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Yaesu FT-101E no transmit, no i.c.
- Thread starter Champo
- Start date
I tell people that the tester is best for identifying a bad tube. A good tester will reveal what's gone bad with it. Gas, shorts, leakage, low gain or all of the above. But a tester is not so good at identifying a good tube.
Only the radio can do that. If the radio doesn't like a particular tube, the tester's opinion is meaningless. A tube that makes noises when you tap on it may or may not flunk the tube tester. But it's a definite flunk in the radio. Today's odd tube noise is tomorrow's dead receiver.
But the tester can save a lot of time sorting out the tubes that will cause one kind of trouble or another.
A tube tester is a tool, but it's not 42.
73
Only the radio can do that. If the radio doesn't like a particular tube, the tester's opinion is meaningless. A tube that makes noises when you tap on it may or may not flunk the tube tester. But it's a definite flunk in the radio. Today's odd tube noise is tomorrow's dead receiver.
But the tester can save a lot of time sorting out the tubes that will cause one kind of trouble or another.
A tube tester is a tool, but it's not 42.
73
Remembering back years ago ( may not be such a good thing as memory deters with age)
I recall something about having to change a cap in the final section if not using the Japanese manufactured tubes for the 101. Causes loading issues and current draw issues as the American made tubes have different capacitance values than the Japanese made.??
changing-ft-101-final-tubes-neutralizing-best-practices
https://www.antiqueradios.com/forums/viewtopic.php?t=82362
last link explains in detail how to perform the modification and what value of caps
good luck with the old hybrid
I recall something about having to change a cap in the final section if not using the Japanese manufactured tubes for the 101. Causes loading issues and current draw issues as the American made tubes have different capacitance values than the Japanese made.??
changing-ft-101-final-tubes-neutralizing-best-practices
https://www.antiqueradios.com/forums/viewtopic.php?t=82362
last link explains in detail how to perform the modification and what value of caps
good luck with the old hybrid
There is exactly one reason to change the fixed cap that dangles from the air-variable trimmer cap that sets neutralization.
If you need to turn that cap beyond its minimum setting. That is, the best result you can get occurs with the plates fully apart. That would be the minimum-capacitance setting of the trimmer. Reducing the capacitance of that series capacitor will extend the range of this control in that direction.
This doesn't happen all that often with either japanese or american tubes.
Biggest root of this advice that I can see is sheer desperation. I suspect that the most-common reason this capacitor won't adjust properly at any setting from end to end has more to do with the choice of a so-called "pair" of final tubes.
The reason the neutralizing circuit has a variable cap in it is the variation from one tube to the next. Change finals and you'll find that the internal appearance has a big influence. If you use new final tubes that look EXACTLY like the old ones on the INSIDE, you may not need to adjust anything.
The 6JS6 tube was developed to use at around 15 kHz. The capacitor you get between the metal elements in the tube has no real effect on how the tube works in a color TV. As a result, those parameters were not controlled tightly from one brand to the next. Hey, it's engineering. Only spend money on features that pay you back.
The wide range of variation in these internal capacitors occurs because each factory that made them used a slightly different internal layout of the metal parts. Naturally this affects what size capacitor they behave like. The whole reason to neutralize the final tubes is because of the feedback INSIDE THE TUBE between input and output that these "piggyback" or parasitic capacitors will cause. That feedback will make the tube oscillate.
The neutralizing circuit takes a sample of the output signal and flips the polarity upside down. Feeds this out-of-phase sample to the input side of the tube. Get this out-of-phase sample exactly right, and it totally cancels out any tendency for the finals to oscillate.
If you haven't gone to sleep or hung yourself from a rafter yet, here's the payoff.
Both final tubes have to have the same accidental feedback level inside each one.
If one tube came from Pennsylvania and the other final came from Japan, you can be sure those internal capacitances are not the same. The proper setting of that neutralizing cap for one tube is NOT the correct setting for the other tube. There is no single setting of that adjustment that will make a mismatched pair of finals settle down and be neutral.
Oops.
Before changing that cap, have a look-see at your "pair" of final tubes. If the size, shape and color of the internal parts look alike, you're probably okay. The brand name printed on the tube has nothing to do with who built it. Only tells you who sold it. GE routinely sold RCA or foreign-made tube with the name "GE" on them. All the other brands did the same thing. It's the sales division that prints names on the tube. The factory ships them out in bulk with only the type number on it, nothing else. The name on the carton tells you who stuffed it into that carton and not one thing more.
The calibrated eyeball test is your friend here.
