[Heathkit] Help with SB-401

[Edward B Richards]

Dave;

I think the ring on the front wafer (B2F) is connected through the wafer
to the rear wafer (B2R) ring. It still seems odd to have a contact (#4)
that is made all the time. Good luck.

73 from Ed Richards K6UUZ
Simi Valley, CA. Home of Air 
Force 1 pavallion

On Mon, 5 Mar 2007 23:23:18 -0500 (EST) Dave <w8qwdave at peoplepc.com>
writes:
> I have an SB-401 with the accessory crystal pack installed.  I cannot 
> get the transmitter to operate independent of the 301, e.g, use the 
> internal crystal pack rather than the 301 crystal pack.
> 
> I have reveiwed the schematic and done the voltage checks.  The 
> hetrodyne oscillator tube is a 6AW8, a triode (V8A)/ pentode (V8B) 
> combination.  In the circuit descriptions located within the manual, 
> it states that I should get voltage at pin 9 of V8B only when the 
> mode switch is in the transceive position.  This is true, measured 
> voltage at pin 9 is indeed 149.8 volts.  However, the manual also 
> states that when the mode switch is in the standby/ transmit/ or 
> spot positions the 150 vdc should be absent at pin 9 of V8B, and 
> appear at pin 3 of V8A - the 6AW8.  This is where I have problems.  
> The B+ voltage is removed from pin 9 of V8B, but never appears at 
> any time at pin 3 of V8A regardless of mode switch position.  So, 
> the natural conclusion is that I have a wiring problem.  So, I 
> figure, no sweat I can track this down, easy enough.  I grab for the 
> schematic.
> 
> My problem is this:  I look at the schematic and I cannot for the 
> life of me figure out how B+ voltage gets to the plate (pin 3) of 
> V8A.  It literally stops at the rear side of the second wafer on the 
> bad swtich.  The cathode is at ground, and I get proper voltage at 
> V8A pin 2.
> 
> This is driving me up a wall.  Can anyone help with some advice on 
> how the plate of V8A receives B+ voltage?  Since I can use the 
> receiver's crystal pack in transmit, I am certain that once I 
> restore the B+ voltage to V8A, e.g, correct the wiring problem where 
> ever it is, the thing will oscillate independent of the receiver and 
> all will be well.
> 
> Any help is appreciated.
> 
> 
> Dave, W8QW
> 
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