It's the second coming: Another Griffin TV set.

Hi Till,

I could be tempted to go for it as is, with the turret in place.. If needs be, it can be extracted at a later time.. It would be interesting to see if that tuner actually works.

Now, is it my imagination, or does this set look more daunting that the other one?

Marion

I would also be tempted to leave the turret in there to fill the hole in the cabinet and also have a go at getting it working to justify it being there.

The Brayhead turret tuner was a very good robust unit. OK the one in the Griffin set doesn't look pretty I'd reckon it's a worker.
The tuner is loaded with only two coil assemblies, channels 5 and 8 which were the 405 channels we had in the North-East of England.
So it would seem that the consensus is that the tuner stays in the set. Removing it would involve trying to disguise those holes in the cabinet side and honestly no matter however one tries to fill in the holes there will always be evidence of a repair.
Of course the set isn't mine so the decision what to do about the tuner is up to the new owner.
I'd reckon the general condition of the set is about the same as mine. Like mine the signals plate is rusty and will need the same treatment. The rest of the chassis sections are aluminium and clean easily.

Till Eulenspiegel.

Firstly, many thanks Till for picking up the set, without your kind offer I couldn't have bought it

I've a preference for the tuner staying, it depends how serviceable it is. A working single channel set will always be better than an knackered tuner and no picture. I think you are in the best position to judge so will go by what you decide, if tuner is disconnected then it canbe left in place - it is still part of the set's history.

TTFN,
Jon

Hi Jon,
I'm sure I can use the Brayhead tuner. Today I will examine how the tuner was wired into the signals section. A good practise was to convert the mixer-oscillator into an IF amplifier. Doing this gives extra amplification of the IF output from the tuner and also ensures that the matching is correct. Here's the link to the Masteradio T851 restoration I did in 2013. In this set a genuine Masteradio incremental tuner had been fitted for the conversion to Band 1 and 3. The job has been done in a incompetent manner, in fact it's amazing the set ever worked properly. That tuner unit was rusty as well, as was the main chassis.
Enjoy the banter between HKS and myself during this topic.
http://www.vintage-radio.net/forum/show ... hp?t=93927

Might even take a chance and go for the "HKS just plug it in" method. You never know the set might well work. Valves required are PL81, PY81 and PY82. Have them.

Till Eulenspiegel.

Check out that weird effect of the CRT dag.

I'll need more than three valves for this set, just about all of them are missing. No problem, I'll find them upstairs.
The chassis sure needs a good clean.
The turret tuner is connected to the receiver IF amplifier simply by connecting the output straight to anode connection of the second valve, the mixer. That's not nice. My plan is convert the former mixer stage into a gain controlled common IF amplifier. You get more amplification and the matching between the tuner and the IF amplifier is correctly done.
I did this to the Masteradio. In that set the coil network in the anode circuit of the mixer is quite complex.

Till Eulenspiegel.

The set now has a full compliment of valves, except one, the EY51 which does not exist in the heater chain.
The on-off switch checks OK, the "on" position reads about one ohm contact resistance. The two mains supply fuses were OC and have been replaced after cleaning up the holding clips.
High contact resistance of the valve holders was a problem, after liberal doses of WD40 the contact resistances have been reduced to an acceptable figure. The total heater chain resistance is 110 ohms when measured at the top of the chain. The mains dropper resistor is OK as is the heater chain thermistor. The total resistance at the mains connector pins is 745 ohms.
So that's the heaters sorted out.
I'll have to find an EY51 EHT rectifier, the original valve is damaged. In the meantime I'll use a stick rectifier.

There is a Radiospares 0.22mfd capacitor that needs replacing, one of those sixties style grey things, replacement it and it'll be time to "just plug it in" HKS style.

Till Eulenspiegel.

Well, it's a start. No signals coming though yet . I've returned the front end of the signals section back to Band 1 only operation, at least for the time being.

Till Eulenspiegel.

Hi Till

Looks very promising already! Out of interest, what sort of resistance figure for the valve chain caused you to think there was a problem with pin contacts.... and after applying the WD40 to clean the holders how did you know that 110 ohms was about right for the total resistance?

Steve

Hi Steve,
to test the heater chain I start from the bottom and work though to the top. One of the ohms meter leads is connected to chassis and the other lead for resistance readings from valve to valve. Wiggling the valves in their sockets to reduce the ohms figure. All but one valveholder responded to this treatment, the bad one is the PL81 socket. I may have replace that one.

The IF frequencies are 19.5Mc/s sound and 16Mc/s vision. I will inject signals into the grids of the IF valves to determine where the fault in the IF amplifiers is.

Till Eulenspiegel.

The tube looks good and the EHT is obviously good too. It is going to come up very well indeed

More progress this evening. I've rewired the mixer-oscillator stage again. Using the other Griffin TV as a reference I was able to rewire the circuit in the correct manner so that the set is operating as a BBC only set. Just for the time being though, I'll reintroduce the Brayhead tuner back into the circuit utilising the mixer stage as an additional common vision and sound IF amplifier. The circuit really does resemble the later version of the TV22.

The CRT is excellent, in fact it is better than my set. The definition is not as good because the IFs have been twiddled. thart'll be sorted soon.

Like the other set a capping job is required to improve the frame timebase performance. Need more picture height. This going to be a great set.

Till Eulenspiegel.

Great progress and all in 24 hours !

What's the interlace like, I recall you were having issues with yours.

TTFN,
Jon

Hi Jon,
No problems with interlace with this set. I will replace the capacitors in the frame sync filters, from the experiences of the first set we know they will go faulty in due course. It's the same with the RF chassis many of the 0.002microfarad Hunts make decoupling capacitors have failed even while I'm working on the set. Like the other set, change the lot!
The next stage is to connect up the turret tuner. In my previous notes I mentioned that the best method is to use the mixer valve grid as the connection point to inject the output from the tuner. The IF frequencies in this set are 16mc/s vision and 19.5mc/s sound. A grid coil with thirty turns is wound on a 1/4 inch former, the tap for the tuner connection is seven turns up from ground.
The attachment shows the connection method.

The signals plate is rusty. I'm going to paint it, this time after scraping off the rust I will use a etch primer before the silver paint is applied.

Till Eulenspiegel.

Is that really a 10µF non polarised capacitor in parallel with the RFC in the anode circuit ...?

Hi Terry,
Error in original Masteradio T850 service manual. The capacitor value is 10picofarads.

Till Eulenspiegel.

Would this cylden tuner be of any use, even if it only supplies a bottom cover ? No Idea what the IF's are.

TTFN,
Jon

Jon, I think I recognise that tuner as the one from a Ferranti T1425 that came from you many years ago.
That would put vision i.f. carrier at 19.6 Megs.

FWIW, the rest of the set went to Mikeymushradio.

Pete

If the IFs of the Cyldon tuner are same as the Griffin TV set then it would be the ideal replacement for the rusty Brayhead tuner.
The Brayhead is designated as "16S". That is vision IF = 16mc/s.
I have not got the service information for the Ferranti T1425 to hand, it's most likely the IFs are the same as the later 14T3 which are 15.75mc/s vision and 19.25mc/s sound.
Another possibility is that the Cyldon tuner is loaded with coil sets for channel B1 or B4.

Till Eulenspiegel.