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 Philips radioplayer 100
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 Return to top of page · Post #: 1 · Written at 2:41:18 PM on 4 November 2017.
Analogue's avatar
 Location: Richmond, NSW
 Member since 27 October 2017
 Member #: 2183
 Postcount: 13

I have just finished totally rebuilding a Philips Radioplayer 100. Everything has been replaced including all the caps, out of spec resistors, 500K pot and rotten rubber wire. Everything is 100% as per the original circuit diagram. The radio is working well now, apart from an intermittent feedback sound. This tone/feedback sound seems to increase at higher volume levels. If I gently tap on the ECH35 I can hear that tapping through the audio. Could it be that the ECH35 is microphonic.

Help please


 
 Return to top of page · Post #: 2 · Written at 2:55:20 PM on 4 November 2017.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 149

Yes could be the ECH35 or perhaps the socket . Pull the valve and reinsert it a couple of times.
JJ


 
 Return to top of page · Post #: 3 · Written at 3:12:17 PM on 4 November 2017.
Analogue's avatar
 Location: Richmond, NSW
 Member since 27 October 2017
 Member #: 2183
 Postcount: 13

Thanks JJ,

I might even try cleaning the socket.


 
 Return to top of page · Post #: 4 · Written at 3:18:07 PM on 4 November 2017.
Ian Robertson's avatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 624

If that doesn't work, valves can be microphonic. I recall a 1Q5 in a battery portable. It would feed back at any time regardless of volume setting, certain frequencies would set it off.


 
 Return to top of page · Post #: 5 · Written at 4:39:58 PM on 4 November 2017.
Analogue's avatar
 Location: Richmond, NSW
 Member since 27 October 2017
 Member #: 2183
 Postcount: 13

Well I cleaned the socket, but that didn't fix the problem.
Considering my tapping of the ECH35 is audible through the audio, I would suspect it is in fact microphonic.
Has anyone else had this problem, and what is the most likely cause

Help please.


 
 Return to top of page · Post #: 6 · Written at 4:49:50 PM on 4 November 2017.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 149

Well, you need to try another ECH35.
JJ


 
 Return to top of page · Post #: 7 · Written at 12:38:57 AM on 5 November 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2747

With not quite the same result, a 6J8 will normally work as a sub as well.

Normally I find that fault to be bad bonding, or instability causing oscillation of a stage. Changing the wire may have precipitated this? The most unstable area is around the second detector, lead dress is critical. Wire away from the chassis can act as a transmitter, or antenna & may also destabilise the whole show & may oscillate.

One of the things common, with "Metalised" Philips valves, is the breaking of the bond of the shield wire just above the top of the base. This is normally the result of pulling the tube out using the glass: Often it can be repaired. As can loss of the "Metalisation altogether". In both scenarios the valve ends up without shielding.

Some times you can repair the wire envelope to pin 1. The last repair I did on one of these is described in Radio Waves. That actually involved replacing the Metalisation as well.

If the glass envelope has broken free from the base, then there is a fair chance of a break.


 
 Return to top of page · Post #: 8 · Written at 4:00:01 PM on 6 November 2017.
Ian Robertson's avatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 624

A bad weld on a grid wire is the most common cause. Not much you can do about it 'cept change the valve.


 
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