Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Oddvar on October 16, 2016, 06:34:15 am

Title: KT66 for EL34 in 5f6a?
Post by: Oddvar on October 16, 2016, 06:34:15 am

Hi.  Is it any way one can swap KT66 into an EL34 figured 5f6a amp?

Best.

Title: Re: KT66 for EL34 in 5f6a?
Post by: tubenit on October 16, 2016, 07:19:55 am

IF your PT can handle the increased current draw on the 6.3V heater wiring and the increased draw on power tube current, then I think you could use KT66. 


I think (?) that there is  KT66 with less heater current draw but that it has a metal base that will not work with bear claws.



You may have to rebias or change the bias reisistor or pot values.


With respect, Tubenit

Title: Re: KT66 for EL34 in 5f6a?
Post by: Oddvar on October 16, 2016, 10:14:35 am

The 6.3 v has 5 ampere?

Title: Re: KT66 for EL34 in 5f6a?
Post by: shooter on October 16, 2016, 11:15:01 am

you're probably good on filaments, but like Tubnit said, you'll probably need to adjust bias, and possibly drive signal to the tube.  I played around on a SE amp and could swap in/out an 88, 34, or 6550 without tweaking until I settled on one, then I re-biased, but you have fixed bias, so that is more critical.

Title: Re: KT66 for EL34 in 5f6a?
Post by: Oddvar on October 16, 2016, 01:21:10 pm

I have installe biaspot, so that would be ok?

Title: Re: KT66 for EL34 in 5f6a?
Post by: shooter on October 16, 2016, 06:50:03 pm

Quote

so that would be ok?

double check it's range before you plug in the new tubes. 
you have 1ohm bias R's installed?  makes it pretty easy to adjust bias, couple meters and you're there.