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1500 chassis: Solid-State Field and modified cct

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crustytv
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Discussion Split off from the 1500 dropper thread here

September 1977 a document covering many updates for the service manual, including the fusible resistor mentioned in the other thread.

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Topic starter Posted : 01/05/2016 5:01 pm
Focus Diode
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Did I see right? A version of the 1500 with a solid state frame stage?!
Brian

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Posted : 01/05/2016 11:53 pm
Cathovisor
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So I'm going to assume that this is what's inside the Ultra here.

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Posted : 02/05/2016 12:04 am
slidertogrid
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Did I see right? A version of the 1500 with a solid state frame stage?!
Brian

Yes you did see right! I never saw a 1500 with a solid state frame stage!
The mod sheet reads as if it deals with updating older sets by fitting a new cabinet and varicap tuner maybe they modded the frame stage at the same time? maybe a PCL805T!
Thorn rentals did recall all of the 1690/1 series from rental because of the amount that caught fire. I did hear that they had replaced them with ex rental refurbished 1500s maybe this mod sheet was what they did ?
The PCL805 wasn't a bad valve though (ITT used it in the CVC series and I don't think failures were any higher than the PL508 which was designed for colour. It seems a lot of trouble just to do away with one valve. I wonder what they did about the heater voltage? Maybe it had a different value heater dropper section I suppose they would fit a new dropper when overhauling a set as most would have had a few" polo mints" or "dropper Piles" hanging on them by then...
ISTR there is a section of the 1500 dropper that goes O/C causing the LT rail to the IF transistors to go sky high. I remember having to replace the lot in one set.
Rich.

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Posted : 02/05/2016 12:36 am
Anonymous
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I thought the LT for the IF stage came from the cathode of the frame output valve or am i getting confused with another set ?
Rob T

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Posted : 02/05/2016 1:35 am
crustytv
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Here's the solid state field stage for the modified 1500 chassis. For speed I've just photo'd but will place a quality scan of the entire modification manual in the data library in due course.

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Topic starter Posted : 02/05/2016 1:54 am
crustytv
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So I'm going to assume that this is what's inside the Ultra here.

Given those sets are from the 1977 brochure and the modification manual is dated 1977, I think that assumption is highly probable.

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Topic starter Posted : 02/05/2016 1:58 am
Nuvistor
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That seems s lot of work to replace a PCL805, possibly there were supply problems and only enough valves produced for service requirements not manufacturing.
Not sure how many B/W sets were sold from 1977 onwards, I don't remember stocking any.
Frank

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Posted : 02/05/2016 11:54 am
slidertogrid
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What a lot of circuit and components just to replace one valve, it looks as if the frame scancoils were part of the mod and a mains transformer!
A lot of work. Maybe it wasn't carried out to previous valve sets then... but did Thorn really do another version of the main PCB right at the end of production just as they were launching a new solid state set?
It is surprising how many manufacturers did a variety of chassis in a very short time. Pye dual standards for instance, 11U for a few years but then the 67 chassis (at least two versions) then a year or so later the 368 and then they went to the single standard 369 169 again of which there were a few variants. They couldn't have made much money having to retool the assembly lines so often? Then you have to provide spares backup for them the stores must have been massive! I can hear the poor old storeman looking at his list " Lopt for a xyv1 MK2 series 7 chassis with modified rectifier base.. Isle 17 row 6 level 14... now where's the step ladder... 

Meanwhile the likes of KB stuck with the same basic design and chassis for the whole of the dual standard production. Even their first single standard was the same with just the 405 bits left out. By that time the chassis design must have been at least 7 years old, to top it all they were more reliable and longer lived than some of the later designs by other brands. Which would you have rather had in 1970 a ITT/KB vc100 or a Bush A774 ? One was a brand new model the other hankered back to the early 60's...
Has anyone seen one of these late 1500's with a transistor frame stage?
My mate Mick had what I thought was a very late 1500 brand new in it's box. it was the plastic cabinet 20" with mechanical tuner branded Marconi I think.
I am sure that had a pcl805. He got it from a mate who had bought it new and never used it I wonder if he can find out the date it was sold?
Rich.

