UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

agardiner · 25th May 2021, 5:53 pm

Hi,

So, if you are not getting anything when touching the volume pot, then the first port of call should be the audio amp. Have you checked the biasing from the centre of the two batteries? It should be going to R15. After that, I would check TR4 and TR5; either of these could cause the problem and also increase the quiescent current.

I would want to be able to hear the amp working correctly before moving to the oscillator section.

25th May 2021, 5:53 pm	#4
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: Roberts R500 Hi, So, if you are not getting anything when touching the volume pot, then the first port of call should be the audio amp. Have you checked the biasing from the centre of the two batteries? It should be going to R15. After that, I would check TR4 and TR5; either of these could cause the problem and also increase the quiescent current. I would want to be able to hear the amp working correctly before moving to the oscillator section.