11 October 2008

Yaesu FL-2100Z restoration (I)

Well, here I am again :-)

This time I am working on a Yaesu FL-2100Z linear amplifier. I am currently working on it so this post, I hope, will be more interactive than my first one.

I got the unit in a pretty sad condition (yes, it seems all units I get lately are that way!). Price was right, though, so I ended buying it.

Here you have some pictures of the unit so you can see the condition.


Trust me, it looks better in the pictures than in the real world... cabinet has several dents as it has in the front panel top (not seen in these upside down pictures)

Well, let's see the inner top side in detail:




Besides the dirt, it can be seen tubes are Cetron and, probably, original ones. I got a set of chinese National tubes... they were dirty so they had been inside the unit for some time. Why were they removed?... I found it easily, as the top cap snapped in one of the tubes (it seemed burnt!) just when carefully cleaning it and in the other tube, it was loose...


I tried to resolder it but it seems they use some special soldering alloy... I guess it has perhaps some silver. Does anybody know what they use?

Well, let's see the lower side of the unit. I found several things which needed some care. First, there is a relay which is used to modify tube polarization when it is or not transmitting and it was flooded with oil. Not a good thing!


As I had some spares for my FT-102, I decided to replace it:


Once the relay was replaced, I checked one of the problems I knew in advance the unit had: it didn't read SWR... do you guess why?. Check pictures...


I got all the faulty items, from completely dark resistors to dead 1SS97 diodes. I also cleaned the PCB and finally got this:


So I need to replace all the parts and, specially, 1SS97 diodes. I have thought on using 1N5711 Schottky diodes. Any opinion regarding this?

See you on Part II !

73 JOSE EB5AGV

2 comments:

SV9OFO said...

schottky looks like you are shooting a fly with a bazooka. Since it is an HF amplifier, any new diode would nearly do it.

1n4148 diodes can easily go up to 50MHz, and they cost next to nothing.

What probably blew the oldies was some static discharge.

Since you have an FL-2100 on hand, check the tank loading capacitors (they are in parallel with the Load variable when 160m are selected at the bottom left of the tubes department) for chipping of the porcelain. This is a potential failure point. If you have those 500pF caps handy replace them. Mine are already underway from Russia.

Anonymous said...

30 years ago I burned the bandswitch. Maybe it would be advisable to install anti-corona washer at the switch where the TUNE padding capacitors arrive. There is RF HV there f.i at the 80m padding capacitor when they are not grounded (in 40m position) and flash.

The diodes not really measure, just compare at high levels of power. Any would do. Originals or germanium have a very low Vip ratio maybe 30V, so maybe a normal silicon one does a better job.

It runs very hot, I placed a fan on top pulling air out. The plate caps usually are rated for 250ÂșC, so it needs some special welding.

Chinese tubes need higher bias voltage for standby (install a doubler) or they may start going with the bias that would stop the Centron tubes.

The main trafo has several secondary connection. When installing new tubes, chose the lower voltage ¿450V? and cook the tubes for degasing. Or they can flash if have not been red for a long time. Getter is in the plate and needs to be red.

After 450VAC you can go up in voltage up to 850VAC.

Cooking is made with some signal in and 100% detuned (0% output), for 160W disipation, so the tubes get red.

73 Javier EA1FC