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Alba T1520 (BRC 1500 chassis) revival

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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Re: Thorn 1500 VT10 type TVT 7

Post by Colourstar » Tue Jun 21, 2016 8:54 pm

Lloyd wrote:Good to see you found one of these sets!


Hi Lloyd- yes I remember asking you some time ago whether you'd ever consider selling your Alba T1520. Everything comes to he who waits, it would seem!

Just ordered a couple more transistors, so there should be some further progress to report before long.

Steve

 
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Re: Thorn 1500 VT10 type TVT 7

Post by Focus 2 » Fri Jun 24, 2016 9:37 pm

I agree Steve, the thread title should be changed to what you suggested.
Ni doubt you'll have a perfectly working 1500 soon. Pictures were never brilliant but they were/are excellent sets. George Wilding agreed when I discussed them with him.
Cheers
Brian

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Cathovisor » Fri Jun 24, 2016 9:57 pm

Following on from Brian's suggestion, I thought it'd be better to split the thread and rename it: all subsequent posts will now carry the new title :)

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by nuvistor » Fri Jun 24, 2016 10:43 pm

Probably going against the flow here but I was never over keen on the 1500, or other Thorn B/W sets, the only thing I would say is that they were always easy to fix. I know there were a lot in use with the rental market and the Jellypot has stood the test of time, but that was my thoughts when they were in service life.

Still the chassis is an icon for the shear number made and good to see one working again.

Frank

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Focus 2 » Sat Jun 25, 2016 7:46 am

Yes, it amazed me how these and earlier Thorn b&w sets can still function reliably 40-50 years after they were made. This is certainly not true from some other makes of the period which perhaps did function better when new.
Perhaps the 960 portables are an exception, but had I replaced that dropper capacitor on sight would've saved a lot of problems I encountered later.
Brian

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by slidertogrid » Sat Jun 25, 2016 11:48 am

One thing to watch for on the 1500 is the high value dropper section going o/c. I think it is 1.5 k on early sets and 1.7K on later models
If that section goes o/c the L.T voltage goes sky high and usually takes out most of the transistors excepting the ones in UHF tuner thankfully.
I had a few sets that had suffered that fate, If I refurbed one for re-rent I always fitted a new dropper. They usually had a section or two fitted with 'Polo mints' by then so needed changing anyway really.
I saw a few sets that had a brown line burnt on the tube face due to drys on the frame transformer customers just got used to giving it a thump when the frame collapsed but then there was always the day they left it running unattended... :bbd
The 20" Mazda tubes seemed a lot more prone to screen burns than the earlier 19" tubes. I saw quite a few 'game burns' on 20" tubes, one particular make of the Tele tennis game was almost sure to burn goal outlines on the screen if the set was run at high contrast and brightness levels. Maybe the phosphor was thinner or cheaper on later mono tubes?
Rich.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by nuvistor » Sat Jun 25, 2016 9:10 pm

I don't think any of the last of the larger mono CRT's were up to scratch compared to the ones made earlier. Focus/astig and emission just did not seem as good. Cannot comment on reliability, sold/rented very few. I think they were imported not UK made, someone may remember a bit too long ago for me.

Frank

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Katie Bush » Sat Jun 25, 2016 9:52 pm

From my own experience, I once had a BRC 1400 chassis, Ferguson with 20" screen, which I sold on to my younger brother when I acquired a 1500 chassis version.. That was a big mistake in my eyes - softer focus overall, and absolutely pathetic at the edges.. Geometry was so poor I actually thought the set had been set up by a school leaver on day release and the sound quality just 'wasn't there'.

Overall, I got the impression that the set was pretty much thrown together rather than assembled, and there was scant evidence of 'due care and diligence' on the part of the assembly line workers.

For a chip shop TV, or even a pub TV for that matter, it was adequate, but was poor excuse compared to the 1400 it replaced - the only good feature I can remember was the absence of intercarrier buzz that plagued the 1400.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Cathovisor » Sat Jun 25, 2016 10:38 pm

nuvistor wrote:I don't think any of the last of the larger mono CRT's were up to scratch compared to the ones made earlier.

