Regentone 143C

[jay_oldstuff]

Hi all this is the set I got through the for sale section of this forum, and with help from more knowledgable members of this forum it was identified as a Regentone 143C. A few days ago I got an opportunity to have a play.As this set uses a solid state rectifier I proceeded a little bit different to my normal plug it in and see approach. What we had was my isolation tx on the mains my veriac connected to that, the output from my veriac connected to my lamp limiter fitted with a 100w lamp with the set commented to that. This setup allowed me to reform the main smoothing caps. I stars at about 50v with the lamp in circuit the lamp starts fairly bright dimming to nothing after a while them repeat at 100v and so on. I did this up to about 200v (at this voltage the lamp doesn't go out completely but you quickly get a feel for if the cap is a good one or not) at this point I felt the cap, still barley warm. Now it's time to show it some mains so connect the set to the mains via the isolation tx
(Not critical if your careful but I just got one for free so I'm using it) switch on and nothing not a peep out of the valve heaters, this was soon traced to R95 being OC, a suitable 33R RS dropper section was found and bodged in this time we have heaters and after a little wait a hum from the speaker then the volume was turned right up, nothing on the Mazda CRM141 but I do have line whistle so turn my attention to the EHT rectifier (not lit) hang on that looks odd for a EY51 so I unsolder it and find a U25 test it and heater is OC so dig out my one and only NOS EY51 and fit that power back up and nothing. I can draw a good lively spark from the anode of the EY51 but only to about 5MM was expecting a bit more than that. Only other thing to note is the visconal cap has already been wired out of circuit so guessing that's duff but not a problem for the mo. guess ill have to have a look at the heater winding for the EY51 and take it from there. Watch this space.


Jay

[Freya]

Is it possible you did not add some turns on the heater winding to allow for the 6.3 volt filament on the EY51

Stephen

[jay_oldstuff]

The winding should already be for 6.3v unless its been modified to accommodate the U25's 2v heater which I doubt as it looked all original. Unfortunately I couldn't find time to visit the workshop this evening but next time I'm up there ill check the winding.

Jay

[FERNSEH]

It's all very strange. The 17" models use Mullard valves and the 14" versions use a mixture of Mullard and Mazda valves.
Information for 143T and 143C can be found in the 1955/56 red radio and TV servicing book. The EHT rectifier is an EY51. Line output valve is a PL81 the same as the seventeen inch model. The line oscillator is the triode section of a Mazda 10C2.
It's an ECL80 in the 17" version.
The Defiant TR1456 employs a similar chassis. The main difference being that all the valves are Mazda. The line output valve is a 20P4, the line oscillator is a 10C2 just like the 143C. The EHT rectifier is the Mazda U25.
I remember working on these sets in the early 1960s. Although the line output transformers look similar I don't think that the transformers are interchangeable between Mazda and Mullard versions.
EHT is 12KV so you should be able to draw off quite a long spark from the anode of the EY51. To check the presence of rectified EHT you need to earth the blade of the screwdriver. The EY51 heater winding can short out to the chassis.

DFWB.

[jay_oldstuff]

Hmmm could I have a Defiant rather than a Regentone Thinking back to last night the line output bottle which I haven't yet removed looks more like a 20P4 than a PL81. Thanks for that you could of very well saved me a lot of chasing my tail. I have the trader sheet for the Regentone 143T guess I would be as well to dig the Defiant TR1456service data out.

Jay

[jay_oldstuff]

Odder and odder the Regentone trader sheet no 1244/T100 that I am working from definitely has the EHT rectifier as a EY51 but it has the line out valve V8 as the 20P4 not a PL81. I am now very confused.

Jay

[FERNSEH]

Info for the Defiant TR1456 is also in the 1955/6 servicing book. I'll post up the circuits of the line output stages of both the Regentone and Defiant models tomorrow. This is indeed confusing.

DFWB.

[FERNSEH]

It follows that if your set employs the 20P4 as the line output valve then the boost diode should be an U301.
Does your set have electrical picture shift controls? The 17" versions have this facility. I kinda remember some 14" sets had electric shift controls even though the diagrams state that only 17" sets had this facility.
One thing is for sure. The Mazda valve models have quite different line output circuits compared with the Mullard equipped versions.
All models should employ the ECL80 in the frame and audio stages.

DFWB.

[FERNSEH]

For comparison. The circuit diagrams of the line output stages of the Regentone 143T and the Defiant TR1456. As mentioned earlier, the circuit diagram of the 143T is of the version fitted with the Mullard PL81 and PY81. The Defiant has the Mazda 20P4 and U301.
Some versions have electrical line shift controls.

DFWB.

[Heatercathodeshort]

I am getting a bit confused here. Plessey who manufactured the Regentone 143C were not tied to any particular manufacturer for valve and tube supplies.
They produced receivers for Defiant the Co-op brand name using the Mazda range due to the need to use British manufactured components, a stipulation of the agreement with Plessey.
The sets supplied to Regentone would have been free of any restrictions and could have been supplied with either Mazda [British] or Mullard [Dutch] valves, a bit odd because the Mullard valves used in UK receivers were made in Britain anyway.

