I don't know about you, but I can never seem to locate a source of suitable grommets of the correct height. For this application, but namely for tuning gangs of radio set's.
They have a large minimum order but they do grommets, rubber washers, all that you could need. And in real rubber too, not PVC! I've used them for several years now and have always been happy with what I bought. In fact, I need to buy some big chassis washers for a couple of 1940 Cossors I own - a 74 and a 77.
The first wax capacitor that will be replaced is the mains RF bypass capacitor. It is a 0.05 uf 750vdc and looks quite innocent just sitting there, but to leave this one in place could be an explosive problem later.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Andrew, what type of RF amplifier valve is employed in the tuner, PCC84 or PCC88?
I've acquired another Pam TV set, a 600F. Paid £25 for it. An HMV radio set was thrown in with the deal. Haven't decided yet what to do with it, restore or just use it for spare parts. The cabinet back is missing and it's not a simple flat panel, not easy to replicate. So for the time being it'll be placed in the storeroom upstairs.
Till Eulenspiegel.
Here is the replacement capacitor as mentioned above.
My next step was to attempt to reform a decoupling capacitor, namely C77 (reference to the Pye CTM17T in the library), in the supply of boost HT to the frame stage and CRT G2. This is a 1uf 500v electrolytic and to get this to reform was like pushing an elephant through the eye of a needle. In other words, it 'aint 'aving it ! The cap is more like an NTC thermistor decreasing in resistance and getting rather hot. So this was replaced with a 1uf 630v polyester.
As C71, the line drive feed to the PL81, was a cracked and broken Hunts mouldseal (poor old thing) of 0.01 uf, I thought it wise to replace this too.
As mentined previously, there are what seems a large number of Hunts mouldseal and wax capacitors around the chassis. I will not be replacing these wholesale, but some of the more critical ones in the HT lines etc may need attention before first power of the set. We shall see in due course.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Andrew, what type of RF amplifier valve is employed in the tuner, PCC84 or PCC88?
Hi Till, it is a PCC84 in the tuner, with a PCF80 as the frequency changer.
Well done for obtaining the 600F.....I saw that on ebay and it reminded me of the 600F I had many moons ago. I got it for a tenner at a junk shop. It made a nice set and gave a good picture after the usual crop of waxies were replaced.
Your example looks quite well baked in places on that chassis ?
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Andrew, it was the 1958 Pye sets that were supplied with the PCC88 in the tuner. As the PCC88 was announced in 1957 I guess it was unlikely the new valve would be fitted in your set. But nevertheless, these hi-spec Pye sets were superb performers in fringe areas. Three stage vision and sound IF amplifiers, flywheel line sync and an effective vision AGC system takes care of that.
The Pam has flywheel sync but has a simple mean level vision AGC system. I'll introduce the set on the Forum when more time becomes available.
Till Eulenspiegel.
Here below are views of general components in the frame, video and audio stage. Valves are PL83, ECC82 for frame, a PCF80 for video, and a PCL83 for audio. The audio transformer is quite large and with two good sized speakers and a fair bit of negative feedback with tone control, I would expect audio quality to be pretty good.
A wider view of the frame stage including sync seperator components....
To understand the black art of electronics is to understand witchcraft. Andrew.
I am really hoping that these two multisection capacitors will reform in circuit. They each contain three sections and the under-chassis rats nest of wires and components make for a very difficult task of disconecting each section in turn. They consist of C41, 66, 124 and C52, 56 and 116.
Circuit references according to the PYE CTM17T in the library will continue to be used as it would be very confusing if I refered to my copy of the PYE manual.
To understand the black art of electronics is to understand witchcraft. Andrew.
Just imagine what might happen in a pub if you announce to a lady ...
" Would you like to see my 7 inch selenium rectifier? "
A bit of a whoppa isn't it? ?
To understand the black art of electronics is to understand witchcraft. Andrew.
The line hold control in this chassis consists of a push-to-operate potentiometer. This indicates that this is a later model (than their sample reciever) as mentioned in the Trader article under "modifications". The switch puts the fly-wheel sync out of operation whilst the control is adjusted. The potentiometer itself reminds me of the type fitted in some foriegn equipment of the time, such as Grundig.
