6 Sep
2008
6 Sep
'08
3:26 p.m.
Subject: Re: vac tubes / was Re: Schematics of Atanasoff-Berry
From: ard at p850ug1.demon.co.uk (Tony Duell)
Date: Sat, 06 Sep 2008 21:34:08 +0100 (BST)
To: cctalk at classiccmp.org
12AX7 at 12.6V @.15A (1.8VA) or parallel connected 6.3V @ .3a and I consider
that trivial. A transformer sufficient to run 10 of those (18VA) is under
2-3pounds. The average 12V at 1A wall wart can run six of those with a comfortable
margin. We are not talking a lot of power yet. If we are in the realm of 100
or 1000 of those then we have some power needs to deal with.. The solution
there would be to use instead of one 12.6V transformer that can give 150A we
can use ten more readily available transformers of a mere 15A (189VA) which
is more manageable anyway.
That same transformer (assume 12.6V AC) could using a voltage multiplier
easily supply 40-45V where the valves would have a decent usable performance.
This is easy as those valves at 40-50V will only need a few milliamps per
plate circuit.
I know this as I built a 5 tube reciever (6AN8, 6AU6, 6BH6, 6CW4, 6dl6/ECL84)
for 80/75M and the whole radio fits in a 7x8 chassis and with the power
transformer and audio output transformer is under 6 pounds. The transformer
used was salvage but had a 150V 100mA winding and a 6.3V 3A winding (total
of 34VA) and that was not even stressed hard and weighed on at under two pounds.
Another example is 40 years ago I had a Beckman EPUT (events per unit time)
counter that used the then typical tube era 5mhz ring counter decades with
neon readout (0-9 with NE2 type neon behind them) (6 ofthem) plus timebase
for a whopping 42 tubes mostly of the 12AX7 types and it was big (19" rack
width by 11" high) but I distinctly remember it as barely 40 pounds
considering it was fully enclosed in a steel case and each decade
was in its own case that plugged into a matching socket in the cabnet.
Powering tubes in that class (ECC83s) is trivial compared to the day of the
ABC where typical dual triode was maybe in the class of 6SN7 (6.3V at .6A) or
worse. Early tubes where power hungry for heater power.
Allison
> I really don't understand this modern
love with making things as
> small and light as possile. I'd rather have things that are heavy
> enough to stay put (in the case of a rack unit, not to topple, or
> even feel wobbly when units are extended ot the maintenance position)
> and that are large enough for me to be able to work on them.
[For the record, I consider the OP's comment that he wants to use a PC
PSU becuase he has one or that it's convenient, or.. to be entirely
reasonable.]
Bigger and heavier means less items in your collection to fit in the
space, and a smaller number before the floor falls out from underneath
of it. I'd hope you could appreciate that. :)
So by that arguemnt we should all collect handhelds, not desktop and
rack-mounted machines :-)
Another problem I seem to have is that the
heavier an item is (and
harder it is to move myself), the less I seem to be able to find people
to help move it.
Fortunately I don't mind having to dismantle something to move it. Many
of my larger machines came into the house in small-ish pieces. I
remember, for example, dismantling a DEC RA60 on the back of a friend's
pick-up truck (fortunately the RA60 is dismantled from the top down, so
this wasn't hard), taking the bits inside and then putting them back
together.
Gettign back to the OP's heater supply, I don't think a mains-input
heater transformer to supply 5 normal-sized receiving valves is going to
make the device impossile to lift. If you used ECC83s (12AX7s), I think
you could use a 20VA transformer with no trouhle at all, and that's
hardly large or heavy.
I in no way said that I wanted everything made of
lightweight (and
easily breakable) plastic, it's just annoying when things are severely
over-enginered and thus increase the weight, or use heavier components
when lighter ones would work in a perfectly acceptable manner.
Well, there are limits, but I must admit I tend to admire solid
overengineered devices.
-tony