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THE AM BULLETIN BOARD => Technical Forum => Topic started by: wa1sth on January 09, 2023, 05:04:40 PM

Title: Yaesu FT101E
Post by: wa1sth on January 09, 2023, 05:04:40 PM
I have a Yaesu ft-101F (and also an "E" that hums (60 cycle)
on AM Transmit.  Yes, I have changed the Caps and have tried,
I believe, most of the simple stuff.  I wonder if anyone out there has had the problem and was able to resolve it??  Thanks for any input.

Title: Re: Yaesu FT101E
Post by: W3SLK on January 09, 2023, 07:20:25 PM
Possibly RF?? ??

Title: Re: Yaesu FT101E
Post by: W1NB on January 09, 2023, 08:00:08 PM

I had that issue in mine. I found that there is ripple on both the 300V and 600V taps on the HV supply. To overcome it I beefed up the capacitor values, then added a 3H choke to both. I removed the DC supply on the back and mounted them there. I also beefed up the diodes and added a step start to avoid any current surge issues. That removed about 80% of the hum. The remainder was generated in the 12V supply. With stock audio it was barely noticeable but I modified the audio chain to increase the low end which made it more pronounced. To clean it up I replaced and beefed up the 12V supply capacitors, then added an LM7812 regulator.

Scott, W1NB

Title: Re: Yaesu FT101E
Post by: wa1sth on January 09, 2023, 08:22:24 PM
Thanks for the input guys.  It is not RF.  I went so far as to take it and  a dummy load to my daughters house and on a monitor radio heard the same thing.  I initially thought it was RF.  Scott thanks for the input I will order the parts and do what you did.  I already beefed up al of the caps on the regulator board but will change the regulator as you suggested.  I changed the two large power supply caps and doubled their capacity.  I am assuming you put those two coils across the caps?  Thanks again for the help. 

Title: Re: Yaesu FT101E
Post by: K1JJ on January 09, 2023, 09:06:00 PM
Hi Steve,

I heard you talking about it on 75M the other day and by the time I fired up you were gone...

I was going to ask if you used a scope probe and o-scope to look at every voltage point in the rig... looking for unusual hum?   You should be able to zero in on the area that is causing the problem.  Start at the low voltage and go all the way up thru the driver tube and 6146 pins. Even if it is not DC, you may see the hum riding on the RF chain somewhere in the earliest stage that the hum begins. 

I wonder how the 12BY7, 6146s  grid, screen and plate voltages look during transmit?

You probably don't have a good second FT-101 to compare with, but running two FT-101s side-by-side for fast comparisons is a great way to provide a knockout punch to the gremlin.

Let us know what you finally find.


Title: Re: Yaesu FT101E
Post by: wa1sth on January 09, 2023, 09:21:43 PM
Hi Tom

Well I had another FT101 I fixed up just for that purpose.
A lot easier to judge ripple with a direct comparison.  BUT the second radio has the same issue, frustrating.  Anyway W1NB apparently already fought his way through this.  Good part is he lives in the next town.  Thanks for responding talk to you on the air soon.  73's

Title: Re: Yaesu FT101E
Post by: K1JJ on January 09, 2023, 09:31:28 PM

Wow... if the second rig has the same problem, sounds like a design issue. Maybe the hum is on the hairy edge when new and ANY further parts degrading is enuff to show the hum.

Scott's ideas sound valid and would be my next move since he made it work.  In the meantime do a scope probe search and see if the hum(s) can be seen festering in some specific areas...  especially in the three places Scott indicated.

Title: Re: Yaesu FT101E
Post by: W1NB on January 09, 2023, 10:01:16 PM

I believe it to be a design limitation. It was really designed for SSB. The baseline hum isnít noticeable there. I reworked mine a few years ago so I canít swear to this but I think the ripple at full, continuous output is around 3%. Some of that may be caused by aging of the capacitors but I still had too much ripple after replacing them. Iíve repaired and owned 101s since the mid 70s but never really noticed it because the majority are used for SSB where itís not noticeable.


The regulator on the PS board is for the 6V. The 12V rail is not regulated so I added the LM7812 and mounted it to the sheet metal that separates the transformer cavity from the rest of the chassis. That area is also where I placed the relay for the step start.

Title: Re: Yaesu FT101E
Post by: wa1sth on January 10, 2023, 10:41:52 AM
Thanks again guys for the input.  I will keep you posted on the results.

