I alluded to this upcoming project in an earlier post. Here is the progress so far and some pics.
The Y2-D3 was a high-end model, selling for AU$800 in 1969. You could just about buy a new car for that! Consequently it is somewhat rare, I only ever saw one in my TV servicing days and I still remember being impressed by the TV sound.
This one had spent most of its life in a rural wheat-belt area and had suffered significant mice infestation. We ended up hosing it out before it went on the truck.
I decided to attack the stereo part first.
Not much to tell, really. After replacing the VR insulated power cables, all the tuner-amp needed was a spray into the pots and switches and it worked perfectly.
The Garrard 2025TC needed the usual strip-down to clean out the grease that had turned to glue and cement. After that was done, it worked flawlessly.
The Sonotone 9TA cartridge has a loose and bent stylus which I was able to repair. Unfortunately it has a deteriorated bridge rubber - only one channel off the record is reproduced in both outputs and there is significant IM distortion. Oh well, I know that 9TAs are Unobtainium which is a pity because they are a nice sounding cart. If anyone knows how to fix a bad bridge rubber I'd love to hear about it.
TV chassis next.
After a cleanup, all looked good, so fired it up.
Not so good. See pic!
Obviously a mouse has sat on the cage and pee'ed on the LOPT.
"I think it's time we got a new one"
It's possible to replace this transformer with several MSP (AWA) types as well as two Philips LOPTs and a Rola/Plessey transformer so there are lots of choices for donor chassis.
That is a monster! Pye did a similar combo called the "Trio" It wasn't often seen, but as you say the price probably put a lot of people off. That and the size! A lot of UK houses were fairly small back then. Only the farmers and the Doctors had the space and the money for one! 😏
Well it's up and running after a LOPT transplant. Managed to find a donor TV (cabinet well beyond restoration, not a desirable model) that happened to be fitted with the exact same transformer. And a 10% emission CRT.
But not before a gallant attempt to fix the original, that would have actually worked if I hadn't been in such a hurry to finish it.
Other minor issues still need attention. Very intermittent flashing looks like it could be a 6Y9 (EFL200) - I'm out of NOS ones. I'll have to remember to add the 1.5k screen resistor 6Y9-saver mod. 25" CRT looked hopeless initially but after a couple of hours running has come up reasonably well (for a Thomas) but with the usual Thomas trademark de-focussing on highlights. Has probably been in hibernation for 30 years or so, so I'll cut it some slack! Nice piccies otherwise.
Getting late tonight, will post pics tomorrow.
Oh BTW, I badly need a 110 degree CRT extension lead so I can run this chassis on the bench. The flip-down chassis is all very well and easy to work on but I can't see the picture! Anyone know where to get a plug same as is on the CRT?
And does anyone have a good Sonotone 9TA that they would be willing to part with for a suitable sum of money?
Well it's nearly finished! The nigglies always take longer.
What I thought was a bad 6Y9 / EFL200 turned out to be an OC connection from the CRT frame (and hence the aquadag connection) to the chassis. It was via a strip of that foil coated roof insulating material bolted inder the brackets. The mice had eaten it!
intermittent vertical line pairing was 6GV8 / ECL85 socket contacts. Cleaned them and fixed it.
Similarly, the intermittent 2 or 3 mm jump sideways was just a dirty hor phase pot.
Screen shots show before and after the replacement hor lin coil was fitted.
Those pictures are using my Macrovision-stripping modulator on AU Ch 2. Oz HMV IF design and performance was always very good.
I thought I had some hum problems but they went away when the chassis was swung back from servicing to normal position. There is a reason that transformer is mounted at 45 degrees!
Now to fix the intermittent crackle/rumble in the LH channel in the gram. Classic AD161 - AD162 design.
TV sound goes thru this and it sounds great.
@irob2345 The video response is very good, great picture on the TV. For its age the CRT looks good, there can’t be many 100% CRT’s about nowadays.
The last of the large screen monochrome TV’s in the 1970’s we had in the UK had poor CRT’s from new. The phosphor had a coarser grain, edge focus poor etc, not a patch on the Mullard CRT’s they produced for the earlier sets.
Frank
That is the original 1969 Thomas 25" CRT, from the Larkin St. Riverwood, Sydney, plant.
It's a bit soft from cold, takes a few minutes to hit its straps.
Of the 3 CRT makers that existed in Oz at the time (the 4th, Anodeon, had just been absorbed by Philips). Thomas probably had the worst performance in terms of focus. But since they were the only CRT maker not associated with a setmaker (i.e. Philips and AWA) they were used by EMI/HMV and Pye.
Pye at this stage were running their all solid state T26 large screen mono chassis, which had 20kV available to make the Thomas tubes look sharper. These TVs were utterly reliable and came with a 4 year free service warranty.
