4 Jun
2002
4 Jun
'02
8:36 p.m.
On Tue, 4 Jun 2002, Sellam Ismail wrote:
So I'm off to look for a 25L6 tube for my IBM 026.
John Lawson says
that the tube is a 25L6 because all the other tubes in the rack are
25L6 types and he believes they are hammer drivers. Not to doubt the
venerable Mr. Lawson, since he did used to service these, but I just
want to make sure this is in fact the right tube type that goes into
the socket that is currently empty. See photo here:
I'm fairly certain it does use a 25L6. According to all the information I
found online, IBM often used them in groups of 6 for counter/multiplier or
driver applications. Without seeing prints, there is no way for me to know
if they used them as drivers or counters, but either way, I doubt the
punch will work very well with a missing tube.
Do the heaters of the other 5 tubes in the same row glow? IBM may have
used 6x 25V heaters in series to avoid using a voltage regulator. If you
find a source for the 25L6, and especially the IBM branded tube, get at
least a couple of extras. Tubes are generally very robust, but they don't
like being jarred around, and theres no telling what kind of abuse the
current tubes have been though.
According to this usenet article from 1995, the 026 used 6 25L6 tubes in a
row as drivers:
http://groups.google.com/groups?as_umsgid=41nefs%241a90%40bigblue.oit.unc.e…
This article states basically the same thing:
http://groups.google.com/groups?as_umsgid=3C194D05.143E4168%40zianet.com
I'd hate to plug in the wrong tube and then
witness volumnious amounts
of smoke billow from within the machine. Can someone verify that the
25L6 is indeed the correct tube for the empty socket?
Well, the tubes are not likely to smoke, but old capacitors are... I'm
guessing that you've already powered the unit up by now, but I'd recommend
using a variac to bring the voltage up slowly when first powering up old
equipment such as this when it has been stored for a long time. Bringing
it up to full voltage slowly allows slow reformation of older caps that
would otherwise fail with a loud 'bang', which would usually take a few
other parts (most often resistors) with them. Note that modern equipment
often does not like this procedure, especially when it uses a SMPSU.
-Toth