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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 17th Jan 2016, 4:01 pm   #1
greg_simons
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Default Philips 634, substitute for the SD4?.

Regret the time may be coming when this rare valve may have to be replaced, has anyone on this forum know to a substitute device or dodge that can be employed here.
Greg.
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Old 17th Jan 2016, 4:22 pm   #2
stevehertz
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Default Re: philips 634, substitute for the sd4?.

Mullard said to use a TDD4. It's covered in this thread:
https://www.vintage-radio.net/forum/...d.php?p=612128
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Old 17th Jan 2016, 4:53 pm   #3
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Default Re: philips 634, substitute for the sd4?.

Many thanks Steve, now, all I have to do is find a TDD4.
Greg.
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Old 17th Jan 2016, 5:26 pm   #4
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Default Re: philips 634, substitute for the sd4?.

There are E444 types available in Europe, electrically identical, but they have a different base. When I was after a TD4 I had 2 offers of E444's from Europe, but no one seemed to have a spare valve socket to suit.
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Old 17th Jan 2016, 6:19 pm   #5
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Default Re: philips 634, substitute for the sd4?.

If you build a valve base adaptor there are a number of possibilities, especially if you fit a small 4-6.3 autotransformer inside. One option would be the dirt cheap ECL80, using the triode section as a diode, or you could use something like a 6BW6 with a Ge diode.
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Old 17th Jan 2016, 7:51 pm   #6
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Default Re: philips 634, substitute for the sd4?.

On the adapter-to-modern-valve-type idea, I wonder if a PC92 / 3AB4 triode could be persuaded to work, with a 2.8 ohm resistor (2x 5.6ohm small carbon film in parallel) feeding the heater from 4V? If you wanted to stay thermionic for the diode rather than use Ge, there's always the 3AL5. Together, they would still take rather less heater current than the original.
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Old 18th Jan 2016, 12:01 am   #7
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Default Re: philips 634, substitute for the sd4?.

I have found a company with the E444 in stock just waiting for the staggering price to come through, if it's truly astronomic the ECL80 seems a good bet more especially since I have some in stock.
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Old 18th Jan 2016, 2:01 am   #8
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Default Re: philips 634, substitute for the sd4?.

The 1958 Mullard Maintenance manual states that the recommended replacement for the SD4 diode-tetrode is the TDD4 double-diode-triode.
This involves rewiring the base which is something we wish to avoid.
The Continental Philips E444 has a different seven pin base, the C7A.
A substitute for the SD4 was discussed here: https://www.vintage-radio.net/forum/...d.php?p=612128 #19
Cossor made a double-diode-RF pentode, the DDPen. I did consider using this valve as a substitute for the SD4 after the base was rewired. G2 and the diode pins must be transposed.
In the Philips 472A the Mulard SP4 pentode was employed as the audio amplifier.

DFWB.

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Old 18th Jan 2016, 11:48 am   #9
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Default Re: Philips 634, substitute for the SD4?.

Nothing wrong with a limited amount of base re-wiring to get a vintage set going in the event of the original valve being unobtainable. After all, the TDD4 route is the one recommended by the valve manufacturer, and wiring can be reversed anyway should an SD4 turn up. I'd rather have a proper 'period' valve sitting there in a rewired base (that you can't see) than a 50s valve looking totally wrong. As ever, each to their own.
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Old 18th Jan 2016, 12:54 pm   #10
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Default Re: Philips 634, substitute for the SD4?.

Seems to be a few Cossor DDPen valves available on certain on-line auction sites.
Only two wires to swop over with this valve.
You could even spray it gold.
Only one drawback with the DDPen, it's vari-mu.

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Old 18th Jan 2016, 12:58 pm   #11
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Default Re: Philips 634, substitute for the SD4?.

Quote:
Originally Posted by stevehertz View Post
Nothing wrong with a limited amount of base re-wiring to get a vintage set going in the event of the original valve being unobtainable. After all, the TDD4 route is the one recommended by the valve manufacturer, and wiring can be reversed anyway should an SD4 turn up. I'd rather have a proper 'period' valve sitting there in a rewired base (that you can't see) than a 50s valve looking totally wrong. As ever, each to their own.
I don't think an adapter should ever be considered a permanent solution. It's an immediately reversible temporary mod that keeps the radio in use until the correct valve becomes available.
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Old 20th Jan 2016, 9:42 pm   #12
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Default Re: Philips 634, substitute for the SD4?.

Well folks, the price was indeed stratospheric!, 25euro for the valve from a french company , not too bad you think but minimum order 150 euro, I think the ecl80 substitute will be pressed into service for the time being.
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