When you say 'Solid state stick rectifier' I thought at first you were referring to the EHT rectifier. I presume from your notes that it is the mains H.T. rectifier. The original would have been a contact cooled affair [nasty] bolted to the chassis or the classic finned type we are all familiar with. This may have been replaced with a silicon diode and surge limiting resistor.
Whatever is in place, leave it be. If it is producing enough AC on the anode of the EHT rectifier it should be ok for at least 'first light'.
The EY51 has a 6.3V heater. The Mazda U25 has a 2v heater. If the type fitted in your receiver is a U25 an EY51 will not light. Connect a 6v pilot lamp across the heater connections and see how brightly it lights. Dim = U25 [plus maybe a timebase fault] Bright = EY51. The U25 will have only a couple of turns of heater winding around the transformer, the EY51 more. As your receiver employs Mazda valves I guess it could well be a U25 but no guarantees! Sort this out first and then we can take it from there.
Without boring anyone I will repeat, disturb as little as possible, no cleaning dust removal or prodding. This will only lead to disturbance, dislodged components or adjustments, damage and frustration. These are very reliable receivers and give a good picture. Good luck with it. Regards, John.

[FERNSEH]

A variant of the chassis being discussed. The Marconi VT64A. This set uses Mullard type valves. N152 = PL81. The circuit is redrawn in a much clearer manner. The CRT is the rectangular Mullard MW36-24.

DFWB.

[jay_oldstuff]

I'm going upto the workshop tonight so will do some investigation. Watch this space.

Jay

[jay_oldstuff]

Ok I'm back from the workshop and think I've made some progress.
I took HKS's advice and replaced the EY51 with a 6V bulb fired the set up and got a very dimm glow from the bulb, so looks like the U25 is correct after all. and we also have a Mazda 20P4 and U301 in with the LOPT.
I'm out of NOS U25's and the original has an OC heater I however pinched one from a very tired worm eaten set from the roundtoit pile. only problem being I don't know its condition apart from it having an intact heater.
Anyway that was fitted in short time and I tried again, heaters up good strong sound but nothing on screen but I can pull a 2-3mm spark from the cathode of the U25 using an earthed screwdriver. The 20P4 is glowing purple inside not sure if its faulty or normal as it's not a valve i'm that familiar with. Next i'm going to investigate the caps round the lopt aria. C48 on the trader sheet looks a likely place to start.

Jay

[FERNSEH]

Hi Jay,
It looks like you have the version that is similar to the Defiant TR1456.
It follows therefore service data the Defiant will be applicable for your set.
The 20P4 should not glow purple, it's likely to be gassy. The 20P4 is the 0.2amp heater version of the more common 0.3amp heater 30P4.
From your description of the spark at the DC end of the EHT rectifier I'd say the EHT voltage is too low. A 1/2inch spark is more normal.

DFWB.

[jay_oldstuff]

Thanks for confirming my suspicions re the valve and EHT ill go have a dig in the valve cellar there should be a 20P4 down there somewhere. Then its on to recaping the line output stage.

Jay

[jay_oldstuff]

Ladies and gentlemen, we have first light. after studying the schematic (Trader sheet 1244/T100) I decided to replace C48 unfortunately I didnt have a 0.1 uf cap rated at 1000V the closest I had was 0.15 uf so that was fitted for now. while I was under there I noticed C47 looked a right mess and a quick check with the meter confirmed it as very leaky so it was duly replaced. time to switch on again so connect up the arora switch on the set, up comes the test tone and something very dimm and uncomprehendable on the screen. With a little bit of fiddling with the band one tuner we have an out of focus and shape test card C. further fiddling and we have a slightly less out of focus test card C. just for fun I put a disk in the dvd player. The audio is pretty good not mega loud but you can't expect too much from an ECL80. The HT is well down so it looks like i'm going to have to do something with that contact cooled rectifier before it gives up the ghost and stinks my workshop out. then i thing its just a case of going through the waxies as some look quite distressed and take it from there.

Jay

[Heatercathodeshort]

That looks good. Replace the old rectifier with a silicon diode [BY127/1N5408 etc] and 25-50 ohm 5 or 10 watt wire wound surge limiter resistor. Keep the resistor clear of any other components, it gets hot. Make sure the interference limiter is turned to minimum and the contrast control is not too far advanced. You may need an attenuator [12db]to reduce the signal input level. Check the H.T. after rectifier replacement to make sure it's not too high as this can put a strain on the LOPT. Adjust the limiter resistor until it is within around 10%. Regards, John.

[Studio263]

Something to do on a rainy day, assuming that all that water is on the outside of the windows...

0.15uF should be fine in place of 0.1uF, unless you need this rather unusual value for something else.

[jay_oldstuff]

Ok had a little time to play this evening so thought i'd have a bash at replacing that contact cooled rectifier, so i turned the set on its side to assess underneath and spotted what i'd assumed to be two replacement resistors in series. one a pretty standard looking Radio-spares 10W 30R resistor and an odd looking thing that upon closer inspection was marked Radio-spares REC, yep someone had been there before me and already bypassed the old contact cooled rectifier with these two components. they weren't fitted very well and where in danger of shorting out on other components so i removed them so i could refit them better and add some insulation to the legs. whilst out i tested the diode which seemed fine. i also used this opportunity to replace the three wax capacitors which where now easier to access with these components out the way. two of these capacitors where HT decouplers and both tested leaky. with this little lot replaced and the diode and resistor refitted with some sleeving the set was switched on and the HT measured and we have a slight increase in HT.
All i can guess is the old wax decoupling capacitors are all a bit leaky and are dragging the ht down. So next step will be to change all the remaining wax decoupling capacitors noting the ht after each replacement. even the two I've replaced have made a notable improvement to the image on the screen.
i will have to put the set to one side for a few days now though as i have work commitments

Studio263 Thanks for the info re the 0.15uf cap I have a fair few of this value so if it's going to be ok ill leave it in.
PS its not rain its the frosting on my workshop windows

Jay