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Old 14th Jul 2014, 12:00 pm   #1
gavinhall
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Default End of my beloved DR101

Well, it's happened, Friday night. Line stopped running, smelt a bit hot so I let it cool down and found the wax under the transformer. RIP old girl, banished to the corner of the garage.

Please share a thought for those sets unable to live again.

Of course, another option is to put the guts of a colour set in the cabinet and make it a bit more modern. Or use a replacement monochrome chassis and the same tube, or is this not allowed? In fact a small chassis may fit inside the set with the existing one, there's bags of space in the speaker compartment.
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Old 14th Jul 2014, 12:14 pm   #2
MALC SCOTT
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Default Re: End of my beloved DR101

Find a loptx for it. Would be a crime to strip it out and fit a modern set inside of it. Place a want add in the forum wanted section, Malc.
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Old 14th Jul 2014, 1:18 pm   #3
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Default Re: End of my beloved DR101

Sorry to hear that, however as Malc says a LOPT may turn up for it, or alternatively you could follow David's example with his DR123 which continues to work really well with a BRC 1400 Lopt:

https://www.vintage-radio.net/forum/...d.php?t=104681

David's informed me the circuits are similar, he'll be keen to help and advise on the LOPT conversion.

With his help I'm confident your set will live again.

Cheers,
Brian
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Old 14th Jul 2014, 1:35 pm   #4
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Default Re: End of my beloved DR101

Another option would be for someone to rewind your faulty LOPT, such as Ed Dinning or Mike Barker (murphymad). They are both members of this forum. Unfortunately, this would be quite costly.
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Old 14th Jul 2014, 1:41 pm   #5
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Default Re: End of my beloved DR101

I'm following up what Malc and Brian just written.
You have one of the most rare and interesting dual-standard sets. To carve it up and fit another chassis into the cabinet would be a regretable mistake.
This DR101, the Bush TV125 and the KB VC series were the only hand wired sets made in the sixties. The rest were just PCB rubbish in comparison.
OK, it's doubtful if the correct replacement Decca line output transformer will ever turn up so the answer is the Jellypot conversion like my Decca DR123.

DFWB.
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Old 14th Jul 2014, 2:03 pm   #6
gavinhall
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Default Re: End of my beloved DR101

OK, I won't destroy the set. I have a 12" b/w portable, an old bush ranger 2 in working order. The chassis would fit in the bottom of the cabinet and all the controls could be wired to the existing as they just plug in. The question is, would it drive the 19" tube that's in there, as there can't be that much difference?
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Old 14th Jul 2014, 2:05 pm   #7
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Default Re: End of my beloved DR101

Be a shame to do that. I would look for a replacement transformer if indeed that is what has actually failed
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Old 14th Jul 2014, 2:42 pm   #8
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Default Re: End of my beloved DR101

Quote:
Originally Posted by gavinhall View Post
OK, I won't destroy the set. I have a 12" b/w portable, an old bush ranger 2 in working order. The chassis would fit in the bottom of the cabinet and all the controls could be wired to the existing as they just plug in. The question is, would it drive the 19" tube that's in there, as there can't be that much difference?
Highly unlikely, as the scanning power required for the wider neck 19" CRT would be a good deal more and the DR101's scan coils are for a 28mm neck, whereas the Bush Ranger is a much smaller CRT neck diameter. Then there's the question of higher peak-to-peak video drive to the 19" CRT's cathode and the 19" CRT's A1 and focus electrode voltage requirements would be higher.
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Old 14th Jul 2014, 3:01 pm   #9
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Default Re: End of my beloved DR101

Quote:
Originally Posted by gavinhall View Post
I have a 12" b/w portable, an old bush ranger 2 in working order.
The Bush Ranger is designed to operate with a 12" tube. EHT would be too low to drive a 19" CRT without extensive modifications which could end up ruining that set as well as being time consuming. EDIT- absolutely right Dazzlevision (above), having just seen your post.

My advice, with the greatest respect, is to leave the Bush Ranger alone and work on your Decca. You did a great job in getting it working initially, it may not seem possible at the moment but it will work again.

First, are you quite sure the LOPT has failed? Is line whistle present? Is line drive present at the control grid of the PL36? Do the valves overheat or run cool? Is the boost capacitor OK? Have you tried new line oscillator, line output and boost diode valves? The LOPTS do unfortunately have a poor reputation but check all other possibilities before condemning it.

Seeing David's excellent efforts with a BRC/Thorn 1400 LOPT working in his DR123 this is what I would personally suggest trying. It could be argued that wouldn't be original, but on seeing the results for myself I believe this reliable transformer should've been fitted to the set in the first place. The set will still function as a dual standard as well!

They are of course other options such as rewinds previously mentioned.

Good luck, don't forget there's many contributors to this great forum who can help and advise, David (FERNSEH) for example as I previously mentioned.

