20 Dec
1998
20 Dec
'98
10:26 a.m.
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Monday, 21 December 1998 11:12
Subject: Re: Electrical knowledge, was Another ~1960 computer kit
Never heard of a DY86, but yes, either that or the damper diode. Can't
remember.
Creeping senility.
A screwdriver
(insulated handle!) blade touched to the top cap of the
1S2 would produce a healthy arc when held somewhere near chassis
1S2 = DY86, I believe. OK, I understand now - that's the EHT rectifier,
right... Normally just holding the screwdriver up to the cap
would draw a spark -
you didn't need to have it anywhere near the chassis. And if you didn't
get a spark, you removed the top cap connector (anode) and tried again -
to the connector. A common fault was that the diode valve would
short-circuit, thus effectively short-circuiting the AC EHT via the
capacitance of the CRT.
Sounds about right. Murphy.
if the line/eht stage was running. This
practice did not survive the
transition
to solid state devices that disliked the spikes etc it could cause!
No, indeed. Producing sparks in transistorised TVs/monitors is a good way
to blow semiconductors all over the chassis. When I was working on a
Barco monitor (actually off a classic-computer graphics display system),
I had an EHT flashover to my fingers (ouch!!) which took out a couple of
transistors in power supply unit. Some valve output transformers could match pretty low
loads. The famous
Williamson transformer has 8 secondary windings which can be wired in
series/parallel to match down to <1 Ohm, I think.
I've seen 3 ohm secondaries on valve gear, so that sounds possible.
The 1930's radio it was in had a field coil loudspeaker, first one I ever
saw.
Cheers
Geoff Roberts
Computer Room Internet Cafe
Port Pirie
South Australia.
netcafe(a)pirie.mtx.net.au