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Old 14th Jul 2019, 4:46 pm   #1
1100 man
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Default KB KV014 - VC4 chassis

Colourstar Steve and I talked about this set a year or so ago, but it took until last week's RWB event to finally meet up & exchange it. He had described it as having a slightly tatty cabinet, no rear cover and a very poor tube- what's not to like?
I had several larger screen 625 only KB's when I was a kid and always knew them as 'slopy back KB's'. 'Handwired in Footscray' always intrigued me: it never occurred to me that it was actually a place in Kent!

Anyway, I plugged the thing in and sure enough it produced a dim picture. Oddly, if the brightness was advanced beyond a certain point, the picture got darker and the highlights went silvery. I measured the cathode & grid voltages and they seemed OK, but it didn't feel like a low emission tube.

To prove the point, not having my CRT tester to hand, I connected it's heater to a variable supply. Low emission tubes are sensitive to heater voltage, reduce it a bit and the picture disappears, increase it and the picture gets better.
Reducing it to 4V & increasing it to 8V made no difference at all, so I was even more convinced the tube was fine.

I decided to do a quick 'back to back' hook up and plug the KB into the CRT from my GEC 2000 which conveniently has the same tube base. Running both sets together so the GEC provided it's own EHT & scanning & the KB provided the signals, produced an equally grim picture on the GEC tube. Hmm..

So I tried it the other way round and plugged the GEC's tube socket into the KB tube. I swapped over the scan coils as well and extended the wires so they would reach. This time the KB supplied the EHT and a bright contrasty picture appeared on the KB tube! All very Heath Robinson, but I now had a good picture on the KB tube.

I then did what I should have done to start with and measured all the tube electrode voltages. Sure enough, the first anode (or G2) was at 40V instead of nearly 400V. This was due to it's 680K feed resistor being very high and the Hunts 0.05Mfd capacitor down to chassis being very leaky. Bridging the resistor & snipping our the cap produced a very good picture.

So I get zero points for correct fault diagnosis, but it was fun going round the houses, which for me is what it's all about!

I'll give the set a good going over in due course and hopefully get it performing to it's best. So thanks Steve for what now promises to be a great set!

Cheers
Nick
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Old 14th Jul 2019, 9:54 pm   #2
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Default Re: KB KV014 - VC4 chassis

"So thanks Steve for what now promises to be a great set!"
Hi Nick,
These are great sets. Back in the sixties I looked after the RGD version of your KB KV014. I struck up a deal with the RGD dealer in Newcastle to supply me with sets at near cost price. He was pleased to sell me the sets because he received extra quantity discounts from the manufacturer. In the early seventies STC dropped the RGD brand and dealers were supplied with KB sets These included the hand made single standard VC100 models.

DFWB.
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Old 16th Jul 2019, 11:13 am   #3
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Default Re: KB KV014 - VC4 chassis

Hi David,
Thanks for that- I love these little snippets of history! I presume they didn't cause much trouble when they were new?

Conveniently, most of the caps in my set are Philips 'mustards'; there are only a couple of Hunts, one of which has already proved to be faulty!

The tube is made by Brimar and as it has transpired, still has excellent emission. Were these made by Brimar or did Mullard have a hand in some of the manufacture?

It's also surprising that a manufacturer continued with a hand wired chassis for so long. PCB's had been common for parts of TV's for at least the last 10 years. It must have increased production line costs & manufacturing errors, so I wonder if they benefited from a reputation for reliability?

Cheers
Nick
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Old 16th Jul 2019, 12:22 pm   #4
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Default Re: KB KV014 - VC4 chassis

Hi Nick,
Very few service calls to these sets, mostly with customers having difficulties tuning in BBC2. Later on to extend the service life the VC4 sets were modified to have a push button UHF tuner fitted.

The Brimar CRT was made by Thorn-AEI Valves and Tubes Ltd.
In the early sixties STC sold the valves tubes division to Thorn-AEI.
https://www.gracesguide.co.uk/Brimar

Your set will have a Brimar 6BW7 in the sound IF amplifier. In later VC51 sets the Mullard EF80 was fitted in lieu of the ST&C valve.

DFWB.
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Old 16th Jul 2019, 11:40 pm   #5
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Default Re: KB KV014 - VC4 chassis

I have always had a fondness for these hand wired KB sets . When I was my early teens I used to buy them from the local TV shop for 25p each! Sometimes a few valves were missing but they never took much to get them going. I would sell them to mates at school for 30 bob, a huge mark up! But that did include installation and the provision of a suitable bit of wire for a BBC aerial.

My best find was a Deep scene scrounged from a neighbour's back garden, it had a broken tube and it took me weeks to find one and get it going!

