Re: Modifying W Plugin to use 6DJ8 Tubes


Bill Perkins <sales@...>
 

On 21/02/2021 10:19 PM, Bill Perkins wrote:
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.
Bill
8416s on eBay for rational money compared to the rest of the offerings:

https://tinyurl.com/sg6acmw1

Bill

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