SB-401 VFO Tube

[Glen Zook]

I hope that you have gotten a satisfactory answer by now (I have been in the Hospital for 5 days).  The difference in the LMO tubes has to do with the heater ("filament") current and not the actual performance of the tube.  In the Heath SB-Line the tube heaters are wired in a series-parallel arrangement and in certain units the LMO tube heater is wired with various other tubes and to achieve the proper current balance in the circuit various tube with different heater current are used.

For example, my SB-110A uses one tube but my SB-401 uses another tube with a different heater current.  If I put the same tube type as is in my SB-401 in my SB-110A the oscillator stops working and the heater "glow" can barely be seen.  But, if I put the proper tube back in the SB-110A everything works fine.

Glen, K9STH

Website:  http://k9sth.com


--- On Sat, 4/10/10, Jim Schnurr <k4jrs at AOL.COM> wrote:

> From: Jim Schnurr <k4jrs at AOL.COM>
> Subject: [HEATH-TEMPE] SB-401  VFO Tube
> To: HEATH at LISTS.TEMPE.GOV
> Date: Saturday, April 10, 2010, 6:36 AM
> I have two SB-401 transmitters I am
> working on. They both had a 6CB6A tube in the LMO unit. The
> book calls for a 6BZ6 .  The first one which I now have
> working I  replaced the  6BC6A with the 6BZ6 and
> it is doing fine. Any reason for using the substitute tube
> 6BC6A as I have both  on hand to utilize. ?
> 
> Thanks, Jim
> 
> 
> 
> 
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