-220 with all the HARBACH mods for $600.00.  At 
1200 W out it would be hard to tell if signal is below the 1500W boys.  Or how 
does it compare to a newer 1500W amp at $4000.00?  I CAN say it is $3400.00 
CHEAPER than the newer amps but only 300W down.  Very acceptable trade off, I 
am sure.


BUY a cheaper amp and put up a biggerhigher higher.  A 2X winner, minimum.

Arne N7KA
-------------- Original message -------------- 
From: "Fern Rivard" <> 

> For crying out loud! Which way are the plates on all of the other plate 
> dissipating caps oriented? Look at those for 813's, 4-400's, 
> 4-1000's.....they'e 
> all with horizontal fins. I don't recall seeing any of them with vertical 
> plates 
> anywheres. I'm not saying that they're really needed but there's nothing 
> wrong 
> with putting them on as it will definitely help somewhat with the cooling. 
> Just my 2 cents worth. Fern 
> ----- Original Message ----- 
> From: "Gary Schafer" 
> To: "'robert briggs'" ; 
> Sent: Friday, August 24, 2007 8:55 PM 
> Subject: Re: [Amps] Heat Dissapating 8877 HV Plate Caps 
> To each his own. But from my point of view if there was to be anything 
> gained the tube manufacturer would have put fins on that part of the tube. 
> I would also guess that they would have had the fins in the proper 
> orientation to air flow with air blowing thru the fins and not across them. 
> I suppose pure silver power cords will be the next fad here. 
> 73 
> Gary K4FMX 
> > -----Original Message----- 
> > From: [] On 
> > Behalf Of robert briggs 
> > Sent: Friday, August 24, 2007 8:54 PM 
> > To: 
> > Subject: [Amps] Heat Dissapating 8877 HV Plate Caps 
> > 
> > Interesting to note all the crapola over the heat dissapating caps.In a 
> > number of HFamplifiers I have built I have used these caps on metal 
> > ceramic tubes.Whats wrong with a bit of extra metal to assist with the 
> > radiation.The other plus factor is those caps make an excellent attachment 
> > point for HT and suppressors.Works for me and full marks to Ron for 
> > innovation. 
> > 
> > Bob VK3ZL........ 
> > _______________________________________________ 
> > Amps mailing list 
> > 
> > 
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