I have a Yaesu FL-2100B amplifier (twin 572b's) that I got which was in pretty rough condition when I examined it. The plate current meter cover had been smashed, and an incorrect replacement was glued over the meter itself. It does at least serve to protect the movement but sure won't win any prizes among the restoration crowd. Heh, heh. Watts is watts on the air! I'm definitely a fan of "run what ya brung" and Operating!
Among other ills it had when I aquired it, was a burned out parasitic resistor assembly.
The power supply interlock had been burned up by previous operators.
More signs of heavy heat buildup are a classic cracked high voltage ceramic capacitor.
Happily, the band switch seemed to be ok.
The underside shows to be reasonably clean despite a couple of mods -- the unit was restored to factory design before beginning upgrades.
Repairs and upgrades include:
1. W8JI relay/center tap bias mod 2. PA0FRI' style parasitic supressor 3. changed "bubbled" 220pF with 500 pf silver mica on grids 4. Replace 1k pF ceramic in HV with one moved from other circuit 5. Replace moved 1k pF with .01 uF 3kV 6. Install HV glitch resistor 7. Install 1k pF added bypass at HV glitch resistor 8. Replace 80M HV capacitors in tank (500/300 by 650/140) 9. PA0FRI' rerouted variable capacitor ground path 10. Diode protection on meters
When I did the W8JI center tap mod, I used a salvaged relay out of an outdoor floodlight unit. This was not the best choice for long term functionality. Nothing wrong with the relay, it was just seriously undersized for the amplifier usage. It was being used to switch dual 80 watt lamps at 120 volts, so it should have been good for at least an amp. W8JI's web page claims that a "...low current relay" will be sufficient in this usage. Not to my experience!
I started getting reports of "Your audio
has some distortion" then finally the amp was merely 600 watts of QRM (ouch).
It seems I
burned up the relay contacts
in the salvaged relay. I replaced the teeny relay with a Guardian
double pole, both poles ganged, rated at ten amps. Fired it
up and have the nice 600+ watts out again, with "good audio" reports.
September 2009
I've found several web sites with good information on amplifiers with two 572b's such as the FL-2100B. In no particular order:
There were two "Dentron" 572b's in the unit when I obtained it. One of these had a part spring loose inside and roll around. I've not run that tube since I noticed that. Cough. Fortunately I was able to loot a Cetron '572 out of a homebrew project I also have. It seems to be a sturdy rebuild so far.
Today (June 2009) I fired the FT-102 up with the FL-2100b and was able to get 700+ watts PEP on 20 and 40 meters. The power reading was indicated on an MFJ989D antenna tuner with the meter in the "peak hold" mode. The meter may be a bit optimistic, but it does seem to show the FT-102 putting out 150 watts when I've tuned the radio up for full power. The '102 has three 6146B's in the final and is know to be able to grunt this hard. I have an MFJ-969 that shows similar power levels out of the '102. Not a Bird, I know... Conditions were terrible on both bands so I needed the extra bit of power. On 20 I used a homebrew 1/4w vertical mounted on the deck railing about 12 feet off the ground, and on 40 I used the 530' loop with an MFJ989D tuner.
I ran it on 15M for many hours during a couple of days of CQ SSB contest into a Hustler 5btv. Lots of fun to work 15 and surprise a few folks with contacts on the band in the contest.
Next up for upgrades are replacing the HV capacitor stack and replacing the HV rectifiers. I'm hopeful that this will bring a modest boost to the power -- I'd fixed a friend's Heathkit that had burned up a diode in the HV stack with a string of much improved modern semiconductors, and his 75 meter pals are telling him "...you're the loudest I've heard you." Pretty good, and he's still using the Heathkit supplied HV capacitor stack. The Yaesu is an older generation amplifier and needs both the diode and capacitor HV arrays upgraded.
Heh, heh well those old capacitors and rectifiers pushed 600 watts so I'm in no hurry to change this out. Like in the book "D-Day on the Western Pacific" and how they had the philosophy of getting the full servicable life out of their locomotive parts.
June 2009 ki6jjw
