LF: Re: Farnell H60/25 PSU

["James Moritz" <james.moritz@btopenworld.com>]

Dear Mal, LF Group,

> Hi Jim/M0BMU es co
> Do you have a cct diagram for this psu Farnell H60/25. I bought one 
> recently and could do with some cct info.

I have been working away from home for some weeks, hence the delay in 
replying... I have scanned the schematics for this PSU and they can be 
downloaded as a pdf from:
http://dl.dropbox.com/u/50525290/FarnellH6025.pdf

I have used this PSU for some time to power my Decca TX. There are some 
things you should be aware of:
It uses a thyristor pre-regulator with linear output regulator - quite a 
popular configuration in its era for high power PSUs. The thyristors are 
connected directly in series with the mains input. The switching waveforms 
result in high peak mains currents with flickering house lights etc., which 
might cause MCBs to trip with modern domestic wiring. It has a hefty mains 
RFI filter with 0.1uF capacitor from L - E, which might also trip modern 
RCDs
The regulation is pretty good for slowly varying loads, but it does not like 
on-off keyed tramsmitters as a load. Going abruptly from zero to full load 
causes a  large transient dip in output voltage. A large electrolytic 
capacitor across the PSU output is helpful.
To make it work, the external (analogue) programming inputs on the back 
panel terminal strip have to be correctly linked. For normal operation, the 
links are B-C-J, D-E-F, G-H-K.
Over the years I have had to replace all 4 pass transistors in the output 
regulator. These usually fail s/c, which causes the PSU to shut down.
Cheers, Jim Moritz
73 de M0BMU