B&W TV Bush TV33 Fault
I am currently restoring a Bush TV33 which I acquired about 25 years ago. At that point it gave a good bright raster with good linearity so I've been looking forward to getting it properly restored, especially as I now have a standards converter. Having cleaned it up, re-wired and re-capped it I've found that there is no line timebase and the cause of this is an open circuit LOPT! I was given a spare chassis for this at the time when I bought the set, so fingers crossed the one in the spare will have continuity.
I have been unable to obtain the service data for this set, which uses the type A63 IF chassis and type A64 main deck chassis. The TV43 for which I have the Trader sheet and manufacturer's service data is similar and uses the same A63 IF chassis, but my TV33 main chassis clearly has substantial differences to the TV43. Does anyone know where I might be able obtain a Trader sheet or the manufacturer's service data for the TV33?
Information for the Bush TV33 can be found in the 1953/54 Radio and Television book.
The TV33 is quite a rare set. Most noteworthy feature of the set is the line flywheel sync system. A phase splitter transformer in the anode circuit of the sync separator supplies anti-phase pulses to a pair of diodes. The flyback pulse from the line output transformer is integrated to supply a sawtooth waveform to the junction of the two diodes. The line oscillator is an ECL80, the pentode section functions as a blocking oscillator and the triode section as a DC control amplifier.
Much of the rest of the circuits are similar to the models TV36 and TV43.
The TV33 was made for reception in fringe areas.
- Click image
- Right click image, "open in new tab"
- Go to new tab, you will see a magnifying glass with a "+", click to enlarge image
There was an even rarer variant of the Bush TV33 series. Never seen one myself but I'm reliably informed there was a model in which the booster diode derived it's heater supply from a winding on the line output transformer. Certain post-war Philips TV receivers made in Holland employed this method of supplying the heater of the booster or should we more correctly call it the line damper diode? A special valve was made for the purpose, the EA40. I believe the Bush TV set employed a PY80.
Thank you very much for all the information. I had wrongly assumed that the main deck chassis used the same valve line up as the TV43 and had stupidly plugged an EF80 in where the ECL80 line oscillator/amplifier should be. I have an ECL80 in the post.
The set originates from Cornwall, which makes sense in terms of fringe area reception. I have replaced all the wax capacitors, but there are quite a few blue RS and mullard mustard types in there which I am leaving in for the moment.
The mixed dielectric RS caps are probably suspect, just something to keep in mind, the Mullard ones are very likely fine.
Yes mixed dielectric as far as my memory goes, RS sold them, apart from the colour and name the packaging was the same, made in the same factory.
We used them and were reliable except in pulse circuits, manufacturer’s still used them as boost caps but not the RS ones, they bought direct.
The RS ones were grey and Dubilier were as you say blue and white.
The ones in the photo look grey to me.
If not replaced already consider replacing the RF deck heater chain decoupling capacitors. It's most likely tuner valve heater decoupling capacitors C41 and C42 are mica types and will not need replacing.
So, once I inserted the correct ECL80 valve and applied power, the short in the LOPT cleared itself. I initially had a bit of a stretched picture at the top, but after replacement of C9 and C10 (the originals tested okay) and careful adjustment of the linearity controls I've had great results.
I have written to DVD the test cards that area available to download and the menu on this works on my computer but not in my blu-ray player, from where I can only get as far as the menu screen. Other DVDs work fine in it which is odd.
Correction: I should have said the open circuit in the LOPT cleared itself, not the short.
The RF deck heater chain decoupling caps have been replaced.
I am continuing to restore the Bush TV33 that I have made previous posts about. Having now got rid of all the 1960s/70s mixed dielectric caps, replaced 6 or so out of tolerance resistors on the timebase chassis and had the tube out of the cabinet and cleaned the glass, I have a fault which occurred yesterday around 15 minutes after switch-on. There appears to be a short circuit occurring somewhere which results in loud mains interference from the speaker accompanied by a loss of height in the picture.
I suspected the 3uF visconol hum reduction capacitor which I replaced this morning but the fault still manifests itself just after the set has warmed up. I did think one of the two PY33 rectifiers could be developing a heater-cathode short, although am unsure whether these valves are prone to this. The main smoothing/reservoir capacitor has been replaced, although many of the other smaller original electrolytics remain in place and I think C21 which is situated between the secondary of the frame output transformer and chassis could be a prime suspect here.
Any thoughts on this would be very welcome.
Moderator Note: New thread merged with previous thread, this to aid context of past works and discussion thereof. 👍
I'm not familiar with the PY33 so I just looked it up. Seems a pretty rugged valve. A bit tougher than the 6N3 with which I'm familiar. Max h-k volts for PY33 is specified as 625v. 325mA per valve, so your two are doing it easy in that set. Normally a h-k leakage in a rectifier goes downhill very quickly.
Loose connection on the mains plug??? That's what it sounds like.
PY33s in a Bush TV33?. Should that be two PY82s? PY33 has an octal base.
I've checked the connections on the mains plugs and tried using a different lead, but this has made no difference. A voltmeter placed between where the HT is taken from the mains dropper and chassis shows no variation at all in voltage when the fault occurs.
One of the most difficult faults to locate. Might be the insulation of the frame output valve's valveholder breaking down between pins 5 and 6. Interesting to note the high tension supply for the frame output stage is derived from the boosted HT rail. I came across something similar in the Dynatron "Fulmar". The ECL80 pentode section can be operated with a surprisingly high voltage on the anode. From the Mullard Maintenance Manual, ECL80 pentode section limiting values: Va(peak) 1.2KV. Va max 400V. Pa max 3.5W. The frame flyback pulse on the anode of the pentode could be as high as 400 to 500 volts.
OK, so the PY82 is the series heater version of the 6N3 we know, which is otherwise known as an EY82.
Never seen a PY82 or a set that used one (two?).
But then I'm in Oz. No bitey chassis TVs allowed here! (not quite true, a few personal imports did make it in...)
Is the boost voltage affected when the fault happens?
Do you have a 2 -channel scope you could hook up to capture the event?
On the subject of the 6N3 / EY82, AWV once decided to make their own version (replacement sales were adequate to justify this) by modifying a 6CA4 / EZ81 which they were already making.
Looking at the specs it seemed as though they might have been on a winner, but for some reason those AWV 6N3s would only last a few months and go low emission.
Ah well, go back to buying them from Philips again!
As far as I know the EY82 was never used in UK made TV sets or anything else for that matter but was used extensively in Europe for TV receivers employing 6.3volt parallel valve heater supplies. Two EY82s employed as a full wave HT rectifier. I believe the PY32/33 is unique to the UK.