Moreton Cheyney Amplifier - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

trobbins · 20th Aug 2020, 12:56 am

Allan, were you planning on using the global feedback loop aspect of that circuit?

allan · 20th Aug 2020, 8:59 am

I'm not sure about the global feedback loop yet.
I was going to connect the feedback loop to see its effect once I've established the performance without it. There are several output windings on the transformer and I am considering trying each. I'm wary of allowing DC through my speaker coil so using a spare winding will avoid this. It looks like around 0.6mA DC with no signal if V1 is perfect.
The first test will be just the double triodes and adjusting R12. Then I'll fit the KT66s with a dummy load. Initially all this will be using an adjustable HT supply. Lots of unknowns such as the condition of the valves and some of the condensers, not to mention the original wound components which looked like they'd been underwater for part of their lives.
Allan G3PIY

allan · 22nd Aug 2020, 12:25 pm

Just a quick word on progress. The amplifier is powered up with the feedback loop in place. I can get 15 watts output without feedback and about 7 watts with feedback with what looks like a perfect sinewave output. I'm about to juggle tappings on the output transformer to get a full 15 watts with decent efficiency.
http://www.radiomuseum.co.uk/MCamplifier.html
Allan G3PIY

20th Aug 2020, 12:56 am	#21
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Moreton Cheyney Amplifier Allan, were you planning on using the global feedback loop aspect of that circuit?

20th Aug 2020, 8:59 am	#22
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: Moreton Cheyney Amplifier I'm not sure about the global feedback loop yet. I was going to connect the feedback loop to see its effect once I've established the performance without it. There are several output windings on the transformer and I am considering trying each. I'm wary of allowing DC through my speaker coil so using a spare winding will avoid this. It looks like around 0.6mA DC with no signal if V1 is perfect. The first test will be just the double triodes and adjusting R12. Then I'll fit the KT66s with a dummy load. Initially all this will be using an adjustable HT supply. Lots of unknowns such as the condition of the valves and some of the condensers, not to mention the original wound components which looked like they'd been underwater for part of their lives. Allan G3PIY

22nd Aug 2020, 12:25 pm	#23
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: Moreton Cheyney Amplifier Just a quick word on progress. The amplifier is powered up with the feedback loop in place. I can get 15 watts output without feedback and about 7 watts with feedback with what looks like a perfect sinewave output. I'm about to juggle tappings on the output transformer to get a full 15 watts with decent efficiency. http://www.radiomuseum.co.uk/MCamplifier.html Allan G3PIY