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Old 20th Apr 2018, 1:31 pm   #61
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

If you are going solid state make sure your smoothing caps are well rated and new.
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Old 20th Apr 2018, 2:22 pm   #62
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

The M.O.V. U10 looks a suitable sub. for the 1829.
Same heater current,too.
Duff soldered joints on valve pin connections seem to be more common than they were. Probably because valves are ageing, and oxidation of the filament wire soldering to the base pin thus being more likely. This will happen even if the valve is still new in the box, as I have found out. Tony.
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Old 20th Apr 2018, 5:29 pm   #63
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Have you reconnected the transformer HT centre tap to chassis, or to the circuit wherever that should be (sometimes to chassis via bias resistors)? I seem to recall you disconnected it earlier..... I have a used 1821 but it has only about 25% emission. If you want it you can have it for the cost of postage. A DW2 is a reasonable equivalent if you can find one. Cheers, Jerry
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Old 20th Apr 2018, 6:32 pm   #64
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Yes, I resoldered the HT CT a few days ago. In this set it connects, as shown in the diagram, to a wirewound pot. and a couple of fixed resistors. This pot. is the so-called Volume control (actually more like an R.F. Gain control). The reservoir & smoothing caps. are both new axial 400v types. Thanks for the offer of the 1821, cathoderay57, but I'll try the other suggestions first.
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Old 22nd Apr 2018, 12:22 pm   #65
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

A few further checks this morning lead me to suspect that the problem is due to the valve-holder - lack of contact between the sockets and the valve pins. The pins, b.t.w., are clean & shiny, and the internal connections are good. In addition, the same symptoms occur if I insert the VU39 instead of the 1821. Possibly the other 4 valve-holders have the same problem, to which applying Servisol super 10 makes no difference. These problems, I guess, should be expected with an 80+ year old radio, though I don't recall having them with the other pre-WW2 Radios I've repaired. Next step, I guess, is to fit a couple of 1N4007s and a series resistor. What I don't want to have to do is change all 5 valve-holders!!
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Old 22nd Apr 2018, 2:26 pm   #66
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

It's unusual for the socket contacts to be so bad as that. You should be able to use a needle file to scrape the inside carefully and squirt deoxit inside the pin sockets. You said earlier you were getting 4v AC at the rectifier winding measured at the transformer. Are you getting the same at the rectifier heater pins? I have seen this issue with a GZ32 rectifier but the problem was caused by oxidation of the wires soldered inside the valve pins, not the socket. An Avo check showed heater continuity but with the relatively high heater current the resistance imposed by the dry joint inside the pins meant that the heaters wouldn't light. Resoldering the wires inside the pins is quite tricky if the oxidation is heavy because the wire doesn't want to tin properly. I have resorted to tinning then pushing a short single core wire into the pin from the bottom which makes enough tight contact with the internal wire to work. On another case with a KT66 I had to file a small hole in the side of the heater pins near the top then scrape the wire inside until I could see bright copper, then solder up the hole. Try to use the rectifier if you can, rather than resort to diodes. Cheers, Jerry
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Old 22nd Apr 2018, 6:20 pm   #67
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

I'll try scraping inside the sockets with a needle file, and maybe re-solder the connections to the valve itself. The voltage reading at the valve holder pins is the same as that at the transformer, Jerry. Might be a good idea to treat all 5 valve-holders this way.
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Old 22nd Apr 2018, 7:10 pm   #68
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

The fault is almost certainly due to tarnished sockets. I find that even after gently scraping the insides of the rectifier socket, I'm getting the full HT secondary voltage at the socket, ut the heater voltage there is, at best, intermittent, whilst being O.K. at the transformer. A better clean, plus re-soldering/rewiring connections will hopefully get the circuit working as it should at last!!
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Old 23rd Apr 2018, 9:47 pm   #69
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Getting there at last!! The fault turned out to be an intermittent connection between a wire from the rectifier valve-holder and the heater winding on the transformer. Cleaning,re-tinning, & re-soldering the wire in question at both ends cured the trouble. The 1821 heated up within a few minutes of applying power via the lamp limiter. I measured, with my DMM, approximately 350vDC at the filter choke, w.r.to chassis. Bearing in mind that this was with no load -i.e. none of the other valves fitted, it seems to me that the P.S.U. is working as it should, so, with a bit of luck, should the rest of the radio. I'll post further when I know more.
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Old 23rd Apr 2018, 9:51 pm   #70
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Result

