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

Sat May 19 01:13:52 EDT 2012

It might prove to be a relatively common problem. That manufacturing 
didn't count on the difficulty of soldering to the strap and large 
conductor coil at the 10 meter tap and so many a linear left the factory 
with that joint poorly soldered from using too small a soldering iron.
Invariably in a multiband linear, the loaded Q of the plate tank on 10 
meters is higher resulting in higher circulating current. This comes 
from the irreducible capacitance of the tubes internally and externally, 
tending to be more than the desired tuning C for a design loaded Q of 
12. A loaded Q of 20 is more likely, because of the tubes and the 
minimum C of the tuning capacitor that will tune to 80 or 160. And the 
circulating current tends to be the terminal current times the loaded Q. 
Part of the reason the 10 meter and sometimes 15 meter plate coil 
segments are a larger conductor than for the low bands. According to a 
old time rule of thumb, for a linear a loaded Q of 12 gives adequate 
harmonic suppression. Any higher loaded Q increases the loss in the tank 
coil.
73, Jerry, K0CQ
On 5/18/2012 10:13 PM, KBØNLY wrote:
> Hmm, never thought of that, I just tore into it when I got it but now
> that I look back at the old switch it was the 10m contact that was
> damaged the worst! It was blown up when I got it, which is why I was
> able to get it so cheap, but now that I think about it I bet that is
> why. It melted the common contact off the old switch and burned a hole
> in the rotor.
>> 73,
>> Scott KBØNLY
>>> -----Original Message----- From: Dr. Gerald N. Johnson
> Sent: Friday, May 18, 2012 9:20 PM
> To: yaesu at mailman.qth.net
> Subject: Re: [Yaesu] FL-2100B, Help Troubleshoot...
>> That may have been a major contributor to the demise of the bandswitch.
>> 73, Jerry, K0CQ
>> On 5/18/2012 8:31 PM, KBØNLY wrote:
>> Roger there is... Didn't think I would need to mention it since I
>> mentioned
>> the SWR. Dug out my old Heathkit HM102 and put it inline, SWR is about
>> 1.5:1 on 10m, a slight tweak of the coil and its flat now.
>>>> The problem was a bad solder joint on the tap at the tank coil, turns out
>> when the amp was warmed up it got intermittent and it was driving me
>> buggy
>> finding it. As you could imagine, I would test it, nothing, let the amp
>> cool and rest and walk away for a while and come back and start going
>> through everything and it all looked good continuity wise through the
>> input
>> and bandswitches, etc. But warm it up and I would get a blip or two of
>> output and then nothing again! Talk about a hair puller. Then I
>> decided to
>> get the chicken stick out, pull the plug and bleed everything off and
>> check
>> continuity quick while it was still warmed up after being on the net
>> and low
>> and behold its an open circuit on the output side! A little heat, solder,
>> and its all better now.
>>>>>> 73,
>>>> Scott KBØNLY
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