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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