17 Oct
2008
17 Oct
'08
10:50 p.m.
----------Original Message:
Message: 28
Date: Fri, 17 Oct 2008 18:01:40 -0700
From: "Chuck Guzis" <cclist at sydex.com>
Subject: Re: Req: Help/Advice on Cromemco System
On 17 Oct 2008 at 12:21, Dave McGuire wrote:
Brute-force linear is definitely the way to go.
I'd be tempted to grab a couple of filament transformers, a couple of
bridge rectifiers and some big caps. The great thing about S100
power supplies is that PSU regulation isn't important. A 6.3VAC
filament transformer hooked through a bridge rectifier and a big
electrolytic should be close enough. +/-16 could be furnished by a
small 12.6v transformer.
The real job of regulation is furnished on each board (usually
something like 78xx 79xx linear regulator ICs).
Cheers,
Chuck
--------------
-----------------Reply:
A misunderstanding, I think: he's talking about shorting out the
regulators on the *cards*, not in the PSU, and running regulated
+5 & +/-12 on the bus; should be doable with a heavy enough
bus and sufficient bypassing, in fact I think some manufacturers
did indeed do just that.
I have a Cromemco PSU BTW, but probably not worth shipping.
mike
Since I have
been unable to find any power supplies which provide
the +/- 8 and +/- 16 volts, I just thought of an idea the other day
of using a PC power supply and shorting out the on-board voltage
regulators to allow them to work at the +5V and +12V of the power
supply. In order to do that though, I would need a small (3-5
slot) motherboard to test a couple of cards together.
I don't think it's going to be possible to short around the +5 and
+12 regulators in a PC power supply, as they're not discrete in that
way. Your best bet (IMO) is to surf eBay for an big open-frame
linear power supply. 
18 Oct
18 Oct
9:19 a.m.
On Oct 18, 2008, at 1:50 AM, M H Stein wrote:
Brute-force linear is definitely the way to go.
I'd be tempted to grab a couple of filament transformers, a couple of
bridge rectifiers and some big caps. The great thing about S100
power supplies is that PSU regulation isn't important. A 6.3VAC
filament transformer hooked through a bridge rectifier and a big
electrolytic should be close enough. +/-16 could be furnished by a
small 12.6v transformer.
The real job of regulation is furnished on each board (usually
something like 78xx 79xx linear regulator ICs).
A misunderstanding, I think: he's talking about shorting out the
regulators on the *cards*, not in the PSU, and running regulated
+5 & +/-12 on the bus; should be doable with a heavy enough
bus and sufficient bypassing, in fact I think some manufacturers
did indeed do just that.
Hmm yes, upon giving the original message a second read, I'm sure
that's exactly what he meant.
The only drawback to his approach is that the boards will make
smoke if used in a "standard" S-100 chassis later on (in case someone
forgets).
-Dave
--
Dave McGuire
Port Charlotte, FL
Since I have
been unable to find any power supplies which provide
the +/- 8 and +/- 16 volts, I just thought of an idea the other day
of using a PC power supply and shorting out the on-board voltage
regulators to allow them to work at the +5V and +12V of the power
supply. In order to do that though, I would need a small (3-5
slot) motherboard to test a couple of cards together.
I don't think it's going to be possible to short around the +5
and
+12 regulators in a PC power supply, as they're not discrete in that
way. Your best bet (IMO) is to surf eBay for an big open-frame
linear power supply. 
10:09 a.m.
On 18 Oct 2008 at 1:50, M H Stein wrote:
A misunderstanding, I think: he's talking about
shorting out the
regulators on the *cards*, not in the PSU, and running regulated
+5 & +/-12 on the bus; should be doable with a heavy enough
bus and sufficient bypassing, in fact I think some manufacturers
did indeed do just that.
Ah, I understand. Seems like a lot of bother when a plain
unregulated linear supply would do the trick and maintain a certain
measure of "authenticity", whatever that might be.
Cheers,
Chuck
19 Oct
19 Oct
8:10 a.m.
On Oct 18, 2008, at 1:09 PM, Chuck Guzis wrote:
Not to mention reliability!
-Dave
--
Dave McGuire
Port Charlotte, FL
A
misunderstanding, I think: he's talking about shorting out the
regulators on the *cards*, not in the PSU, and running regulated
+5 & +/-12 on the bus; should be doable with a heavy enough
bus and sufficient bypassing, in fact I think some manufacturers
did indeed do just that.
Ah, I understand. Seems like a lot of bother when a plain
unregulated linear supply would do the trick and maintain a certain
measure of "authenticity", whatever that might be.
5909
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