BANDPASS ADJUSTMENT PROCEDURE (78 / 374A AMPS)

Use a cover over the RF side of the amp (left side) to adjust the 
bandpass caps.  Make a "test cover" that is a bent piece of aluminum 
that fits over the left side, with holes to allow the cover screws 
to be put in the middle, rear, and left side.  Without the screws 
it tunes differently then when the real cover is put on. Drill 
holes in your test cover to line up with the 8 capacitor shafts, 
and the cover mounting screw holes in your amplifier chassis.

1) Equipment required: electronic cw keyer, peak-reading wattmeter
(P-3000 or equivalent), HF transceiver, 240vac Variac, test cover.

2) Use 240vac from Variac to power amplifier. Install test cover with
access holes for bandpass capacitors on RF section of amplifier. Use 
as many screws as possible to fasten the cover to the chassis.

3) 3.5 MHz:
78 only - On 3.60 MHz, select CW SUBBAND, peak Tune and Load bandpass
capacitors for max power of 750-900w on LV/CW (Ig up to 75-80 ma OK).
Switch SUBBAND to SSB (still using LV/CW on amp). Output should be
fairly equal +/- 1dB) at 3.75-3.95 MHz.  For the 374A amps - Tune 
as above, but on 3.870 MHz.

4) 7-14-21 MHz:
78 only - On 7.050, 14.050, and 21.100 MHz, select CW SUBBAND, peak 
Tune and Load bandpass capacitors for max power of 750-900w on LV/CW.
Switch SUBBAND to SSB (still using LV/CW on amp), check output on 
frequencies in SSB part of each band.
For the 374A amps - Tune as above, but on 7.150, 14.200, 
and 21.250 MHz.

5) For all above, 1.5kw PEP or keyed CW (fast 'dits') should be 
possible in HV/SSB.  Read power on P-3000 wattmeter.

NOTE : For all 76/76A/374A/78 amps (untuned inputs) use short coax
between transceiver and amplifier, 4 ft or less. 

NOTE : Viewed from the left side of the amplifier (78/374A), 
the 8 capacitors for tuning the Bandpass section are:

     TUNE                        LOAD
40m      15m                40m      15m

80m      20m                80m      20m