UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Bush VHF-41 Refurb.

davidgem1406 · 2nd May 2019, 9:33 pm

Thank you Boater Sam, I will keep that in mind.

Today I took the bull by the horns and realigned the FM, both IF and RF.
I was not surprised that the RF was out as I had striped the tuner of to replace the hunts moulded capacitors.
However I was surprised to find the IF was off and did need to peaked up again.

The result was worth the effort as FM is now much better, particularly on the stronger stations.

What I was considering was how to put an extra stage of audio amplification, for FM only, in front of V5.
However I do not understand how the audio is derived as I expected it to feed to the top of the volume control, but when switched to FM by S1k it switches to an HT line so no audio there. I also do not understand how the VC VR1 still controls the volume as it is DC coupled to the triode grid.

Can somebody explain how the audio is obtained from the discriminator, and how the VC is able to turn the triode of V5 up or down.
And would it be possible to put an extra stage of amplification in front of V5 for the FM only.

I am using the manufacturers service information for references.

Many thanks,
Regards,
Dave.

2nd May 2019, 9:33 pm	#16
davidgem1406 Heptode Join Date: Feb 2011 Location: Sheerness, Kent, UK. Posts: 936	Re: Bush VHF-41 Refurb. Thank you Boater Sam, I will keep that in mind. Today I took the bull by the horns and realigned the FM, both IF and RF. I was not surprised that the RF was out as I had striped the tuner of to replace the hunts moulded capacitors. However I was surprised to find the IF was off and did need to peaked up again. The result was worth the effort as FM is now much better, particularly on the stronger stations. What I was considering was how to put an extra stage of audio amplification, for FM only, in front of V5. However I do not understand how the audio is derived as I expected it to feed to the top of the volume control, but when switched to FM by S1k it switches to an HT line so no audio there. I also do not understand how the VC VR1 still controls the volume as it is DC coupled to the triode grid. Can somebody explain how the audio is obtained from the discriminator, and how the VC is able to turn the triode of V5 up or down. And would it be possible to put an extra stage of amplification in front of V5 for the FM only. I am using the manufacturers service information for references. Many thanks, Regards, Dave.