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Old 1st Oct 2021, 7:00 pm   #1
Heatercathodeshort
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Default PYE 838 9" TV Radiogram 1938.

I don't usually post threads about the fun the two curators namely Peter and myself have when bringing back to life vintage television receivers.

This PYE was such fun [if you believe that ] I thought I would let you know the basic work needed to get it to the stage that you see now.

The chassis of the 838 is basically the table model 815 less the audio output stage. The chassis employs mainly side contact [CT8] valves Mullard type EF6 in the sound and vision RF stages, line oscillator and two in the sync separator, one for line and one for frame. The frame oscillator/output valve is a one off Mullard 6153T Triode/Hexode specifically designed for this chassis. I presume the T stands for television. The line output valve is an AC/6PEN, H.T. rectifier a UU5, EL3N voltage regulator and to complete the picture a Mullard HVR2 to rectify the high voltage supplied by a mains transformer to produce 5KV EHT.

I cannot find any circuit or manual that includes the EL3N regulator valve. I guess it was only fitted in certain models.

The CRT again a Mullard/Eindhoven product is a 9" magnetic MW22-1 with a 4V heater and a side contact base. At first sight it looks very much like the familiar post war MW22-14 series but that is where the similarity ends. It is described in most valve data books as a tetrode but is actually a hexode requiring only 15V swing to fully modulate the tube compared to around 30V for the MW22-14 series. I have scanned the 1938 Mullard data sheet and the actual PYE circuit to compare.

The PYE 838 does not have a video amplifier. The tube is grid modulated at high level direct from a couple of single TV1 [EA50] vision detector diodes in push pull. I expect a video amplifier could be easily constructed to allow the much less sensitive MW22-14 series to be fitted.

As mentioned the combined mains transformer supplies all the heaters including the CRT, H.T. and EHT voltage. Very early on during the initial testing this transformer broke down with an inter winding short destroying the UU5 H.T. rectifier. To be honest I was just waiting for it to happen. Mike Barker carried out a truly excellent rewind that performs exactly as it should. Thanks Mike!

Some of the chassis wiring was perished and replaced by Peter. He loves changing leaky capacitors and carries out all the Donkey work.

The chassis must be the most difficult to work on ever! The service manual states this but blames the horrendous access due to the 'scientific construction' needed..

Pye went loopy over screening. Each section is contained in a tight fitting black tin box as can be seen in the picture. It really is almost impossible to take voltage readings as the bases of the side contact valve holders are completely covered in components and inaccessible!

A picture was obtained quite easily after replacing all the paper capacitors, the electrolytics and a couple of the flimsy presets. If you thought the ones fitted to the HMV 1807 were rubbish, think again.

I spent far too long tracing the lack of frame sync. There are two EF6 pentodes fed from the video output via 100K resistors. The two sync separators are almost identical and the line was locking strongly. To cut a very long story short I measured the current drawn by the screen grid and anode. ZERO. The cathode voltage was correct being obtained from a potential divider across the HT line. The valve was OK checked by substitution but the anode voltage of the frame EF6 was 150v. The manual states 90V, the same as the line. The valve was clearly not passing any current but why?

It had to work.. Sync pulses were arriving at the grid but that was it. Connecting a .1uf capacitor between the top cap grid and the sync winding on the frame blocking oscillator transformer produced full lock? At this point the Devil sat on my shoulder and I must be honest I had thoughts of making this 'modification permanent..

AI decided to hook up a B9A holder with a simple EF80 wired to the base of the offending EF6. Full frame lock! The real cause was a damaged socket clip on the screen grid pin of the CT8 holder. It looked OK visually but fell to bits when I released the retaining clip. It was suffering from a bad case of verdigris. I robbed an unused socket from the tube base and with the EF6 in place obtained frame sync with the correct 90V on it's anode.

With the chassis set up it gives a surprisingly good picture if a little low on 'punch'. The CRT is over 80 years old and gives full emission on my trusty tube tester. It really needs a video amp to add that last 10%.

An early example of the RCA phono socket mounted on the side of the chassis supplies the audio output to feed the amplifier in the radio section. Connecting this to the low level input on the Dicotrgraph amplifier rewarded me with very clear sound and lots of it. This surprised me. I usually spend a lot of the time sorting out lack or low sound faults! Rear preset controls set the level of sound and vision gain on the RF amplifiers from a negative line obtained from the bottom end of the HT rail. Another phono socket serves as an aerial input using standard co-ax cable.

