Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MakerDP on July 18, 2016, 11:11:42 pm

Title: D'MARS choke choice
Post by: MakerDP on July 18, 2016, 11:11:42 pm

I am (finally) building a D'MARS ODS and I have two chokes on-hand that I can use. Which one would be most appropriate and why? Choke choice is still one of those mysteries to me.

1) Hammond 156G - 9H @ 40mA

2) Custom Hammond (built for London Power) 3H @ 100mA

My gut tells me the safe choice is the 3H/100mA version simply because it can handle more current, but the 156G was spec'ed for and came out of a 50W stand-alone power amp that I built using KT77 power tubes so I don't know...

Thanks.

Title: Re: D'MARS choke choice
Post by: Glennjeff on July 19, 2016, 08:05:14 am

An opinion,

40mA seems a little on the light side for a 2 X 5881 design.
3mH is a bit on the low side but I have built a great D'Mars with no choke.
I then started experimenting and putting in high gain circuitry blocks and ran into problems that were resolved with the addition of a 10H 150mA choke.

Crazy man rule of thumb, if stuff is getting too hot to touch it is most definitely under-rated.

Title: Re: D'MARS choke choice
Post by: MakerDP on July 21, 2016, 12:32:05 pm

Thanks.

I've been reading-up on it, especially at Aiken's site.

It looks like the 9H/40mA is the way to go. The 40mA rating only needs to apply to the 5881's screen and the preamp tubes' current draw because the choke is after the 5881's plates. Also 3H is a little on the light side for this application. This choke was spec'd for (and installed in) a KT77/EL34 50W amp, so I think it will be fine.