1967 Decca CTV25

The “Battersea” Chassis

Model: Decca CTV25

Year:1967

System: 405/625 Line Colour

Original List Price : £377 gns

Valves:
V200 PL802 Luminance output
V301 ECC82 Frame Oscillator
V302 PL508 Frame output
V303 PCF802 Line Oscillator & Reactor
V400 PY500 Efficiency diode
V401 PL509 Line output
V402 PD500 EHT Stabiliser
V403 GY501 25kV Rectifier
V600 PLC84 R-Y Amp & clamp
V601 PCL84 B-Y Amp & clamp
V602 PCL84 G-Y Amp & clamp

Transistors: 35

Diodes: 40

CRT: A63 11X

General Info:

Dual standard television incorporating 11 valves, 35 transistors, 40 diodes and providing the following:-
Colour and Monochrome on the 625-line system on U.H.F channels 21 – 68 inclusive and V.H.F. Channels C – H inclusive and suitable for colour modulation to the PAL system. In addition monochrome on V.H.F. channels 1 – 13 inclusive in bands 1 and 3 operating on the 405-line system. The set is provided with a multi-band tuner controlled by a six push button channel selector mechanism which also selects the transmission standard appropriate to the desired channel. The tuner however, has the attribute, ” any button, any channel, any system”.

decca1

decca2 decca3 decca4 decca5 decca6 decca7 decca8 decca9

 

Powered on, I cannot get a good locked colour. When fine tuning to the testcard I can get a good B&W picture, but tuning to tune it for colour sync and colour lock go out is impossible. Looks like it might have decoder issues/ref osc.

decca10 decca11 decca12

To get to the bottom of colour issue I need to disable the colour killer to shed some light on the fault condition. Checking the manual I found the colour killer can be overridden by shorting D600. I fed in colour bars from the Philips 5515T, powered on and the truth be confirmed, the reference oscillator is off hence unlocked colour.

decca13 decca14

Now what’s needed is to follow the oscillator tuning procedure, this entails scoping pin 1 of the decoder and checking the waveform present matches the one in the manual. The amplitude needs to be 2V p-p. Then I need to connect the scope to the left hand of R658, then adjust L604 for maximum output which should be 6V. Again a sine waveform is given as an example. Fingers crossed this sorts it. Checked the waveform at pin 1 of the decoder, it looks correct and reads about 1.8V p-p, it should be 2V but I guess that’s close enough.

decca15

Next up is setting the tuning of the oscillator and peaking it to the stated 6V p-p unfortunately the colours are still unlocked need to put my thinking head on now, I wonder if I need to now perform Burst tuning followed by setting up the phase discriminator.

decca16

Checked the burst, it should be 30V p-p +/- 5V I have roughly 23V p-p again pretty much within spec. I will check the phase discriminator next.

decca17

Success, adjusting the phase via VR602 has given colour lock. I think I need to sort the delay as I have blinds. Still much improved on what I had.

decca18

decca19

7 thoughts on “1967 Decca CTV25

      • Thanks for the interest. I think I am the last of the 3 main engineers who designed all the Battersea chassis’s.

        0

        • Hello David,

          I’m speechless!

          What an absolute pleasure to hear from you, very honoured to actually have one of the original Decca Battersea design engineers take the time to comment on this website. As you can see this CTV25 although requiring a little more work, still gives excellent service 50 years later. A true testament to the quality of the circuit and chassis you designed.

          You might also be interested to see that I have the later version of the Battersea chassis in a very rare Decca CTV22C. That one as I’m sure you know uses a solid state tripler, you can see it if you click here It needs a fair bit of work as its been got at, however its certainly on the list to tackle and should make a lovely example of a rare 22″ dual standard.

          Once again thank you for taking the time to say hi.

          0

          • It was my pleasure Chris. I was interested in the bit on vectorscopes. I made one in the early days. Very easy as it’s only an NTSC decoder with the U & V outputs going to the X and Y amplifier inputs on your scope. If you want a test circle for line up you can just inject an unlocked amplitude of 4.43618 Mhz.
            Have sent you an email.
            Best wishes

            0

Leave a Reply

dialog-information.png
Important Notice: To leave a comment use the box below. You must tick "I'm not a robot" and then complete the puzzle, otherwise the automated comment system will reject your post and treat it as spam.
 

Your email address will not be published. Required fields are marked *

*