Bush SW41 - just starting

[coopzone]

Hello,

I'm just beginning a repair/restoration on a Bush SW41 from 1937.

I have completed a list of the pre startup stuff:

1, remove old mains cable - temporary one in place. Including an earth to chassis.
2, check switch on volume on/off
3, check for open / short circuit in the transformer.
4, check for leakage to chassis.
5, check short/open circuit at plug top.

Then

6, removed all valves.
7, powered on via a lamp, all looked ok so..
8, power on normal, 1 amp fuse in plug.
9, checked transformer output. All good.
10, left running just the transformer, to make sure it does not get hot (short in transformer)

Then

11, put rectifier back in, after disconnecting reservoir capacitor (it's a duff anyway so will need replacing.
12, added temporary capacitor in.

At this point since i don't have a speaker yet, i can't go much further.

13, Put a 2k resistor in place of the field coil.
14, added a temp replacement for the smoothing capacitor.
15, powered back up and everything is about right.

Checked out the controls and mechanical bits and pieces, cleaned, lubricated etc. And all look on for now. Except for the 50k tone control - i think some one has attempted a previous repair on it - not good, bit's missing. I've posted a request for a new one if anybody has one!

So before I continue, next stage is to rig an output transformer and speaker then get the output stage working.....

Anyone worked on these sets before, any gotcha things i need to know about?

anyone got the following:

control knobs for it?
speaker?
New tone control?

Thanks

Derek

[Mike. Watterson]

I'd have checked more capacitors before adding valves.

[coopzone]

I did actually checked all the caps, and so far only one valve back in place the rectifier and thats had all the relevant capacitors replaced. But good point anyone looking to repair a radio like this should check, double check, take it slow and always look at the safety first!

I'm going to have a go at re-stuffing the original card-box condensers - as they are called. Attached photo of the stripped boxes ready for the new caps to go in.

Derek

[crackle]

Dont forget to change C17 and C19 (Trader) before putting the output valve back in.
Probably worth while to also change any other wax paper caps, it is not even worth checking them in a radio of this age.
C15, C18, are likely to need replacing.
Mike

[Ed_Dinning]

Hi, note that the AVC capacitors (usually below the earth rail on most schematics and connected into the grids of RF and IF valves). These are on a high impedance rail and although they have very small voltages across them can much reduce a set's performance if leaky. They do not need to be replaced with expensive 630v caps, 50 volt miniatures work just as well here,

Ed

[coopzone]

Hello, Update time - it's working!

Still needs a lot of work, but all three bands up and running.

Does anyone know where i could get a 3k 10watt resistor from?

Derek

['LIVEWIRE?']

You almost certainly will not get a 3K of any wattage now. The nearest 'preferred values' are 2k7 or 3k3 - I'd be inclined to opt for the latter, which should be available from the usual suppliers such as CPC, Farnell or RS.

[ajgriff]

Might be worth considering if you don't mind waiting a while:

https://www.ebay.co.uk/itm/10W-Watt-...2a906c9e32c0ad

Alan

[coopzone]

Thanks Alan, while i was looking at that link i spotted someone selling a 3k 10 Radio Spares (new old stock) one for a £2.00 - so I went for it.

The phot show the resister fitted and working, it arrived at 10.30 today I fitted it in my lunch break! No patients ! - no wait - if that where true i would have fitted it on my coffee break at 10.31.

Derek

[ajgriff]

Good result!

Alan

[Herald1360]

Originally Posted by 'LIVEWIRE?'

You almost certainly will not get a 3K of any wattage now. The nearest 'preferred values' are 2k7 or 3k3 - I'd be inclined to opt for the latter, which should be available from the usual suppliers such as CPC, Farnell or RS.

3K0 is a standard E24 value. Nearest E48/E96 value is 3K01. RS do several but only up to 9W.


Easiest would be two 1K5 in series- 6W Welwyn W22 is one possibility.


Edit: Just noticed problem solved anyway, but 3K0 comment still valid.

