1973 Rediffusion CU2213

 redmk1 Rediffusion MK.1 Series Chassis – Hybrid

Model: CU2213


System: 625 Line

Original List Price : £347.00

Technical Specifications

V500 PL509 Line Output
V501 PY500 Efficiency Diode

Transistors: 47

Signals Panel
TR001 BF196 1st I.F. Amplifier
TR002 BF194 2nd I.F. amplifier
TR003 BF197 2nd I.F. amplifier
TR004 BF197 I.F. amplifier output
TR005 BF194 Distribution amplifier
TR006 BC148 A.G.C. detector
TR007 BC157 A.G.C. amplifier
TR008 BC158 Audio Driver
TR009 BD131 Audio output
TR010 BD131 Audio output
TR011 BF197 A.F.C. amplifier

Decoder Panel
TR200 BC1489 Luminance Delay Line Driver
TR201 BC148 Luminance emitter follower
TR202 BC194 Gain controlled amplifier
TR204 BF194 2nd chrominance amplifier
TR205 BF194 3rd chrominance amplifier
TR206 BC108 PAL delay line driver
TR297 BC147 7.8KHz identification amplifier
TR208 BC147 R-Y chrominance emitter follower
TR209 BC148  Burst Amplifier
TR210 BC157 “”
TR211 BC148 D.C. amplifier
TR212 BC147 Sub-carrier oscillator
TR213 BC148 Sub-carrier driver
TR214 BF197 B-Y amplifier
TR214 BF197 G-Y amplifier
TR216 BF197 R-Y amplifier

RGB Drive Amplifier panel
TR300 BC147 Red amp emitter follower
TR301 BF337 Red output amplifier
TR302 BC147 Green amp emitter follower
TR303 BF337 Green output amplifier
TR304 BC147 Blue amp emitter follower
TR305 BF337 Blue output amplifier
TR306 BC148 Beam current limiter
TR307 BC148 Brightness pulse generator

TimeBase Panel
TR400 BC158 Sync generator
TR401 BC147 Line sync generator
TR402 BC149 Line oscillator
TR403 “”
TR404 BF337 Line driver
TR405 BC158 Field oscillator
TR406 BC107B Field driver
TR407 BC148 Field oscillator
TR408 BF337 Line & Field blanking

TR600 2N3055 Field output

Convergence Panel
TR700 AC128 Line convergence clamp
TR701 AC128 Field convergence clamp

Diodes: 45

Signals Panel
D001 OA90 Sound & vision detector
D002 OA90 “”
D003 1N4148 A.G.C. delay
D004 1N4148 “”
D005 OA90 Discriminator diode
D006 OA90 “”

Decoder Panel
D200 OA90 Burst isolating diode
D201 AA143 Saturation control
D202 BA155 PAL switch
D203 BA155 “”
D204 1N4148 Phase detector
D205 1N4148 “”
D206 1N4148 A.G.C. oscillator
D207 BA102 Oscillator control
D208 OA90 7.8KHz restorer
D209 OA90 B-Y demodulator
D210 OA90 “”
D211 OA90 R-Y demodulator
D212 OA90 “”
D213 1N4148 Pulse shaping
D214 HG5008 Threshold diode
D215 1N4148 A.C.C. restorer diode

RGB Drive Amplifier Panel
D300 BA145 Red clamp
D301 BA145 Green clamp
D302 Ba145 Blue clamp
D303 BA145 Pulse limiter
D304 Ba145 Pulse DC restorer
D305 BA148 Red amp protection
D306 BA148 Green amp protection
D307 BA148 Blue amp protection

Timebase Panel
D400 BA514 Line Flywheel
D401 BA154 “”
D402 HS9078 Field oscillator
D403 HS9078 Field timing
D404 HG5008 Field discharge
D405 BA145 Blanking DC restorer
D406 HG5008 Protection diode
D407 BA145 Negative line rectifier
D408 BA145 Protection diode
D409 1N4148 Protection diode

LOPT Panel / EHT Tower
D500 BA148 Line shift rectifier

Power Supply
D600 BY127 H.T. rectifier
D601 TRC100P L.T. rectifier
D602 TRC100P “”
D603 BA148 Field pulse limiter

Integrated Circuit: 1

IC001 TBA 750 6MHz Intercarrier

CRT: 22″ Mullard A56 120X

General Information:

Here is a brochure photo showing the CU2213, followed by the actual set in my collection.



The Rediffusion has an EHT tower in this set, there’s NO dangerous shunt stabiliser employed though just two Valves, a PL509 for line output, PY500 efficiency diode, the LOPT, LOPT PCB and the tripler. Seems a good way to trap a load of heat so perhaps that was their reasoning, then again maybe it was shielding interference out from the rest of the circuit.

Below is a picture showing what you will find in the tower.


Saturday 3rd October : The pick-up

Well its arrived, spent a very nice day with Gary ( 405 Fan ) travelling down to Manchester to pick it up from Mike ( Mike66). Had a super chat about all things TV and got to look around Mikes very nice vintage collection and his workshop.

