eHam.net - Amateur Radio (Ham Radio) Community

Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net



[Articles Home]  [Add Article]  

New Life for an FT-101E Power Transformer

from John, ZS1ZC on March 12, 2017
View comments about this article!

New Life for an FT-101E Power Transformer

This old beauty came to me via a swapshop advert earlier this year and I gave it a good once-over, cleaning moving parts and replacing the HV electrolytic capacitors. Once it was done all worked well, but I kept hearing a hissing or sputtering sound from the mains transformer, and it quickly got very hot. On closer inspection with a variac on the primary, I noticed the heating was producing a distinctly chemical smell, so it was clear that there was some actual damage under way. This pointed to either a replacement or a repair job. Since the only source of second-hand FT-101 transformers seemed to be overseas via eBay, I embarked on the journey of a partial rewind.

The whole FT-101 series uses the same spec transformer. It has two primaries to cope with different mains voltages. It has four secondaries: 1.5V-0-1.5V (for the DC-DC converter), 0-120V for the screen voltage and -100V bias, 240V-0-240V for the HT supply, and a multi-tap low voltage winding for the tube filaments and low-voltage electronics.

My winding setup is pretty straightforward. I have a lathe that I can run slowly enough to control winding alignment with my fingers (around 40 rpm). You can see the lathe chuck at the top left. I placed a short length of 10mm steel rod into it and positioned a block of green HDPE that I had lying around about halfway along it, securing it with a 4mm bolt and a hole that I threaded accordingly. I chose the block specifically to fit into the rectangular hollow of the bobbin – you can use any material for this and fix it in place any way you see fit.

I also made a jig for mounting the wire coil, which was just more white HDPE and a 15mm rod that I had available. Any mechanism and mounting will do for this.

The main challenge in a transformer wind is counting turns. So I modified my PIC-based CW keyer (PICAxe with an LCD display) by utilizing the dit and dah paddle inputs and downloading new code to it. I made another “key” cable and connected each line to a reed switch mounted on some hot-melt-glued pieces of veroboard (see left). I mounted that assembly on a magnetic base that came with my lathe’s dial test indicator. I then took another piece of HDPE, placed a small magnet into the end of it and secured it with duct tape, and then mounted it on the winder shaft in the same way as the bobbin former. This was quite a learning experience, discovering how reed switches actually work and the way they need to align with the magnetic field (but that’s another subject).

The way it works is that as the lathe winds, the magnet end of the arm sweeps down past the upper reed switch and then the lower one. The PICAxe code figures out the direction of travel from that and either increases or decreases the turns count accordingly. This is very convenient when you have to undo windings that haven’t gone quite where you want them to. That’s when the lathe gears are disengaged and the chuck rotated by hand to get the positioning you need.

I added a feature to the PICAxe code whereby I could use the keyer speed potentiometer to set an initial winding count – I found this useful when taking a break in the middle of the 480V winding (just under a thousand turns in total).

I should add that none of the above is actually needed to wind a transformer, it just makes it a lot easier. A manual winding jig will work fine, and a bit of concentration and careful note-taking will eliminate the need for an automatic counter.

It took around half an afternoon to get the transformer out in one piece with most of the connecting wires intact – this and regular photographs would prove very useful later when piecing everything together again.

The copper band around the transformer is easily removed by melting its solder joint with a hot air gun (it’s an electromagnetic shield). It has the various winding voltages written on it, so I marked it to make sure I kept the correct orientation at reassembly.

Of course, a major challenge was still ahead – separating the windings from the core. I don’t mind saying that this is a major job and requires that the entire tranny be baked at over 100°C for a few hours to melt the varnish, and then prying the layers apart with gloved hands. So I didn’t do it. The short version is that when I took the tranny to a well-known local transformer manufacturer for a quote and advice, the owner very kindly offered to have one of his staff do it for me – free of charge. What a gentleman, exemplifying the best of ham spirit.

So below is what I was left with (along with a box of neatly piled E and I pieces). You can see how the original manufacturer used cardboard as a mounting for the crimped terminals. I cut across this carefully with a craft knife (red line) to fold the lower mains-side terminals outwards and then cut the secondary terminals away from the outer insulation layer for use later (yellow lines). I then proceeded to peel away the secondary windings layer by layer. Bear in mind that power transformers usually have the primary closest to the core and the secondaries towards the outside.

In the second picture above you can see the various layers, and how the designers used a basic cardboard bobbin. I would say Yaesu used pretty basic engineering on this given the absence of a more solid pre-formed bobbin.

