[Heathkit] SB-230 retrofit plans

[wa7zze at gmail.com]

Kurt,

The SB-230's heat sink is made out of beryllium. DO NOT drill, cut, grind or do anything to make dust or filing. Beryllium is very toxic. 

I think there are warnings about it in the manual. 

Best,

Chuck / WA7ZZE 

"Remain open to the possibility of the fantastic." -- Terry Hansen

> On Dec 1, 2016, at 6:09 PM, Kurt Fitzner <kurt+hk at va1der.ca> wrote:
> 
> 
> 
> Hi All, 
> 
> I was recently gifted with a great SB-230 (including a working 8873!) by
> a friend who knew I had always wanted to complete my SB-104 set. And
> while it causes me a certain kind of pain to be using a well and truly
> irreplaceable tube, I'm not one to bubble wrap my equipment. So, I have
> to plan for a future when it finally gives out. 
> 
> In planning for the 8873's eventual replacement, I want to keep to the
> original design philosophy as much as I can. Seeing as the single most
> unique aspect of the 230 is its conduction cooling, I intend to keep
> that. The usual tube to replace an 8873 with is the GI-7B(T). The GS-9B
> seems a little more appropriate for an amplifier, but the GI-7BT will
> operate at a higher temperature. I have both to experiment with. Those
> with more experience than I, though, suggest conduction cooling for
> these tubes is inadvisable. The experiment most often cited for this is
> http://gi7b.com/sb230/cooler/index.html [1]. However the large aluminum
> block used in that experiment seems ungainly to me, and a needless
> impediment. While it will offer a little bit of a thermal reservoir in
> the short term, over the long term it acts simply as added thermal
> resistance. I think I've come up with an idea to make conductive cooling
> work better. 
> 
> My idea is to remove not just the heatsink from the tube, but to modify
> the tube itself a little and cut off the heatsink's mounting thread.
> Once done I can then mount the tube horizontally along the amplifier's
> fore-and-aft axis and have the top of the tube mate directly with the
> BeO block on the amp's heatsink. There is room to do this without moving
> the coils, though I will have to make clamps rather than using a socket
> for the electrical connections. Upon removing the heatsink from the tube
> you see that the mating surface area is actually rather small (only
> 4.4cm²). I was surprised to see that it's not lapped, and is a bit rough
> on both sides, which can't do much good for the thermal conductivity
> there. If this is the way the normal heatsink is attached, I can't help
> thinking that once lapped and with a thin layer of a good modern diamond
> thermal conductive paste, that having it connected in this manner to the
> SB-230's giant heatsink might be, even without a fan, equivalent to the
> original heatsink and a blower. 
> 
> I'd love feedback on this, especially if you have a retrofitted SB-230. 
> -- 
> 
> KURT FITZNER (VA1DER)
> YOU DON'T KNOW THE QRO OF THE DARK SIDE! 
> 
> Links:
> ------
> [1] http://gi7b.com/sb230/cooler/index.html
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