View Single Post
Old 5th Dec 2017, 12:08 am   #4
JasonKillbourn
Retired Dormant Member
 
Join Date: Dec 2017
Location: Potters Bar, Hertfordshire, UK.
Posts: 14
Default Re: DAC 90A Smoothing Capacitor replacement

Thank you Tony and Mike for your kind replies, I should be able to make it down to Cricklewood on my travels either tomorrow or Wednesday, so I'll definitely try to get those capacitors.
As regards the X2 rated capacitor, that one is included in the repair kit I ordered the other day, which should be turning up shortly, along with a C18 replacement. In fact, here's the spec.

5x 0.047 (473) to replace 0.05
3x 0.01 (103)
1x 0.001 (102) this is to replace the 0.003 for improved sound
1x 0.1 (104) this is x2 rated 275 volt ac

So, hopefully with the addition of the 33uF and 16uF ones, that might cover the capacitor situation adequately? Then of course there's the question of resistors, so I should really get busy with the multi meter and draw up a shopping list, especially if I am going to Cricklewood, as it looks like they might be a one stop shop for those too. Speaking of which, has anyone got any advice on the choice of resistors?

Other than that, there's only some disastrously degraded insulation on the wire from the mains dropper that clearly needs replacing, but I've got an old iron in the cupboard that I didn't get round to throwing away, which I can probably salvage some suitable wire from its power cord, so that shouldn't be a problem.

Then of course there's the valves themselves, but I guess I'll see how the radio performs after the caps, resistors and wires are taken care of first. However, I haven't removed any of them yet, as I did give them a gentle pull and they seemed pretty firmly stuck in place, so I'll definitely bear your advice in mind about the spring rings and proceed with caution, especially as there's a fair bit of rust in evidence and those springs might possibly be corroded and sticking.

On the subject of the lights, I've got two bulbs coming with the repair kit, but the advice on those seems quite varied, and seeing as they're getting a bit thin on the ground, I think I'll stick with the standard 75ohm resistor, as a dim glow doesn't bother me too much, though I might toy with the idea of removing the flammable celluloid diffuser screen and replacing it with a bit of light frost lighting gel, as I am pretty certain I've got a roll of that somewhere in my garage from when I closed my old studio (I was a studio photographer for years). I suspect that it will do a perfectly good job of diffusing the point source of the bulbs, but will allow a little bit more light through.

Finally, there's the lack of LW, but I guess there's a good chance that might come back with a thorough clean up of the selector switch, so fingers crossed on that.

As regards the issue of safety and the live chassis design, that was what actually what lead me to this forum, as the first thing I noticed about the radio was the peculiar, and rather worrying, reversible mains lead plug and two pins on the back, which started me googling the DAC 90A in the first place.

Anyway, thank you again for all the advice, it's much appreciated. I shall certainly let you know how I get on
JasonKillbourn is offline