From: Garey Barrell 
Subject: Re: [drakelist] 12jb6's in T-4x


George -

Same tube, different filament.   The TR-3 used 12JB6's, but the TR-4 and all 
T-4(any) transmitters used 6JB6's.

The filaments for the finals are just wired in series in the T-4's, so a simple 
wiring change to parallel.  The TR-4 used a series parallel arrangement that 
makes it a little more difficult.

Your "finicky to load" may be a result of the neutralization not
being right. 
I'd check the alignment of the driver and final stages at least.  A new pair of 
finals would probably be a good idea also.  A properly aligned T-4 is stable and 
smooth to load on any band.  Try to find Sylvania, RCA or Zenith brands if you 
can, and preferably both of the same brand.

73, Garey - K4OAH
Atlanta

Space Charge wrote:

> Hi All,
> I just traded for a Drake R-4/T-4x pair. The T-4x  appears to have a few 
> undocumented features.
> Seemed a bit finicky to load, pulled the finals to check in tester and 
> found them to be 12jb6's. One was to the low side of good and the other 
> is questionable. Being new to Drake equipment (this pair is my first) I 
> was wondering if this is a normal tube mod.? Is it as simple as changing 
> the heaters or is it more involved? Should I change the tubes back or 
> leave them alone? Looking for tubes I see the new 12jb6 are abt 1/2 the 
> price of new 6jb6. This tx will never be original again, so I dont mind 
> the 12jb6's as long as the work the same as the original 6jb6's. 
> Searching the www I found the TR-3 came with 3-12jb6 tubes. Want to get 
> the tx on the air with the least cost and aggravation.
> Thanks in advance for any input, George KB2Z

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