Extra points for sticking with it

Cheers

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Old 23rd Apr 2018, 10:28 pm   #71
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Still some way to go, though, Mike, though, unless any of the other valves are below par, the radio should work, as I've already re-capped it, and checked out the resistors, which are all fairly close to their specified values, quite amazing in a way, given that the set dates from 1933/3!, and all the resistors are original!
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Old 23rd Apr 2018, 10:33 pm   #72
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Is the make and model of the radio known, have you got any photos?
Mike
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Old 24th Apr 2018, 8:55 am   #73
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Yes, Mike, it's a Philips 'Superinductance' 274, which has been in my 'to do it' pile for longer than it should have been! I'll take some photos and post them ASAP.
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Old 24th Apr 2018, 11:12 am   #74
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Question Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Pictures of the 274A chassis, as promised, plus an inquiry. The top cap connector pictured in photo #4, which, AFAIK is original, will not fit on the top cap of the Mullard SP4 valve, which was in the 'L4' position on the chassis, when I first received the radio. Assuming the SP4 is correct, is there something missing from that top cap connector, or was there some kind of adapter for the SP4, which, from its appearance, was made to take the once-standard top cap connector? N.B. I had to use a length of modern heat-shrink sleeve on the wire visible in pictures 3 & 5, as I have no systoflex. The wire in question was the one causing the 1821's heater not to work, b.t.w. The original Electrolytic caps. are 'just for show'. As may be visible, I've fitted two modern axial electrolytics underneath their mounting bracket.
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Old 24th Apr 2018, 11:32 am   #75
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Early SP4 had a screw top cap, I assume this is the B5 pin version, there is also a later B7 pin version.
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Old 24th Apr 2018, 12:17 pm   #76
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

All the valves in the 274A have B5 Bases, Sam, although the 1821, like other rectifiers of its era, only uses 4 pins. The SP4 I have, as I noted, has a once-standard top cap, which takes a push-on connector. Oddly enough, the SP4 data I've obtained via the Valve Museum website, describes it as a Screened Pentode usable either as a first detector or frequency changer, but it can also be used as a 'normal speech detector' (Mullard's description back in 1934) It can also be used, they state, as an H.F. Amplifier.
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Old 24th Apr 2018, 8:59 pm   #77
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

There is no way that the top cap connector shown in picture 4 in my post 74 will fit on the top cap of the SP4 valve to which it's supposed to connect. Besides that I discovered that the ML4 valve now has a small hole in it's glass envelope(don't ask how that happened!), making it useless, so I now have the almost impossible task of finding at least two replacement valves.
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Old 25th Apr 2018, 8:00 am   #78
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Hi Livewire,

Looks like you enjoy a challenge, and this set does not disappoint. Good work on the rectifier wires. From you pics it looks as if there is a top-cap detached from an old valve still stuck into the receptacle inside the screened outer cap. Careful probing with a pair of tweezers should allow you to extract it and the cap should then fit comfortably onto the top cap of the SP4. The Valve Museum shows the following equivalents to the ML4: AC/P, CV1179, NR57. I checked my spares box and nil stock on any, I'm afraid. Good luck with your search. Cheers, Jerry
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Old 25th Apr 2018, 8:25 am   #79
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Someone on Ebay is selling some CV1732s which he says are equivalent to an ML4. Search for "ML4 valve"
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Old 25th Apr 2018, 8:55 am   #80
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Thanks, Jerry & Stuart. I'll follow up on your suggestions. Not being familiar with those screened T.C. Connectors Philips used in the 30s, I wasn't sure what they should look like. The other one, b.t.w, just has a small diameter hole into which the stud on top of the valve in the L2 position-in my case an Osram MS4B. I will almost certainly order that Valve, Stuart. The seller in question is a long-established reputable firm from whom I've bought various valves over the years.

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