[Yaesu] FL-2100B, Help Troubleshoot...

Fri May 18 12:47:58 EDT 2012

I'd still say it's in the output circuit, and the fact that you replaced the switch might well be the key. The tank aint resonating since there ain no dip! Check the 10m coil tap and measure for continuity when it gets switched in. Most likely you are trying to get power out through a tank that's either resonant near 15 or else the whole coil is in circuit, not sure how they switch that.
Cheers
Martin, HS0ZED
-----Original Message-----
From: yaesu-bounces at mailman.qth.net [mailto:yaesu-bounces at mailman.qth.net] On Behalf Of KBØNLY
Sent: 18 May 2012 23:40
To: Yaesu Reflector
Subject: [Yaesu] FL-2100B, Help Troubleshoot...
Hey all! I got a question here on the Amp I have been working on, I have worked on a few of these but this one is acting odd.
Here is the story... The amp had a burned band switch, I helped Multi Tech Industries design a new one, it will be on the market soon in case anyone needs one, and I got the switch installed. New tubes.. A couple new capacitors, the 1000pf cap on the plate end of the RF Choke was broken by the previous owner removing the blown bandswitch. And one cap on the T/R relay, a bypass cap, was broken as well, looks like someone just caught it on the bench and cracked it while trying to work on the amp.
Tossed in a new set of tubes, let it warm up a bit, checked the bias, adjusted. Tried 80m, perfecto... 600w output with 50w drive and the tubes are looking good, voltages and current looking good, no problems. Drop to 40m, same thing 600w and no problems. Drop to 20m, again no problem and 600w output. Drop to 15m, about 400w output and a very hard to find dip on the plate, but otherwise the current is where it should be and it looks ok, I think on 15m I actually just have a bit of an input SWR problem and the coil for that band has been adjusted its not in the stock location so I will have to put the analyzer on it and tweak it.
Now comes the problem... 10m is dead. According to my radio the input SWR is below 2:1 as its not backing off, the current on the amp comes up but the plate capacitor has no apparent dip, meter never moves, tuning capacitor doesn’t seem to make any difference either, there is ZERO output on 10m. I mean dead dead dead. So the only thing I can think, since the output bandswitch is brand new is that I have a problem in the input section of the amp. I checked the input bandswitch for continuity in the 10m position and its fine, I inspected it with a flashlight and a small dental mirror, no contact problems there. The coil for 10m looks ok, and the tuning slug doesn’t appear to have been moved. 
So, could the cap on the 10m input, 1000pf, be bad causing this? If so why wouldn’t my radio be complaining about a high input SWR? And why would the plate current come up when drive is applied but no output? Very very odd....
73,
Scott KBØNLY
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