I picked up this little set from the recent RetroTech event, it’s one that’s been on my bucket list for many years! But they seem a little thin on the ground, certainly not as common as the good old Bush TV22. The chassis layout is similar to the Bush, with its double decker design, and it lives in a one piece Bakelite cabinet, but that’s pretty much where the similarities end.
Today I managed to lug the set into the workshop, and set about doing a few tests, mostly on the CRT, as these are notorious for being trouble, from heater to cathode shorts, disconnected cathode, or shorted heater, and this one is no exception, sadly! I started by testing around the tube base with the multimeter, checking continuity of the heater, and sure enough it has continuity! It measured 2 ohms… from what I’ve read this tube should have a 10.5V @ 300mA heater, which I’m sure should be a little more than 2 ohms! I connected it up to the bench power supply, and slowly wound it up, with the current limit set on 300mA I could just about get it to 3V, I didn’t want to push it too much and blow it open, so left it at that, it did begin to glow after a while, so I tried the Megger trick on the tube, but got nothing on screen, so it either wasn’t hot enough, or the tubes also low emission! I think for getting the set going I’m going to have to borrow a tube from something, probably the 385U again!
I did try to get some life from the chassis whilst I was at it, showed it some mains via a lamp limiter and the variac, the 100W bulb glowed a dull orange at 200V, and nothing else seemed to be happening in the set, I didn’t see any valves glowing, so next job is to check continuity of the heater chain.
What a lovely set! I had a look on Radiomuseum. GEC certainly liked the Z77 ! I will follow with interest! I have my fingers crossed for you that the tube will be OK...
I really like the look of these - there was one at the BVWS Wootton Bassett auction in December which I was outbid on. I wonder if this is the same set that has been sold on to you?
I will follow your progress with interest too.
Laurence
It probably is! Probably found the tube to be toast so passed it on! I should have spotted the fresh solder on the tube base when I was looking at it, but I just wanted the set, and went for it anyway!
In that photo the focus magnet is not present, I do have it, I took it off to try testing the tube with the Megger.
I did some testing last night, the heater circuit is fine, I got some life from the set! The frame stage started up, firstly with some odd squeaking noises, then the usual rattling noise of a frame stage running too slow. No sound from the speaker, and no life from the line stage, I was still running through the 100W lamp limiter, which was glowing quite brightly.
I hope if the set was purchased from a BVWS auction it wasn't sold on for a profit.... We all got a Bollocking (not a swear word, I checked 😀 ) about that in "The Bulletin" a few years ago after someone bought a Decca Decola and then sold it on for a profit. We were told that "we will investigate" any further breaches in the future... Some members were banned apparently... 🤐
Oops! I’m sure the guy I got it from said it had been with him a while, and he had 3 of them!!
Re: "bollocking" - I would rather see that word used than the frequently substituted "rollicking", which has a completely different meaning.
Oops! I’m sure the guy I got it from said it had been with him a while, and he had 3 of them!!
I'm sure that is true, to be honest my post was a little tongue in cheek. I won't comment further as I don't want to drag your thread off topic.. The only thing I wonder when people say they have a few of something is if the one they are selling has been the parts department for the others...Let's hope not.. ( I can be a cynical old Hector at times)
@cathovisor Yes I bought a couple of radios from Harpenden years ago only to find the wrong chassis lobbed into a cabinet and the back firmly screwed on. The worst was a lovely PYE multi band portable that had had the main PCB chopped out and again the back screwed... I bit how I felt when I looked inside!
I have been burning the midnight oil tonight, trying to coax some life out of this thing!
I started by tipping the set over to have a look under the chassis, it can be seen that someone has been in before, they extended the speaker leads, and it looks like a replacement smoothing can went in some time ago, it’s an RS replacement with some of the plastic sleeve removed. I found why there is no sound, one of the speaker wires had fallen off of the output transformer!
with that reattached I now had sound, as soon as the set got power it immediately buzzed loudly! A check with the meter showed quite a lot of AC on the HT, with 80V DC on the HT, switching the meter to AC showed 50VAC! I tacked in an 82uf cap across the section connected straight after the rectifier, and that sorted it out. A new smoother will be required. There was also a wax cap connected between one end of the primary of the output transformer and ground which was either very leaky or shorted, as snipping that silenced the instant buzz from the speaker before I’d sorted the smoother.
The selenium rectifier has been replaced sometime in the past with one that doesn’t fit, it’s hanging on one bracket, and at one point when I turned the set on there was an arcing sound followed by the awful stink of a dying rectifier! I have tacked in a large wirewound resistor and a 1N5406 I had to hand to replace the stink bomb.
After a lot of careful winding up of the mains I came to the conclusion that I wasn’t going to get anything out of the line stage with just a single 100W bulb, so dug out the double bulb adapter and stuck in a 60W to get some more juice to the set, this got the line stage running, and I was able to draw a spark from the top of the EHT rectifier. The CRT heater is out of circuit currently, so I rigged it up on the bench power supply, and fired up the set, the CRT heater was drawing about 380mA at only 3.4V, but was glowing, and once the line stage was running again i finally got something on screen!
I call it the first glimmer of hope! The photo was taken in a darkened room, with the light from the lamp limiter in the background. I also had to enhance the photo a bit so you can see it.
Next job, check the EHT, see what it’s producing. Then maybe throw some caps at it, and hope for the best!
