29 May
2013
29 May
'13
1:15 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 29 May 2013 19:46
To: cctalk at classiccmp.org
Subject: Re: Spec of Motorola 7339 Transistor
current
After my stupidity it started to run open
(chatter) in local mode as
well as line mode. But this could simply be because two of the fuses
blew. I have
Yes, it might well be.
One of the big differences between most UK(Creed) and American
(Teletype) amchiens is that the fobmer use double-current signally (a one way for a mark, the other way for a space), the
latter use
single-current
signally (curent = mark, no current = space). In the
case of the Model 33,
if
the receiving magnet driver loses powre (maybe because
the fuse has
blown...), there will eb no current through the receiving magnet and the
machine will 'run open' (or 'space out' or whatever you want to call
it).
> new fuses on order and I hope they will be here soon. It was suggested
> to me (and you said it too) that transistors fail faster than fuses
> and that this would be an obvious one to test. I thought the voltages
> I reported to you were suspicious, didn't you say they indicated it is
leaky?
It looks leaky, but it might well be germanium and they tend to leak
anyway.
I am wondering what my first step should be once I get the fuses. Just
turning it on would seem a bit risky. I could do the light bulb trick
to limit current perhaps, someone suggested I do this, but disconnect
the motor as it will try to draw too much current.
I don't think you wil ldo any real harm by fitting the correct fuses and
powering up. There are no custom, delciite semiconductors in a Model 33,
You are not going to burn out the receiving magnet either. The worst that happen is the new fuses will blow and maybe some small
components in the
manget driver.
Amazingly (given my normal caution) I would fit the fuses, power up and
see
what happens.
Indeed, this does surprise me! :-)
-tony