[Heathkit] SB-230 retrofit plans

Thu Dec 1 22:28:43 EST 2016

Why would anyone want to modify the cooling for the SB-230 amp as the factory set up works very well.
I’ve had several of these amps and they work very well as factory supplied.
The only issue is the now non obtainable 8873 tube.
73 from Fern

-----Original Message----- 
From: Kurt Fitzner 
Sent: Thursday, December 01, 2016 8:16 PM 
To: Doug Shields 
Cc: heathkit at mailman.qth.net 
Subject: Re: [Heathkit] SB-230 retrofit plans 

Thanks for the replies and the heads up. When I mentioned lapping, I
meant only the tube. The danger of working the BeO block is the reason
why I intend to modify the tube and cut the heatsink mounting threads
off. This will present a fully flat surface at the top of the tube which
I can polish and mount against the BeO block with little trouble. I can
even retain the existing two mounting bolts and, instead of using the
current metal cross bar, use a thickness or two of bakelite PC board
with a 35mm hole that will press against the GI-7BT's grid lip. 

On 2016-12-01 22:30, Doug Shields wrote: 

> Kurt,
> The heatsink on the SB-230 is extruded aluminum. It is very safe. The heat conduction block that goes between the 8873 tube and the heatsink is made of beryllium oxide. Beryllium oxide is a known carcinogen. It is safe as long as it stays intact as the block. Do not under any circumstances sand, file, grind, or otherwise try to modify the block. Beryllium oxide dust is the really bad stuff. As long as it stays intact as the block it is not terribly hazardous.
> 
> Doug W4DAS
> 
> -----Original Message-----
> From: Heathkit [mailto:heathkit-bounces at mailman.qth.net] On Behalf Of wa7zze at gmail.com
> Sent: Thursday, December 01, 2016 8:57 PM
> To: Kurt Fitzner
> Cc: heathkit at mailman.qth.net
> Subject: Re: [Heathkit] SB-230 retrofit plans
> 
> 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] [1 [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 [1]
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-- 

KURT FITZNER (VA1DER)
YOU DON'T KNOW THE QRO OF THE DARK SIDE! 

Links:
------
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