It's got a valve gone!
 

My old faithful Dynatron TV.48V packed up today!
Was it really 2011 when I got this set?! how time flies! It was the subject of this thread: https://www.vintage-radio.net/forum/...ad.php?t=74776
Since my somewhat rudimentary repairs back then the set has housed my standards converter and DVD/VCR which provides signals for the downstairs 405 sets.
I never really finished the poor old Dynatron I meant to fix the LOPT cover and refit the lower part of the back cover to cover the tuner but modified to allow access to the VCR and make final tweaks to get the frame linearity better, I think the frame output valve is a bit slow warming as it improves after a run...

Anyway today I needed some 405 signals so I powered the converter and turned on the set.
(I use the set to select / display what is coming out of the converter before I send the signal to the desired set)
Sound.. 405 whistle.. No picture! After I had got over my surprise I took the back off and looked inside. lots of dust and a huge cobweb!
I checked for EHT and the arc seemed about right from the rectifier top cap but I couldn't see the rectifier alight.
My first thoughts were that the LOPT had finally given in But I thought it would be worth trying a valve...
I looked around the chassis thinking how dusty it had become when I noticed another valve not alight.. I switched off and pulled the valve, A Mazda 6F28 it looked quite black and heat stained plus the getter looked thin and dull.
Nipping into the workshop I trawled through my box of second-hand telly valves, nothing! everything but!
I checked on line because I wondered if an EF80 may do but the valve museum says not.
Then I looked in my valve rack (which are mainly radio valves) Success I have a new one!
I fitted the valve switched on and Bingo the set came to life! So the EHT rec must have been alight all along!
Just like the old days of field service! have a look for the obvious first!
It's got a valve gorn mate!
Quick dust out, back on, spin it round...
Exit.. (not perused by a bear..;D)
The LOPT still waits patiently for its Perspex...
:thumbsup:
Rich

Re: It's got a valve gone!
 

Looks like it has lost its vacuum. Is there a crack on the base possibly emanating from one of the pins ?
My Ekco TMB272 when restoration was almost complete gave a good picture one evening, Next time I ran it the next day I had a frame collapse. The ECL80 in the frame stage had fractured where the glass button base was fused to the bulb. The bulb could be removed leaving the valve cage and button with pins in its valve holder. It was a Mullard one as well !!

A replacement was a complete cure. I have no idea why it just decided to crack.

Christopher Capener

Re: It's got a valve gone!
 

Hi Christopher
It is difficult to see if there is a crack there are some marks around the pins in the glass but I wouldn't say they were cracks . Normally when a valve has lost it's vacuum the getter goes white and it is easy to spot in the chassis.
The getter on this has gone sort of see through with a slight silvering maybe the vacuum went slowly when the valve was hot?
It's definitely gone to air though as the heater has continuity but doesn't light up.
The set worked last time I used it until I switched off it didn't fail when on then it failed to work today when I tried it so as to when the valve failed is anyones guess!

Re: It's got a valve gone!
 

That looks like an EMI elliptical speakerr (8" x 5"?) in there. Never knew Dynatron used these during this period. More usually Goodmans.

Re: It's got a valve gone!
 

Lovely looking set, bet the sound is good with what looks like a large speaker!

Alan

Re: It's got a valve gone!
 

I have had a couple of valves go to air very slowly like that so that the gettering fades away without going white on the way.
I have got one laying around that might reveal something if I put it under a microscope.

Re: It's got a valve gone!
 

Hi Edward It is and they didn't! When Mick and I picked up the Ekco and the Dynatron the speaker and speaker transformer was missing from the Dynatron all the valves had been removed and were in a bag inside. Mick's Ekco had the speaker transformer also missing I can't remember if the speaker was there or not.
When I got the Dynatron going I just used parts I had to hand the speaker transformer came out of a record player amp I can't remember what donated its speaker or if I bought it from a swap-meet. I remember for a while it just had a small speaker laying in the bottom of the cabinet.
The sound is pretty good but then compared to modern flat panel set anything does!