SB-102 15m "ghost"

[Kenneth G. Gordon]

On 12 Nov 2007 at 17:10, jsloss wrote:

> In TUNE mode all is well on all bands except 15.  
> 
>  Grid current peaks w/ DRIVER and plate current dips as it should. 
>  BUT when I move the CW GAIN full CCW I still have RFoutput w/ Ig and
>  Ip,.  On all other bands, in TUNE, rotating the DRIVER  reduces Ig
>  and Ip as it should.  Have replaced 6CL6 to no avail.

Sounds to me, too, as though your final amp is oscillating.

What type of final amp tubes are you using? If 6146Bs, that 
is probably part of the problem.

The neutralizing "wire" for the driver should not stick down 
into the hole provided for it more than about 1/4" at most.

Make sure that the shields on the driver and the tube next 
to it (second transmitter mixer?) are making contact with 
their ground connections.

Do a thorough and accurate alignment "by the book".

Then use Heathkit's suggested "alternate" method for 
neutralizing the finals. I.e., remove plate and screen 
voltages from the final amp tubes, stick an o'scope probe in 
the antenna connector, and adjust for minimum RF output 
on 10 meters while in the transmit condition and with 
everything peaked for maximum output.

Make certain you are using 6146s or 6146As only.

Check the bandswitch as Eddy Swynar suggested. Some 
DeOxit might help with this.
  
> While I'm here does anyone have any comments or cures for "hot"
> running tubes especialy the IF's and 6CL6.   An internal fan may be
> the only answer.

Make certain you are using only #47 lamps, NOT #44s. 
Also, some Heathkits showed up with 6EA8s which were 
mislabeled in that the tubes had 5 volt filaments instead of 
6.3 volt filaments. Since the current distribution would be 
effected in OTHER tubes, this could make these other 
tubes run hot.

Ken Gordon W7EKB

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