[Drake] T4XB tubes

[Garey Barrell]

Ed -

ed brooks wrote:

> Looking for a place to conveniently (yeah, that word) purchase a set 
> of tubes for the T4XB.  (Excepting finals.)
>
> Surplus Sales has some of them.
>
> The Tube Store has some of them.
>
> Anyone know a place that might have the full line in stock?   I hate 
> to order from three different places because it means three different 
> shipping costs, but if that's what I have to do, I will.  Have not 
> found the 6HS6 in stock at any of them so far.


Try ESRC in Florida.  They usually have stock, although the 6HS6 IS
getting hard to find.  (And expensive!)   No matter where you buy, be
sure you get "name brand" US made tubes.  Some of the "off" brands do
NOT work well, especially in RF functions.

>
> Any suggestions?
>
> Symptom:  Suddenly the T4XB has low ouput, low plate current reading.  
> Was working fine.  Still has very high plate current off resonance, 
> indicating finals are good.  I suspect premixer or IF amp, or sidetone 
> osc.  (although audio ouput for sidetone is good, so probably not that.)
>
Check R26.  This resistor is often damaged by using a metallic alignment
tool to adjust the trimmer caps.  It's very easy to short the cap to the
chassis, putting the full, "unlimited" +250V across that poor little
resistor.   Also check the resistance of the screen resistors for the
finals, and the cathode resistors too.   You may also have a weak driver
tube, but more likely one or more of the above.

> But figured I'd replace all the tubes at one whack rather than one now 
> and one later.
>
I would strongly recommend against "shotgunning" ALL the tubes.  More
than likely they are all perfectly acceptable, and starting alignment
with all new tubes, especially of different brands, can be a real
experience.   I rarely find any weak tubes other than finals and a VERY
occasional driver.

73, Garey - K4OAH
Atlanta