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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 31st Dec 2017, 6:04 pm   #1
EdWilliams
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Default Philips 274A

I bought this radio because I fancied a go at something pre-war. I originally tried to buy a Philco 444 on ebay but got totally annihilated in the bidding, so on the rebound I had a look on Gumtree and found this Philips 274A TRF set not too far away from me.

I arranged to meet the seller at his house, who turned out to be the grandson of the original owner. The seller plugged in and switched on before I could stop him, which resulted in a mixture of motor boating and very loud mains hum. He wanted 50 for it, but when I explained that I wanted to restore it to working condition his price went down to zero. I've never had the experience of a seller trying to negotiate the price downwards before! So I started the unusual process of the buyer trying to negotiate the price upwards - in the end we settled on 30.

On getting it home I took the back off and had a look inside. First obvious problem - the anode connection to the second RF valve (S4VB) was broken off flush with the valve top leaving no visible wire to connect to. Drat! I then took the chassis out from the case and spotted the second obvious problem - the winding for the volume control was broken in at least two places. Double drat!

As the success of this project was clearly going to depend on the health of the valves, I thought I would do a minimum set of fixes first to see if it could live, and then come back and have second and third goes to be a bit more complete. So first I attempted to fix the S4VB by carefully filing down the glass pip on the valve top until some of the anode connection wire became visible (trying not to let the vacuum out), then blobbing some solder onto the anode wire so a new connection could be made to the top cap connector, and finally I araldited the top cap back onto the valve. Next I replaced the wire wound volume control with a new log pot (shunted by a lower value resistance so that the correct combined resistance was obtained) and finally I replaced the output valve grid coupling capacitor and the two smoothing electrolytics. I finished this work at 11 pm one evening, switched on in great anticipation, and - nothing, apart from a copious amount of mains hum. Went to bed in disgust.

The next evening I had another look and quickly spotted the deliberate mistake. On this radio there is a plug used to select either radio or gram operation, which I had inserted into a completely random socket on the rear of the chassis. I moved it back to the correct place and success, the radio worked, normal mains hum only.

I discovered two things about the set over the next few days: 1) the HT was very low at around 90 V, 2) the volume control behaved strangely - on a strong station it was impossible to turn it down quiet enough.

I then bought some more capacitors and set about replacing those above 1 nF. In the spirit of getting on with things I disconnected those in the metal container and replaced them with 6 new ones connected as I saw fit (see photo). The volume control worked properly after this; looking at the Trader sheet for the equivalent Philips 834A I think that C3 (0.1 uF) must have been horribly leaky and preventing enough control voltage reaching the grid of the MM4V first RF valve.

With hindsight I think that the use of a log pot for the volume control is wrong. Due to the unique way in which the volume control works on this set (adjustment of front end gain) I suspect I actually need a linear pot or even an antilog one if such a thing exists (presumably the fixed tapping on the original wire-wound pot is an attempt to get a decent control law). As it is, as the volume control is increased from zero you get, nothing, still nothing, heck that's loud!

The rectifier valve had been replaced in the past by a DW3 which I thought might be poor and explain the low HT. I got lucky and bought an original 1821 rectifier which is clearly in better condition - I now get 190 V, still lower than spec but a lot healthier and not too bad I hope. The performance is better for it.

The set now has the correct complement of valves except for the 994V triode detector which has been replaced by a Z8154 (does anybody know what this is - I can't find out anything about it?)

I replaced the non-working scale lamp with a new one (sold as a tail-lamp for a 6 V moped), and started using the radio on a daily basis.

The sensitivity and selectivity are pretty good for a TRF set, but the anode bend detector doesn't like the strongest local station - Smooth radio - and distorts noticeably. I don't like Smooth radio either so the feeling is mutual. It's OK on other stations though.

Over the Christmas break I dismantled the metal can containing the six capacitors and fitted the new ones inside. The can was date-stamped February 1934. Not too hard with the aid of a blowlamp to melt the solder holding the base on; the worst bit was fitting the completed can back in the chassis and getting the screws re-engaged.

The wooden case for the radio is in reasonable condition - a few minor dints and scratches but really quite good for its great age. I'm looking forward to it being 100 in 16 years' time!

Some more things to do: 1) I'd like to re-instate the original volume control if I can think of a way to fix it; 2) it's now occasionally showing instability on high volume settings - I think this is intermittency in the metallised screening of the MM4V first RF valve. It behaves itself if I wriggle the valve envelope a bit or temporarily make a connection from the screening to chassis. All good fun though.

Photos below.

Ed
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Old 31st Dec 2017, 7:45 pm   #2
Sideband
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Default Re: Philips 274A

Lovely sets! It's very unlikely you'll find a new 994V....they've been unavailable since the 70's! An AC/HL is probably the best you'll find as a replacement or try a 164V. I restored mine about 10 years ago and you can read about it here.... https://www.vintage-radio.net/forum/...ad.php?t=11743

The volume control is difficult to replace but someone on these forums was offering replacement elements. A search will probably come up with an answer
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Old 31st Dec 2017, 7:58 pm   #3
Cobaltblue
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Default Re: Philips 274A

Yes a lovely set and you got a great buy there I paid considerably more than that more than 25 years ago

It's got extra status as the set on the front cover of Radio Radio.

Cheers

Mike T
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Old 1st Jan 2018, 10:14 am   #4
vinrads
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Default Re: Philips 274A

A most enjoyable write up Ed ,I like these old Philips TRF's they have there little quirks as most Philips set's do ,well done with the restoration . Mick.
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Old 1st Jan 2018, 3:51 pm   #5
EdWilliams
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Default Re: Philips 274A

Sideband: I had already looked at your restoration thread - in fact I used the photos to make sure I was connecting up the capacitor block correctly. You clearly managed a higher quality and more in depth job than I have.

Mike T: Guess which book I asked for for Christmas?

Cheers

Ed
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Old 1st Jan 2018, 6:12 pm   #6
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Default Re: Philips 274A

Nice methodical/pragmatic work Ed - and a great result too ...... lovely set!
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Old 1st Jan 2018, 6:43 pm   #7
Sideband
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Default Re: Philips 274A

Quote:
Originally Posted by EdWilliams View Post
You clearly managed a higher quality and more in depth job than I have.
Hi Ed.....don't underrate yourself! You've done a good job and you should be very pleased with your results. There is no right or wrong way to restore and you do what suits you (with possible guidance from 'old hands'). I try to keep older sets as original as practical by re-stuffing capacitors etc. Later sets I just replace components as required but try to keep the top of the chassis original so that it looks 'right' when the back is removed.
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Old 3rd Jan 2018, 9:24 pm   #8
PJL
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Default Re: Philips 274A

If you find a 2nd hand 994V chances are it will be low emission. The MH41 is the nearest you will get but they are fancied by the audio folks.
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