need help with FL-2100

[W0WDF]

I bought a fl-2100 from a ham fest and it had low power out on all bands so I put a new set of 572b's from RF Parts. I let them burn in for about 18 hours then put the anode caps on. Now with the amp in standby after it runs for about 2 min. it keys itself. You can hear the relay click and it starts drawing plate current.
I hooked up a switch to the keying relay conection and it will key like it's suppose to but then it will also key itself.
Any ideas or sugestions?



Thanks, W0WDF

[AF6LJ]

Have you downloaded the manual?


The keying line needs to be pulled to ground to to pull in the T/R relay.
Something on that line is drawing enough current to cause that relay to pull in.
Could be a leaky cap.

[W1QJ]

This is a common problem with some of these amps especially the ones prior to the "Z" model. Even some of the Z models have this problem. In fact I just had the same problem with a FL-2100Z a couple weeks ago. The problem is that the cut off bias voltage may be too low for tubes that have high gain (like new tubes). I thought the tubes were bad in this 2100 and so I put my SB-200 tubes in it and it worked fine. I then put the same tubes in the 2100 in my SB-200 and they worked fine. So the tubes were Ok but it's just that those tubes would not bias to cut off and then the amp goes into self oscillation. This is why the Z model used a voltage tripler to increase the cut off bias voltage. The SB-200 is not a problem because they use 120vdc instead of 12vdc. So as a result any tube(s) with high gain will break out into oscillation in standby. Check the W8JI website. Tom covers this problem with the 2100 in deatail. Some tubes work fine and others don't. it's a crap shoot and a fine line seperates oscillation from stability in standby. Read Tom's site for in detail info on this.

[KE6YX]

I did almost all of the mods I could find for my AL2100B. The two that are most important would be the circuit which uses a relay to place a resistor in series with the grid and ground in standby. when in transmit, the relay bypasses the resistor to ground. It completly cuts off the tubes in standby.

Also I would reccomend the Glitch resistor & 630 ma. fuse in the anode circuit. That can save your bandswitchs and a lot of other parts too.

I also replaced the wimpy fans with 12V 70mm computer fans and built a 12V supply for it off the filiment winding.

I bypassed the meters with reversed pairs of diodes and new disc caps.

Lastly I installed a soft start which really works well. Before I installed it, you could heard a loud "twang" from the amp when I first turned on the power. Now it's silent.

Having read all of the horror stories about these amps, I did all of the modes prior to applying power to it, and it works like a champ!

Good luck,

David

[W0WDF]

Thanks for all of the usefull info guys, I know it needs alot of mods for sure. When I got home today and turned it on again one of the new tubes arc, flashed , or something so I put the one good old tube in it with one new one and the problem went away and when I tuned it up I am getting 600 out on 40 meters.
I know it still needs work.
Thanks, WoWDF

[WB2WIK]

Thanks for all of the usefull info guys, I know it needs alot of mods for sure. When I got home today and turned it on again one of the new tubes arc, flashed , or something so I put the one good old tube in it with one new one and the problem went away and when I tuned it up I am getting 600 out on 40 meters.
I know it still needs work.
Thanks, WoWDF

Don't feel bad, they all needed work even when they were brand new.

That's not a joke.

[W9GB]

I know it needs alot of mods for sure. When I got home today and turned it on again one of the new tubes arc, flashed , or something so I put the one good old tube in it with one new one and the problem went away and when I tuned it up I am getting 600 out on 40 meters.
I know it still needs work.

These HF amplifiers are 35 to 50 years old, and we're never designed or built for that service life -- without major maintenance.
At a minimum, the electrolytic capacitors are far beyond the manufacturer's rated " hours of service".

Couple this with design shortcomings, operator abuse (intentional or ignorance) / operator errors throughout their history, and lower quality of replacement glass tubes (811A, 572B, 3-500z) ... they all need work.

[WB2WIK]

These HF amplifiers are 35 to 50 years old, and we're never designed or built for that service life -- without major maintenance.
At a minimum, the electrolytic capacitors are far beyond the manufacturer's rated " hours of service".

Couple this with design shortcomings, operator abuse (intentional or ignorance) / operator errors throughout their history, and lower quality of replacement glass tubes (811A, 572B, 3-500z) ... they all need work.

The FL-2100 series were never good amps from the start. I can't even count how many I've had to repair, simply due to Yaesu using some really bad parts from the beginning.

I've been offered these in "looks like brand new" condition for $100 and wouldn't do it. Too much work! The Heath SB-200, which also uses two 572Bs, is a better design and used better components.

[AF6LJ]

If the relay pulls in after a period of time like the OP says I would undo whatever mods were done to the relay circuit and see if the amplifier works correctly.

[WB2WIK]

If the relay pulls in after a period of time like the OP says I would undo whatever mods were done to the relay circuit and see if the amplifier works correctly.

I think that's probably good advice.

However it's evident Yaesu at the time didn't know how to design an amplifier, so they winged it. There are so many issues with the whole FL-2100 series that I wouldn't bother taking the time to fix them all.

Funny thing is you can often buy a 40 year-old Henry 2K that will last another 40 years without any service for about the same price.