VOX Beatle Original Transistor Data DIY Style

[CJ]

that's right, we scored some original transistors, Fets, you name it, for the troublesome Beatle amp,

they were like 8 bones a piece, so knowing what they do can mean realizing a cheaper alternative if you can dig where i'm coming from, or not.

so if you want to upgrade or buy a lot of NOS and sort, you can use this data for the three transistors pictured here>

 

[CJ]

the paint on the transistors means they went thru some sort of matching process, and i imagine the Fets were screened as well,

here are the parts we tested, they comprise the first 4 transistors of the preamp

 

[CJ]

FET data,  this guy turned out to have better gain than the data sheet graph, which is why we suspect they were screened, since it is the first stage, we want to get above the noise floor as quick as possible, but wait, no free lunch, more gain = more noise? or not.

here is one of two graphs for the N Ch Fet>

 

[CJ]

and a gm curve for the fet,

anybody know how to translate ma per volts into u-mhos? 

 

[CJ]

Fairchild "blue' transistor graph>

 

[CJ]

and the NPN transistor  (Green/Yellow)

 

[CJ]

here is the circuit where these transistors are used,

that's it. nothing more to see here folks, you are now free to resume your life as you used to know it, 

oh, as a side note, some folks like those 2N2925's in their wah wah pedals, so now you know how to match up with the 60's!

 

[PRR]

> anybody know how to translate ma per volts into u-mhos?

Change the mA into uA and the answer is right there.

4.75mA/V is 4,750uA/V so 4,750uMho.  (More than most tubes.)

However in this VOX plan, you don't really need to know. The Q101 Q102 pair is locked in NFB. Gm of the Q101 only matters for the extreme of the Top-Boost.

 

[CJ]

Thanks PRR! again.