Cheers,
Brian

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Old 14th Jul 2014, 3:44 pm   #10
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Default Re: End of my beloved DR101

Thanks so much for the encouragement guys, there is no line drive but then again I do have tinitus so always seem to hear it anyway. The LOP valve gets very hot but the transformer is not open circuit. The ECC82 oscillator has been changed, it's anode feed resistors are ok and the boost diode has been changed just in case. All the valves glow as they should, even the CRT, I just assumed the transformer had fried as it's wax was on the bottom of its enclosure (2 pools, one from each winding)
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Old 14th Jul 2014, 3:50 pm   #11
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Default Re: End of my beloved DR101

Hi Gavin,
I'm sure you will have read my topic about the line output transformer subsitution in a Decca DR123. The DR123 has printed circuit boards, however, much of the line timebase circuitry is similar to your DR101.
I'll swot up on the circuit of the DR101 I'll report my findings about the viabilty of fitted a 1400 LOTx in your set. The mechanical considerations will be much easier in your set than the later model. You'll need one of my famous adaptor plates.
I have to say I was disappointed when I found my set was fitted with the PCB chassis, I'd rather have the hand wired set.

Have you checked for line drive to the PL36 line output valve? There should be at least 40 volts negative at the control grid of the PL36.

DFWB.
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Old 14th Jul 2014, 11:07 pm   #12
gavinhall
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Default Re: End of my beloved DR101

Thanks for the tips folks, the next thing to do is like has been said, check for a line drive to the LOP valve which I'll do when I get it back in the workshop. It was smelling rather hot before it stopped though so the transformer could be shot. Is it worth disconnecting the o/p of the LOP valve to test for line drive or will that damage the PL36? If the problem is elsewhere, could the transformer have survived even though it got very hot? If the line stops running, does that put DC through the windings, therefore overheating it or would the line stop because the transformer has shorted?
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Old 14th Jul 2014, 11:20 pm   #13
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Default Re: End of my beloved DR101

If you disconnect the screen grid feed to the line output valve, you can then run the set without damaging the LOP valve. It will enable you to check for line drive (or the lack of it) without the LOP valve getting red hot. If you should find that the line osc isn't working, you can fault find for as long as you like. Once drive is restored you just connect the screen feed again.

Check the boost cap before condemning the LOPT.
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Old 15th Jul 2014, 1:09 am   #14
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Default Re: End of my beloved DR101

There is a quick method to establish if the boost capacitor has failed, that is gone short circuit. Disconnect the top cap of the boost diode, if the EHT returns, the capacitor is SC.
Negative volts greater than 40 at the control grid of the PL36 indicates the line drive is present.
As the PL36 is biased by grid current, lack of line drive will result in the valve drawing excessive current. The anode can glow red hot. The failure of the line output transformer can cause the same effect.
I examined the circuit of the line output stage and sure enough it is very similar to the later DR1 series. So if the line output transformer is faulty the set is a candidate for a jellypot conversion.
The scan coils can fail although it is uncommon. disconnect them and see what happens.

DFWB.
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Old 15th Jul 2014, 8:12 am   #15
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Default Re: End of my beloved DR101

Placing the set in the garage will result in fast deterioration especially once the summer is over. It's worth having the transformer rewound. It should be a straightforward job. I don't know your engineering skills but if limited, you only have to make a note of the connections making refitting an easy job. The rest of the receiver is completely reliable so it will give years of service once you have done this. We had the 23" version, the DR404 in our living room for a while in mid 1960's. It will look hideous with other chassis cobbled together to fit. Just my thoughts, Regards, John.
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Old 15th Jul 2014, 1:13 pm   #16
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Default Re: End of my beloved DR101

I strongly agree with what's already been said. Even if the LOPT has failed it is not the end. You still have two good options with either a rewind or conversion using a 1400 jellypot LOPT. If you have to store the set make sure it is somewhere dry and warm.
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Old 18th Jul 2014, 8:25 pm   #17
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Default Re: End of my beloved DR101

Hi All, Where has the wax come from? I'm thinking it is possibly the EHT overwind? You can prove this by removing the overwind and if the line output bottles come alive (draw a spark with an insulated screw driver from the top caps) then it will be your EHT overwind that has shorted turns and the primary will be o.k. You can then fit a tripler connected to the line output top cap and add a 5kV 150pF or thereabouts from there to ground and all should work again. Would save a 1400 l.o.p.t.
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Old 19th Jul 2014, 11:41 am   #18
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Default Re: End of my beloved DR101

Just to add my call to those above not to destroy a good set - find a way to fix it.

A point of clarification here, forgive me if you already know; the best/easiest way of discerning whether there is line drive to the PL36 is, as said above, to see if there is around -45V or so at the control grid but you really need to measure this using an AVO 8 or similar analogue voltmeter with around 20KOhm/Volt sensitivity. Using a very high impendance meter, a cheap 1K/Volt meter or a digital type won't give you the same result and may even disturb the operating conditions.

The AVO was such a universally adopted and respected instrument even when it wasn't giving a 'true' reading (i.e. with pulse waveforms) its 'interpretation' was regarded as a standard measurement.
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Old 19th Jul 2014, 2:42 pm   #19
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Default Re: End of my beloved DR101

Could Mike Barker rewind it? BVWS
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Old 19th Jul 2014, 3:19 pm   #20
gavinhall
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Default Re: End of my beloved DR101

Hi gents, please be assured that I will not destroy the set, it's just too nice. It's sitting in my lounge and I'm hoping that the lopt has just got hot and melted the wax and that the fault is s simple one. There were 2 pools of wax, one light yellowy under one winding (few turns) and one brown under the other winding (many turns). I need to re-roof my workshop before I get it back to the bench, but before that is holiday and work stuff so it will be safe as it'll stay indoors until then.

I'm sure when I do get back to it, someone will help guide me through what has to be done to restore it back to working order.
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