I just received a 2 tube 572B amp. The tubes have been replaced with new. The DC blocking capacitor has been replaced as well, the old one blew up. From my understanding the guy that had it before drive it hard. Over a 150 watt DK into it. I was told that there was a device that would shut it down and feed the power thru without going into the amp. Which is exactly what it is doing. I have plate voltage and the filaments have voltage. Any idea what I should look for or has anyone else ran into this problem? Any help would be greatly appreciated. Thanks in advance.
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Yaesu FL2000B
- Thread starter Crusher
- Start date
First, I would recommend that you do nothing to that amplifier until you have the manual to it. Use that manual to see if/how the thing has been modified.
If it's an FL-2100B instead of an FL-2000B (never head of it), there was no 'swamping' circuit. One could certainly have been added though. I also hope those replaced tubes were of the 'lay down' variety rather than the 'stand up' variety, there really is a difference!
And since that thing is dangerous if you aren't sure of what you are doing, I would be very, very careful of it.
Get the manual first.
- 'Doc
If it's an FL-2100B instead of an FL-2000B (never head of it), there was no 'swamping' circuit. One could certainly have been added though. I also hope those replaced tubes were of the 'lay down' variety rather than the 'stand up' variety, there really is a difference!
And since that thing is dangerous if you aren't sure of what you are doing, I would be very, very careful of it.
Get the manual first.
- 'Doc
I agree with Doc. BTW Doc., here ya go. A real FL-2000B
RigPix Database - Power amplifiers - Yaesu FL-2000B
If the tubes are Svetlana be very carefull. They do not work in the Yaesu amps, as well as others, unless there are changes made to the bias circuit. Here is a link to the FL-2100B manual but the amps are very similar AND the Svetlana bias info is at the end of the pdf file.
http://www.rigpix.com/linears/yaesu_fl2100b_manual.pdf
It is definitely a FL-2000B. I have the instruction manual copied from RFParts. Yet I cannot find anything That would be in the circuit that would cause this. The only thing modified is The high voltage safety switch has been disabled. This was so that if the top was taken off, it would short out the high voltage supply. If I put a 10 watt carrier into amp, I see about 8 watts out. I have made sure that the band switches are in the right position. It is as if the power going in goes thru circuit but has some loss as the load and tune affect the few watts going into it. I have worked with some high voltage and yes i have a shorting stick laying around just for working on stuff like this. I am sure it is something simple I am missing. I do have to replace relay after I get it working as the output side is pitted and shows signs of heat/ wear. The band switch I checked out as well. Has some signs of a possible arc as well. Carbon build up on the plate of rotary switch. Cleaned all that up and nice and shiny now. Good contacts.
In looking at the schematic, if you disconnect C220 (coupling capacitor) between the input bandswitch and the tube filaments, do you still get 8 watts out? If so, then the relay isn't kicking in, if not, and your input SWR went up, then the relay is functioning properly.
What are you driving the amp with? IIRC that amp,and most amateur amps, do NOT have RF switching and MUST be keyed by an external switch somehow. Usually the amateur radio will have this connection available but a CB or export radio will not. You will need an external switch such as an external RF sensing relay or a foot switch. Regardless of this issue check those tubes to be sure they are not Svetlanas and if they are modify the bias circuit before running the amp.
If it was driven real hard I would suspect a mica cap in the tuned input being toast. Switch your exciter and the amp to a different band and see if it will load into a dummy load then. If the bandswitch is burnt looking it might be a good thing to check it closely also.
It uses a footpedal to key amplifier and yes when pressure is applied to footpedal relay kicks in. The replacement tubes are Taylor tubes.
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