[Amps] Heat Dissapating 8877 HV Plate Caps

Sat Aug 25 01:45:36 EDT 2007

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.

 BLOWER NOISE IS PART OF HIGH POWER OPERATION UNTIL WATER COOLING IS USED.

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+ amps.

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.

DO NOT GIVE UP ON THE OLDER AMPS.  THEY ARE THE BEST BUY ON THE AMATEUR MARKET.

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

Arne N7KA
-------------- Original message -------------- 
From: "Fern Rivard" <crc at cyberlink.bc.ca> 

> 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: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On 
> > Behalf Of robert briggs 
> > Sent: Friday, August 24, 2007 8:54 PM 
> > To: amps at contesting.com 
> > 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........ 
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> > http://lists.contesting.com/mailman/listinfo/amps 
> 
> 
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