1. Use a 120VAC supply with decent 250V/500V regulation.

2. Always feed a 50 ohm dummy load or ant.

3. Use the set long enough to know how it works and where it will and won't load before PI net mods.

4. Align it on the nose. Align 160M so drive can be peaked at both ends of the band.

5. A 6146 likes 2.5ma grid current and a good tube will easily load to 120ma at 500V and will make about 40W out.

1. An HV glitch may destroy the meter, the 6146 or power supply.

2. The PI net was made for low Z mobile ants, not for 50 ohms.

The stock PI net will normally load OK at one end of 10M but not the other end. Loads too heavy on 15 and 20, 40M OK, 80M OK at 4.0 but NG at 3.5, loads very light on 160M.

3. Drive is too high.

1. is a killer, so fix it first.

Fix the HV terminal strips behind the 6146. These two 2-terminal strips handle HV and RF. They almost all develop charred arc paths underneath and then vaporize suddenly, shorting HV to ground. Think they absorb moisture... When the top one goes, it takes out the choke, maybe the tube and maybe the power supply rectifiers. When the bottom one goes, it takes out the HV meter shunt and the meter if it's in the plate current position. Unhook the choke and wires, remove 1 screw on top and 2 under. Remove metal bracket, then replace both terminal strips with new ones. Or use standoffs. If the .47uH PS wires break, replace with 6T #18 wound on 47/1W. If one pie of the choke fries, cut it out and go with two pies.

Put a 1N4007 power supply diode across the meter terminals. Band or cathode to negative terminal. This will not affect the meter readings but in case of an HV glitch, will limit voltage across the meter to about 635mV.

Put a 500ma fast blow fuse in the HV line someplace to save the power supply rectifiers and the tubes.

Locate and clip out the only jumper between the middle and bottom bandswitch wafers. Solder a jumper across both sections of the loading cap. Now both loading cap sections are active on all bands. Check smooth loading at both ends of 10-40M. Then remove wire from front section of loading cap to bottom wafer of bandswitch.

Only works if 10-40M fix done. From the outer end, reduce the 80M coil to 24T. At the bottom bandswitch wafer, remove the jumper from the 80M contact and hook a 430pF silver mica from there to ground. Note plate dips both 80 and 40M. 80M dip is near max C.

Only works if 10-40M fix done. From the outer end, reduce the 160M coil to 25T. At the bottom bandswitch wafer, remove the jumper from the 160M contact and hook a 820pF silver mica from there to ground. Locate the 160M terminal on the top bandswitch wafer. Unhook the wire going to the plate tuning cap and remove the jumper between the 80 and 160M terminals. Then hook the plate tuning cap wire to the **80M** terminal. And hook a good quality 240pF silver mica from the 160M terminal to ground underneath the band switch support bracket. Since caps vary a bit, if the plate tuning cap won't dip the final at one end of the 160M, raise or lower the 240pF cap one size.

Most sets with good tubes and alignment make at least 4ma grid current all bands. Some over 5ma. 6146 likes 2.5ma drive. More spoils power out. Reducing grid current by detuning the grid cap not good idea as spoils the waveform at the PA grid.

1. Feed the 6AQ5 screen from 250V thru a 33K/1W resistor. This will help the high grid current but not completely.

2. Install a good quality 50-75K pot in the hole at the top left of the dial. Feed the top of the pot from 250V thru a 22K/1W resistor. Ground the bottom of the pot. Hook the arm of the pot to the screen. Turn the pot full on at startup. Peak grid current then peak and load final to 120ma and check loaded grid current. If more than 2.5ma, reduce with pot. Then reload final.

End

73 - John Conley, W7ZFB
1400 CATRON SE
ALBUQUERQUE NM 87123
USA

Homebrewer since 1947 CW BoatAnchors Norcal # 930

BA CW frequencies - 3578, 7050, 7118, 14050, 21050, 28050 kHz

Part 2 - Includes QSK/Spot/Keying modification, Pi-Net Mods and AM Mods. (Adobe PDF)