In professional equipment, tubes like the A61-120W and the A50-whatever could give very good results. Used to be used as floor monitors in their 24" guise before domestic colour TVs with isolated chassis became freely available.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by nuvistor » Sat Jun 25, 2016 11:05 pm

Cathovisor wrote:
nuvistor wrote:I don't think any of the last of the larger mono CRT's were up to scratch compared to the ones made earlier.

In professional equipment, tubes like the A61-120W and the A50-whatever could give very good results. Used to be used as floor monitors in their 24" guise before domestic colour TVs with isolated chassis became freely available.


The earlier A50/A61 were good, its also possible that the domestic market were fitted with a cheaper lower quality product than professional equipment, in fact very likely.

Frank

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Cathovisor » Sat Jun 25, 2016 11:29 pm

Not sure if the 20" ones were likely to have expensive Illuminant D tubes in them (often made by Brimar) as they would be used as camera preview monitors; but the 24s? I genuinely don't think the CRTs were anything other than the standard "off the shelf" product. Certainly in the days of the older Grade 1 colour monitors (Melford DU1/Prowest PM2), they were standard Mullard A56-120Xs.

The real attention was in the circuitry: regulated EHT, wide bandwidth video drive and proper black-level clamping.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by slidertogrid » Sun Jun 26, 2016 10:35 am

Mike has a point there maybe the poorer pictures and shorter life was down to how the tube was driven by the chassis rather than the tube? In my experiences the Mazda tubes were the worst in general but Mullard failures were also fairly common. for some reason the Philips 210 seemed to have a shorter life with a Mullard tube than most other makes.
The problem is that as time passed it seemed you couldn't rely on the Mullard label being a Mullard tube some it seems may have been re labelled imports.
My mate had a very late Marconi 1500 with a purple labelled A50-120W, the set was very clean and low use but the tube still wasn't brilliant definitely not an old school Mullard!
The usual story! Produce something good, then slowly cut the quality and trade on previous reputation until the buyers twig which sometimes takes years. we see it all the time these days. it has even spread to some car makers.
Rich

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Sun Jun 26, 2016 7:19 pm

A bit of an update on the Alba: I have a couple of BF184 transistors which I believe are suitable replacements for the suspect BF194 lockfits VT6 (3rd IF amp) and VT11 (sound IF amp).

Tackling VT6 first, with the BF184 fitted, the base is now at 0.6v and the emitter at 0v, which seems more normal. The base was at 25v and the emitter at 0v with the old lockfit in place.

The collector voltage should be 11.5v. With the old lockfit it was 25.7v. With the new transistor fitted it's 7.27v, which is a bit low. I wondered if R20 (3.9K) may have drifted but it reads 4.2k so it's not far off.

(I should really put the above info into a table for better legibility but I can't seem to fathom how to do it!)

Steve
Last edited by Colourstar on Sun Jun 26, 2016 7:36 pm, edited 1 time in total.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Cathovisor » Sun Jun 26, 2016 7:30 pm

Colourstar wrote:The Law of Cathovisor (see further up the thread) decrees that "thy base shall be 0.6v above that of thy emitter'

Not my law - 'tis a law of physics.

More to the point, what did you do with that shield connection on the BF184?

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Sun Jun 26, 2016 7:39 pm

I left it floating in the breeze for the moment, ensuring it's not touching the body of the transistor or anything else. Presumably it can be snipped off if not required... or is that a tremendous no-no?!

Steve

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Cathovisor » Sun Jun 26, 2016 8:41 pm

Colourstar wrote:Tackling VT6 first, with the BF184 fitted, the base is now at 0.6v and the emitter at 0v, which seems more normal. The base was at 25v and the emitter at 0v with the old lockfit in place.