The set is very tidy and the water stains on the top and general cabinet scuffs were easily dealt with, in about 30mins it was looking much better for it. I’ve only had a scant  look Inside, its very clean and seems to be untouched, I will give it a thorough inspection over the coming days to evaluate the state of play.

rediff-01 rediff-02

Rediffusion like so many manufacturers around this time, adopted the modular approach to their design of the chassis. This would eventually help usher in the era of field engineer panel swapping, leaving the bench techs to component level fault find when panels were returned to base. This greatly speeded up the number of calls a field engineer could make and customer down time reduced in the process.

The MK.1 chassis has two sprung twist locks top left and right, with a central hook lock . When the spring locks and hook are disengaged, the whole chassis can be tilted forwards. **

In this forward position the inner boards and components are revealed, along with the customer controls on/off, brightness, colour. volume and tuner etc.

** Caution you must ensure you first flip up the convergence panel which is mounted on the top centre of the frame. Failure to do this could prove disastrous. With the convergence panel left in the down position and the chassis is tilted forwards, means it comes into direct contact with the Tube neck and could snap it off. 

Picture below shows the chassis in the locked up position.

rediff-03 rediff-04 rediff-05

Monday 5th October

Well this set is D.O.A. quick inspection reveals FS601 the 3A power supply protection fuse is blown. Will now need to do some investigations looks like I get the fun one to fix again.

Update: R453

Well I thought I would take a look at the Time-base panel in case there was something obvious on there that might be causing the power up fault. No sooner had I looked at the panel a glaring problem leapt out at me. R453 was broken away at one end. This 39K 5W is part of a potential divider fed by via the 290V rail to  feed to the collector of TR408 BF337 which is the Line & Field blanking transistor. Could this be the cause? We shall see. Sods law though, I have a myriad of TV fuses in stock but would you believe no 30mm 3A.

3A protection fuse blown
Timebase panel removed

tmb-02 tmb-03 tmb-04

Update: Timebase and filter cap C901

R453 repaired and the timebase board now reinstalled into the chassis. Before power up I snipped the filter cap C901 .1uF out of circuit as it was one of those grey Plessey caps. I didn’t want it going pop, I’ve now replaced it  with an X2 cap (see below).


The Newly replaced C901 X2 0.1uF Filter cap


Whilst at it I thought I would test the A56-120X, after all if its a dud I don’t really want to waste time, effort and parts. Looks like I have a set with a ReGun tube its labelled ” Suffolk Colour Tubes” and has a date of 22/8/80 so looks like 22nd Aug 1980.  Thankfully its looks to be a reasonable tube. The blue gun was low ( down in the yellow section of the meter) and didn’t recover with sustained running. I performed a clean & balance and blue reads as good as Red & Green. This CRT should give a good picture.

All I need to do now is wait for the 3A 30mm fuses I ordered to turn up then this story can continue.



Tuesday 6th October

Spoke to Malc ( Ex Rediffusion Eng) I was looking along the lines of filter cap, boost cap, he suggested the possible cause for the 3A blowing to be D600 BY127 H.T. rectifier being s/c. On the PSU board we also have D601 TRC100P L.T. rectifier & D602 TRC100P . This is a tiny little panel located behind and below the decoder. The decoder has to be removed to gain access. The little panel can then be unclipped from its securing spring. Its a tight job as the leads are not very long making it a tricky board to get at.

Will check the diode and report back.

decremoved redmk1dec1 psuboard

Here is the RGB drive PCBrgbdrive

Update: PSU Checks

Removed D600 ( BY127 ) its tested OK ( see below) so that’s not the cause of the 3A fuse blowing.

Being thorough I checked  D601 or D602 ( TRC100P) which form the full wave rec’s to provide the 24V and 22V rails I knew these would be OK as FS601(2A) protection fuse was fine also but doesn’t hurt to check. I also replaced C606 & C607 both .01uF as both were very cracked Mullard tropicals.

So the hunt for the 3A fuse killer continues….


Diode Under test

d600-1 d600-2 d600-3

Update: FS601 not blowing now but the cut-out still trips.

OK all panels back installed on the chassis. To recap on what’s been done. Repaired R453, Replaced C606 & C607, Checked D601, D602 & D603.

I decided to use a 3A 20mm fuse which luckily makes contact with the in-line holders contacts. Powered on and the cut-out trips but the 3A fuse does not blow, well that’s an improvement. The protection via the cut-out works in two ways and has two elements.  One for mains current the other cathode current of the line output bottle. So excessive current in either or both will activate the cut-out

To prove if the fault lies on the timebase board I replaced the timebase board with a spare. Powered on same scenario. So what’s the chances of two boards having the same fault, not likely. So the fault must exist elsewhere. Now to check the 24V on PL4B/3 or DC short-circuit somewhere, Line output valve or the RGB panel. This is turning out to be my usual extended PITA…… the s/c fault could be anywhere.


