monitoring ft-101 plate voltage

[kb3ouk]

Does anyone know of a way of monitoring the plate voltage on an ft-101. the power output seems to vary  lot, and i want to see if the plate voltage may be varying,too.
shelby kb3ouk

[Opcom]

Might be he best way would to connect a piece of 5KV test probe wire to the HV supply just before it enters the RF cage and watch it on a meter. If your meter does not go high enough, you might select a tap on the HV filter stack. The old time honored way would be to string ten 1 megohm resistors in series and put in series with a 100uA meter so that full scale would be 1KV.

[kb3ouk]

can i also monitor it by sticking volt meter probes in the acc jack, i'd just need to know what pins the probes should go in.

[WQ9E]

The plate voltage (around 600 volts) is available at pin 5 of the accessory jack, B+ is at pin 4.

Be careful, even though you should never trust the bleeder resistors to discharge a power supply in the case of most Yaesu transceivers the bleeder resistors are of such high value that even when working it takes a long time for the HV and B+ to drop to low levels.

Rodger WQ9E

[N3DRB The Derb]

 buy one of these . then you can rule out problem electrolyics.


http://cgi.ebay.com/Yaesu-FT-101E-HF-Transceiver-Capacitor-Replacement-Kit_W0QQitemZ130282345537QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item130282345537&_trksid=p3911.c0.m14&_trkparms=66%3A2%7C65%3A15%7C39%3A1%7C240%3A1318#ht_1341wt_688

[AMroo]

  Better still rule out the rice box

[ka3zlr]

Well I wouldn't rule it out.. ... they're cool little rigs..

If yer having stability problems, do the little things first, Check the Drive Pot operation and clean..Inspect the machine for obvious circuit problems......Check the toobies.. do a General House cleaning of the rig..Clean all Pots, Pull the boards out clean the Traces..and check the Seating...Check the relays and replace...They're fun to work on...

All the while waiting on the Caps to come in..This is a Must do, do them while you have it down...if they haven't been serviced...

Her's a gud Web Site for reference..an has the Neutralization Mod on it..an it's very easy to do...

http://www.qsl.net/nw2m/ft101.html

73
Jack.

[KL7OF]

Shelby,...the ft101 is a good radio....I have one(ft 101 E) that I bought new in the 70's that is still in use at the AK QTH....I have replaced the power supply filter caps twice and the driver tube a couple times....It still has the original finals......It is a pretty decent AM rig...  If your finals (6JS6C) tubes are american made, there is a cap change that is necessary to make them operate properly...I believe that info is available on this site.  That could be your problem...  Others on this forum may be able to elaborate on the change necessary when going from foriegn to domestic tubes..  Good Luck...Steve

[N3DRB The Derb]

yes, there is a fixed value cap strapped across the variable neutro cap that needs to be brought down in value radically if the rig is going to make stable power and neutro ok.  Discharge the HV and get into the final cage. Check and see if the final tubes are Toshibas  or not. If so the existing 100pf value cap is correct. if they are USA made, the value needs to be brought down to  5~10pf @1000 silver mica dipped.

the plate structures are radially different between the jap and US made tubes.

the board that sits next to the final cage has many HV electrolytics that you MUST change out.

Check the padder across in series with the adj neutro cap first. if it is a square block, it's the 100 pf and US made tubes will never work. Try to find a 5 to 7 pf silver mica @ 1000 volts. Cut the leads right where the block  is and use them as supports for your new cap. solder it in, short leads.  re neutro the finals. use a PLASTIC screwdriver to adjust.

and AM roo, quit hating. FT-101's are great radios when serviced and restored. Lots of other problem areas, but KW-1's have them too. I should snap some pix.

[kb3ouk]

Been a while since I've been on here, but the problem seems to occur the most when it is first turned on , then allowed to warm up. If I key it up then let it sit at about 10 watts for about 5 minutes, the output drops down about half. then i give it more carrier and let it sit a little longer and it stays pretty steady at 10 watts.

[ke7trp]

Your problem is Capacitor C13.  Its the Driver coupling capacitor. Its 80PF at 1000V mica. 

Open bottom cover.
Remove all screws holding the internal chassis cover.
Remove the two screws holding down the TC board (small adjustable caps)

C13 is located under the top edge of that board near the chassis edge. This cap is brown in color is is a rectangle shape.  This cap couples the driver to the output tubes. Its old and its changing in value. This changes the output.

THis is a very common problem with FT101s.

As stated before. If your tubes are american made, use a 10PF 1000v mica cap on the neutralizing cap. This cap is number C125 and has an original value of 100PF

While your there.. Replace C131.  Its a 1000PF cap near the preselectors.  This cap often fails and causing the Fuse to blow when you go on 160 meters.

If you need further help with the FT101 feel free to email me or post here.

Good luck with it.  Keep the IC at .15 on AM. With good tubes it will key 18 to 20 watts and talk at 50RMS.

Clark
KE7TRP