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Old 26th Mar 2024, 8:08 pm   #1
thermionic
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Default Marconiphone VT63DA

I’ve had this set for a good few years, it’s been patiently sitting on a high shelf waiting for me to decide what to do with it. I remember winning it at a BVWS auction for a fiver as no one seemed to want the poor thing.

…..And no wonder! It doesn’t have much going for it. There is no back panel, no valves and no CRT. Its only saving grace is that the cabinet is in a pretty fair condition and it has the correct knobs on the front. Well, its day of reckoning has come, I’m struggling for space so if it’s beyond hope then it has to go.

I have a couple of possible replacement CRTs I could use, the original CRT would have been an Emiscope, so my plan is to see if the set is viable before I go to much effort. The replacement valves can be sourced from my ‘pulls’ box. Nothing too exotic here….EF80’s ECL80’s the usual PL81 and PY81, an EB91 and one not so popular EBF80. Not a PCF80 in sight!

I will run up the set without the CRT in, bridging the heater pins and connect the EHT meter onto the final anode connector. I want to prove the wound components before anything else.

These Marconiphone chassis are fun to play with….and there doesn’t seem to be many around now, so well worth trying to keep.

No need to rush back, this will be a slow burner, as time permits.

Cheers.

SimonT.
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Old 27th Mar 2024, 11:16 am   #2
Heatercathodeshort
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Default Re: Marconiphone VT63DA

Just for the record. It is a Plessey Chassis. The tube is a 14KP4 Emitron [thankfully not an Emiscope] that may be equivalent to the Mullard MW36-24/44. J.
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Old 27th Mar 2024, 4:22 pm   #3
German Dalek
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Default Re: Marconiphone VT63DA

This little thing is a keeper.
Storing a CRT takes about the same room as a complete TV set!!!!!!
And last but not least - the CRT has to run again, before it gets gassy!
So its up to you to spend both a new life!

Regards,
German Dalek
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Old 28th Mar 2024, 5:12 pm   #4
thermionic
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Default Re: Marconiphone VT63DA

Quote:
Originally Posted by Heatercathodeshort View Post
Just for the record. It is a Plessey Chassis. The tube is a 14KP4 Emitron [thankfully not an Emiscope] that may be equivalent to the Mullard MW36-24/44. J.
Hi John.

Thanks for the clarification. I had assumed ( incorrectly) that this was a HMV Chassis. I’m probably lucky that it ‘ain’t! What threw me was the lack of Mazda valves. However, a Plessey skinflint decision of not including a HT choke is in this set as well as my Plessey Defiant chassis, so that should have been a clue!

Cheers.

SimonT.
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Old 30th Mar 2024, 7:06 pm   #5
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Default Re: Marconiphone VT63DA

The signs are promising....

The chassis was populated with a set of valves. The main reservoir & smoothing capacitor was checked, then reformed.........but after 12 hours the 200uF section was not interested. I temporarily ‘lashed’ in an equivalent capacitance ( 200uF reservoir, 500uF smoother).

One section of the mains dropper was open circuit (9 Ohm ). The mains filter capacitor was snipped out ( C70, 0.01uF) the audio output coupling capacitor (C34) was temporarily snipped, and the chassis connected to the lamp limiter.

Heater chain intact and warm up commenced. Smoothed HT quoted at 215 Volts with 240 AC input. I monitored the HT during warm up. It wasn’t looking very good. With the lamp limiter bypassed, the HT was only reaching 140 Volts. HT current is given as 200mA, and when checked, measured 186mA, so nothing dragging the HT down.

The metal rectifier was blamed, and was soon replaced by a BY127 diode. Now the HT was 210 Volts and a faint line whistle could be heard and the gentle 50 Hz ‘ticking’ coming from the frame output transformer. No EHT though!

After 3 capacitors in the line stage were replaced (C45,0.5uF, C66, 0.25uF, and C67, 0.005uF, ...all measuring between 100k and 200k on my Avo 8) the line whistle was much stronger and the EHT meter rose to 7.5kV. The manual quotes 12kV. I decided to switch off, and to pass a DC current through the over wind for a few hours and see if this helped. Well, 12 hours later with 60mA running through it brought it nicely warm to the touch. Re testing now gave me 11kV, so there must be a bit of dampness in there! After 10 - 15 minutes it gradually starts to drop away to 9 kV, so I’m going to let it warm through a bit more to see if this will cure it.

It looks hopeful though, and I’m pleased with progress so far.

Thanks for following!

Cheers... SimonT.
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