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Old 10th Apr 2019, 3:52 pm   #1
thx1138
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Default Another 19 set rebuild

Hi,

i came across this 19 set on that auction site and took a chance as it was less than Eur 300 with the bits, and to my suprise it arrived in good shape. More interesting the VHF set is all there and it seems to be factory. It hasnt been modified whatsoever, a rare thing given the amount of "improvements" done to them.

Reason I post, this set works (I did wind it up v slowly, so nothing melted) caps are going to need changing, we already had a few waxies end up forming piles on the kitchen table, and i didnt run it long to challenge it. So before I go on an OCD cap change, is there anything i need to do beyond 1 by one replacing the caps and I suspect tidying up the psu. Its the mk3 with the fabulously quiet dual dynamotors .) My neignbour wont be pleased for sure. All advice appreciated.

Heres a few pics if link is allowed- https://drive.google.com/folderview?...BPs_rV14HoB8hw

Serial number may have been logged already, but I took a shot of the plate for reference.

73s David
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Old 10th Apr 2019, 7:29 pm   #2
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Default Re: Another 19 set rebuild

Hi David,

Welcome to the 19 set owners club!

Looking at your pictures I see that you have a British Mk3 made by E.K.Cole (same as mine). Don't be too hasty in replacing the all capacitors. The Sprague metal clad types are usually still good with very little leakage. My set still has all its original decouplers and is still working perfectly. The only capacitor that I've replaced is the one electrolytic from HT2 negative to chassis. I believe that the large decoupler in the PSU should also be replaced to avoid a possible explosion!


Good luck with the project,
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Old 10th Apr 2019, 7:49 pm   #3
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Default Re: Another 19 set rebuild

The Sprague caps with a dull-grey outer and red printed text are some of the better WWII-era parts.

"Trust, but Verify", as the late Ronald Reagan was famed for saying.

TCC Metalpack/Metalmites - with aluminium outer-cases and rubber bungs in the ends - don't need to be trusted or verified - they need to be replaced! same goes for Dubilier "Type 4703C" metal-cased-with-rubber-end-bungs capacitors.
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Old 11th Apr 2019, 6:55 pm   #4
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Default Re: Another 19 set rebuild

Hi,
this made me laugh a bit "I believe that the large decoupler in the PSU should also be replaced to avoid a possible explosion!"...
OK, will do the PSU first and carefully find my way into the 19 set afterwards. Seems I have a few things to do at psu first, but the set is working and on frequency which is a bonus even though it clearly needs urgent work. Will report as things progress.
Last thing, the watch holder. Does it screw apart in order to fit the watch into it. I have one of that era to sit in the holder.
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Old 12th Apr 2019, 11:15 am   #5
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Default Re: Another 19 set rebuild

The standard WWII-era watch-holders do indeed unscrew; though I've seen a few where the Bakelite has aged and swollen so the front unscrewable bezel is really tight on its threads. Gentle heating with a hairdryer will usually expand the bezel sufficiently for it to come free.
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Old 12th Apr 2019, 1:36 pm   #6
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Default Re: Another 19 set rebuild

Somewhere on YouTube there is a video showing one of those baked-bean-tin-sized capacitors in the power supply exploding when powered without first reforming it.
You wouldn't want to be near it...…………!

Andy
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Old 17th Apr 2019, 4:43 pm   #7
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Default Re: Another 19 set rebuild

14 posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=155785
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Old 22nd Apr 2019, 10:54 am   #8
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Default Re: Another 19 set rebuild

Just a heads up, the microphone element was more or less open circuit (same as the phones) and unrepairable despite my best efforts to resolder the uber thin wires from the coil. I reluctantly took a spare mic element from a clansman speaker/mic lead which I had put aside for "spares" as the cable covering from it had totally disintegrated and I had purchased another one complete...
So in the google folder above I put the photos of the fix for anyone's curiosity. Was tempted to by a few scrap mics for the sake of the element but decided Id end up having to do a repair at later stage.Decided practicality over another 1943 era mic element.

Ive a list of capacitors and thanks again for advice as to what to replace on site. I have a DMM with capacitance range so it will be interesting to actual state of this radio as its never been serviced. Will follow up as things progress slowly (in between work ofc)..73s David
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Old 2nd May 2019, 11:38 am   #9
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Default Re: Another 19 set rebuild

Hi, I got a handful of 0.1uF 1kv caps as what was locally available and put a few in the No1 mk3 PSU and also luckily had a 47uF 450v cap that I used to replace the orig 30uF cap on ht1.

So at least the PSU is running ,loud and all..

I've to replace the 1uF 1kv ht2 cap perhaps, but feeding the receiver is first thing. Now I can work on the radio itself.

I added more pics to the google folder in my first post if anyone's interested.

This is great fun in fairness compared to the day job.. 73s
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Old 4th May 2019, 2:13 pm   #10
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Default Re: Another 19 set rebuild

Well I got the RX going to some extent. I replaced about 9x 0.1uf (500v) caps and that 1500v 0.1 also which was smoking.. The joy of wax.

Only thing is bfo is very weak and disappears after some time. Also the avc level never goes above 50% on the meter although plenty of deflection when on a carrier. The front end seems very good esp 4-8mhz range.

