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

quantum · 2nd Oct 2004, 11:34 pm

Just to be clear - have you replaced the energised speaker or simply replaced the coil?

With your new coil and possibly replacing the output valve with one which takes less anode current you are altering circuit conditions; the set was designed with the PenB4 drawing sufficient anode current for the energising coil to activate the speaker - there is no guarantee that a valve with lower HT current requirements and a higher resistance coil will work effectively.

If you have to replace the speaker I'd be inclined to use a PM type and a choke in the place of the energising field coil for smoothing.

2nd Oct 2004, 11:34 pm	#10
quantum Retired Dormant Member Join Date: Mar 2003 Location: Birmingham, West Midlands, UK. Posts: 785	Re: Bush PB53 Output stage problems Just to be clear - have you replaced the energised speaker or simply replaced the coil? With your new coil and possibly replacing the output valve with one which takes less anode current you are altering circuit conditions; the set was designed with the PenB4 drawing sufficient anode current for the energising coil to activate the speaker - there is no guarantee that a valve with lower HT current requirements and a higher resistance coil will work effectively. If you have to replace the speaker I'd be inclined to use a PM type and a choke in the place of the energising field coil for smoothing.