[coopzone]

First of all, thanks for all the help from everyone. The suggestions for the resistors will be filed away for future use! As i have managed to find a 3k 10w NOS radio-spares one.

I have now completed the following to get this radio back in the land of the living - and i’m quite surprised at it’s sensitivity even on a short wire it works very well.

1, Re-stuffed the paper-box condensers and re-wrired all the leads to them.

2, Replaced all the old paper caps. To get to two of them you have to strip the coil / switch box on the side of the chassis. So i took the chance to clean the switches and coils while i had access to them.

3, Fitted a new speaker and the 3k resistor that acts as a replacement for the field coil in the original setup

4, Re-wired a lot of old rubber covered cable.

5, re-wired mains cable

6, treated the case for woodworm, i think it was long dead - but better to treat it anyway.

7, filled all the woodworm holes, not an easy job. The little blighters made hundreds of them!

8, Cut the old varnish back and covered the scratches with wood stain colouring, then re-polished the case. I deliberately did as little as possible to the case to try and preserve it’s ‘old’ look.

9, re-covered the speaker, the old cloth was worm food!

10, replaced the dial glass.

Still to do;
1, maybe check/align it, it’s seems ok so again i don’t like to mess to much.

2, further work on the case

3, find some controls for it - like spotting hens teeth Any ideas?, i was even contemplating making some.
4, finish fixtures and fittings for the chassis

5, replace the a small square of asbestos with a heat proof tile, extend it to cover the 3k resistor. It does get hot to the touch and is close to the case. May move it.

Couple of photos attached for anyone that’s interested. I’m really pleased this radio is up and running again for 83 years old it’s a real nice piece of work.

Derek

[coopzone]

Forgot to say, i also replaced the tone control. 50k pot.

[cathoderay57]

Nice work - I see you need knobs. I looked at the RM website but even scaled up the image of the SW41 isn't high enough resolution to id the knobs. Anybody able to post a decent image of the right knobs? Might help us all to search out spares boxes - this project deserves a nice finish. Cheers, Jerry

[cathoderay57]

Here you go - see pic, I'm assuming these are the correct knobs?? Sadly I have none to match in the spares box but maybe somebody else does.

[David G4EBT]

Unfortunately the picture of the set on the first page on the otherwise excellent 11-page Bush Service Data is rather indistinct and I haven't seen an image in 'Radio Radio' or elsewhere. I guess that any four matching vintage knobs for 1/4" shafts wouldn't look out of place, either brown or black.

Well done on bringing the set back to life.

A wise move to sidestep the issue of rewinding the field coil, but instead, going for a replacement PM speaker. It's always a trade-off between safety and functionality on the one hand, and originality on the other, and whether or not a particular set warrants a huge amount of effort, time and expense, simply because it's old.

No-on is going to look at the set and say that the speaker fabric or knobs aren't original. Who would know anyway?

It's a set that could easily have been skipped, but with considerable effort, now has a new lease of life, and hooray to that!

Ooops - Cathoderay57 has posted a pic of the genuine article!

[Mike. Watterson]

How original is this one?
https://www.radiomuseum.org/r/bush_sw41.html

[Hoveradio]

Hi,the knobs will be the same as the SW43 as in the link.
https://www.***********/photos/gary_c...ey/22371821187
Regards John.

[Trifocaltrev]

Hi, I agree with Hoveradio, the Bush knobs have scalloped edges and are the same as the SW43, they were also fitted to the PB65 and other Bush Sets of this period, the knobs shown above are incorrect.

In fact if you look at the Radiomuseum pages for Bush SW43, PB65, SUG52 and the all push button PB50 you will see that they are all from the same period and use the same knobs.

The Radiomuseum page for the SW43 has a Bush advert for the period showing these scalloped knobs.

I hope this helps.

Trevor,

[Trifocaltrev]

Having just checked the Radiomuseum page for the SW41, I see that is does have one correct knob, the bottom right hand one,

Regards
Trevor.