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Posted : 02/05/2016 12:26 pm
Focus Diode
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I remember a rented 20" 1500 in October 1977 which could well have been brand new. The 4-p/b tuner looked like a conventional mechanical one, only for them to be light press action switches. A door in the back had the tuning presets as would be seen on a 3500 chassis. It was a super set with excellent gain. Never seen this version since. Can't have been very common as Radio Rentals were still hiring out mechanically tuned earlier versions into the '80s.
Brian

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Posted : 02/05/2016 12:39 pm
Jayceebee
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I certainly remember seeing that manual but never saw any modified sets. For the few customers that didn't want colour we "De-Crystalised" an old 3500 or 8500, as the name suggests it involved removing the 4.43Mhz crystal and fitting a shorting link shutting down the PAL decoder. A failed A1 beam switch on a 3500 could totally confuse the customer "My pictures have gone green on my black and white set!"

I don't recall any shortage of PCL85/805 in the late 70s or 80s but there certainly was around 1970/1 while I was working for an RBM dealer, we ended up fitting the much more expensive 30PL15 but never saw one of these fail.

Shortages that did affect us with the 1500 in the 80s were lack of BF197s used in VT7 vision IF amp and VT8 video driver positions. The supplied replacement was a four legged metal can device (can't remember the exact type) but nothing performed as well as the BF197, usual problems after fitting the so called TVT5 "equivalents" were mild intercarrier buzz and/or some clipping of peak whites.

Decent CRTs were also a problem around the same time, some were sourced from the Eastern bloc. Put side by side with a good UK produced CRT the pictures looked almost sepia in comparison.

The solid state 1615 chassis was supposed to take over from the 1500 but any out on rental were withdrawn due to fires caused by arcing around the line linearity coil.

John.

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Posted : 02/05/2016 1:22 pm
slidertogrid
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I remember a rented 20" 1500 in October 1977 which could well have been brand new. The 4-p/b tuner looked like a conventional mechanical one, only for them to be light press action switches. A door in the back had the tuning presets as would be seen on a 3500 chassis. It was a super set with excellent gain. Never seen this version since. Can't have been very common as Radio Rentals were still hiring out mechanically tuned earlier versions into the '80s.
Brian

I wonder then if it was a refurb with a new cabinet, varicap tuner etc..
British relay certainly did it. I remember seeing a 20" relay set which looked like a two year old TV however inside was a old Pye chassis full of greasy black wax capacitors. It seems they had simply fitted old chassis into a new cabinet with a modern 20" Russian made square tube. The front controls and station switch buttons were also new wired to the old chassis. Maybe it was a way of renting smart new looking sets as decontrolled?
Much later on in the 1990's a firm in Norfolk refurbed early Radio Rentals Baird TX10s. The version with the PIL tube and large plastic flap that covered the channel up down buttons. They fitted a regun tube, put the set in a black plastic "monitor style" cabinet with glass screen and supplied it with a new remote and 12 months guarantee. They had done a proper job on the chassis they were spotlessly clean and all the common faults done. They called it the "Tristar", There was a news report on Anglia news at the time "The worlds first recycled TV.."
It seems they weren't the first!
Sorry ! A long way off the subject of 1500 mains droppers I know..
Maybe we should split the thread.. Mystery Thorn 1500?
Rich.

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Posted : 02/05/2016 1:41 pm
Till Eulenspiegel
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The modifications are so extensive that the chassis should be re-designated with a different series number, something like 1550.
Rental controls were reintroduced in late 1973 so the modified sets could be refurbished models to get around the "over three years old" rule ordering sets under that age were subject to 42 weeks advance rental. There was still a market for rented mono TVs in the 1970s, although most firms were trying to ease themselves out low cost mono rentals.
Anyway, the modification resulted the wasteful mains dropper was removed so there is a useful reduction of heat in the cabinet.
Rediffusion and British Relay were masters at the refurbishment of older TVs in order to get around the hiring rules.
In some respects the modifications didn't come cheap, in fact a new set wouldn't have cost much more.

Till Eulenspiegel.

