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KI4GIF
10-27-2011, 04:59 AM
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.

KI4GIF
10-27-2011, 05:04 AM
oh and theres no output at all on any band. the tubes are good i checked.

ZS1J
10-27-2011, 05:08 AM
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.

73 Roger

W5RKL
10-27-2011, 06:50 AM
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.

73s
Mike

ZS1J
10-27-2011, 08:20 AM
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.

W5RKL
10-27-2011, 01:24 PM
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.


73s
Mike

KI4GIF
10-28-2011, 05:20 AM
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.

ZS1J
10-28-2011, 12:04 PM
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.

73 Roger

KI4GIF
10-30-2011, 05:03 AM
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,

KI4GIF
10-30-2011, 05:24 AM
I disconected the +180 and I still have I.C. It's the Same as with it connected.

VU2NAN
10-30-2011, 12:26 PM
I disconected the +180 and I still have I.C. It's the Same as with it connected.

Hi OM Brandon,

Looks like the problem is with the meter shunt resistor R12 at the cathode of the final.

It's a wire-wound resistor - maybe the termination has gone bad or there's a dry solder problem.

I suppose the final current is not really high but is, in fact, really low and the indication is faulty.

73

Nandu.

KI4GIF
10-31-2011, 03:19 AM
But would that cause the radio to not put out power?

KC8VWM
10-31-2011, 04:31 AM
You have a dirty or faulty open circuit connection somewhere.

Get the service manual (free download) and measure the voltages present on the tube pins on the base of the tube socket. Also check the relays using a VOM and check any resistors or shunts (ie. R12) in the final stage for continuity. They can look ok to the naked eye but may actually be functioning as open circuits. Only your VOM meter knows!

Confirm the tube pins at the sockets are getting voltage according to the specs indicated in the service manual. Also ensure the ACC plug on the rear has the jumper properly configured for TX operation. Without it, the rig won't TX no matter what you do because the ACC jumper is intended to send the required voltage to the final stage for TX operation.

FT 101 E ACC socket jumper ie:

http://i629.photobucket.com/albums/uu18/kc8vwm/MVC-012F-1.jpg

Relays often perform a similar function so check them using your VOM for proper operation too. Pull all the boards and clean the contacts using a pencil eraser. Spray the bandswitch and RF ouput control switches with deoxit and give them a good workout to clean the internal contact wipers etc etc etc..

VU2NAN
10-31-2011, 05:33 AM
But would that cause the radio to not put out power?

Hi OM Brandon,

It's probable.

The meter reads the cathode voltage as a measure of current. Increased resistance would increase the cathode voltage resulting in a higher reading when, in fact, the increased resistance would have increased the negative bias on the control grid resulting in low current and no output.

73

Nandu.

KL7AJ
10-31-2011, 05:41 AM
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.

I suspect a shunt resistor is fried or non-existent. Measure the resistance across the meter with the meter switch in the IC position. It should be less than an ohm or so.

Eric

ZS1J
11-01-2011, 01:15 PM
All sounds sensible to me. What I would like you to do first though is either remove the final tubes altogether and see if the meter still goes high on Tx or failing opening the final box, remove the heater link as shown in the picture posted. This removes the heater voltage from the finals only. If you still get a reading on the meter there is something very strange happening. Let us know the outcome.

ZS1J
11-02-2011, 05:25 AM
The reason I am replying again is that when the screen voltage to the 6JS6Cs was removed and then you went to transmit, there should have been no current flowing through the tubes at all and the meter should not have moved. Exactly the same with either the tubes removed or the heater link removed. There should be no current flowing. If the meter still reads, it is not the bias, it is not the tubes but it must be some corrosion either on the meter switch or the relay that switches the meter from 'S' meter to IP.

73 Roger

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