As mentioned Peter carried out a lot of the drudgery with this very heavy chassis leaving me to enter with a posh frock and just wave a wand over it! The radio chassis is now working thanks to P leaving just the mangled Garrard RC4 for me to sort out. At some time in the past the pick up arm had been forced due to the whole unit being seized solid. All freed off now but I can't work out where one of the leavers that tracks with the control cylinder goes! It was bent out of shape and I think the only way I can sort this out is to take a look at another working example. The pick-up coil is O/C [Oh what a surprise!] so that will be another fight with 50 gauge wire, a sheet of white card and some patience.. Maybe I will rewind it as I did the HMV No. 15 head in the DICTOGRAPH thread in the audio section a few weeks back.

I don't like side contact valves due to the awkward base. Fortunately they had a short introduction in the UK mainly in broadcast receivers. I'm glad they didn't catch on.

There is still a lot of tidying up to do but I thought you might like to see an example of a receiver we both rebirthed for the museum at Dulwich. The cabinet is about the size of a middle range radiogram. There is a quirky door midway down on the right. You slide it open to reveal the tiny screen. It's a bit spooky, more like a hidden camera in a 1930's spy film.
Regards, Peter and John.
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Old 1st Oct 2021, 9:34 pm   #2
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Default Re: PYE 838 9" TV Radiogram 1938.

Hi John,
you've motivated me to do something with my Pye 838. The last time I did any work on it was in 2017 and that was to install the correct Garrard RC4 record deck. When the set was first acquired in 1988 it was was equipped with a cream coloured BSR Monarch record changer. Later the BSR deck was replaced with a Garrard RC60, a post-war record deck. Then in June 2017 I was tipped off that a mid thirties radiogram equipped with an RC4 was on offer from an online auction site. I wasted no time and placed a bid for it. It's the radiogram we eventually determined to be made by a firm called MRG, Mains Radiograms Ltd.
Link to some work carried out to my Pye 838 in 2016:
http://www.vintage-radio.net/forum/s...d.php?t=131324
The last post in page two shows the removal of the RC60 and the RC4 taken from MRG radiogram.

DFWB.
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Old 2nd Oct 2021, 5:06 pm   #3
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Default Re: PYE 838 9" TV Radiogram 1938.

Hello John & Peter.
Great work as usual.I have a sales leaflet for the 838 which I will pop in the post to you.
Regards Steve.
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Old 2nd Oct 2021, 5:23 pm   #4
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Default Re: PYE 838 9" TV Radiogram 1938.

That will be brilliant Steve. Thanks very much. John.
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Old 5th Oct 2021, 7:34 pm   #5
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Default Re: PYE 838 9" TV Radiogram 1938.

Well done John- fantastic job. I wouldn't mind seeing the sales leaflet when you get it.
Thanks also for entertaining me and Eugenio last week. He was over the moon with the radio you kindly gave him.

I fired up my 838 today for a couple of visitors. The picture is good with plenty of contrast. But I have no TV sound at present. I am still looking out for a Garrard RC4 to fill the hole where it should go.
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Old 5th Oct 2021, 9:30 pm   #6
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks Steve, your very welcome. It was great to see you both. Your welcome anytime.
Yes at last it is working. The black level is fine in a room with subdued lighting, sharp and clear.
Managed to sort out the voltage regulator red wire! It was simply connected to the H.T. line from the valves anode. It is a EL3N which is basically a short stubby version of the familiar EL3. I really can't see it's purpose other then to slightly stabilize the H.T. supply in the days when it was a bit saggy in some areas. Regards, John.
PS For your no sound fault, carefully check the side contact valve bases on the EF6 RF amplifiers. I'll scan a copy of the sales leaflet for you.

Last edited by Heatercathodeshort; 5th Oct 2021 at 9:40 pm.
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Old 6th Oct 2021, 9:03 am   #7
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Default Re: PYE 838 9" TV Radiogram 1938.

Hello David,

Did you put the R60 into the MRG? I quite like MRG gear...
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Old 6th Oct 2021, 12:10 pm   #8
Niechcial,Steve
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks for the scan John. Like you- I very much suspect that my sound problem is down to side contacts. I've had similar before!
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Old 6th Oct 2021, 9:34 pm   #9
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Default Re: PYE 838 9" TV Radiogram 1938.

Brigham wrote:
"Hello David,
Did you put the R60 into the MRG? I quite like MRG gear..."

Hi Colin,
The MRG radiogram is now equipped with a Garrard RC120 record deck. Still looking for a good home for this radiogram.
The RC4 is now installed in the Pye 838. It was not a straight forward task.
A special framework was made consisting of four parts. The parts are fitted in the cabinet in a certain sequence and lock into position without the need for any screws.
The TV chassis is on the work bench receiving attention.