I now have a few in my collection from VC1 to 53 none have taken much work to get them going!
I have one the same as yours the biggest problem with that was that all the glue had dried out and the cabinet was coming apart in all directions.

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Old 17th Jul 2019, 12:16 pm   #6
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Default Re: KB KV014 - VC4 chassis

25p was about the going rate for TV's at jumble sales when I was a kid. Nobody ever wanted them except me as everyone was trying to get rid of B/W and switch to colour. My mother was less than happy when I would wheel another one back in dad's wheel barrow from the jumble sale in the village hall!

I was at school in the early '80's when the ZX81 became popular. I took it upon myself to fix all the old crappy TV's that parents donated. We had several larger screen KB's which were good as the whole class could see them. They worked well with the ZX81. The teachers just seemed to accept that I was the kid who fixed the tellys in the lunch hour or after school until the care taker came round to lock up!

I can't imagine schools would allow kids to play with live chassis valve tv's these days!

Cheers
Nick
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Old 17th Jul 2019, 12:29 pm   #7
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Default Re: KB KV014 - VC4 chassis

The VC series was an example of a dated design that was continually improved and tweaked, but still was very much the old VC1 in posh clothes. No-one else was using a hand-wired chassis or a PL36 in the late Sixties, and everyone else's single standard mono chassis used those odd three-legged devices in the IF strip. Mind you, the VC100 did have one transistor to make up for the lack of VHF tuner!
If you're amazed at the hand-wired mono chassis, you need to see a rare CVC1 dual standard colour which is a miracle of engineering. I have a single standard CVC2 which is still something of a jungle underneath but they were amazingly reliable sets, let down by a somewhat unconventional decoder.
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Old 20th Jul 2019, 8:26 am   #8
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Default Re: KB KV014 - VC4 chassis

The VC series was a pleasure to work with and always produced a smile when one appeared on the workbench [especially on a Monday morning]

ITT/KB produced one of the finest ranges of television receivers that evolved from the VC1, massively reducing tooling costs.

The CVC5/9 hand wired colour chassis despite it's hybrid construction was probably one of the most reliable of all time, much liked by repair guys and customers alike.

I sold the VC4/VC52 new and other than a rare unsoldered joint [that usually showed up in the first few months] very rarely generated a service call.

ITT/KB. Sadly missed.

To be fair the P/C VC200 was also very reliable but had lost that 'magic'. John.
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Old 20th Jul 2019, 11:22 am   #9
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Default Re: KB KV014 - VC4 chassis

That's a really great result Nick and hats off to you for doing the detective work! I'm so pleased the set has plenty of life left in it.

It certainly had me fooled, with the crt exhibiting all the classic signs of running out of emission. Just goes to show...

Now you need to find a back cover for it. It should be a cream colour on that model.

Steve
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Old 20th Jul 2019, 11:30 am   #10
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Default Re: KB KV014 - VC4 chassis

Quote:
Originally Posted by Heatercathodeshort View Post
The CVC5/9 hand wired colour chassis despite it's hybrid construction was probably one of the most reliable of all time, much liked by repair guys and customers alike.
"Hand wired"? Surely not?

I entirely agree that they were very reliable (for a hybrid CTV chassis) and fairly easy to work on. The 20" sets had (usually) CRTs from the far east and they tended to get rather tired much sooner than the Mullard 22 and 26 inch European made ones.

Of course, the CVC5/8/9 series and the VC200 were all based on designs from ITT's German set making operations (Standard Electric Lorenz - SEL / Schaub Lorenz).
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Old 20th Jul 2019, 1:44 pm   #11
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Default Re: KB KV014 - VC4 chassis

Quote:
Originally Posted by Heatercathodeshort View Post
I sold the VC4/VC52 new and other than a rare unsoldered joint [that usually showed up in the first few months] very rarely generated a service call.
Hi John,
My chassis has a label that says 'VC4' and another label that says 'VC52' (or VC53, can't remember which). Does this chassis have two designations?

As far as I can recall, the KB's I had as a kid were 625 only but had a hand wired chassis that looked very similar to the VC4. Was there a similar single standard chassis or am I misremembering and they were actually dual standard? Obviously, back then in the early '80's, I would have ignored the 405 side of things anyway as it was 625 I was after!

I must say there seems to be a wide variety of KB, RGD & Regentone (I think) sets from the '60's, most of which have very nice styling. It must have been a pleasure being a dealer for these brands back then!

What was LOPT reliability like? I believe Steve acquired my set with no LOPT and managed to find a NOS one? This is larger than the original as the EHT rectifier socket won't fit in it's original space. The EHT overwind is potted in a plastic material.