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Posted : 02/05/2016 6:34 pm
colourstar
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The modifications are so extensive that the chassis should be re-designated with a different series number, something like 1550.

Till Eulenspiegel.

Well here's a coincidence: I was reading the April 1984 issue of Television mag over breakfast only this morning and on the readers' queries pages was one headed 'Thorn 1525 chassis'. The enquirer had never come across one before. The response states that 'The 1525 is a variant on the well-known 1500...' Could that be that be our revised 1500?

Steve

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Posted : 02/05/2016 9:04 pm
Focus Diode
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I might be wrong but guess the 1525 chassis is the version with varicap tuning.
Certainly the 1977 Ultra models 6823 and 6844 are classed as 1525s.
Whether they have solid state frame timebases of not I don't know.
Brian

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Posted : 02/05/2016 9:43 pm
Till Eulenspiegel
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Original 1500 series: The +25 volt supply for the transistors is developed across resistors R79 and R136. These resistors are at the bottom of the heater chain. The supply is smoothed by two capacitors C56 and C58. The heater supply diode W7 supplies the chain with positive half waves which is a neat method of reducing heat inside the set. Not so nice is that the set is supplied from only the positive half cycles of the mains supply. The mains supply authorities must have hated these 1970s TVs what with the asymmetric demands from the mains waveform.
In the modified chassis with the solid state frame timebase the signal transistors are supplied from the new 25volt power supply transformer.

Till Eulespiegel.

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Posted : 02/05/2016 10:53 pm
Focus Diode
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One certainly learns something new everyday, especially when discussing the 1500 series which everyone knows. There was no mention of the solid state frame timebase in the 1976 "Television" articles although the varicap conversion was covered. The articles also commented the chassis was still in production.
Perhaps ironic they reverted to a mains transformer last seen in the 950 MkII chassis.
Brian

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Posted : 03/05/2016 8:12 am
steve1010
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"British relay certainly did it. I remember seeing a 20" relay set which looked like a two year old TV however inside was a old Pye chassis full of greasy black wax capacitors. It seems they had simply fitted old chassis into a new cabinet with a modern 20" Russian made square tube. The front controls and station switch buttons were also new wired to the old chassis. Maybe it was a way of renting smart new looking sets as decontrolled"

I worked as a bench engineer for British Relay and did many of these conversions, these were a way of getting around the 3 yrs decontrolled regulations
We got an extra £1.50 in our wage for every one we did, we received from the store's a box which contained a nice looking 20 inch cabinet and tube this was fitted with a UHF transistor tuner new controls and a small IF preamp PCB to make up for gain lost due to the lack of the VHF tuner.

The tube used was a cheap east European thing the screen looked like the surface of the moon, we removed the chassis from an old Pye 11U soldered up the system switch to 625 line and fitted the chassis into the cabinet, these sets then became model number GS20

They were awful sets with far too much IF gain buzzing crackling and going completely unstable unless the preset contrast was backed off, later as a field engineer i found they often worked far better with the IF sub PCB bypassed.

We also did a similar conversion with a PYE relay chassis (i cannot remember the chassis number) this became model number RV20

Steve

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Posted : 03/05/2016 5:28 pm
malcscott
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Hi Steve, i remember those sets. The tubes were from Poland (Unitra). Very rough phosphors and had a bit of a green tint, Malc.

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Posted : 03/05/2016 6:10 pm
Till Eulenspiegel
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I remember taking delivery of Ferguson 1500 series sets in 1976 and possibly 1977. By then the CRT and many of the valves were sourced from various Comecon countries, except that is the 30PL1 and 30FL2. The latter was made by Mullard, a sort of modified PCF80.
In 1975 I received a big delivery of Marconi 4808 1500 sets from Newcastle wholesaler Michael Black, many pounds cheaper than direct from Thorn. The 4808 was a rather ugly set but the customers seemed happy with it. When you consider the wholesaler had to make his profit I was becoming aware that buying direct from the manufactures was often not a good deal.
I'd certainly would have liked to to have seen one of those modified 1500 receivers. I like these lash up sets.

Till Eulenspiegel.

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Posted : 03/05/2016 6:18 pm
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