DAC90a Number Three.

[Joe]

Thanks, Rob. Nothing very revolutionary yet. I've stuck the main break with epoxy and it's currently clamped up.

   

- Joe

[Joe]

Well that stuck OK:-

   

The next job was filling the chips.

I rubbed some wood on rough glass-paper, across the grain so the resulting dust was quite fibrous. I then stained that and left it to dry:-

   

I then mixed that with epoxy and used this as a filler.

The colour-match isn't great but I'm hoping it will improve with polishing:-

   

There's now the crack along the bottom left edge to attend to.

On the electronic front, I've ruled out the rest of the valves. I changed the fixed tone corrector which, like the AF coupler was leaky but not too bad - the neon in my AVO bridge flashed whereas it usually just lights up and stays on. It's sensitive enough so I will direct my enquiries toward the AF stages - then get the scatter-gun out.

- Joe

[Joe]

I've been doing some more on this today. The case isn't perfect but is about as good as I think I can get it.

   

As for the electronics, the RF bypass cap caused the AVO Bridge to flash like a strobe. Changing that improved the volume but it still seemed quiet.

I then screwed my courage up to the sticking plaster and tested the UL41 grid with the VVM. I couldn't see it doing any harm as that is isolated so should have been at no more risk of going bang than anything. This proved to be the case and there was over a volt on the grid so that got changed.

I still didn't like having the old capacitors in place so checked the V2 and V3 cathode bypass cap and found that to be the leakiest to date.

I'll try and please Mark and leave the rest along but to me it looks like a job half done and I can't help but think it's spoiling the wireless for a quid's worth of caps and five minutes time. We shall see.

Here's another photo which gives a better view of the rewiring and the chassis after a bit of a clean:-

   

- Joe

[Bushbaby]

Joe,
The case looks good, you appear to have made a good job of it. I'm sure that you'll have that mains dropper smoking nicely as the set bursts into life.

Rob

[Mark R]

I'll try and please Mark and leave the rest along but to me it looks like a job half done and I can't help but think it's spoiling the wireless for a quid's worth of caps and five minutes time. We shall see.

- Joe

Looking good Joe. I suppose changing all the caps is up to each Individual. Personally I do not, unless it is "that" cap, which I always change. The rest on the HT line get checked for leakage. Just the way I was taught.
If it still does not work the set is fault found stage by stage, like the KB Toaster. I guess it just helps me understand the radio and the circuit.
I know there are many advocates of changing all the waxies/hunts on sight, but the cost can soon mount up if you do a few radios a month.

Just my thoughts

Cheers Mark.

ps PUT THAT SCATTER GUN AWAY YOUNG JOE!!

[Aerodyne]

Neat case repair, Joe. Are you sure all the valves are OK? Running on too low a mains setting will have overrun them and inevitably shortened their lives. I din't like wax-coated caps, especially not the ones found in Bush DAC90A's, so I tend to change them all - bearing in mind that they'll be the best part of 60 years old and that they do tend to deteriorate with age as well as poor storage. After this, I'd do voltage checks to see if any resistors are way off spec before checking to see if the phantom alignment fiddler has been up to his tricks. Sometimes the fault you encounter is the reason the set was discarded in the first place.
Finally, caps across IFT windings and dampness or corrosion in the RF and IFT coils can all contribute to low gain.
Just my take on things. Each to his own!
-Tony

[Joe]

I've put it back together to give it a better run:-
   
I'm not calling it finished yet as for one thing I want to up the dial lamp shunt a bit. I've also fallen victim to horizontal gravity again. One of the bits of Bakelite into which the chassis retaining screws go has snapped off. There had been an attempt at gluing that back so I spent some time cleaning it up but now can't find it. Besides that more polishing won't go amiss.

I've changed all the valves one at a time and, apart from the rectifier and output ones, these swaps made no difference. It's certainly loud enough, in fact my other brown one is too loud.

I think the AF alignment may be a smidge out as the stations aren't in quite the right place.

It's certainly been fun and I agree that not just going mad with the side-cutters teaches you more; the two bypass caps I have changed were tested after looking at the diagram so I must be getting SOME idea what I'm up to.

- Joe

[Tedzed1]

Hi Joe, instead of upping the shunt, you could try a couple of these from Maplins.

http://www.maplin.co.uk/round-mes-type-e10-1977

You need 6V 0.6W, they worked a treat in the one I had,
If you have not got a local Maplins, I could pick you a couple up, and pop them in the post.

[Yorkie]

You've certainly done a top job on the cabinet Joe - a marvellous transformation!

You wrote:

"I think the AF alignment may be a smidge out as the stations aren't in quite the right place"

Small typo - you obviously meant RF alignment.

Just so you know I'm paying attention!

As to replacing the waxies, one of the good things about the DAC90A is that at least they're all accessible on the tagstrip, whereas on some sets they're amongst a rats' next of wiring, often calling for other components to be disturbed. In such cases the 'Col Coiler' really comes into its own - just snip off the old cap leaving about 1/4" of the wire ends in place, coil the wire ends on the new cap, slip it over the old wires and solder in place. Minimal disturbance, minimum time and effort. Such a simple and clever device - a real spark of genius!

[Joe]

Well spotted, David.

Thanks for the tip and offer, Paul. There are a couple of Maplin's in Sheffield but I think I'll be able to get the same rated ones cheaper from Bardwell's. There aren't on the web-site but that's nothing to go on. They do have listed 2.5V 0.2A and 6V 60mA so at 13p each it may be worth blowing some up.

When I first started fiddling I got two 6.5V lamps from Maplin's which cost around a quid each and one blew as soon as it was connected. As it went white it obviously hadn't been sealed properly.

I've got the DAC90a on now playing Paul Jones's Radio Two programme thanks to the radio on my 'phone and a pantry transmitter. It certainly sounds pretty darned good.

- Joe