The collector voltage should be 11.5v. With the old lockfit it was 25.7v. With the new transistor fitted it's 7.27v, which is a bit low. I wondered if R20 (3.9K) may have drifted but it reads 4.2k so it's not far off.

So if I assume that the HT is about 26V, we can safely say the previous transistor was o/c b-e.

I'm a little unsure about that floating shield lead: I'm wondering if there's enough of a stray capacity issue to detune the circuit. The trouble is, the circuit is designed in such a way that the DC potentials around VT6 are somewhat dependent upon the hFE of the transistor.

A BF254 or BF594 may have been a better replacement, to be honest.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Tue Jun 28, 2016 8:05 pm

Cathovisor wrote:I'm a little unsure about that floating shield lead: I'm wondering if there's enough of a stray capacity issue to detune the circuit. The trouble is, the circuit is designed in such a way that the DC potentials around VT6 are somewhat dependent upon the hFE of the transistor.


Well, funny you should say that, as since fitting replacing that transistor I've lost the picture! Just a blank grey raster remains. Perhaps one of the other transistors you suggest would be a better way to go...

Steve

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by nuvistor » Tue Jun 28, 2016 9:15 pm

Have you checked that the transistor is faulty or perhaps you have you another fault?

Frank

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Sat Aug 27, 2016 2:38 pm

Nurse! More transistors please!

Back to this sickly 1500 to pick up where I left off. It looks as if the sudden loss of signals is due to the 1st and 2nd IF amps (VT4 and VT5 respectively). They were reading pretty much spot-on when the set was first woken but appear to have now thrown in the towel. Both are BF196 types. The equivalents book suggests a BF167 which I don't have. I wonder if there are any others I could try?

Steve

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by CTV » Sat Aug 27, 2016 2:51 pm

Colourstar wrote:Nurse! More transistors please!

Both are BF196 types. The equivalents book suggests a BF167 which I don't have. I wonder if there are any others I could try?

Steve

All these BF198, BF225, BF310, BF367, BF596 will all work as substitutes.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Sat Aug 27, 2016 4:36 pm

Great stuf, thanks Chris. I'll see what I've got kicking around...

Steve :aad

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Wed Sep 07, 2016 10:42 pm

Hi again from the land of dead transistors.

It seems the battle is finally won. After replacing every single transistor in this set, it's now a runner at last. I'm well chuffed! :bba The picture has that odd trait that I always associate with 1500s of having decent amounts of brightness in reserve, but appalling corner focusing. I don't remember other similar sets having that issue for some reason. The crt is a Mazda Goldstar and I have another I can try to see if that improves matters. Not that the present incumbent isn't perfectly watchable.

The broken tuner buttons need attending to and there are some cosmetics to address, but it's great to have an example of the set I grew up watching back in action.

Steve
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Katie Bush » Wed Sep 07, 2016 10:52 pm

I say, Steve, that's pretty ruddy good! :aad

I know what you mean about the corners being defocussed, and to be honest, that's one thing that always put me off owning one of these - so went on the get through four of them, although they were never what I'd call "keepers".

I recently took delivery of a 1500, though I was fresh out of hospital that day so never really looked at it... Perhaps I should give it due consideration?

Marion

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by marc » Wed Sep 07, 2016 10:54 pm

Hi Steve,

So it lives ! :aad
Nice one that man :bba

Marc.

 
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Re: Alba T1520 (BRC 1500 chassis) revival

Post by Colourstar » Wed Sep 07, 2016 11:06 pm

Thanks folks! And I forgot to say a very big THANK YOU for all the advice received from members along the way.

This 1500 was a bit of a basket case and has had far more effort expended on it than would normally be justified. A complete re-cap, a new dropper and all new tr*ns*stors. Blimey. I'm old enough to remember these sets being ten-a-penny and generally always working, so it was quite a strange experience carrying out something more akin to a full restoration than a mere repair. It was just that this was the particular model I was after and they are thin on the ground now.

And very well done Marc on your new G11- it's a cracker! :aad

Steve

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