Title: Re: Yaesu FT101E
Post by: K1JJ on January 10, 2023, 12:28:39 PM
Yep, I agree, Steve/ NB.  The hum is still there on ssb, but it hides itself in the dynamic range of complex speech waveforms.  However, if you were to whistle a single tone into the mic on ssb, you would surely see this hum riding on the carrier produced by the single tone.  It is worthwhile to get rid of it cuz it just adds to the inter-mod distortion when it mixes with the audio. (on both ssb and AM)

Yes, filter chokes for further HV filtering, fatter caps and a 12V regulator are probably the best approach.  Though you could go crazy adding just more capacitor ballast and never quite quench it. In this case it appears you need some more inductive reactance to drop the HV ripple across.  The 12V regulator will also take no prisoners.

This should do the trick for you, Steve / STH!


Title: Re: Yaesu FT101E
Post by: ki4nr on January 10, 2023, 05:51:31 PM
Not sure how you are testing for hum, you maybe chasing your tail. If you are using another radio as monitoring receiver with small antenna, you absolutely will get hum. It comes from the 60 cycle AC line modulating the RF in a
ground loop between rigs. Have a station close to you listen for hum, you may find its not there. The only way to listen with another receiver is to build a RF sampler and make sure both the transmitter in test and receiver are at the same ground potential to eliminate the ground loop.

Title: Re: Yaesu FT101E
Post by: wa1sth on January 11, 2023, 10:30:08 AM
Hum testing was not done just on a local basis.  Hum is reported on air and therefore local testing began.  This is a problem that has existed for a while and I am getting around to fixing it.  I am very aware of not building in problems while troubleshooting (chasing my tail).  I am very interested in getting rid of the hum, and I will.  Others have reported they have no hum while still others do.  Obviously there are a lot of variables.  Ideally I would love to have another 101 that does not hum to do some comparison testing with the scope.  Chokes my fix the problem but it does not answer the question of why some and not others??  LOTS of possibilities here.  I am still pursing suggestions from others.  Which I appreciate very much.  It has been suggested that it is a design issue and it could be. Then why some and not others??  ALL input is welcome.  FUN FUN FUN

Title: Re: Yaesu FT101E
Post by: wa1sth on January 16, 2023, 06:03:01 PM
Ok, I have apply two 3H 500ma chokes to the 600 and 300 volt lines.  This seems to have lower the hum to an acceptable level (55db down).  Will try to filter the 12 volt line through regulation.  Hopefully I (with the help of others) will get rid of all hum.  MANY thanks to Frank, W2SDR and Scott, W1NB.  Also
Thanks to all others for thoughts and contributions  Oh, the chokes are big and need to be used outside of the radio (that sucks)

Title: Re: Yaesu FT101E
Post by: ki4nr on January 16, 2023, 06:55:58 PM
I'm not understanding why you have to mount big external chokes to fix a problem that others like it don't have.

I know a few people that still use those radios occasionally and they have no hum, I own one and it has no hum.

The only thing I remember was in the service manual there was a Hum modification to adding a capacitor to T-12 and resistor to pilot lamp. Also a ground loop issue on the voltage regulator/ calibrater board and you cut a trace & drilled a hole to correct it. Pages 6-20 & 6-21 in service manual

Sound like your not troubleshooting the problem correctly in your particular problem radio and going with some kind of crazy band aid fix instead.

Title: Re: Yaesu FT101E
Post by: wa1sth on January 16, 2023, 08:15:05 PM
Well all opinions are good.  Many people smarter than I have consulted with me on this.  All suggestions have been pursed.
I agree with you to some extent.  Others have looked at with strong technical abilities.  A perfect solution has not been found YET.  I think you or another person who has one that does not hum should sell it to me and then I can use it as a troubleshooting tool.  I have an E and an F and they both have low level hum.  I have others look closely at theirs and they also have low level hum.  I cannot explain when some do and some don't.  The 600 volt line had 7 volt ripple (which is below the one per cent considered acceptable).  It now has 200 mv.  While that reduced the xmit hum it did not eliminate it completely.  If you have any constructive insight I would be glad to check it out.  Thanks again for any help.

Title: Re: Yaesu FT101E
Post by: ka1bwo on January 23, 2023, 11:47:47 AM
Just a thought, try using a dc source for the filament circuit on the driver stage.

Title: Re: Yaesu FT101E
Post by: wa1sth on January 25, 2023, 08:08:46 PM
First, thanks VERY much to all for comments and help.
I am reporting here the results so this is not just another "dead end" post (Which I hate).  My hum issue was being exaggerated
by my test setup.  On air it was not nearly as pronounced as I believed.   It was resolved by increasing the size of the chassis
filter caps as well as all of the caps on the regulator board. A step start is also in use to mitigate in rush current.  Now on to the next problem with this radiio "xmit overshoot".  It may not be a big issues with 3-500's but with my Commander it is.  Man, this is all such fun.  Thanks again  73's
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