Quote:
Now you need to find a back cover for it. It should be a cream colour on that model.
Hi Steve,
Conveniently, there is the exact same model on Ebay at the moment, with a good picture of the rear cover. It's hard to tell what the colour is but it looks a sort of beige. The bowler hat would be a good start, but the rest would be possible to recreate. Just need a CNC mill or a laser cutter...

All the best
Nick
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Old 20th Jul 2019, 2:21 pm   #12
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Default Re: KB KV014 - VC4 chassis

The single standard version of the VC series was the VC100. These were quite rare at the time.

The CVC5/9 was a hybrid colour chassis I think PL509 PY500 PCF802 PCL805 and PCL86 valves employed and hand wired of course.

There were many model variations with the same basic chassis, VC1/2/3/4/52 etc mainly cabinet differences, push button tuner etc but were all basically the same. John.
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Old 20th Jul 2019, 3:00 pm   #13
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Default Re: KB KV014 - VC4 chassis

Quote:
Originally Posted by Heatercathodeshort View Post
The CVC5/9 was a hybrid colour chassis I think PL509 PY500 PCF802 PCL805 and PCL86 valves employed and hand wired of course.
I'd be interested to hear what your definition of "hand wired" is. Surely these sets were not "hand wired" (in the way the VC1/2/3/4/11/52/53/100 chassis were), as almost all of the circuitry was on printed circuit boards?
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Old 20th Jul 2019, 3:32 pm   #14
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Default Re: KB KV014 - VC4 chassis

The VC4 was fitted with the Philips AT7650 miniature turret tuner, similar to the one in the Philips Style 70 sets.
In the original VC1 chassis the triode section of the PCL84 video amplifier was used as white spot clipper on 405 lines. Later on the KB service division suggested a modification which involved using the PCL84 triode as a frame sync pulse amplifier and shaper. The OA81 interlace diode was replaced by the grounded grid amplifier. All subsequent models incorporated the modification.
VC1 and VC2? receivers had a two stage sound IF and intercarrier amplifier using Brimar 6BW7 pentodes. VC3/4/5 models had only one 6BW7.
In the early dual standard chassis the FM sound was picked up from the video detector diode. In the VC3 models the FM intercarrier was amplified by the PCL84 pentode and then passed to the single stage sound IF amplifier.
The VC1 chassis didn't have a stabilised line timebase, the width was adjusted by tappings on resistor chains in the HT supply to the boost diode.

DFWB.
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Old 20th Jul 2019, 5:06 pm   #15
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Default Re: KB KV014 - VC4 chassis

There were other significant differences between the VC1 and subsequent chassis:

The change from an ECC81 line oscillator to a PCF802.

The VC1 used two customer accessible line hold controls: 405 and 625, but later chassis only had one, to allow separate 405 and 625 contrast controls to be provided.

The VC1 used an HT smoothing choke, whereas subsequent chassis used a high power resistor in its place.

Last edited by dazzlevision; 20th Jul 2019 at 5:12 pm.
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Old 20th Jul 2019, 6:34 pm   #16
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Default Re: KB KV014 - VC4 chassis

Ah, I see what you mean. Yes the main board construction was printed circuit with a lot of wiring connecting up components mounted on the main frame, yards of it!

Yes their were circuit differences but considering this series of chassis ran for 10 years with substantially the same basic circuit and metalwork, it did very well. John.
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Old 20th Jul 2019, 8:25 pm   #17
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Default Re: KB KV014 - VC4 chassis

Another modification to the VC1 chassis which became standard in all later VC models.
Very early production sets employed for switch-on surge protection a Brimar CZ4 thermistor in series with the mains supply. This arrangement proved to be unreliable and the approved modification was to remove the CZ4 and insert a Mullard VA1026 thermistor in series with the heater chain. To compensate for the removal of the CZ4 a 13ohm 10watt resistor was inserted between the "top" of the mains dropper and the silicon diode HT rectifier.

DFWB.
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Old 21st Jul 2019, 7:20 am   #18
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Default Re: KB KV014 - VC4 chassis

Rank Bush Murphy had a similar problem (and subsequent factory mod) in their A336 chassis, used in the Bush TV125 and Murphy V879 series.
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Old 21st Jul 2019, 9:39 am   #19
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Default Re: KB KV014 - VC4 chassis

Was there not a frame sync mod with the early chassis? From what I can remember it involved removing the triode section of the PCL84 [spot limiter]and rewiring it as a frame interlace filter.
It cured the intermittent frame roll with change of camera on 625 only. It was a long time ago!
I do remember the thermistor mod. On removing the back there were just two curly wire ends with the body of the Thermistor lying on the chassis.
John.
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Old 21st Jul 2019, 9:50 am   #20
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Default Re: KB KV014 - VC4 chassis

See post #14 (from Fernseh).
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