need help with ft-101e
i am trying to fix an ft-101e and i cant seem to get it. i need help with the i.c, when i set the bias to spec the i.c is out of sight, it pegs the meter. the rx is fine. any info is apreciated.
oh and theres no output at all on any band. the tubes are good i checked.
Depends how capable you are. First thing I would do is disconnect the screen voltage from the finals. This will stop you blowing the tubes. Check IP again and see what happens. hopefully no IP at all. Then with a VOM check the bias voltage on the control grids on the finals and see whether the negative voltage can be varied and between what range.
Get back to me soonest with results.
It appears there is no bias voltage on the grids (pins 5 and 6) of the final tubes.
Check the bias supply output, anode of D6, on assembly PB-1076B. Loss of bias
voltage will cause the final tubes to conduct to saturation in transmit (plate current meter full scale).
If there is no bias voltage at the anode of D6 on assembly PB-1076B, it's quite possible that D6 is bad.
If D6 is found to be bad, replace it with an equal voltage and current rating silicon diode.
I have been thinking about this and when you are in receive the output tubes are cut off by high bias voltage, so I think that your bias supply is working otherwise your tubes would melt in receive mode.
To do any tests, please remove the screen voltage from the finals to stop them drawing maximum current. Then check the bias voltage on the finals in receive mode and also in transmit mode, (no drive) and see if the bias voltage varies when you adjust the bias control. In Rx it should be at least -100 volts if not more.
I agree, loss of bias voltage, whether in receiver or transmit, would result in the final tube's conducting to saturation levels. The meter only indicates cathode current (IC) during transmit because of relay terminals A10, B10. and
A9 actions that switched the meter from being an S meter to indicating ALC, HV, IC etc, depending on what position the meter switch S8 is set to.
I had a Hallicrafters FPM-300 that exhibited similar symptoms this 101 has. The final tube appeared to be biased to cut off in receive. Measuring the bias voltage with a DC volt meter showed good bias voltage level in receive. However,
in transmit the meter pegged full scale, the bias pot had no control over the cathode current, and the plate of the final tube turned red. The problem turned out to be failed bias supply filter capacitors which allowed AC
ripple to appear on the bias voltage.
In receive, the bias voltage level was sufficiently negative that the positive half of the AC sine wave never caused the grids to go positive which gave the impression the final tube was biased to cut off. In transmit, however, the bias
voltage is less negative and with AC ripple on the bias supply, the positive half of the AC sine wave caused the grids of the final tube to be significantly positive resulting in the tube conducting to saturation and the plate turning
red. The bias pot had no control over the excessive cathode current. The fix was to replace the bias supply filter capacitors which solved the problem.
the bias is at -60 on rx on pin 5 an -50 on tx. pin 6 rx is +180. i dont know which is the screen voltage is or how to disconect. d6 on 1076 is -178. i am fairly new at fixing this old stuff.
Just quickly, what is the history of this set. Has it been out of action for many years or did the fault suddenly occur. One thing that I would do is to clean the relay contacts with switch cleaner as well as the band switch. A rig of this age may have corrosion on these contacts.
The +18o volts sound correct for the screen grids. disconnect this wire on each pin of the two tubes and make sure that it does not occur on other pins. Once you are happy, go on to Tx momentarily and watch the IP meter. I hope the meter switch is not switched to ALC. Withe the screen voltage removed there should be no current flowing through the final tubes.
Post what happens.
I didn't have time last night to mess with it. The history that I know of it is I got this one and a EE and he said they have been sitting for a few years. The E, that I'm trying to fix does the most of either so it's the first to get fixed. I already cleaned everything with contact cleaner with lube. When I first hooked this up it put out about 5watts but I.C was high like it is now, when it stopped putting out I checked all the tubes in a friends 101 and they are still good,
I disconected the +180 and I still have I.C. It's the Same as with it connected.