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Old 29th January 2015, 06:20 PM   #1
wahee is offline wahee  United Kingdom
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Default Got some PX4 valves from an old radiogram

Hi

I had to get rid of an old radio gram which was pretty beaten up. I decided to have a look at the innards and pulled some of the valves.

There are 2 PX4's and a few other valves.

I know very little about valves but have experience with Quad solid state amps and also vintage synthesizers.

I would really like to build a valve amp and attempt to use these PX4's in it. I believe they are well regarded as far as audio quality goes.

I also pulled the old amplifier chassis which is quite nice. I believe it is mono. Possibly an RGD 1046

My questions are..

is it worth trying to use the old chassis to build an amp?
Are here any kits to guide one in building a valve amp from scratch?

many thanks


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Last edited by wahee; 2nd February 2015 at 06:16 PM.
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Old 29th January 2015, 10:04 PM   #2
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take a look at:

Vacuum Tube Schematics: SE PX4 (EL86-6FQ7) Amplifier

and

PX4 audio valve, triode amplifer tube
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Old 29th January 2015, 10:14 PM   #3
Bigun is offline Bigun  Canada
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I do believe those PX4 valves are quite valuable, perhaps $1000 for the pair ?
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Old 29th January 2015, 10:18 PM   #4
wahee is offline wahee  United Kingdom
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hey thanks guys. Wow $1000 dollars. I just hope they are working now. I have not tried them. They 'look' in good condition but i'm not sure how sturdy they are
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Old 30th January 2015, 12:06 AM   #5
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I would replace the control grid capacitors on the PX4s and power it for half an hour with a light bulb in series while monitoring the temperature of the capacitor cans.
Once they run cool you should have a nice amplifier and it can then be powered at full voltage.
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Old 30th January 2015, 01:04 AM   #6
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I had no idea these tube were so rare/expensive. Whatever you do, be careful!

PX4 audio valve, triode amplifer tube
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Old 30th January 2015, 03:41 AM   #7
multi is offline multi  Australia
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wahee.
The PX4 amplifier may be worth a lot to a collector. Most likely you would get sufficient money to build, buy yourself a pair of very good amplifiers using valves that are more easily obtainable.
The amp in your photo is likely to be one designed by Osram GEC.
I think I have a circuit, the same circuit also used KT66's as triodes.
Phil
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Old 30th January 2015, 04:13 AM   #8
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Quote:
Originally Posted by wahee View Post
hey thanks guys. Wow $1000 dollars. I just hope they are working now. I have not tried them. They 'look' in good condition but i'm not sure how sturdy they are
Under no circumstances, should power be applied to that old carcass. The ancient electrolytic caps. have all but certainly dried out and applying power could destroy the valuable tubes and "iron".

The 1 getter I see looks STRONG. That means the envelope is quite intact, which is highly encouraging.

1K$ would fund any number of nice projects. OTOH, you already have power magnetics that can be recycled. It's not an easy decision.

SE O/P "iron" is big. Therefore, I suspect a new chassis will be needed, should you decide to use the PX4s in a stereo setup. The PX4 sockets should be reusable.

Any rational design will begin with the PX4 data sheet. FWIW, I'd use an operating conditions set that does not dissipate the max. 15 W. Doing so will extend the service life of the PX4s.

Please notice that you will need upper 90s sensitive speakers, as power O/P is very limited.
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Last edited by Eli Duttman; 30th January 2015 at 04:15 AM. Reason: spelling/grammar
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Old 30th January 2015, 09:39 AM   #9
wahee is offline wahee  United Kingdom
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Quote:
Originally Posted by Refugee1 View Post
I would replace the control grid capacitors on the PX4s and power it for half an hour with a light bulb in series while monitoring the temperature of the capacitor cans.
Once they run cool you should have a nice amplifier and it can then be powered at full voltage.

hi many thanks for the advice. Is that the 0.1UF metal caps across the wiring ladder with the resistors? I think the larger ones on the topside of the amp are smoothing?
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Old 30th January 2015, 09:53 AM   #10
wahee is offline wahee  United Kingdom
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Quote:
Originally Posted by Eli Duttman View Post
Under no circumstances, should power be applied to that old carcass. The ancient electrolytic caps. have all but certainly dried out and applying power could destroy the valuable tubes and "iron".

The 1 getter I see looks STRONG. That means the envelope is quite intact, which is highly encouraging.

1K$ would fund any number of nice projects. OTOH, you already have power magnetics that can be recycled. It's not an easy decision.

SE O/P "iron" is big. Therefore, I suspect a new chassis will be needed, should you decide to use the PX4s in a stereo setup. The PX4 sockets should be reusable.

Any rational design will begin with the PX4 data sheet. FWIW, I'd use an operating conditions set that does not dissipate the max. 15 W. Doing so will extend the service life of the PX4s.

Please notice that you will need upper 90s sensitive speakers, as power O/P is very limited.

hi advice much appreciated. I think I will take this one slow and easy as I recently destroyed a rather nice spendor speaker magnet through my own stupidity.

I would like to keep the 1046 chassis as I do enjoy refurbing old kit.

Is it wise to replace all the old electrolytics? I was looking at Jenson, F&T etc which seem to do decent enough replacements. I would perhaps use the metal can shell for the smoothing caps to keep the look.


The resistors I will check with a meter before power up.

I currently don't have the knowhow to build my own amp but it's something I would love to do in the future.


I also have some higher resolution images of the valves...which may or may not show more detail

thanks again


https://picasaweb.google.com/1137870...eat=directlink
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