Re: Modifying W Plugin to use 6DJ8 Tubes

Dave Wise

?They're being used as: 1) current source, 2) cathode follower, 3) top half of a cascode. Within limits, mu and gm aren't critical. It is so easy to try I'd be ashamed not to.?

Dave Wise

From: <> on behalf of Bill Perkins via <>
Sent: Sunday, February 21, 2021 9:19 PM
Subject: Re: [TekScopes] Modifying W Plugin to use 6DJ8 Tubes

I know, it's seven years later. But I just acquired a Type W in the usual state, to wit, 8416's stolen.

It looks to me like there's enough empty space to fit a small mains-powered 18V regulated supply.

6DJ8 heater is 360mA vs 180mA 8416.
Normally R290 drops 77-50 = 27V at 180mA. We need to drop 20V more.

1) Add R9290 110 ohm 5W (20V at 180mA) in series with R290
2) Add isolated regulated 18V 6.3VAC-powered supply
across V124-V214-V114. It will put out 180mA, raising
V124-V214-V114 to its nominal 360mA so they will drop their
nominal 18V.

This can be done with a 24V transformer on pins 13-14 with
primary and secondary reversed, rectifier, filter, and LM317.
The transformer needs to have low magnetic field because it's
right next to the tubes.

Unless a miracle drops a few 8416's in my pocket, I might try this sometime.
But I'll try 12AT7s first.
I wouldn't, those parts aren't even remotely alike. The 'DJ has half
the mu and three times the gm.


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