[Amps] Longshot - looking for 8873

[Roger (K8RI)]

On 4/6/2012 3:40 PM, Paul Decker wrote:
> Probably a dumb idea, but what about cutting and grafting a custom convection cooling anode to an 8874 or to a 3cx800?  Similar to how some of the Russian tubes have interchangeable coolers.

It can be done, but I don't know what the success ratio would be and the 
8874's are already very expensive. The 3CX800 has a larger anode inside 
the radiator, I don't know if it'd clear of not.

The main problem in creating a "Conduction" cooled version is that 
unlike the Russian tube the anode coolers are soldered on the Eimac 
tubes, so once you remove the radiator you have a very irregular surface 
that has to be trued and polished while remembering the insides of these 
tubes are fragile. On top of that you have no surface to which you can 
bolt the new radiator.  You could build a threaded adapter to fit over 
the top of the tube that would need to be soldered in place, but the new 
cooler would have to simultaneously fit tight against the top and the 
entire anode area on the sides.

It'd probably be easier to machine the cooler to fit the anode and use 
solder paste to fasten it to the anode. I'd think the clearance would be 
relatively critical.

About the only way I can think of to true up the anode for the new 
cooler would be to chuck it up in a lathe and use a small belt sander on 
the tool post.  Considering the anode is nothing more than thin sheet 
metal, I'd think this would be a very risky undertaking.

Converting the 230 for the Russian tube (GI-7B) and machining a 
conduction cooler to fit would be far easier, and probably run about the 
same power even if the IM is not as good. Getting the anode cooler 
aligned would become a non issue unlike soldering one on a Eimac tube.

Any one know what the IM figures are for the GI-7B or GI-7TB?  I think 
this is a planar tube, but not sure.

73

Roger (K8RI)


>
> Paul, kg7hf
>
>
>
>
>
> Date: Fri, 6 Apr 2012 10:27:25 -0400
> From: "Jeff DePolo"
> Subject: [Amps] Longshot - looking for 8873
> To:
> Message-ID:<3B6AE450F3944139B9917B1FCA9F3F19 at OUTLAW>
> Content-Type: text/plain;	charset="US-ASCII"
>
>
> Anyone know of a working 8873 available anywhere?  Resurrecting an SB-230
> for a local ARES/RACES group and haven't been able to find one...
>
> Thanks.
>
> 				--- Jeff WN3A
>
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