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Old 9th Jun 2018, 9:29 pm   #21
FERNSEH
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Default Re: Decca DR101 dual standard TV

Hi John, the B7G plug will be gratefully received.

It's a very easy task to remove the chassis from the cabinet. Disconnect the loudspeaker leads, the five control panel plugs on the left side of the chassis, remove the two 2BA hex head chassis securing screws and withdraw the chassis complete with the CRT.

Only one waxie found in the frame timebase, C96, a 0.2mfd TCC component - and it's leaky. The cathode bias capacitor C97 500mfd is OK but the PCL85 screen grid decoupler C98 might be suspect.
Lots of black tubular Hunts capacitors to check for leaks.
The attachment shows the circuit diagram of the model DR39.

DFWB.
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Old 13th Jun 2018, 3:33 pm   #22
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Default Re: Decca DR101 dual standard TV

A little work did wonders for the performance of the set. Note how the chassis comes out complete with CRT. Bit hazardous if children were around if serviced in the home I would have thought.

The components are beautifully laid out with each component relatively easy to get to.

Much work still to do. The CRT is as good as new.

Photos taken with David's kind permission..

What a cracking set!

Cheers
Brian
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Old 13th Jun 2018, 7:58 pm   #23
FERNSEH
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Default Re: Decca DR101 dual standard TV

Thanks to Brian for posting up the pictures. Still work to do on this set before it can be signed off. The width control doesn't work, it's likely the coupling capacitor between the line oscillator and the grid of the PL36 has a leak. The Decca has a stabilised line output stage which employs a VDR as the device to rectify the flyback pulse to produce the controlling negative bias for the line output valve.

The picture needs more height, it's likely more capacitors need replacing. The vision AGC isn't working properly and again it'll be those Hunts capacitors.
Switching over to 625 lines is facilitated by selecting the "UHF" position on the VHF tuner, except it doesn't, that's something else to look into.

DFWB.

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Old 17th Jun 2018, 7:13 pm   #24
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Default Re: Decca DR101 dual standard TV

Hi David,
that look like Philips tuners in the Decca set.
If so could you make a close-up picture and/or tell what is written on the labels?

Cheers, Pieter
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Old 17th Jun 2018, 9:36 pm   #25
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Default Re: Decca DR101 dual standard TV

Hi Pieter,
The VHF tuner is a Philips AT7639/22. When the control panel is removed we'll find out the type of UHF tuner, it is a Philips, that's for sure.

John HKS has kindly donated a B7G plug to replace the burnt out one.
The set does work well on 625 lines UHF but there is a problem with the standards switch solenoids.

DFWB.
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Old 18th Jun 2018, 9:55 pm   #26
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Default Re: Decca DR101 dual standard TV

Hi David,
thanks. The UHF tuner will then likely be the AT6360/02 (PC88 and PC86), but let's see. Would be great if you can find the 12nc codes on the labels too.

Pieter
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Old 20th Jun 2018, 3:38 pm   #27
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Default Re: Decca DR101 dual standard TV

Pictures of the VHF and UHF tuners, both sourced from Philips. The VHF tuner has a cam at the rear to actuate the standards switch solenoids.
The label might help to identify the country of manufacture.
The UHF tuner has no identifying labels but it's safe to assume it was made by Philips.
I'll take look at the Tuners in the Decca DR123.
The decoupling capacitors in the vision AGC circuits had leaks, particularly the two parallel connected 0.5mfd capacitors which were reading 500Kohms on the Simpson 260 multimeter.

DFWB.
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Old 20th Jun 2018, 5:01 pm   #28
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Default Re: Decca DR101 dual standard TV

A thought about the solenoid. I guess it'll be fused?
Some sets, notably Thorn fitted a fusible resistor. Philips used a fuse.

Don't know about Decca though.
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Old 20th Jun 2018, 8:15 pm   #29
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Default Re: Decca DR101 dual standard TV

Hi Brian,
The Decca DR101 employs the two series connected smoothing chokes as the system switch solenoid. There is no DC passing through the switches, instead, the charge on C65 actuates the switching function. It's most likely that a leak in C65 is the reason why the system switch doesn't work properly.

The circuit diagram extract is from the information in the 1963/64 R & T servicing book for the Decca DR31.

DFWB.
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Old 21st Jun 2018, 1:50 pm   #30
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Default Re: Decca DR101 dual standard TV

Hi David,
that Philips VHF tuner looks like the ones that were used in the STC sets (KB etc.) which had the advantage of remembering the fine tuning setting for each of the VHF channels.

Do let me know if you need any solenoids rewound.

Cheers
Andy
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Old 21st Jun 2018, 3:48 pm   #31
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Default Re: Decca DR101 dual standard TV

Hi Andy,
I've been tracing the system switch circuits and there are differences in the DR101 compared with switching circuits in the DR31. For starters there are no connections to the system switches SW3 and 6 from pins 6 and 7 of the B9A plug.
Also, the 0.25uF capacitor C65 can't be found.

In the DR101 pin 7 of the B9A plug goes direct to the HT reservoir capacitor C64 and pin 6 goes direct to the HT smoother C66. Pin 2 of the B7G plug goes to a 600 ohm 5watt resistor which must supply one of the sub-HT lines in the receiver.
A full service manual is needed for this set.