DFWB.
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Old 8th Oct 2021, 2:07 pm   #10
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Default Re: PYE 838 9" TV Radiogram 1938.

Hi John,
thanks for a good write up as ever.
I remember seeing David's set working years ago (I've got a screen shot somewhere). I was very impressed by the results with such a compact chassis. Not really what I expected from a pre-war set. I do feel it is a shame that they put that lovely compact chassis in such an enormous cabinet.

A few years ago, I went to a BVWS TV event at the museum, one of the last when the house was still in use (when was it?) and I saw the 838 in the hallway. I wondered when it would be restored. I opened the lid and noticed the RC4 deck. That got me thinking and enquired about David's set and that was when I found that the original deck was missing.
From that point I felt compelled for some reason to regularly check for RC4 decks on Ebay. I eventually found the MRG radiogram which I pointed David to, but it took a couple of years or so to find. So Steve, it is worth looking for radiograms on Ebay regularly and one might just turn up at some point. I think some RGD radiograms may have used the RC4 deck as well.

Keep up the good work.
Cheers
Andy
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Old 13th Oct 2021, 1:27 am   #11
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Default Re: PYE 838 9" TV Radiogram 1938.

Hi again,
I've dug out a couple of pictures of David's 838 that I took over 20 years ago, including a screen shot.
The third picture was taken a couple of months ago, showing David's 838 chassis receiving attention on the bench.
The fourth and fifth photos show the first time I spotted the 838 in Gerry's hallway, this was in September 2016. You can really see how the compact chassis seems lost in that big cabinet!

Cheers
Andy
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Old 14th Oct 2021, 9:41 am   #12
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Default Re: PYE 838 9" TV Radiogram 1938.

That looks great Andy. Camera pictures can vary enormously depending on the camera! I think these examples of the 838 have survived due to the cabinet being almost identical to a radiogram of the period. With the lid raised and the spy door closed there is nothing to give the game away that it is a TV!

Used as a radio and maybe even the gramophone section it could well have been used into the early 60s and was fitted with an early 13A plug.

The weird presets can be seen on the left of Andy's picture. While on the hunt for some caps for the Philips G8 I came across a small box of NOS ones! They are marked AUSTRIA-SATOR who I think are the makers. I will replace the 'modern' rotary presets I fitted to get the 838 working.

I did not fully mention the access for testing valve voltages etc on the 838. The only satisfactory method is to unscrew the timebase panel [4 screws] and extend the leads to the scan coils power supply etc. With the screening cans removed you can then just about get your soldering iron and meter prods into places man has never reached.

I must admit I find it amazing that a television receiver manufactured in 1938 with it's original Mullard tube is still capable of giving pictures of good entertainment value and all down originally to that genius team at EMI. John.
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Old 19th Oct 2021, 11:41 pm   #13
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Default Re: PYE 838 9" TV Radiogram 1938.

As always a superb account from the 'Guv'nor' Mr John.
What an exciting 838 write-up!!
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Old 20th Oct 2021, 3:16 pm   #14
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks for that tip on the RC4 Andy. I shall check the radiograms. If you happen to see one, I would be very grateful to hear thanks. All the best.
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Old 20th Oct 2021, 5:12 pm   #15
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Default Re: PYE 838 9" TV Radiogram 1938.

Quote:
Originally Posted by Niechcial,Steve View Post
Thanks for that tip on the RC4 Andy. I shall check the radiograms. If you happen to see one, I would be very grateful to hear thanks. All the best.
Hi Steve,.
Will you need the wood frame to mount an RC4 in the gram space?
When an RC4 was found thanks to Andy's help a frame consisting of four specially shaped interlocking battens was made for the Garrard unit.

DFWB.
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Old 20th Oct 2021, 6:20 pm   #16
Niechcial,Steve
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks David. If I'm lucky enough to find an RC4 I will come back to you if I may. BTY is 'MRG' an abbreviation for something?
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Old 20th Oct 2021, 7:17 pm   #17
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Default Re: PYE 838 9" TV Radiogram 1938.

Quote:
is 'MRG' an abbreviation for something?
MRG = Mains Radio Grams, I had one a few years ago, pretty good quality.


Mark
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Old 20th Oct 2021, 7:40 pm   #18
Niechcial,Steve
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks Mark
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Old 20th Oct 2021, 8:32 pm   #19
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Default Re: PYE 838 9" TV Radiogram 1938.

Mains Radiograms Limited was acquired after WW2 to make radios and later TV sets.

DFWB.
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Old 25th Oct 2021, 7:27 pm   #20
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Default Re: PYE 838 9" TV Radiogram 1938.

Thanks David
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