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

ppppenguin · 1st Nov 2006, 10:03 am

The KT66 is a much beefier valve than the KT61 so the valve itself is not going to come to any harm. The pinouts are the same. You will need another 300mA of heater current. The KT66 has lower gm so you may be a bit short of gain. You may need a bit more bias to get the anode current down to something sensible. That's probably the major worry if you just plug a KT66 straight in and end up cooking the output transformer. I'm not sure the output mis-match will matter too much since you are not trying to extract maximum output.

PS: Nigel replied while I was still typing. I agree with everything he says.

1st Nov 2006, 10:03 am	#3
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: KT66 as substitute for KT61 The KT66 is a much beefier valve than the KT61 so the valve itself is not going to come to any harm. The pinouts are the same. You will need another 300mA of heater current. The KT66 has lower gm so you may be a bit short of gain. You may need a bit more bias to get the anode current down to something sensible. That's probably the major worry if you just plug a KT66 straight in and end up cooking the output transformer. I'm not sure the output mis-match will matter too much since you are not trying to extract maximum output. PS: Nigel replied while I was still typing. I agree with everything he says. Last edited by Darren-UK; 31st Jul 2007 at 11:51 pm. Reason: Harmonising with post #1.