Now the set is stuck on 625 lines. I can report the set works very well on 625.

DFWB.
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Old 21st Jun 2018, 8:28 pm   #32
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Default Re: Decca DR101 dual standard TV

The attachment shows the twin smoothing chokes which also function as solenoids to actuate the system switch lever.

DFWB.
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Old 24th Jun 2018, 9:54 pm   #33
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Default Re: Decca DR101 dual standard TV

Hi, been reading with great interest.

One thing worth noting is that the standards changeover will only operate when the set is fully warmed up and operating with current passing through whichever choke is in use.
(Apologies if I'm teaching my grandmother to suck eggs lol.)

I repaired a Decca DR303 (similar if not identical chassis) a while back and here is the restoration....
https://www.radios-tv.co.uk/communit...tandard-dr303/
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Old 29th Jun 2018, 9:26 am   #34
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Default Re: Decca DR101 dual standard TV

I spent ages getting mine running and it's interior was full of woodworm. It was working for a few weeks (courtesy of talking pictures TV) and the audio began to fade out, then the LOPT overheated and dripped wax on the bottom of its cage.

Sad to say it's no longer operational (still looks nice though) and to be honest I got a bit fed up with it so I don't know if it's salvageable. There was no smoke or smell, it was working when I switched it off but didn't come back on so I left it after the wax discovery.

Mind you it does make a nice shelf for some of my Hacker radios.

Gavin
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Old 29th Jun 2018, 8:40 pm   #35
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Default Re: Decca DR101 dual standard TV

Hi Gavin,
Keep faith with your Decca DR101. I'm sure a BRC jellypot transformer conversion will solve your LOPTx problem.

The attachment shows another system switch actuating circuit.
That's three attempts by the manufacturer to make the system switch work properly.

DFWB.
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Old 1st Jul 2018, 10:20 pm   #36
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Default Re: Decca DR101 dual standard TV

Hi David,
Thanks for the Tuner pictures!
The VHF one is obviously the AT7639/22, which did have the Memomatic channel pre-set memory as well as the VHF-UHF switch on top (with the large spring clearly visible in the pictures). This is by itself interesting, because the Philips sets of the period (1964) did not have this switch yet. Having the built-on switch also meant that the UHF IF signal was fed into the VHF tuner where it used the PCF80 pentode section - in VHF mode used as mixer - as IF amplifier. This is probably the explanation of poor UHF performance in many early (Philips) sets.
The AT7639 in your DR101 was produced in Eindhoven (as identified by the code A04 on the label, "A" referring to Eindhoven). So it looks that the Decca sets of this period, with Decca being considered a third party, obtained more modern tuners from Eindhoven than the AT7639/21 version developed and produced in Croydon.

The UHF tuner, with the PC88 and PC86 valves and no PCB on top is almost certainly the AT6360/02. Pity the lable is gone.

Cheers, Pieter
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Old 2nd Jul 2018, 12:52 am   #37
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Default Re: Decca DR101 dual standard TV

Hi Pieter,
The later Decca models DR1 and DR123 are equipped with Philips VHF tuners.
I'll find out the tuner type tomorrow.

DFWB.
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Old 2nd Jul 2018, 8:29 am   #38
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Default Re: Decca DR101 dual standard TV

Quote:
Originally Posted by gavinhall View Post
I spent ages getting mine running and it's interior was full of woodworm. It was working for a few weeks (courtesy of talking pictures TV) and the audio began to fade out, then the LOPT overheated and dripped wax on the bottom of its cage.

Sad to say it's no longer operational (still looks nice though) and to be honest I got a bit fed up with it so I don't know if it's salvageable. There was no smoke or smell, it was working when I switched it off but didn't come back on so I left it after the wax discovery.
Sorry to distract from David's fine work on his set but recall the post from Gavin. Perhaps someone could provide a link?

Probably a long shot and you've already checked these: the boost capacitor, PL36, PY801 and the line oscillator valves. Is there line drive minus volts to the PL36's control grid?
Is there line whistle?

Alternative to the Jellypot conversion is the possibility of having the original Lopt rewound. David's Jellypot conversion in his later Decca set works wonders though. It'll have to be a dual standard one of course, such as the Thorn 1400 if you require 405 as well as 625.

Brian
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Old 2nd Jul 2018, 1:35 pm   #39
FERNSEH
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Default Re: Decca DR101 dual standard TV

I mentioned in post No.35 that there has been three attempts by Decca to effect a system switch actuating circuit.
The attachment shows my interpretation of the switch circuit in the Decca we are currently discussing. In the Trader service sheet 1656/T260 for the DR101 the circuit diagram shows us that a smoothing choke is disconnected leaving the other energised. In the diagram that accompanies this post a choke is shorted out leaving the other energised.
The circuit of the switch circuit in the earlier DR31 is also attached with this post. How does it work?

DFWB.
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Old 2nd Jul 2018, 1:53 pm   #40
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Default Re: Decca DR101 dual standard TV

Looks like one actuates the system switch one way and the other the other way?

Lawrence.
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