Invicta T105

[beery]

Great stuff so far, I'm enjoying your thread
Re the CRT, I'm sure the getters on some of my working MW22-14 tubes look a bit off. I say don't worry until you can really test it. On the positive side you did get light on the CRT and it apears to be sharply focused, so it can't be too soft.

Cheers
Andy

[mark pirate]

Hi Lee, it certainly looks a bit different from the Pye LV20, it seems Invicta had their own way of doing things!
Apart from the RF strip, it appears to share most parts with it's Pye equivalent.

Good news on getting first light, I see what you mean about the getter.
It's the white patches that indicate that it may be gassy, although I have a Mazda CRM 92 that looks similar, but amazingly produces a pretty good picture
Have you got a valve tester? Both my Avo and Taylor have the ability to test these CRT's.
I made up a lead for the Taylor, and it works well, you can actually watch the emission rise as the CRT wakes up!

For comparison, here are a couple of pictures of my LV20 chassis (after recapping).

Mark

[Hunts smoothing bomb]

Hi Andy,
thanks for the comment! I do hope the CRT is ok, the picture shows just the line stage operating at the momment as I haven't yet recapped the rest of the reciever and I've had to disconnect the HT from the other stages as they were dragging it down. I've measured the EHT and it is only 2.5kv. The trace is very dim with brightness turned all the way up so not sure if the CRT is ok or not yet.

Hi Mark,
Thanks for the pics! Nice looking set, I can see all the familiar components to the T105, just laid out very differntly!

Cheers

[mark pirate]

I've measured the EHT and it is only 2.5kv

At that level, I certainly would not expect to get much on the screen!
Which probably means the CRT is OK.

I would check the EY51, PL38 & PY31 as well as the HT voltage. The EHT is only around 6Kv on these sets.

One of my LV20's had frame collapse, recapping the frame section sorted this, but it needed the frame output valve replacing to give a full frame.
I always keep a few spare EF50's on hand, I have had several that tested very low indeed. Replacement of these really perks up performance.
The metal Sprague caps are usually OK, but I replace these anyway.

Mark

[Tazman1966]

Good luck Lee! It's certainly older than your usual era...

[Mikey405]

Well done Lee. It's looking good so far.

Kind regards.

From Mike.

[Hunts smoothing bomb]

Thanks Tas and Mike, yes it sure is older than the type I usually like to collect. I think it will look great when restored though, just hope that CRT is ok.

Cheers.

[FERNSEH]

Originally Posted by mark pirate

Hi Lee, it certainly looks a bit different from the Pye LV20, it seems Invicta had their own way of doing things!

Invicta service manuals were generally presented in a different style compared with those of the parent firm Pye.

Well into the fifties certain Invicta TVs were quite unlike anything made by Pye.

DFWB.

[Hunts smoothing bomb]

Hi all,

I am hoping to resume work on this set tonight if I get time, I know that the metal rectifier is not supplying enough volts so was going to replace with a 1N4007 and 47R resistor, I also wanted to prove the PY31 boost diode, is it possible to prove by supplying the heater at the correct voltage from an isolated variac and passing a current from an HT PSU between anode and cathode?
e.g. can I expect to see x amount of mA flowing at a certain anode voltage?
Or can I "assist" the boost diode by connecting a 1N4007 diode and limiting resistor in parallel with it?

I have a working PL38 in the TV22 that I can try too.

Regards
Lee

[Mikey405]

Hi Lee.

I guess a silicon rectifier and series resistor would be perfectly fine for the HT - You can probably work out the value better than me - whenever I try it always ends up completely wrong.

As for the efficiency diode, although a silicon rectifier would be okay in theory, if it were me I'd not really go to all the trouble of measuring it like that unless you think there is something actually amiss in this department. (Just re-read your previous post and you do have reason to suspect it.) I can't see any reason why just a plain old suitable silicon diode wouldn't be perfectly fine bridging the PY31 just to try it - I'm not sure I'd bother with a series resistor though.

Probably no help at all.

Thanks Lee.

Kind regards.

From Mike.

[Hunts smoothing bomb]

Hi all,
Firstly Mike, no not at all, your input is a great help, regarding the PY31, I'll give it a try tonight if I get time but first I will update you all.

Well, I went into the workshop last night and spent about an hour and a half on it, in that time I can report the following.
First I hunted around for a 47R resistor but didn't have one but I did have a nice 100R 10 watt job so that was connected up in series with the 1N4007 HT rectifier.
I also connected the HT rail back up to all the other stages, frame, rf and audio as I had these disconnected because of leaky capacitors, there are still a few to do but wanted to get an idea of what was happening.
The set was switched on and after a fair wait I had a ticking noise which confirmed to me that the frame output was working, after a bit longer I had a gentle humming through the loudspeaker and then the line drive started up and became quite a healthy strong whistle this time the CRT illuminated brighter than before because of the higher HT and I actually had a raster that was full width by about 2” high.

Checking the main HT rail it was sitting at 218vdc. Hmm, 27v under par so I switched off and dug around for another resistor, I could only find 10R which I thought would be too low , anyhow it was subbed for the 100R. It proved not successful as using the variac to control the mains input I had 245vdc on the HT rail with everything warmed up and only a mains input of around 200vac .

I refitted the 100R resistor and as I was just giving the underchassis another look before powering back up when I noticed an old grey cement type resistor in the heater circuit that was wired to the underside of V10 – PL33. I checked and checked again with the schematic and this resistor which measured 100R did not appear to exist, sure enough R72 and R73 are present and are the only resistors in series with the heaters according to the schematic. Now this made me curious as this resistor looked ancient and original and I wondered what sort of voltages the heaters were seeing so I powered back up at the correct mains input and waited for everything to warm up and stabilize, the CRT came up as it had done so just previously and so I measured the heater volts of a couple of the EF50’s.
I only had between 4.9-5 volts on them, so 1.3v or 20% too lower heater voltage!

I took the resistor out or circuit and I am sure now that it wasn’t original as the wire leads were not wrapped around the valve holder tags. I powered up again and this time had 6.2-6.3v on the EF50 heaters so this was looking better already, the stages came to life and this time I had a much brighter and focused raster but still only a few inches in height, think I might have to look out for some known good replacement valves for this set EF50's in particular I'm also going to have a proper hunt for a more suitable resistance to go in series with the HT rectifier

Cheers

[Hunts smoothing bomb]

I meant to say in the last post that if anyone can help with spare valves then please see my wanted post here

Cheers

[mark pirate]

Have you tried putting a signal into it yet Lee?
Changing around EF50's in the receiver can affect the alignment
I think most of the problems with your set will be the old leaky caps, I would get them done before replacing the valves.

Mark

[Hunts smoothing bomb]

Thanks Mark,

Yes you are probably right, I haven't tried a signal yet, although tapping the aerial input with a screwdriver does not produce any audio crackles at the speaker or spots on the screen.

Cheers