[Heathkit] SB-102 low drive problem

[Bwana Bob]

Bob:

Don't forget to peak the heterodyne oscillator coils on transmit. THe 
adjustment of these coils has little effect on the receiver, unless the 
HFO actually drops out of oscillation, but peaking these has  a very big 
effect on transmitter output. The HFO coils are not in parallel, like 
the driver coils, so they don't need to be peaked in sequence, but they 
must be peaked for maximum transmitter output.


			73,

			Bob WB2VUF

Robert Nickels wrote:

> My SB-102 has low output on every band except 75 meters.  40 is about 
> half, and 20 and above will output produce a few watts.  The tubes in 
> this radio all test very good and it receives fine.  The main problem 
> was is was VERY dirty, but cleaned up well.
> 
> I've aligned the receiver per the instructions using the crystal 
> calibrator as a source.   Every coil peaked, no broken slugs and uisng a 
> good signal generator I can hear a 1uv signal on all bands 80-10.  I've 
> checked signal levels all the way up to the 2nd Transmit Mixer V6, the 
> 6CB6 just before the driver.   The driver grid coils are in the mixer 
> plate circuit and  the RF level at the grid of the driver drops just 
> like the output, even though the level of both of the mixer inputs are 
> the same on all bands.  It's pretty obvious that only the 80 meter coil 
> is being tuned right, yet they are peaked.  . In all the SB-100 series 
> the 80 meter coil is in the circuit all the time, and a the 3F wafer on 
> the bandswitch switches the coils for the other bands in parallel as you 
> change bands.   I suspected dirty contacts - and they were - and I've 
> cleaned them with DeOxit twice.  Checked and replaced a couple of 
> resistors but no improvement.
> 
> Here's what's really got me stumped:   The same coils and capacitors are 
> used on Receive as well as Transmit so how can there be anything wrong 
> with them?   That's why the alignment is done using a received signal, 
> once they're peaked they are supposed to be good to go on both Rx and 
> Tx.     My coils are peaked, as proven by the receiver sensitivity.  Yet 
> the drive level out of this stage falls like a rock as you move up the 
> bands!
> I would really appreciate any ideas where to look as I know this same 
> scheme was used in thousand of HW and SB radios.  I'd normally suspect 
> weak finals but like the rest of the tubes, they test high on the good 
> scale, and even weak finals should put out more than this.
> 
> Thanks!
> 73 Bob W9RAN
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