Can anyone suggest how to improve bfo and maby there is something obvious I need to replace.. As this is my first ws19, I'm all ears for advice.
I added a short video clip in my folder above for anyone.
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Old 4th May 2019, 2:40 pm   #11
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Default Re: Another 19 set rebuild

Well, you have replaced the caps, which tend to fail catastrophically - or cause something else to fail similarly, because they go dead short.

Now you need to start on the resistors. Most of them will have changed value, and most will be out of tolerance now. That can often lead to a receiver that sort of works, but is low gain.....and other symptoms of poor performance.

Its a tedious job, and some resistors don't need to be changed even if they are out of spec. An example would be grid leak resistors, which might be 470k for instance. If they now read 600k (say), then I wouldn't bother to change them. On the other hand, resistors feeding anode, screen grid or cathode need to be in tolerance, because excess ohms here will mean loss of voltage at that particular valve connection, and potentially loss of gain, because resistors tend to go high in value, and reduce current levels.

Other than that, check the valves (on a valve tester if you have one), and re-align the set, which will not help a weak BFO, but it will give you an even performance across the whole frequency range.

Richard
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Old 4th May 2019, 8:55 pm   #12
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Default Re: Another 19 set rebuild

The BFO level has been weak on both 19 sets that I have owned - I assumed it was a design "feature". The solution (as with many receivers of this era) is to turn down the RF gain control. This will allow CW/SSB signals to be resolved.

Also the meter on the AGC setting normally sits at about one third full scale with no signal (RF gain at max), only dropping to about one quarter for a strong signal.

The receiver should be very sensitive, with a 1uV signal easily giving 10dB s/n. Don't forget that that the PA Tuning capacitor needs to be peaked as it is part of the receiver input tuned circuit. The peak will probably not correspond to the dial calibration.
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Old 5th May 2019, 3:05 pm   #13
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Default Re: Another 19 set rebuild

Thanks for suggestions and help Richard & Keith. The BFO is now nonexistant, it got weaker over time, as this set has only been running a few hrs since whenever it was last in service, I assume there is more to do to restore this "feature". However at least the set is no longer smoking and the waxies are almost done. I need to order more as I ran out ofc. Still its worth it I guess from reading no bfo means no tx (at a later stage to sort). Also I notice no HT2 600v on meter when selected.I have restored the psu fully and its supplying 602v without a load when I kick the relay... Despite all this, yes its extremely sensitive receiver compared to my R209.. maby that also need work too.. Anyway if someone can point me to bfo restore area let me know what i should check.
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Old 5th May 2019, 3:46 pm   #14
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Default Re: Another 19 set rebuild

Sorry, I forgot to add, there is Drive current when switched to it, when I try tx and all relays seem to kick into position. Maby its just the resistor on the HT2 line from the switch.. We will see..
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Old 5th May 2019, 4:23 pm   #15
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Default Re: Another 19 set rebuild

David,
If you're getting Drive in transmit, it implies that the BFO is working in this mode. In TX the HT to the BFO is via the relay so maybe there is just a problem with the Net switch in receive. Check either side of the switch with a meter. I have had problems with these paxolin layer switches due to dirty contacts - they can be dismantled for cleaning by drilling out the rivets and replacing with 8BA bolts/nuts to re-assemble. Try switch cleaner first, of course. Other than that, just check all the components around V2B triode (R1D, R6A etc) - it's basically a simple tuned grid oscillator (L5A/C41A) with anode feedback via C19A/L5B. One other possibilty is that it has moved some way off frequency - on mine the small ferrite core fell out of it's plastic insert so had to be glued back in.
The lack of HT2 meter indication is quite common. R25A is a 1.2Mohm - these often go very high.
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Old 7th May 2019, 5:29 pm   #16
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Default Re: Another 19 set rebuild

Digging around in bottom right of underside I came across I assume a resistor somewhat cooked. Does anyone know the value of this or recognise it.
Its directly underneath the if coil on a tag strip.
See attached photo.
Am still investigating the bfo issue.

On another thing I removed the watch holder but cannot unscrew it. Trying as carefully to heat it and it still won't budge. I have a watch to go into it so hence the need to open it.
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Old 7th May 2019, 5:44 pm   #17
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Default Re: Another 19 set rebuild

Can't tell from the photo - there are 3 IF coils and you don't say which one. You need to trace it through with an ohmeter, assuming it is damaged. Can't help with the watch-holder - never had one!

PS It could be R5b or R5C (2K2). Either of these would have been overheated by a leaky decoupling cap.
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Old 7th May 2019, 7:01 pm   #18
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Default Re: Another 19 set rebuild

That waxy cap may have taken that burnt res out.
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Old 7th May 2019, 9:35 pm   #19
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Default Re: Another 19 set rebuild

Hi, thanks. I think it is the 2k2, resistor has many red bands at least on edge. Will check this tomorrow. Also yes I prob better finish off the recap. Have to order more.. Will hold off further operation until this is done.

Thanks again..
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Old 8th May 2019, 8:59 am   #20
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Default Re: Another 19 set rebuild

Re the watch holder, the bakelite has probably swollen slightly over the years from absorbing moisture. I had a WS31 microphone with the same problem. A few days in a warm airing cupboard dried it out enough to allow it to unscrew.

Gordon
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