23-10-2015, 03:16 PM
(This post was last modified: 23-10-2015, 03:18 PM by Nowhere-Man.)
(23-10-2015, 02:11 PM)pwdrive Wrote: Don't forget that some of the old electrolytic cans contained the HT capacitors and sometimes the audio output cathode bypass capacitor, it pays not to get the connections wrong on those.
Lawrence.
You can see in the pic attached a German rectifier and smoothing circuit in a vintage German tube radio. The layout and design of the set is very different from vintage British sets. One other factor is it's a transitional set from mid sixties so part of the radio actually uses printed circuit board, including the tube pins of the other tubes soldered to PCB. I can't recall what the rectifier tube was on the German set.
When the idea of silicon rectifiers first came out in the early sixties, the fact was a lot of rectifier tubes were being discarded by HAM enthusiasts and silicon was considered a better alternative. I recently read some interesting comparisons between silicon rectifiers and tube rectifiers and am becoming inclined more towards silicon. Suffice it to say I got great results using semiconductor diodes with a resistor capacitor network.
On the HMV the rectifier is a standard U10.
I did make a few more tests with the U10 last night, especially the transformer leads. It kicks out close to 390 volts DC Ripple which is pretty high although the manual data states the workshop test result was about 380.
Objections were raised by some other posters about my testing the H.T. smoothing can on the HMV. This simply involved charging the 16 mF capacitor and then also testing how long it took for the charge to dissipate across a lamp. I've found differences in these tests between different sets and was curious.
I was likewise curious over the rectifier wiring on the HMV and it seems I may well modify this to see if I can improve on the original layout. I did like the use of 2 one amp fuses in the mains supply on the rectifier mounting platform but some things about the rectifier layout I don't like as it stands.
As for the German set, nothing beats German engineering at that time.
