Ekco TS105.

[Geordie McBoyne]

Trevor has kindly sent me the CRM92A CRT that was in his Ekco TSC30.  The original tube in the TS105 is broken and for many years I had been on the lookout for a replacement CRT.  Now I have the tube for the set it's time to start rebuilding the set. Unfortunately many of parts belonging to the set are scattered about the shop so the search is on to find the missing bits.

Way back in 2006 I tried out a Mazda CRM93 in the set but good focussing was not possible.
A B12A CRT base socket is presently fitted so this will have to be replaced with a Mazda Octal socket for the correct CRM92.  How the 12.6volts heater supply for the CRM93 was found in the circuit will have to be investigated. The CRM92A has a 2volt heater.
The TS1051105 has a switch tuned radio receiver. A modified version of this chassis was fitted in the pop-up CRT 15" model TSC113.

Geordie McBoyne.

[ppppenguin]

ISTR the TSC113 used mains derived EHT. How does this set get its EHT?

[Murphyv310]

Hi.
That looks like a big oil filled LOPT in that set. Should be an interesting restore David. Looking forward to the seeing the results with the CRM92A.

[Freya]

One of my favourite sets, I have three fine examples plus a scrap chassis should you need any spares.
Very interestingly the two sets that came from the London area had the radio chassis voltage selector set to the incorrect voltage, this is a separate dropper setting to the one on the back.

[Geordie McBoyne]

Hi Jeffrey,
             The EHT is derived from the line flyback.   The line oscillator is of the Miller "transitron" type. Uses an SP61 pentode, a valve that in 1949 might have been considered old fashioned but it's likely there was thousands of these valves on surplus market, so why not use the things up?  Also, the SP61 has all the right characteristics for the Miller oscillator.  A Mullard PY31 is employed as the effifciency diode, the reclaimed energy is supplied to the cathode of the 6P28 output valve.  
                                                                                                                                       

The mains derived EHT in the TSC113 uses a voltage doubler circuit to produce 10KV for the CRM151 CRT. Real scary stuff!
                                                                                                                                          

The frame oscillator employs a Mazda 6K25 thyratron.  Particular regard to the frame sync circuit which employs an inductor (L21) to perform the sync integrator function.

Geordie McBoyne.

[Terry]

Uses an SP61 pentode, a valve that in 1949 might have been considered old fashioned but it's likely there was thousands of these valves on surplus market, so why not use the things up?

This is a bit off topic but reminds me of a tale from our Mullard rep back in the 60s. When he first joined Mullard, one of his jobs was to attend the government surplus auctions to prevent as much Mullard product as possible getting onto the market. Of course, all the dealers from Lisle Street saw no point in bidding against each other, so they just put in a united bid and divvied the spoils up afterwards.

He was ordered to stop a batch of several thousand EF50s that came up for auction getting onto the surplus market. He knew where the dealers used to meet up before the auctions so he turned up and did a deal with them. If they let him have the EF50s, he wouldn't bid against them for anything else.

The deal was done and sealed with a shake of hands and then they went off to the auction where he bought the EF50s for a very good price.

A couple of weeks later, Mullard received an order from a different branch of the services for a large number of EF50s, so the batch he'd bought were resprayed in the appropriate colour, re-stamped and sold back to the government at a substantial profit!

[Murphyv310]

Uses an SP61 pentode, a valve that in 1949 might have been considered old fashioned but it's likely there was thousands of these valves on surplus market, so why not use the things up?

A couple of weeks later, Mullard received an order from a different branch of the services for a large number of EF50s, so the batch he'd bought were resprayed in the appropriate colour, re-stamped and sold back to the government at a substantial profit!

Things never change then Terry. This still goes on in other ways, procurement for the NHS for example.

[Geordie McBoyne]

In the models TS88 and TS105 Ekco must have liked the SP61 so much that they even used one as the frame output valve. Note the position in the circuit of the bias resistor R28, a degree of negative feedback is introduced presumably to improve the scanning linearity.
Earlier Ekco TVs employed large Mazda beam tetrodes for the frame output, in the TS46 a PEN45 and in TSC30 an even bigger valve, the PEN46. A valve intended for use in the line output stage.

Geordie McBoyne.

[Geordie McBoyne]

The perished leads to the scanning coils were replaced last night.
The attached picture shows that the chassis metalwork doesn't look all that pretty.  

Geordie McBoyne.