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Re: [Amps] Yaesu FL2000B amp and input tuning problems

To: "" <>
Subject: Re: [Amps] Yaesu FL2000B amp and input tuning problems
From: Morris Wideman via Amps <>
Reply-to: Morris Wideman <>
Date: Mon, 6 Apr 2015 02:19:24 +0000 (UTC)
List-post: <">>

     On Sunday, April 5, 2015 8:59 PM, Alek Petkovic <> wrote:

 G'day Morris.

The method you described is probably more appropriate for setting the 
output pi circuit settings.

I don't think you can use that method for the input.

I would have thought that you would be better off leaving the tubes in 
situ and leave the resistor out of it and then do the procedure you 
described. That should allow you to tune it with all the effects of the 
tubes' capacitance/inductance in circuit. Dunno if it would work but it 
must surely get you closer than with the resistor.

Good luck and 73,
Alek. VK6APK

On 6/04/2015 9:34 AM, Morris Wideman via Amps wrote:
> Hello
> I have a old Yaesu FL2000B amp that has been giving me fits and thought I 
> would see if group has some thoughts that might help out here. I have had 
> this amp many years and used it with very little problems even though it has 
> always showed reflected power on the input side. Back when I used a Drake T4X 
> to drive it no problems with the reflected. I now have a FT1000mp and its 
> built in ant tuner takes care of the reflected. About 3 months ago one of the 
> tubes shorted grid to plate and burned up a grid resistor and trashed the 
> electronic bias circuit I had put in many years ago. I thought this was 
> opportunity to work on the reflected problem. I fixed the aforementioned 
> problems and I have a pair of tubes in that put out resonable power now so I 
> beleive the tubes are good. That leaves only the amps input ckt reflected 
> power to deal with.In my searching I found a article detailing a method using 
> a resistor to simulate the tubes input impedance and use something like a MFJ 
> 259B fo
 r tuning to match with the amp off. I tried this method and used a external 
supply to activate the changeover relay. I was able to change capacitance 
values to obtain a very good match on those bands that were bad not all needed 
this but those that did turned out very good this way. However when firing up 
the amp my new match is now worse than before. The manual for the amp 
recommends disconnecting the HV leads from the transformer and tuning the input 
I also tried this with the same poor results. Most of my efforts have been 
spent on 10M as this is one of the worse bands with at least a 2.1 swr and I 
noticed that the plate and load adjustment greatly affects the SWR reading max 
out is not the lowest SWR point. I have tested the changeover relay and the 
band switch to make sure they are properly making contact and swiching as they 
should. I have correct idle current and decent output power.I just need to get 
the reflected power down but nothing I have tried seems to work I w
 as hoping someone might have a new suggestion.Thanks for your time73 Morris 
Hi Alex
I did not remove the tubes I placed the 100ohm resistor across the cathode to 
ground as this is a cathode fed amp. No AC power just powered the changeover 
relay so that the input ckts are in ckt. Thanks Morris wa4mit73

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