I Know a guy in Finland who had, a few years ago, a couple of the original
HEATH beryllium blocks. I would not touch and repair a block - very
dangerous and poison.
73s de Hans SM5KI
----------
>Från: nospam4me@juno.com
>Till: amps@contesting.com
>Kopia: dimtcho@attcanada.net
>Ämne: [AMPS] 4CX350A vs 8560 conversion of an SB-230
>Datum: tor 31 aug 2000 07.27
>
>
>re: SB-230 conversion
>
>I'm trying to provide Dino some information about his proposed SB-230
>retrofit. I've received two Emails from him.
>
>[snip]
>:From: Dimtcho <dimtcho@attcanada.net>
>:There is another reason for me to go away from the
>:SB230's cooling system - due to the thermal overheating
>:the conductive block ( Beryllium Oxide) cracked into two pieces..
>
>The block can be repaired using Varian Torr Seal To order call
>1-800-8-varian for part number 953-0001 Hold your breath, a
>small batch (epoxy tube size worth) is about $40 US. If you send
>yours to me with return postage, I'll fix it free and get it back to you.
>
>
>:I suspect that it will arc so that is the air cooling appeared as
>alternative.
>
>If you fix it right, your back in the conduction cooled tube game again.
>
>:I agree with you 100% on the replacement tube plus conductive material
>:sounded hard to find. The 8560 tube exists in the catalogs but have not
>:found any around.
>
>See my earlier reply below and previous amps postings about
>the 8560, a commercial conduction cooled tetrode which may be
>used in the SB-230. It was popular in two way radio amplifiers and
>often found cheap on Ebay.
>
>:I am not that sure for the Ebay trading what you get.
>
>A mixed bag, mostly good if your careful. Lots of sharks and dealers.
>
>:What does Motorola use to cool the 8560?
>:It is better to wait for the tube and then find a schematics.
>
>A very large Al heat sink. I have some pics of these commercial amps
>that I could send, but that wouldn't be any help for your SB-230. The
>tube is pretty much and exact physical fit for the 8873.
>
>Yep, find a tube first. I have two full size file cabinets full of
>commercial
>8560 amplifier circuits which I can photocopy and send out anytime. Most
>are Motorola Commercial Two-Way Radio Repeater Amplifier circuits
>which work very well. The data sheet can be found on the web, if not,
>I can send one out or scan it in later.
>
>:Skipp, I hope that life is rewarding you for the unique know - how.
>:Best wishes
>:73!
>:Dino
>:ve7xdt@rac.ca
>
>I used to be quite selfish and greedy about sharing my amplifier,
>information and "tricks". People like Rich, Ian and Peter made me
>quite ashamed of myself for having such an attitude. The amps
>list server gives me a chance to share what I can and make up for
>some lost time. The servers I have pages on are another location
>for myself and others to share.
>
>cheers Dino
>skipp may wv6f
>http://sonic.ucdavis.edu
>http://pilot.ucdavis.edu
>
>####
>Below is a copy of the first Email I sent to Dino.
>[snip]
>From: skipp <skipp@pilot.ucdavis.edu>
>To: Dimtcho <dimtcho@attcanada.net>
>Hi Dino,
>I think I read your post on the amps list server. I was going
>to answer your there, but I've been crazy busy. Yes, I've
>re tubed some sb230's in my past. I prefer to keep them
>stock if I can, but they can be retrofit without a heart attack.
>You might also know there is the commercial 8560 tetrode
>available which is an exact physical size fit for the 8873.
>It's pretty much the 8873 tetrode version which would
>keep you from having to deal with a blower and the noise.
>My choice might be to find some of this tube type to save a
>lot of work.
>I see the 8560 on Ebay quite a bit, since it's not well known,
>you can buy them used and cheap. If your on a real tight
>budget, let me know and I'll look around for a good used
>one over here.
>Motorola and other commercial radio mfgrs were always
>using the 8560 and I can provide many circuit diagrams
>if you do go that way. You could run it or most any common
>tetrode grid driven and simply terminate the grid into
>a resistor. If you need drive voltage, the various grid swamp
>resistor values can be selected with a toroidal 1:1, 1:4 or 1:9
>input ratios. That would bring up your impedance and drive
>voltage to what ever you needed. Works on the 4cx250/350
>what ever you want to use.
>No tuned inputs...
>You would then be looking at a screen and bias supply. I
>feel the amplifier cabinet is large enough that you could
>find a transformer for them and fit it in with some careful work.
>There are people using the 4cx series tubes in grounded
>grid, but you should then try to use a tuned input. I have
>seen gg cathode driven tetrodes with a resistor in the cathode
>for swamping. Not my cup of tea, but they seemed to work ok.
>I would imagine the circuits distortion products are not as
>good as other circuits.
>
>hows that for starters..?
>73's
>skipp
>
>
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