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 My next Project . A Murphy D36 240Volt Hot Chassis
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 Return to top of page · Post #: 1 · Written at 2:24:36 PM on 21 November 2023.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2146

This is one interesting project I will be attempting over the next few months. I have sent a photo and schematic to Brad . Its too good to not do.

Murphy D36 Circuit Diagram

Murphy D36 valve radio


 
 Return to top of page · Post #: 2 · Written at 7:57:12 PM on 21 November 2023.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5221

Don't see many of them, but you can find "Hot" printed circuits as well. European trick is to use a tapped ballast coil, which to the unwary, looks like a transformer.

An isolation transformer really is a must & beware, when considering using mains powered test equipment on it; Nasty things can happen.
Any caps going lines to the chassis should be line caps.

Do make sure Neutral is the chassis, whilst a bit more intrinsically safe. The output of an isolation transformer still has a Neutral & Active and be very sure it is an isolation transformer.

Marc


 
 Return to top of page · Post #: 3 · Written at 10:22:38 PM on 21 November 2023.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2146

Hi Marcc I just emailed the schematic and photo to you.


 
 Return to top of page · Post #: 4 · Written at 12:16:51 AM on 24 November 2023.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2146

Photos and schematic sent


 
 Return to top of page · Post #: 5 · Written at 10:37:12 PM on 24 November 2023.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5221

Interesting design did you manage to get the specs.? I note delayed AGC


 
 Return to top of page · Post #: 6 · Written at 6:32:19 AM on 25 November 2023.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7278

Photo and circuit diagram uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 7 · Written at 7:01:11 PM on 25 November 2023.
BringBackTheValve's Gravatar
 Location: Linton, VIC
 Member since 30 December 2016
 Member #: 2028
 Postcount: 465

Very nice. You can run it with DC also.


 
 Return to top of page · Post #: 8 · Written at 8:04:10 PM on 25 November 2023.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5221

Interesting set, one does not see double yet alone triple conversion sets, that often.


 
 Return to top of page · Post #: 9 · Written at 8:20:41 AM on 26 November 2023.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 830

You can make it somewhat safer by having the B- (radio ground) line connect to the neutral (grounded conductor) of the powerpoint via the switch (which also switches the hot wire). Maybe jumper over the grounded line switch contacts, so if the hot switch should ever fail to open, the entire set doesn't become hot.


 
 Return to top of page · Post #: 10 · Written at 9:35:44 AM on 26 November 2023.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2146

Marcc
Can you explain in layman's terms what triple conversion means.

Wa2ise
I will take your suggestion to the tech who will work on this. I am more than capable in fixing most sets but this one deserves someone more professional than me. I appreciate all the advice you guys are giving.


 
 Return to top of page · Post #: 11 · Written at 12:26:52 PM on 26 November 2023.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5221

With the mains and a "hot chassis" there are two types of those. One floats the chassis above the mains & has often a resistance and hopefully line cap to the chassis. There will be no actual connection to ground. The early type has the mains direct to chassis. Most of those can handle DC bearing in mind it is the more dangerous.

With the Mains you could run it from an isolation transformer. The one I use I fitted with a "kill switch". I have mentioned several times that the object is to keep neutral on the chassis, it should also be noted, the line cap is often the RF path to ground.

With caravans / mobile homes and such these are fitted with double pole switches so you could change the bench sockets to them. The hanging power points here are switched double pole.

We then have the RCD / US GFCI and I think its Sunday name has been changed? With these neutral is an entity after the device even that it may still be at earth potential. Ensure the line has one, even if its "Plug in".

I would not back away from that radio as far as ridding it of tired components like bad wax caps & dud resistors. Where you may come unstuck is with the conversion and setting the IF frequencies: Yes! plural. You may get an idea from this lot, albeit you need to be careful with some of the legends there. https://swling.com/blog/2017/07/the-tecsun-pl-880-triple-conversion-architecture/#comments

Basically, mainly on SW, the signal comes into the normal superheterodyne mixer stage but is then passed onto another, on a completely different frequency, hence the two pentagrids. That helps filter out the side frequencies (narrow); ultimately that means that you could have two or three different IF frequencies within the same unit.

It should not be that difficult, as long as the typical Monkey has not been in there. Not always the case 1935 Car Radio here has "Die Cast" and one bit I need to remake as it's disintegrating. Did not need the Monkey just Mr cheap & nasty.

This is a very "upmarket" set.


 
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