Another DAC90A - back from the dead!

[ajs37]

I have been trying to get into the garden for the last 3 weeks, without much success, so I have had time to organise my workshop, finish off some jobs and pick a radio to restore from my 'reservoir'.

I picked on a DAC90a that I had previously taken from its' knackered cabinet and proceeded to check it over.

My first thought was; why didn't I pick one of the other DAC90s to do? This one looks like it has been left out in the rain for a few years, then kept in a damp shed!

Anyway I started, so I decided to finish, however long it took.

Briefly:
- changed the waxies, they were all well out of spec.
- checked the electrolytic tub, seemed ok.
- mains switch (volume control), knackered - bypassed for now.
- speaker coming away from its frame for about 90 degrees at the bottom edge and coming away near the magnet (not the cone, but the surround).
- chassis, looked like it had been attacked by a tin worm!

I used a lamp limiter to power up. Lo and behold, red glows in the valves and some noise from the speaker, not much hum but plenty of audio, no RF though. Some noise from the wavechange switch sometimes. Time for some valve waggling! V3 made lots of noise when waggled, even got a bit of RF but could not sustain it. OK, clean the valveholders and a chance to use my newly purchased DeoxIT spray (available from all good BVWS stalls).

However, on examining the valveholders, I noticed that some of the pinholders were distorted, so they would not be making very good contact with the valves. The valveholders were made by Morganite and I have had trouble with these before. Nothing for it, I had to change all 5 valveholders and that took all afternoon. I used some holders that I had bought from a French guy at NVCF a couple of years ago and they seem to be fine (didn't cost much either).

Applied power again and Radio 5 coming in loud and clear with no hum! No need to re-align as every station was in the right place and coming in strong.

- Changed the switch on the volume control (exchanged with a spare of the same make).
- cleaned the chassis.
- re-sleeved the wiring around the mains dropper.
- greased the tuning mechanism.
- cleaned a DAC90A cabinet / knobs etc (whose chassis is awaiting an output transformer replacement).
- mounted the dial, using plastic sheathing on the 2 long edges (cheapskate!).
- glued the speaker cone back (used Gorilla glue).
- put a proper fixed mains cable on it (2 core at the moment, may put in a 3 core and earth the speaker).
- found a clean back and some screws.
- put it all back together again - job done in less than a day.

I didn't take any 'before' photos and I'm not showing underneath the chassis as my soldering there is not my best. It is sound, it just isn't as attractive as I would like! Anyway, the photos show the old valveholders and the finished chassis and radio.

Not the most difficult of repairs, but replacing valveholders is a pain in the neck and to have to replace all 5 - ugh!

PS: just been checking another DAC90A chassis and the UL41 and UY41 valves have OC heaters! May have been caused by the voltage adjuster being set to 230volts (I did change it before I applied power).

Cheers,
Andy

[HamishBoxer]

Andy, it looks excellent!

David

[Steve_P]

Well done. These sets will always just work!

As for the PS - Setting the heater volts at 230 won't have caused that. Somebody in the past has been valve swapping at a guess. There are no little capacitors to deck in between the valve heaters here, so I'd check the wiring and the resistance. Or maybe V2 Heater-Cathode short.

Cheers,

Steve P.

[vinrads]

Very nice, lucky to have five good valve holders they look new! well done.

Mick.

[Tim]

Nice job Andy.
Those green droppers are generally OK, and the smoothing cans in these sets usually re form too. Your completed resto gives me hope to do mine!

[kalee20]

Originally Posted by ajs37

The valveholders were made by Morganite and I have had trouble with these before. Nothing for it, I had to change all 5 valveholders and that took all afternoon.

Bit late for you, but the Morganite B8A valveholder uses the same pins as their B9A valveholder. It is easy to just do pin swaps! I like these holders, but I agree that corrosion doesn't do them any favours.

Good work with the DAC90a. They do seem to come back from the dead rather well!

[ajs37]

Thanks for the comments.

It does look good in the photo, I have one of those cameras that makes everything look good (apart from me!)

I will check the valves using the Mullard HSVT, Steve, thanks for the pointers.

The valveholders are new, Mick, I remember being very surprised to find them at NVCF and I have tried the pin swapping trick before, but there were just too many faults to correct. Good tip though!

Thanks again.

Cheers,
Andy

[dazzlevision]

Hello,

Aren't the valveholders made by McMurdo rather than Morganite?

Regards,

Dazzlevision

[ajs37]

Just retrieved them from the bottom of my workshop bin, before emptying into the main bin - and you are right, they are McMurdo. Apologies to Morganite!

Cheers,
Andy