small valves and RE: OT

[Allison]

>
>Subject: Re: small valves and RE: OT
>   From: ard at p850ug1.demon.co.uk (Tony Duell)
>   Date: Sat, 23 Apr 2005 23:45:16 +0100 (BST)

>It would be interesting to know what's going on in this set. Can you get 
>a schematic? Being an American set, it's not in Poole and Molloy :-(

It's an RCA 8BX5  lineup is 1R5, 1U5, 1T4, 3V5 and 117Z4 if memory serves.
I don't have the schematic for the set.  I expent I could find it if needed.
Being functional I'm reluctant to tear into it and hand draw the schematic.
If it breaks I will.  Believe it or not I use it to listen to local station
for ball games.


>It's one of the better electronics magazines available over here. It has 
>some interesting projects, and they've now started making microcontroller 
>source code available for most, but not all, of them. 

I know the magazine, rarely see it.

>The circuit in question was a pretty standard inverter circuit, running 
>at about 50Hz (not a typo, they wanted to keep RF noise down), feeding a 
>normal mains transformer used in reverse. Looks like it should work with 
>no problems.

I've done this before.  The simple version use saturated switching 
transistors and tend to have high noise due to high current spikes
from charge storage in the transistors. I usually run them at 
100-400HZ with a common mains transformer for better filtering 
and use a bit of feedback to run the switch transistors such that 
they are turned off before the core saturates.  The end result 
is less current, better efficientcy and less noise. 

It's a  side effect of my years of working with older commercial
VHF/UHF twoway radio that used things like vibrators, Dynamotors 
and even transistors for generating HT. Often the hybrid and tube
radios would be in service for years after expected retirement
do to replacement cost.  The result was desinging and implmenting 
replacement circuits that would replace sometimes hard to find 
hardware, especially those dynamotors.


Allison
Kb1gmx