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Old 14th Dec 2018, 11:28 pm   #1
Michael Maurice
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Default Portadyne 1940's radio

I am restoring a 1940's portadyne radio which I believe to be from the 1940's.

Curiously though there is a plate, there is no model number and no serial number stamped into it

This is an AC/DC set, The valve line up is: C36D, VP13C, PEN/DD/4020 and 1D5. Although the rectifier's heaters are working. the rectifier is shot, so I bypassed it with a modern silicon rectifier and series resistor.

The radio works, but I was asked to fit an external input to it.

Naturally being a 'live' chassis, I added isolating capacitors but I get lots of hum from it.

Looking at similar radio diagrams, it seems a typical arrangement.

The resistors in series with the jack plug are 2.2K.

The circuit is shown below.
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Old 15th Dec 2018, 1:13 am   #2
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Default Re: Portadyne 1940's radio

If you haven’t already, use screened lead for all the new wires.
Good luck!
Peter
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Old 15th Dec 2018, 1:38 am   #3
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Default Re: Portadyne 1940's radio

the line input might need a terminating resistor perhaps? eg 10K?
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Old 15th Dec 2018, 1:47 am   #4
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Default Re: Portadyne 1940's radio

Does the external input need to be a high impedance? If not connect a 47K resistor from the junction of the input 0.01uF cap and switch down to chassis.

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Old 15th Dec 2018, 9:29 am   #5
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Default Re: Portadyne 1940's radio

Isolating audio inputs with caps on both lines can be a frustrating and hummy game. An audio isolating transformer or go "modern" with an isolation amplifier is a much less demanding way to go.

The 10k resistor idea will cut the hum down but it will also act as a high pass (bass cut) filter with the series capacitors.

Or use a closeup and personal pantry transmitter...... this is about the only way to do it "safely" from a liability viewpoint since it doesn't involve modifying the set which is a whole can of worms if it's not just for your own use
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Old 15th Dec 2018, 9:59 am   #6
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Default Re: Portadyne 1940's radio

Quote:
Originally Posted by Herald1360 View Post
Isolating audio inputs with caps on both lines can be a frustrating and hummy game. An audio isolating transformer or go "modern" with an isolation amplifier is a much less demanding way to go.

Can you give me examples please



Quote:
Originally Posted by Herald1360 View Post
Or use a closeup and personal pantry transmitter...... this is about the only way to do it "safely" from a liability viewpoint since it doesn't involve modifying the set which is a whole can of worms if it's not just for your own use

This may be the best way to go
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Old 15th Dec 2018, 10:42 am   #7
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Default Re: Portadyne 1940's radio

What about bluetooth? The adaptors I bought from ebay cost 99p.
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Old 15th Dec 2018, 6:06 pm   #8
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Default Re: Portadyne 1940's radio

That sounds a good idea too- though the receive side will still be a modification to the set it's at least inside and out of sight with no physical connection to the live parts of the set presented to the outside.

Audio isolating transformer:

https://uk.rs-online.com/mobile/p/au...7207/?sra=pstk

Has a 1000V isolation rating, doesn't say anything about standards (UL/IEC/whatever, though).
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Old 15th Dec 2018, 7:26 pm   #9
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Default Re: Portadyne 1940's radio

Hi Michael, it would be better if the caps you use to couple the external circuitry to the input were Class Y types, not simply 1000v rated.
Audio isolating transformer is by far the better way to go.

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Old 26th Dec 2018, 9:04 pm   #10
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Default Re: Portadyne 1940's radio

I went for the AM transmitter solution.

I managed to make an aerial on the inside of the back cover so that all the inards were covered.

I decided to fit a NOS 1D5 rectifier so as not to put a strain on the other valves as they were warming up. The VP13C valve was loose and intermittent so that was replaced as well.

The main smoothing block was replaced with a 16uF+16uF/500V capacitor. Other Wax and electrolytic capacitors were replaced along with a couple of out of tolerance resistors.

The set performed well after this work was carried out.
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