Bought this Pye Continental CTM4 at the NVCF.
The cabinet is a bit rough and further examination reveals that the loudspeaker is missing. Also missing are the tuner valves, PCC84 and PCF80. The two PY82 HT rectifiers are missing. Way back in 1966 I replaced the PY82s with a pair of PY81s, a quick fix solution at the time because I didn't have any PY82s in stock.
The electrolytics are dated Feb/Mar 1956. Curiously, the AW36-21 CRT is date stamped R7J, late 1957 or is it 1967?
The chassis is a slightly modified version of the late production VT4. The IFs will be the BREMA values, 34.65Mhz vision and 38.15Mhz sound.
Like the VT4 the tuner is attached to the left side of the cabinet.
Way back in 1953 the Pye V4 chassis was considered hi-spec having features such as flywheel line sync and and a proper vision AGC system.
The VT4 was the first UK made receiver to have a Band 3 tuner.
Geordie McBoyne.
Use the late production VT4 service manual and the supplement for the CTM4.
Cabinet presentation apart, the only difference between the VT4 and the CTM4 is the type of CRT used. An electrostatic focus Mullard AW36-21 or Cathodean C14-3A in the CTM4.
Geordie McBoyne.
(16-05-2018, 09:18 AM)Geordie McBoyne Wrote: [ -> ]Curiously, the AW36-21 CRT is date stamped R7J, late 1957 or is it 1967?
R = Mitcham
7 = 1957*
J = October
* Two reasons: no domestic valve so, presumably, no CRT production at Mitcham by 1967 and, to differentiate between the 50s and 60s, a week number from 1 to 5 was added, thus B7J2 would be Blackburn, 1967, October, second week of month but B7J would be 1957.
Testing the CTM4. Found two PY82 HT rectifiers diodes and fitted the correct valves in the tuner. Quite a few problems with the heater chain not helped much because some wires in the chain had been snipped off.
Been using a RS components RS14 digital multi-meter for fault finding, its a rather disappointing instrument but for £24 what can you expect?
Also there is evidence of some creative '50s and 60s servicing solutions to sort out.
A suitable elliptical loudspeaker has been found, a slightly smaller replacement for the original 7 X 4" 'speaker.
Hi Terry,
It's most likely the CRT was replaced sometime in 1957 or 58. It's unlikely anyone would have a new Mullard CR tube fitted in this set in 1967 or 68.
Geordie McBoyne.
(16-05-2018, 09:00 PM)Geordie McBoyne Wrote: [ -> ] It's most likely the CRT was replaced sometime in 1957 or 58. It's unlikely anyone would have a new Mullard CR tube fitted in this set in 1967 or 68.
As I said before, that CRT could only have been made in 1957.
I've been wondering when the set was actually sold because a tube replacement would have been extremely expensive for the owner at at a time when Purchase Tax rates were sky high - up to 66⅔% at one time - if the original failed after the expiry of the 12 month guarantee!
Have you, looked at the date codes on the EF80s as these are most likely to be originals?
Possibly a set that may have been in stock for some time as 17 inch sets were gaining a foothold by 1955-1956.
Then perhaps the original CRT failed within the guarantee.
All surmise of course but the upside is the CRT "could" be good.
I fitted a Mazda Electrostatically focussed CRT to a V4 in 1970 and the result was quite remarkable very bright indeed and with excellent focus.
The set was used for testing Relay Vid boxes, the V4 had been already converted to 625 line operation. it was a CME14??
The Pye CTM4 is connected to the main via the variac. Supply set to 200 volts because the mains dropper resistor is open circuit and is at present shorted is out.
The 250mA line output stage fuse removed for the preliminary tests.
Oscilloscope analysis reveals the line and frame oscillators are working delivering sawtooth drives at the correct frequencies to the grids of the output valves.
Sound output stage working but no activity from the tuner. The HT supply to signal stages was found to be missing, the 200ohm decoupling resistor R45 was found to be disconnected from it's anchor tag.
Now signals can be heard and after turning down the sensitivity control a video waveform is present at the video detector load resistor.
The video amplifier stage is not working so that stage will be next for testing.
Will report back my findings later today.
Geordie McBoyne.
In fact the fault in the video amplifier was a simple one. The 15Kohm anode load resistor was short circuited to the centre spigot of the valveholder. Repositioning the component effected a cure.
40 volts of active video + syncs is present across the load resistor of the video cathode follower.
Assuming the CRT is OK this set will display a well contested picture.
Geordie McBoyne.
Hi.
Well you certainly are getting a lot of stick from John Wakely about the set. I had to laugh when he said its a VT4 in a posh frock....... Blimey a CTM4 posh.... I don't think so.
We do know of course that the series of these sets didn't have the best line output transformer and the early V4 had indifferent scan coils, they were improved though later on so the CTM4 could be OK.
Yesterday I picked up a Philips 14 inch set from Norman, for a 14 inch it's big, I'll be starting a thread soon on it. Not sure of its fate as yet as it's too big but if good I'll pass it on if there are major issues and the tube is OK it'll go into my V4. Anyway let's wait and see before making rash decisions.
Hi.
I was reading about the CTM4 on the UKVRRR forum and my V4 has come up re a LOPT transplant. Indeed it has a Ferguson transformer fitted. It works perfectly although I had to alter the scan coil wiring from parallel connection of the coils to series. Line linearity is pretty good and really the only way to see it's off a little is to measure the squares on the test card. EHT is 12kv and with much improved regulation no serious defocussing on increasing the brightness. The transformer though is decidedly loud, that 10, 125hz whistle is painful according to Anne.