I think it's fair to say all 3 CRT makers held up their quality right to the end of production in the mid 70s, when the Oz electronic component industry was killed off by Gough Whitlam's ill-conceived tariff reforms.
@irob2345 The poor mono CRT’s in the 1970’s were imports but not sure where from, Mullard and Mazda were just making colour CRT’s. In fact the Thorn/RCA colour CRT factory closed in the middle 1970’s, it was making delta CRT’s and the information I have is that neither company wanted to spend money on upgrading to inline CRT’s.
Frank
Nobody ever made colour CRTs in Oz, although Thomas used to re-gun them.
I remember one of their 30AX re-guns. No "spooky" available so they had a set of ring magnets like everyone else used. Worked well, lots of flashovers initially though.
Thomas were rebuilding CRTs for aviation and military markets until about 2010. I just had a look at 12 Larkin St. Riverwood on Streetview and it looks like they are gone. Factory buildings still there though.
Got onto the rumbly audio left channel yesterday.
With the left channel having higher gain than the quiet right channel, it just had to be R42, 7.5k ohms, gone high.
Measured it, sure enough, 11k. So I replaced it, and the one in the right channel for good measure, as they were both IRH carbon composition resistors.
Gain now the same, rumble still there!
So I measured the centre voltage on the outputs. Right channel was bang on 14 volts, left channel 13.2 volts.
A leaky Redcap ceramic coupling cap (C27)? Tapping it with a screwdriver gave a loud "bong" - the one in the other channel didn't.
So both were replaced with nice poly greencaps.
And that fixed it.
Hum and noise is impressively low, for such a simple design. And I didn't have to replace any of the 55 year old electrolytics.
Next I did an alignment of the ratio detector, which cleared up a little "caption buzz" on the TV, and it's now a pleasure to watch! And the sound is impressive.
@irob2345 Appreciate the germanium transistors we’re not has robust as silicon but I always liked the AD161/162 amplifiers and after saying that about germanium, this pair gave me little trouble.
Frank
Appreciate the germanium transistors we’re not has robust as silicon but I always liked the AD161/162 amplifiers and after saying that about germanium, this pair gave me little trouble.
Of that era, I had far, far more trouble with those IC-based amplifiers - the 76003/76013/76023 than I ever did the AD161/162 pairs. I only ever had to replace one such pair in my youth, whilst the ICs readily supplemented my pocket money.
The worst germanium power transistors were the AL102/103 devices - great bandwidth product but at the cost of reliability. Ask any Armstrong 400/500 owner.
@irob2345 The poor mono CRT’s in the 1970’s were imports but not sure where from, Mullard and Mazda were just making colour CRT’s. In fact the Thorn/RCA colour CRT factory closed in the middle 1970’s, it was making delta CRT’s and the information I have is that neither company wanted to spend money on upgrading to inline CRT’s.
In the broadcast world we were using Brimar CRTs in the 1980s as they were also military suppliers but in later years (1990s) we had FIVRE tubes, which were Italian. Getting illuminant D CRTs was problematic.
A lot to respond to!
We used to replace lots of AD161 - 162 pairs in HMV gear when they were new and under warranty. I always wondered why HMV ran them right at the limits. Using an unregulated, nominally 29 volt supply, the AD161 is vulnerable with a Vcb0 of 32 volts and a Vce0 of 20 volts. It was common to get mains voltages up to 10% over - even more common these days in Sydney where most houses have rooftop solar back-feeding the grid. So the nominally 240 volts is often well over this.
Other makes using AD161 / 162 pairs usually ran a regulated supply, never a problem with those.
Re IC audio amplifiers, yes, many of the early ones were quite fragile and unreliable.
One part stands out, though, for being unbreakable, and that is the Natsemi LM1875.
Back in 1989, not believing this part was as good as it was claimed to be, but wishing to use it in a new 4 channel 30 watts per channel design, we torture-tested it on +/- 30 volt rails, driving 2 ohms at full power sine wave for a week. No failures, so we tried shorted loads and no heatsinks. They just sat there happily turning themselves on and off for another week. Finally, we tried shorting the output of one of them to the negative rail. It exploded like a firecracker!
We used it in the product, made thousands of them, never had a single reported failure. At max ratings they do need good heatsinking though, or they will periodically shut down.
With ratings of 60 volts, the ability to drive 5 or 10 amps into a load and pinned as an op amp, the LM1875 is a handy replacement for many CTV vertical output stages, both IC and discrete.
Re the phosphor colour, Thomas B&W CRTs were always much hotter than 6500 degrees K. You can see this in the screen shots. The one in my 23" Pye console is bluer still, and the persistence is very short, making it hard to photograph. Philips CRTs were usually somewhat closer to "white".
