Wireless Set 19 repairs question.
 

Spent a happy pm with an old friend delving into my ws19 mk3. We sorted the meter and a few other items, found our way round it and so on but the bottom line is, no HT1.

Its a well modded mk3, got an inbuilt psu for example so can be directly mains fed. I unfortunately have no control box (its not actually my set but another friends). Anyway, no HT1. We had to stop to take the dog to the vets...

Still no clue as to HT1... Its certainly getting into the set at the transformer end, just no further.

D

Re: Ws19 set repairs question
 

If it now has an internal mains PSU the wiring must have been changed significantly,. Is there any circuit diagram or modification record?

Orackle42

Re: Ws19 set repairs question
 

Ha ha...have a guess!!

I am being facetious, no, there's nothing at all. Absolutely zilch. Such a shame.

Davdi

Re: Ws19 set repairs question
 

Just a point, is there a relay fitted anywhere I wonder?

Re: Ws19 set repairs question
 

Yes. The tx/rx relay. Theres no ht on it at all

Re: Ws19 set repairs question
 

The person who built and fitted the on-chassis PSU might have fitted a fuse (or two): might be worth a close look. The obvious option, of course, is to try to trace out the wiring, PSU output to the set's innards. And yes, I do realise that that is not going to be easy! 8-\ Hopefully, all of the additional wiring will not be of one colour, i.e. pink!

Al.

Re: Ws19 set repairs question
 

Just a thought, did the previous user use PL2 to connect to other devices, if so could it now include a continuity link to only allow HT to connect when all the devices were plugged together? I only have a MkII circuit so do not know how the MkIII connections differ.

Orakle42

Re: Ws19 set repairs question
 

is there HT on to and out of the rectifier?

Re: Ws19 set repairs question
 

Try checking the A set switch for continuity. These sometimes need a bit of exercise amd/or switch cleaner after many years lack of use.

Re: Ws19 set repairs question
 

Thanks guys

The rectifier does have ht in and out. Somewhere it is being dropped. Thanks for the tip ref switch for A set.

Re: Ws19 set repairs question
 

See November 1967 and March 1969 Short Wave Magazines for two articles by F G Rayer G3OGR on mods for the WS19, the second includes a mains PSU. might be helpful for yours?

73

Roger/G3VKM

Re: Ws19 set repairs question
 

Brilliant. Thanks. Ill find them online

Re: Wireless Set 19 repairs question.
 

For WS19 MKIII :

Proceed with caution when bottom plate is removed from set.

Attached are the depot engineer's voltage and resistance charts.

Either with the schematics or a tube manual test all the 280 volt
points with a voltage supply attached to the set so the meter
reads the voltage when set to H T 1 .

A good place to start is pin 4 (screen) of V8A
6V6G , always HT1, when A set is switched on.

Excuse duplicate image.

Re: Wireless Set 19 repairs question.
 

Thank you

D

Re: Wireless Set 19 repairs question.
 

I have made progress on this now and my guide and I actually managed to receive off air signals! We found that the 12v modification that has been done had a fault: of the two feed through diodes coming from the secondary winding to the capacitors and hence the radio, one of them was dead. Thus the valve heaters were getting low volts. We fed 12v directly and presto...but what a run-around.

So, I need two new diodes of the right rating. Sadly the present diodes have no part numbers on them.

I need a heater transformer (thinks bubble) to act as an audio output trf so that a speaker can be used. Someone did mention this once on the forum IIRC. If anyone has one spare...


Anyway, a few minor things to do and I can get the set back to it's rightful owner and out of my workshop. Thanks for all the input. I really must join VMARS, I have used their resources a lot.

David

Re: Wireless Set 19 repairs question.
 

If this 12v supply is feeding the heaters the startup I is quite high.
In a similar application I have used either 10A10 series (wire ended) or chassis mount bridges like the KBPC25-04, they are almost indestructible in this type of application. It may have been the turn on surge that killed the original diode.

Orakle42

Re: Wireless Set 19 repairs question.
 

David,
Well done on getting the receiver working. I think the output impedance is about 100 ohms. So, if you want to drive a modern 8 ohm speaker you ideally need a transformer with about sqrt(100/8) ratio. i.e. roughly 3.5:1. I managed to find an valve audio o/p transformer with a tertiary winding that was orginally used for tone control purposes (from an old Philips receiver, I think). This works fine with perfectly adequate speaker volume. Alternatively, you might find that a suitable mains transformer will work - after all, you're not after hi-fi!

Re: Wireless Set 19 repairs question.
 

Now you've got it sort-of working:

Remember that it's full of 70+ year-old parts.

There's dozens of old "waxie" type capacitors. Just because they're in metal-cases doesn't mean they won't have become leaky in ways that will at least compromiose performance and could lead to catastrophically destructive failure taking other parts out in the process.

Similarly, the resistors - the ones with the white ceramic body and an orange/brown mastic plugging the ends - are known to drift horribly after half a century. What was once a 500KOhm resistor could now happily be 1.5Megohm.


Think about it: would you want to fly in an aircraft that was built in the 1940s and has had none of its strategic parts inspected/replaced since it was made?

Check, and if-in-doubt-replace!

Re: Wireless Set 19 repairs question.
 

Whilst agreeing with G6Tanuki in principle, if the set is a British Mk3 it may use Sprague metal clad capacitors. Although they are still paper dielectric capacitors, I have yet to find any leaky ones in my set and this was stored in a damp garage for at least 30 years before I got hold of it. The only ones that could cause serious damage are those from the anode of V3A to chassis - these might be worth replacing as a precaution against excessive current in the primary of the output transformer, which is known to be fragile. There is one electrolytic in this set, C18C from HT2 -ve to chassis. I replaced this to avoid losing the -ve bias on the 807. It sounds like you're presently running the heaters from 12Vac. This is fine if you only plan to use the receiver but if you want to energise the relay for transmit you'll need dc, of course.


Good luck - Keith


http://www.tibblestone.com/oldradios...radio/army.htm

Re: Wireless Set 19 repairs question.
 

You don't want OMCCD! Obsessive Mass Change Capacitor Disorder. Changing all caps without a good reason (which there rarely is) can cause untold grief. Yes, there are the usual suspects ie grid coupling and caps across output transformer etc but that is as far as is normally advisable.