WHAT AM I DOING WRONG?

[Mark Graalman WB8JKR]

   Hi Jerry,

  I just finished rebuilding a SB-401 and I basically
followed the instructions in the manual except
I made final adjustments tuning the driver grid
and plate coils for maximum final grid drive.
 Instead of using a RF probe and VTVM, I used
a 35 Mhz scope and a X10 probe, I've found the RF
probes do load the circuit a respectful amount and
can cause confusion during alignment.
 I also did all tuning at the bottom of the band segments
with the driver tune cap set one mark up from the
extreme left position (approx 9:30)
 Until I did the final touch up using the final grid current
meter, I had problems with decent output on 15 and 10
meters, only about 60 watts on 15 and about 40 watts on
10 meters, but after adjusting for maximum grid drive
I obtained the following outputs measured on a Bird 43
 With a line voltage of 123 volts:

80 meters 120 watts
40 meters 120 watts
20 meters 100 watts
15 meters 85-90 watts
10 meters (all segments) 75-80 watts

  Also, make sure you reconnected the screen and plate voltage
to the finals after the neutralization process.

73,  Mark  WB8JKR


On Tue, 19 Feb 2002 01:00:26 -0700 ejforwood Jerold Forwood
<ejforwood at MSN.COM> writes:
> Hi all,
>
> I need help!
>
> I have 2 SB-401's and I seem to have the same problem with both
> transmitters.
> The first one was working but had low output, only about 40 watts.
> So I started by cleaning all the relay contacts and band switches.
> Then I bought a complete set of new/old stock tubes and started to
> realign the whole thing according to the alignment procedure in the
> manual using my SB-301 connected as a transceiver setup.  I could
> not get more than .2 Volts RF at pin 2 of the 6CL6 driver as I
> adjusted the grid coils.  This was also the same case as I proceeded
> on to the wire between the pins 5 on the 6146A finals and the plate
> coils.  I have the 50ma bias, but I now have no output at all.  I
> have good high voltage, but no grid or plate current.
>
> I bought the second  transmitter an it is a good one.  The LMO dial
> works, even the hairline.  It had about 50 - 60 watts out.  So I
> cleaned and re-tubed and started with the realigning.  This time I
> used the xtal pack as a stand alone.  I have good DC voltage at the
> oscillator test point but low RF voltage from there on.   Now I have
> the same result, NO OUTPUT!
>
> HELP!!!
>
> Thanks and 73's,
>
> Jerry, K0EJF
>
> E. Jerold (Jerry) FORWOOD
>
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