Lastly, a picture of the fairly large audio output transformer.
To understand the black art of electronics is to understand witchcraft. Andrew.
Today, the new smoothing capacitor can arrived. I fitted it to the chassis after reforming it. The chassis was now ready for a brief power-up with it connected to the CRT in the cabinet.
So...power was applied through my lamp limiter and the valves begun to glow. I was feeding in a test signal on CH9 when the sound arrived. Good so far. Line whistle started and EHT came up. I awaited some kind of raster, but all I could get was a bright blob in the middle of the screen. It could be altered in focus and brightness, but there appeared to be no line or frame scan. I switched off the set and double checked all the connections. All seemed fine. I tried again, alas just the same fault. I unplugged the scan coils and tested the resistance. I found both line and frame coils open circuit !
So this would appear to be the end of the road for this set. Just look at the corrosion and green-spot on multiple sections of the scan coils. They are useless. There is no evidence of damp anywhere else, so I wonder if it was a chemical reaction of some kind. There is marked corrosion inside the scan coil housing too, but nothing on the outside.
So, unless I am fortunate to ever get scan colis for this set, it will remain as it is. ?
To understand the black art of electronics is to understand witchcraft. Andrew.
That's a real shame, Andrew. As it's a Pye in disguise, one can only hope a woodworm-infested Pye appears on the 'bay or somewhere for you to raid for bits.
Thanks Mike.
Of all the things that could be an issue, I would never have thought of the scan coils !
To understand the black art of electronics is to understand witchcraft. Andrew.
This is one of the reasons why I like to get a TV powered as quickly as possible by doing minimal work initially just replacing essential parts to power it up reasonably safely. I even hang several capacitors in if necessary to temporarily replace smoothers just to get HT. It doesn't matter how misshapen the raster is or how hummy the sound is (if there is any) as long as some sort of raster is obtained it proves that line TX and scan coils are OK.
Of course this doesn't prevent them from failing later......
That's a nasty attack of verdigris you've got there, Andrew.
You've obviously had no trouble breaking the unit down into its individual coils. Have you considered the possibility of winding replacements yourself?
That's a reasonable thickness of wire so should have a high breaking strain. You can experiment with the old coils, leaving one of each pair as a pattern, to see how much of the shaping might have been done after winding. If you can wind them flat and form them afterwards it will make the job easier, including fabricating formers to wind the coils on.
When all else fails, read the instructions
This is one of the reasons why I like to get a TV powered as quickly as possible by doing minimal work initially just replacing essential parts to power it up reasonably safely.
Indeed, that is good sense. I only replaced a couple of caps, so no great loss.
However, I will be looking at the possibility of re-winding as Terry suggested above.
Then, there is plan B....
It just so happened that the below set was on ebay for buy it now at silly money. I put in an offer of £30 and believe it or not, it was accepted. It is a Pye of what seems to be of very similar, if not identical, chassis. It is fairly near to me, so tomorrow morning I go to collect it.
What will transpire from this? Well, let's see.
To understand the black art of electronics is to understand witchcraft. Andrew.
It's a harsh thing to say, but that set will be no loss compared to the Pam.
Well I must admit, that Pye is not exactly the greatest looking set I have seen. However, it may yeild an excellent source of spares in order to maintain the Pam. Has to be worth the £30 for that reason alone.
To understand the black art of electronics is to understand witchcraft. Andrew.
The set in question is a Pye CTM17 and therefore should be pretty much identical to the chassis in the Pam.
The only thing I'm hoping that will not be identical is the shocking state of the scan coils. In one half of the frame winding alone, I counted no less than 5 breaks in the wire.
To understand the black art of electronics is to understand witchcraft. Andrew.
Unfortunately, after going to collect the set today, it turns out that the seller had used a stock photo and it was not the actual item for sale. Instead, it was a damp snail-ridden heap of crap of unkown model. Totally useless except the for the tip.
So, back to plan A. Re-wind of the scan coils can be the only logical choice.
To understand the black art of electronics is to understand witchcraft. Andrew.