Well the answer to how much EHT is it producing is not much! It was about 2.5KV. So I kicked the lamp limiter out of the equation, and just wound it up on the variac, the set came to life at just 180V, and the line stage was very loud! I wound it as far as 210V, and left it at that, the EHT came up to 5.5KV, and the blob on screen became a more well focused line. I had the tube heater up to about 4.2V, which was drawing 400mA. The line could be viewed under normal lighting, but still isn’t very bright.
I think I’ll have to do a tube swap whilst getting the chassis going, the TV12 has an MW22-16 that I could borrow, but it needs an ion trap and an A1 voltage.
I also need to check the HT, as I think it may be a little high after my resistor/diode bodge! The resistor was about 36ohms at 50W, maybe that’s why the line stage was so loud!
@lloyd I'm not familiar with these sets, should the tube have 6.3 Volts across the heater? If so do you think you have a partially shorted heater? If that is the case dare you give the neck a tap? It might clear... Do you have a heater transformer you could try to see if that helps? If not I have one you could borrow to see if it helps. I may need it back at some point though as I have a couple of TV22s and a grotty Pye to get going one day...
Rich
the tube is an Osram 6505A, or at least it should be, which is rated 10.5V 300mA, I was toying with the idea of a transformer, possibly with a thermistor to bring it up slowly, I do have some somewhere.
I do wonder if this really is a 6505A tube, or if someone fitted something similar, it does have the GEC pimple EHT connector, and the flat face plate, so it probably is a 6505A, but with the partially shorted heater, as you say.
I’ve been having more fun with this little box of horrors over the last week or so, finally found out why it was all so loud, the other section of the smoothing can is also duff! I was getting line and frame scan noise coming out of the speaker, not a pleasant experience! This also caused another interesting effect once I had the frame scan up and running, the low height raster looked wobbly!
everything in the set was interacting with everything else! With the smoothing bodged with a Christmas tree of odd caps the scan was much straighter.
Now getting some frame scan turned out to be interesting too, early on I could hear frame scan, but once the line was focused it was clear that if there was any frame scan, it wasn’t making it to the scan coils. After checking the wiring, and looking for shorted caps, I discovered the primary of the frame output transformer was open circuit… I decided to give it one chance before giving up, and gave it a zap with the Megger! I have managed to get some audio output transformers to come back to life doing this before, and didn’t expect it to work, but it did! It probably won’t last, so I’ll have to find a replacement at some point, I do have that other GEC telly I could rob for parts.
Other things I’ve done include greasing the slider controls, which surprisingly are still good! Checking for coupling caps, the line stage uses mica caps for that, so I’ve left them alone, audio coupling is on the RF chassis, so for now it’s just snipped out, and I’m still working through the frame stage! I did also try to get a signal through, I couldn’t get anything from the Hedghog, but I could get something from the signal generator, just really weak.
So this is how it’s looking now:
thats with the heater cranked up to 420mA! Tapping on the neck does have a tiny effect on it, but not enough to take it back to 10.5V. Maybe it’ll display a picture of sorts!!
Finally got the set apart today, and also got it on the actual bench, rather than in the drawer under the bench! As I was pulling the chassis out I spotted what I thought was the label from the CRT, but it turned out to be this:
@slidertogrid Rich, you were right! It did come from a BVWS auction! It looks like it was some time ago though, looking at how yellow the paper has gone, and they certainly didn’t make any profit at all on it. Is there any way of finding out when that auction was?
Its not an easy set to get apart, well, not as easy as the TV22, you have to take 4 funny double sided bolts out from underneath, then put it the right way up again, slide the chassis out, and disconnect the speaker as it doesn’t come out with the chassis… I prefer the TV22…
@cathovisor I’ve just had a scan of auction results, they go right back to 2003! I couldn’t find the GEC, although some auctions didn’t seem to have lot numbers, using the search did bring up ‘GEC TV’ in December 2003’s Wooton Basset auction for £130, but it was lot 46 rather than 62.
@lloyd Yes there is a lot to be praised about the way Bush constructed their radios and TV sets. The layout and the use of tag strip makes servicing easier than many. Some 50's Pye radios for instance are 'knitted' in layers of components, not only does it look untidy but it makes fault finding and component replacement difficult. The neat layout of Bush products must have made assembly easier and the chance of mistakes less. I remember a friend who worked for GEC when they were producing sets in the late 50's saying the fault incidence on the assembly line was fairly high. The rework dept employed a fair few! He stayed there though right up until the takeover when he retired.
If you put GEC TV into the BVWS auction results search it will list the sets sold, the date and the venue. But as Mike says your set must have been some time ago, I don't remember the "till rolls" and I attended Harpenden since about 2004 your set's sale may predate the results listings.
I think the BVWS inner sanctum were only 'after' members that bought and resold at a profit fairly quickly so I think the seller of your set is safe from their wraith ! 😜
@slidertogrid Ever had to repair a (real) Ferranti? The build procedure seemed to be:
- Get chassis.
- Get components from stores and fill a bucket with them.
- Tip contents of bucket into chassis.
- Solder together.
I did a 145 for a friend and all went well... until the cheap frequency changer valveholder started flashing over.
It's right under the wavechange switch: colourful language ensued.
It's also notable that in the 1930s whilst many manufacturers offered as little as a ninety day guarantee on their new sets, Bush were offering a full year. This was attributed to full component testing prior to assembly.
