Bush vintage radio DAC90A.

[60 oldjohn]

Originally Posted by Paul_RK

Good advice unless the set is from fairly late in production, in which case there aren't any retaining screws for the front knobs and they do pull off. Rotate one of them while shining a torch through the nearest hole underneath and you'll soon see whether or not a screw is used.

Paul

Hi Paul, You learn something every day. Are these the knobs with perspex inserts ? I've seen plenty DAC90/A knobs with chips from attempts to lever the knobs off.

John.

test valves first

Why? Most valves are fine and where to test? (If I wanted to test a valve it would require a bit of a ride to Gerrys to put them on his tester) With a meter any dodgy valves will be obvious, if there are any. I have only had one properly dud valve in all my restorations.

[Glowing Bits!]

The reason for testing is incase I need to buy a new one, it allows time to do the rest of the work.
I have a basic emissions and shorts tester which showed a fault with a valve in a DAC90 without the A, it had no cathode!

[kalee20]

Originally Posted by merlinmaxwell

Why? Most valves are fine … With a meter any dodgy valves will be obvious, if there are any. I have only had one properly dud valve in all my restorations.

I'd agree, valve faults are rare in radios, and in-circuit measurements will reveal if there is a problem.

Just treat each valve as another circuit component, albeit one which is less likely to be faulty (which means you'd suspect other items ahead of the valve).

[ms660]

UL41 anyone.

Lawrence.

[Radio Wrangler]

I see your UL41 and I'll raise you ECC85! But there isn't one of those at least in a DAC90.

There are relatively few famously short-lived valves. Who knew, back in the days of new sets, when valves were specifically excluded from warranties?

David

[ms660]

Back in my TV servicing days, at least the Mullard top ten/twenty were in my service van.

Lawrence.

[Paul_RK]

Originally Posted by 60 oldjohn

Hi Paul, You learn something every day. Are these the knobs with perspex inserts ? I've seen plenty DAC90/A knobs with chips from attempts to lever the knobs off.

John.

Hi John,

Yes, I've never met screws on the last generation of DAC90A front knobs, those with the perspex backing disc. I've a feeling screws were used on the intermediate knob type, the chunky ones that don't taper toward the front: probably I've a set that uses them hiding somewhere, but can't at present find one to check.

[Heatercathodeshort]

I may be mistaken but I'm sure there is a version of the DAC90 that employs a PX4. The model number is DAC90P. I have one somewhere but it would take months to find it. I suppose they substituted the PX4 due to the UL41 playing up. John.

[Herald1360]

Could a PX4 even physically fit in a 90A? Maybe a 90? The filament would be a major mismatch let alone the gain and the load impedance required.

[Station X]

This thread is getting silly and recent posts are of no help to the OP.

[HamishBoxer]

Start with checking any caps that have been changed for correct values, after that checking resistance of mains dropper .
After changing UL41 grid coupling , then remove replace cap across mains input with the correct type.
Then , having made sure o/put transformer is ok, measure voltages, starting from the smoothing cap.

NOTE, this set has a "LIVE" chassis. If in doubt use an isolation transformer. If you have no experience in valve set repairs, pass on to someone who can safely service it.