The tube on this TV takes a long time to warm up and the picture stabilise, If I had given the tube another minute to warm up on the second photo then the image would have been the same size as the before photo.
That's an interesting comment Mike.
A flat tube will not affect picture size. It could certainly affect the time taken for a watchable picture but not the size. Have you tried changing the boost diode or line output valves? Either of these will affect picture size and the time taken for any picture to appear. My Fergy 45 used to take about three minutes to produce a picture. A new PY800 reduced it to just over a minute.
Cheers
Hi Rich
Please excuse my ignorance, is V8 the line OP valve and V9 the boost diode?
I dont think I have either.
circuit is here download/file.php?id=18967&mode=view
Mike
PL36 Line output
PY83 Efficiency (Boost) Diode
U26 EHT Rectifier
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A PL36 I can help with but not a PY83. There are alternatives but I'd need to look it up. There was a time when I could recall the equivalents......
Ho Hum, I thought I had finished the set, and put the case back on, but if I can get more improvement then why not try.
The picture does take an age to come on about 3 times the time for the sound.
Right, Ill get the case of it again and probably the best thing is to give the PL36 a test on my Sussex valve tester. If it looks like it is down, I wouldn't mind buying your one Rich, if it is in good shape and spare.
Not sure if I can test the PY83 boost diode. Would this test like a normal rectifier diode.
Thanks
Ill update tomorrow, my back is giving out now.
I have a number of NOS PL36's so would be quite happy to pass one on for cost of postage. My bet is the boost diode though. I find PL36's very reliable. With regard to the PY81/800, yes I remember that being used as a replacement. The difference in heater voltage is only 2 volts and shouldn't have any effect as this will be distributed across the entire chain. In fact I think that's what I'm using in the Fergy 45.
Hi Mike, and Terry,
I don't know if you sorted out what that "ferrite" looking ring is, but Terry's surmise is correct, it is an ion trap, and is the same as type used on my GEC BT2211.. I have to confess, it's a bit of mystery as to how exactly you set it correctly, because it bears no resemblance at all to the usual Mullard type with its destinct magent and clamp screw.
I would surmise though, that the set up procedure is the same.
Marion
That's interesting the TV already had a PY81 fitted. I found I had a handful of PY81/800 pulls from a batch of valves I bought a while ago. I tested the PY81 fitted in the TV, at 50v it was conducting 44mA, this was marginally better than any of the other pulls that I had.
The PL36 however tested rather low. with the valve tester set as per the figures below.
The anode current was 43.4mA and the GM was 6.3 mA/v.
What benefit do you think I would see if the PL36 was replaced?
Thanks
Mike
The PL36 `s are so cheap NOS why not just replace it ?
... I don't know if you sorted out what that "ferrite" looking ring is, but Terry's surmise is correct, it is an ion trap, and is the same as type used on my GEC BT2211.. I have to confess, it's a bit of mystery as to how exactly you set it correctly, because it bears no resemblance at all to the usual Mullard type with its destinct magent and clamp screw ...
Thanks, Marion, it's nice to have that confirmed as I must have encountered many thousands of conventional ion trap magnets in the past, but never one of these ...!
As for adjustment, it will just be the usual 'tune for maximum smoke' - I wonder if there is (or was) a point spot to indicate where to start?
... I would surmise though, that the set up procedure is the same ...
Precisely!
When all else fails, read the instructions
What benefit do you think I would see if the PL36 was replaced?
Difficult to say without actually subbing.....
Usually an increase in width but if the boost diode is down as well and this is also replaced, an increase in boost HT, quicker warming up and a possible worthwhile increase in EHT which will further improve the picture.
When I was finishing the Fergy 45, there was sufficient width with a little in reserve and I spent 20 minutes or so getting the width, height and line linearity as best as I could, went for a break and switched on again after half an hour. Came on with slightly reduced width which opened out slowly so I changed the PL81.....
Spent the next 10 minutes reducing the width, readjusting the line lin........!
After 40 odd years fiddling with sets you'd think I would be aware of the effects of reduced emission bottles......!
the width is on the max setting
the width is on the max setting
That would tend to indicate that one or both bottles are low, especially if there is only just sufficient width
It probably won't be on max when both bottles are changed.....!
... If the LOP is running above correct power this can overrun the EHT rect heater giving it a short life ...
With the exception of the design error in one range of Thorn sets, which led to the introduction of the special TY86F (the T = 7V heater, rather than Thorn, so Mullard added the F suffix for Ferguson!), I can honestly say that I have never encountered a set with a short lived EHT rectifier ...
When all else fails, read the instructions
The TY86F for the Fergy 306T and 308T. I used one as a temporary sub for an EY86 and it worked well enough.
I recall noticing that the highly insulated and enclosed bases for EHT rectifiers often had grooving for a short length of resistive wire/small resistor, the choice of connected and "N/C" valve pins allowing for length tweaking- the implication being that the high volts per turn of LOPTs meant that a spot-on heater voltage couldn't always be neatly achieved with a low (often just one!) number of heater turns. Also the exact RMS heating effect of the pulsey waveform might have been difficult to calculate precisely and subject to a degree of uncertainty until prototype testing.
No idea how accurate this would be.
Used to be how RF power was measured. One bulb on RF and other on DC PSU and calibrated in watts. Diffuse plate and thin wall in the box. Should be better than 10%.
Hot wire ammeter in series?
Wouldn't any True RMS meter give an an accurate result?
In the days of the EY51, presumably this would have been a moving iron meter ...?
When all else fails, read the instructions
A moving iron meter on a block of dry hardwood with children and animals kept well away... 
or was it necessary to rettrofit existing sets.
Yes that was it. The sets were already on the market and the EY86's were dying rapidly so the TY86F was produced as a 'drop-in' solution for the field engineers rather than pull the sets to bits and modify.
