yaesu 2100b load adjust seems wacky

[kc9vzb]

new to power amps.I got a 2100b and read allot on how to tune.using a kenwood 450s to feed amp.dipping plate works as described,but load only increases output when turned all the ways counter clockwise.seems odd and power ain't what it should be.cranking load back and forth has very little affect on meter.I'm on 80 meters lsb, in cw things look a little more normal.But I don't really know what normal is.any ideas what I'm doing wrong?

 

[wavrider]

take a look at the loading cap, It may be bad.

Do the other bands have normal output?

I do ot have the schematic in front of me but there should be a doorknob style cap for extra capacitance on 80 meters.

Trace out the band switch and take a look at the cap.

Also you may want to take a look at the input impedance on 80 meters, you may have to adjust the input tune to get it to play well with a solid state rig.

 

[wavrider]

FL2100 Yaesu Oscillation

good link here for the amp.

 

[kc9vzb]

thanks,looks like some upgrades are in order.I'd rather work on it than talk anyway.

 

[Shockwave]

If you can tune it up on a dummy load this would give you more of an idea if the amp is the problem or if it's just running out of range on the load control with your particular antenna. You have to make sure you are tuning the amp correctly. It is possible to tune these amps incorrectly and still find a dip in plate current with what looks like a peak in power output. This usually results in one of the controls being all the way at it limits.

I think if you download a copy of the instruction manual it will provide you with pre-settings for each band. Start there and slowly move each in the direction that increases power. Making sure you have the plate tune dipped for current between the two peaks. You may find this produces different settings that provide more power than your first attempt. Keep in mind the load and tune work together and may require that you go over the adjustments several times to find the best match.

The W8JI page talks about oscillations. This is a common problem on the FL-2100 now because the grid bypass caps are old and have lost value. The symptoms you are seeing do not resemble that of an oscillation problem. They are most noticeable on the upper bands and not the lower bands. They show up as very unstable or large changes in output and current with adjustment of the tank circuit. More than 90% of those oscillation problems are cured just by installing new grid bypass caps.

What you have is either an improperly tuned condition or an amplifier that does not have the range to match your antenna on 80 meters. Could be as simple as a dirty contact on the bandswitch that connects the additional padder capacitor to the load control on 80 meters or a bad cap as Wavrider mentioned. I wouldn't be too quick to start upgraded many components until the this specific problem can be identified. Too many changes at one time make it difficult to trace out if you happen to make just one mistake in your upgrades.

 

[jimthomas47]

new to power amps.I got a 2100b and read allot on how to tune.using a kenwood 450s to feed amp.dipping plate works as described,but load only increases output when turned all the ways counter clockwise.seems odd and power ain't what it should be.cranking load back and forth has very little affect on meter.I'm on 80 meters lsb, in cw things look a little more normal.But I don't really know what normal is.any ideas what I'm doing wrong?

This is old post, but replying in case anyone else has this issue.
I'm reparing a FL2100-B with the same symptom. The problem turned out to be the copper foil leads from band switch to the big inductors below the outboard tube were mashed together shorting out the tuning for the low band. Easy fix to straighten them out.
73 Jim AI5EG