So I’ve established the 3A fuse is now OK but the cut-out is still tripping. The 2A fuse is OK. Replaced the Timebase panel and the same scenario. Then reset the cut-off and powered on whilst checking PL4B/3 on the timebase panel, there should be 24V here…. well there’s nothing, the cut-out operates and monitoring PL4B/3 just shows a few millivolts, getting closer? Doesn’t feel like it I reckon the 24V is a red herring, its likely shutting down before.


Whilst scratching my head trying to figure out what is the cause of the cut-out tripping, I noticed the core of L501 which is on the LOPT panel, had dropped through its core and was resting on the chassis.

I pushed this back in and temporarily secured with a bit of blutack. I then further observed that RV503  (1K ) the Vertical Shift pot, had a bulge on one side. Poking this bulge with a screwdriver made it drop off ( see below) revealing the core wire-wound track. Must have over heated at some point in it life. I decided to replace the pot (see below) seeing as I was in there with an identical NOS 1K I had in stock.

Could this be having anything to do with the cut-out problem? Whilst I find these faults, they may as well be addressed. Back to scratching my head ……….

rv503-1 rv503-2

Further observation

After the above I reset the cut-off and powered on, I hear the Degauss thump and I noticed the heater light up in the PL509 then after 5 seconds the cut-off tripped. I then reset it again and this time no PL509 heater glow but the cut-off still tripped after 5 seconds. Checked the heater on the PL509 and its OK.

First Light

As I stated above,  removed the PL509 to test the heater continuity, reseated the valve, reset the cut-out and powered on. Again degauss thump heard, audio hiss from speaker noted, PL509 heater lights up, 9-10 seconds later cut-out tripped.

Reset, cut-out, tried again,  this time efficiency diode PY500  also now lights up ( that’s a new step) and the set stays on a little longer before tripping. Reset cut-out for the third time and this time the set  stays on. A raster appears fills out screen then fades out.

With the set still operating I connect up the test card generator and start tuning. I can see faint flashes as I tune,  then when on signal, bingo! up pops a Black & White test card F. Setting the brightness and adjust colour, it all comes alive albeit a little in the dark side but that probably due to brightness set up required or component drift/failure.

Need to run through the full set up procedures as detailed in the manual, then leave it on soak to flush out the stressed components.




Wednesday 7th October

No work today other than reading up on the electrical set up procedures for decoder,RGB board, timebase, convergence and EHT.

One thing I have noticed is the three A1 switches S700, S701 & S702 on the convergence panel have been removed. Checking the board on my cable chassis shows them to be missing too. By the way I plan to get the cable chassis up and running too, if anyone has a Rediffusiion frequency translator box ( Telebox ) going spare, I would be interested.

redmk1con1 redmk1con2

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6 years ago

Hi Chris,
Might have found the reason for RGB gun switches not being fitted. In the technical suggestions section of Rediffusion Engineering journal dated September 1979 a proposal was put forward to the committee.

Quote from journal: Mr Dodd’s suggestion, which will be incorporated in a Technical Circular from R.C.E, concerned the tracking problems associated with the A1 switches on Mark 1 receivers.

He proposed that the switches should not be replaced but removed, and the connections linked on the back of the board. When needing to turn off a gun for setting-up purposes, the lead to the RGB board can simply be unplugged.


6 years ago

Hi Rich,

Excellent thanks for that piece of the puzzle, I was contemplating putting the switches back in but won’t now.

On loan I have volume 5 of Technical Circulars, it only covers the period 1968 – 1972. Its a huge manual I can only imagine what the complete suite of volumes would reveal about all the series of sets over the years.


6 years ago

By the way anyone looking in and unfamiliar with the site, there is a stock faults section under the service menu at the top of the page.

I’m adding to this as time permits, you will find many early Colour TV set stocks faults, among them the Rediffusion MK.1 and a fault finding guide.

6 years ago

Hi Chris,
Excellent write up so far on the Mark 1 chassis. I see L501 core has dropped out in your set and this issue was covered in the May 1979 Rediffusion Engineering journal Vol 2 No.14 page 421.

“Mr Quick had noticed that if the core of this inductor falls out, the receiver displays a lack of width, and there is a risk of overheating and damage to other components.
He suggested that the core should be glued in place, and R.C.E. have agreed to issue a Technical Circular about this”


6 years ago

Hi Rich,

Once again many thanks, its nice to know these discoveries are in fact old problems that have been encountered before. Rediffusion acknowledge gluing the core to be the working solution, is exactly what I shall do

After a break and reading the set up guides I will embark on all the electrical set up requirements. I also want to see what EHT I’m running at and get to the bottom of the rather dark appearance of the raster, might just be the beam current and pre-set brightness.

4 years ago

Our firm had a few of these sets out on rental. They were badged “BWE President”. I much preferred them to the later solid state Doric chassis.

Would love your thoughts, please comment.x