Bush BP90

[Joe]

I won this set last Friday and is arrived, safely, on Wednesday.
       

I'd been out and about on Monday, chiefly to pick up a Murphy U198H, and while I was in town I bought ten PP3s so soldered these together and gave the radio a quick try. It worked very nicely as was.

   

Since then I've given it a good clean and polish. Electronically I've only changed THAT capacitor as it needs several of which I'm out of stock. The 2μF HT reservoir is also leaking and is the biggest single capacitor I've ever seen, apart from those on motors.

All told I've very happy with it as I've wanted a battery valve set and a DAC90 (rather than the 'a' version) so this more or less fulfils both desires.

I've got a few ideas for a battery eliminator floating around my head which will add further interest to it.

The Murphy is still largely un-touched but I have discovered that their 'mad' reputation is well-earned!

[tiv48]

lovly set jo
at the moment i am trying the idea of a voltage tripler circuit runing from a 1kc multivibrator have not got the cap values right yet
but it may work i will let you know
rob t

[Tedzed1]

That looks rather nice Joe, and it's a little bit different, well done.

[Yorkie]

Well done on winning that Joe.

An interesting set, which came out immediately after WW2, launched in 1946, using low consumption valves. The HT consumption is only 9mA, and the LT 250mA. Expensive when first launched - £14.14s.0d plus 33% Purchase Tax, but reduced in price in April 1949 to £13.11s.4d, including batteries, (PT extra).

From serial No 13/15001 there were several modifications, which included altering the battery wiring so that separate LT and HT batteries could be use - apparently due to difficulties in obtaining combined batteries. (Unlike Ever Ready, Vidor etc, who had a vested interest as battery manufacturers, and sold radios as an aid to that, Bush on the other hand, will have had a vested interest in trying to ensure economical battery consumption).

I think that combined batteries were a similar con trick to the present day situation with some printer ink cartriges which are often combined in one unit, so if magenta runs out but you've got plenty of cyan and yellow left, tough - the whole cartidge has to be replaced, and often, you can't print black either till a new colour cartidge is installed. Same I guess must have applied to combined batteries, if the LT ran down and there was some life left in the HT. Valves are quite happy to work on much lower HT voltages that a fresh battery - say down from 90V to 60V, but soon fade when the LT voltage drops.

You're right about the very large 2uF smoothing cap. Unlike in a mains set, where it might need a high ripple rating to smooth the AC, that doesn't apply in a battery set, and that is recognised by the low value of 2uF. A modern replacement will be puny by comparison, so no doubt you'll need to stuff the old one, with oodles of space to spare!

Enjoy the set Joe- it's polished up very nicely!

David

[Joe]

Thanks, David. I was listening to it earlier. That leaky capacitor means I need to disconnect the HT when I switch it off. As for restuffing, I think I'll just hide the new one behind the old as it looks like it would be a devil to get into.

I'd thought the exact same thing about the combined batteries. Mine is one of the later version meant to have separate ones.

I'm certainly pleased with it and as I haven't really done anything to it yet there's scope for further improvement.

- Joe

[Joe]

I've now finished re-capping this. When it's switched off though there's still 2mA of HT disappearing somewhere.

The switch only disconnects the LT positive and I was wondering if there'd be any harm in using the spare pole to break the HT.

- Joe

[Yorkie]

I've now finished re-capping this. When it's switched off though there's still 2mA of HT disappearing somewhere.

The switch only disconnects the LT positive and I was wondering if there'd be any harm in using the spare pole to break the HT.

- Joe

That's odd, because the only path to ground from HT would be via C2 or C17 on the Maker's circuit. The only other place that the HT could be leaking to chassis is via an inter-electrode path in one or another of the valves.

It might be worth removing one valve at a time while monitoring the HT current, to see if the culprit can be found.

It was normal practice of course to only switch the LT, because with no volts to the heaters, the valves go to sleeep and no HT should be drawn.

That's the theory, but of course the difference between theory and practice in practice is greater than the difference between theory and practice in theory, if you get my drift!

No reason why if theres' a spare pole on S3, that it can't be used to switch the HT if desired.
David.

(Who is pleased that it is now raining here in biblical proportions, which I hope will cool things down a bit. 25C outdoors, 27C indoors at present).

[Joe]

Send the rain westwards when you've done with it please!

It's odd but from what circuit diagrams I've been able to find it looks like other manufacturers DID switch both batteries, certainly Roberts and Ever Ready did, despite the latter having a vested interest in batteries not lasting.

Right, I can get that one put back together properly now.

Thanks
- Joe

[Bushbaby]

Hi Joe,
That a nice set and the early forerunner of the DAC90.

Well done

Regards

Rob