Regentone A133 HT smoothing capacitors, V4 cathode resistor

[space_charged]

OK, that confirms my view its probably the EL41. I did check for leakage with a meter and saw a very slight deflection on the ohms X10000 on my Taylor 88. Oddly enough my more up-to-date Fluke saw nothing. The Taylor does apply a higher voltage when measuring high resistance (15V).

The pin I observed the slight reading was control grid to screen grid, which is reasonable as their pins on the base are close together and the grids inside the valve are close too. The internal mica supports may be coated with sputtered metal liberated from the hot anode.

[Thyratron Valve]

Originally Posted by turretslug

The presence of an EZ80 may indicate a late production version- the Rimlock valve series had a relatively short reign before Noval types steadily displaced them. Radiomuseum lists an EZ40 for this model but, whilst it's a very useful and wide-ranging site, many of its model descriptions are single-example snapshots and it's not unusual to find some differences in the set that's in front of you, so to speak. The EZ80 spec. suggests that it would be more amenable to fitment of a larger reservoir capacitor, too, which could explain the apparently original 50 + 50uF component.

Colin
Sorry that was a typing error is a EZ40 rectifier I must double check my typing before hitting the send button

John

[space_charged]

I'll look at the wiring on the EL41 base to see if any n/c pins are being used as tagstrip - good thought. I've seen that done before. Floating them might help but really the EL41 looks a mess! Its obviously been "hammered"! Nasty brown deposits on the inside of the glass and some silvery deposit on the glass at the base where the pins come out. Looking at photos of new ones, they don't have either of these "features". Only place I've seen worse hammered valves is TV line output valves. Some of them work fine, but then the function of a line output valve is ON or OFF and as little in between as possible!

I've already put a 100K across the existing (680K) grid leak resistor.It helps and the cathode current does decrease. I've got it down to 36mA so just within spec. The grid is now down to about 0.5V.

A new valve or two are on order and I'm fairly sure that will sort the problem out. I'll increase the cathode bias resistor value, as discussed here earlier, so prolong the life of the new valve.

Been spray varnishing the case this afternoon. It looks very nice indeed. Needs a rub down now and some more spraying tomorrow - oops, later today.

[G8UWM-MildMartin]

Since you have a new EL41 coming, there's not so much to lose by giving it the same treatment as with UL41s. A search here will give details of gas hob ignition sparks, and I've had success with clearing leakage similar to yours (that I was thinking about leaving as it wasn't that bad) with 1000V from an insulation tester between grid and cathode, giving a very satisfying internal flash and it then testing like new on a valve tester (AVO VCM Mk1).

[space_charged]

I have already had a go at it with my EHT supply, though it can't supply much current. It produced a glow inside the valve but didn't have any effect on the leakage between control grid and screen grid. that was more out of interest than any expectation it might cure the problem. A pulse from an EHT capacitor would probably do better.

I'm obtaining a set of NOS valves for the set which is something I usually do for a restoration that I'm going to use. They are readily available, though not cheap!

[space_charged]

While waiting for the EL41 to arrive I have been spray varnishing the wooden case, which looks very much like walnut. I sanded it down to remove all the old varnish and managed not to remove the logo on the top.

The varnish is from a well known source and is supposed to be gloss, but persistently dries matt.

Any suggestions as to the best (preferably spray) varnish to get a gloss finish on this wireless?

[Thyratron Valve]

Originally Posted by Herald1360

Sounds like the EL41 is getting tired. Another possibility (thinking UL41 DAC90A problems here)- have any of the unused pins on the valveholder (3,4,6) been used as tie points for wiring? If so, there may be some mileage in "floating" any such connections.


You can try reducing the grid resistor from 680k to ~330k to see if this helps a bit and just increase the cathode resistor to get the total current down to around 35mA. This will allow the valve to soldier on a while longer- probably for ever if the set is not used much!

Thanks for that I will check those pin connections, and will check the current and adjust resistors accordingly
Regards
John

[space_charged]

I got the replacement EL41 today and fitted it. With the new valve (NOS Philips) the cathode current is normal and the positive voltage on the grid is gone with the original grid leak resistor (680K). I have left the 220 ohm cathode resistor in place.

[space_charged]

I finally got round to reassembling my A133. The wood looks quite good now I have managed to get a good varnish for it.

A few photos attached of the final result.

[John10b]

The cabinet looks really good.
Cheers
John

[space_charged]

Thanks John for your kind comment. I was collecting something else from a guy and he mentioned he had "some radios" and was I interested. The Regentone A133 was in his garage and looked so sad. It was a complete mess. The cabinet was almost black, then insides rusty and dusty. There were bits of the drive cord and a red needle lying amid valves and IFTs. Still I like a challenge so took pity on it. Sadly I omitted to take a "before" photo.

Charles