73
If you need to turn that cap beyond its minimum setting. That is, the best result you can get occurs with the plates fully apart. That would be the minimum-capacitance setting of the trimmer. Reducing the capacitance of that series capacitor will extend the range of this control in that direction.
This doesn't happen all that often with either japanese or american tubes.
Biggest root of this advice that I can see is sheer desperation. I suspect that the most-common reason this capacitor won't adjust properly at any setting from end to end has more to do with the choice of a so-called "pair" of final tubes.
The reason the neutralizing circuit has a variable cap in it is the variation from one tube to the next. Change finals and you'll find that the internal appearance has a big influence. If you use new final tubes that look EXACTLY like the old ones on the INSIDE, you may not need to adjust anything.
The 6JS6 tube was developed to use at around 15 kHz. The capacitor you get between the metal elements in the tube has no real effect on how the tube works in a color TV. As a result, those parameters were not controlled tightly from one brand to the next. Hey, it's engineering. Only spend money on features that pay you back.
The wide range of variation in these internal capacitors occurs because each factory that made them used a slightly different internal layout of the metal parts. Naturally this affects what size capacitor they behave like. The whole reason to neutralize the final tubes is because of the feedback INSIDE THE TUBE between input and output that these "piggyback" or parasitic capacitors will cause. That feedback will make the tube oscillate.
The neutralizing circuit takes a sample of the output signal and flips the polarity upside down. Feeds this out-of-phase sample to the input side of the tube. Get this out-of-phase sample exactly right, and it totally cancels out any tendency for the finals to oscillate.
If you haven't gone to sleep or hung yourself from a rafter yet, here's the payoff.
Both final tubes have to have the same accidental feedback level inside each one.
If one tube came from Pennsylvania and the other final came from Japan, you can be sure those internal capacitances are not the same. The proper setting of that neutralizing cap for one tube is NOT the correct setting for the other tube. There is no single setting of that adjustment that will make a mismatched pair of finals settle down and be neutral.
Oops.
Before changing that cap, have a look-see at your "pair" of final tubes. If the size, shape and color of the internal parts look alike, you're probably okay. The brand name printed on the tube has nothing to do with who built it. Only tells you who sold it. GE routinely sold RCA or foreign-made tube with the name "GE" on them. All the other brands did the same thing. It's the sales division that prints names on the tube. The factory ships them out in bulk with only the type number on it, nothing else. The name on the carton tells you who stuffed it into that carton and not one thing more.
The calibrated eyeball test is your friend here.
73
Please be patient with my ignorance. That was an excellent explanation! I'm still digesting it as I write. What are some symptoms that would be readily identifiable if the caps aren't neutralized? You mentioned that the tubes will start to oscillate. How will this manifest on the receiving end? Low output? Distortion? How about on the transmitting end? I bow before your greatness! 
Erratic behavior from the preselect, plate tune or load controls. Changes in power should be smooth when a knob is turned. A sudden jump up or down in plate current and/or wattmeter power suggest a stability problem. If a CB or ham radio is turned on nearby, you'll probably hear odd noises as well.
Forgot to copy my cheat sheet from work before coming home today. For whatever reason, memorizing which way to turn the neutralizing cap didn't work for me. I still have to use the cheat sheet. But it's on the air-gapped computer. With any luck I'll remember to copy it next time I'm there.
73
Forgot to copy my cheat sheet from work before coming home today. For whatever reason, memorizing which way to turn the neutralizing cap didn't work for me. I still have to use the cheat sheet. But it's on the air-gapped computer. With any luck I'll remember to copy it next time I'm there.
73
Yeah he was spot on. This was cross posted and I got a direct message. Not even a forum response. After a few back and forth's he said "call me if you want" and gave me his number. Turns out he's the ARRL coordinator for Kansas. He had me describe in detail how I was tuning the rig and when I got to the loading phase and described the symptom he paused for a moment and then exuberantly said "it's the driver tube. Guaranteed!" I've tried messaging him back but no response. As quickly as he came, he went lol! Anyways I'm stoked. I appreciate everyone's help! Especially the knowledge you've dropped on me Nomad. So thank you!
Question for you Nomad. I ordered an IF board with an AM filter already installed. The board is "untested." If I were to install the new untested IF board in place of the current board would I be risking damaging anything else on the radio if that board has some sort of issue or will the radio potentially just not operate correctly? The other option is to remove the AM filter from the new board and install it on the existing board. I was trying to avoid this option so that I could keep the original board original and intact. I will then do the mode switch changes. Thanks!
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