Anyway, it was now time to find out what was really wrong with this component and the only way with a transformer is to unwind it until you find something significant that explains the symptoms. I unwound the outer 3V centre-tapped winding and the 120V winding – both were fine. But this is what I found underneath where the 480V winding should have been:

What a mess. The insulation and enamel have been burned well and truly to cinders, whatever paper insulation was there had been carbonised (creating shorts), and it clearly happened over a considerable period. This winding needed to be peeled back completely. After stripping it back and carefully counting the turns, I reached the low-voltage secondary (on the right), and this seemed to be in perfect condition. I decided to wager that I’d found the only fault in the transformer and cleaned and prepped this layer with a solid coat of transformer varnish to smooth the surface and provide extra insulation against the 480V that will be generated by the replacement layer (third picture above). Once that dried for a day, I gave it a few layers of polyester tape as a bed for the new HT winding. You can get the idea here (although this picture is for the 120V secondary winding):

This is the famous polyester “yellow tape” - a high-temperature variety used by transformer manufacturers. It has a dielectric strength of over 4kV and is happy up to 130°C.

It’s good practice to try and align adjacent turns in a winding. The problem is that once you’re a few layers up the surface gets bumpy and the placement of each turn is difficult to control. The only real impact will be on reliability, in the sense that turns crossing over each other are vulnerable to compressive weakening and possible shorting with the ones underneath – so I figured that as long as we weren’t having wild deviations across the winding it would be low risk.

I had measured the various wire thicknesses with a micrometer and the 480V winding had used 30SWG, the 120V used 35SWG and the 3V had been wound with 25SWG. Luckily the 3V winding was only six turns, so I was able to reuse its wire. However, I had to buy a roll of 30SWG for the HT winding and then used the same for the 120V secondary.

The initial 480V HT winding requires eight layers of around 120 turns each (this transformer runs at about 2 turns per volt), each alternating with a layer of insulation. I initially used Kapton (a high-temperature insulation tape) on the lower layers, but found it very unwieldy with a tendency to tear, curl and stick on itself. So I settled on the yellow polyester tape for the remainder (which is also a lot cheaper!).

Once all windings were in place I covered the outer layer with masking tape and more polyester tape to mount the terminals that I’d kept aside. I was then able to scrape, tin and wrap each secondary wire end to its respective terminal. A series of continuity checks and resistance measurements confirmed that the connections were correct.

Now the big challenge – final assembly of the core into the windings. This is just a slow process of interleaving E-sections from opposite sides of the winding and then inserting the I-pieces in the gaps that remain. You can see from this photo how they should be arranged in layers, the left pair on top of the right pair, repeating until all are in place.

A few solid taps with a rubber mallet gets them all properly aligned. The only part that requires patience is getting the last few sections squeezed in, and even then I lost about 5% of the core weight because the fit was just too tight. I don’t know whether that was because the former got distorted in the winding process or because there had been warping of the sections during disassembly. From what I’ve read on the internet, some loss of core material is inevitable unless you have the right sort of assembly jig.

A quick reflow of the solder on the ends of the copper band, four new bolts through the core and she’s assembled. I insulated the bolts from the core by wrapping them in polyester tape to prevent them shorting the laminations and increasing eddy currents.

I then put it on the variac and measured secondary voltages with a low input, eventually winding it up to full mains once I was confident nothing was misbehaving. All was good. More importantly – quiet as a mouse, no mains buzz to be heard at all, which is something of a relief since I hadn’t varnished it yet.

I then put it under a more demanding test with a 100W soldering iron on the 480V winding but with half mains on the input. An input of 118V yielded 250V on the soldering iron plug, which means that our 230V mains will yield 487V when under load – that is close enough for the FT-101 power supply. Also, there was barely any discernible warmth from the transformer (and no hum), which is a good sign.

So – mounting brackets on, time to install and test. This was quite a labour because the FT-101 cabinet is quite cramped around the power supply. This is where the photos taken during disassembly were extremely valuable. Powering up slowly via the variac, all functioned correctly. The rig needed a basic alignment, which I did, and aligning the transmitter on all bands put the PSU through its paces. It was only after an hour of dummy load tuneups that the transformer became just too hot to keep a hand on for any length of time (which is around 50-60°C).

So I call this venture a success. What would I do different next time? I think I need a mechanism for better control of the winding path around the bobbin, and this should be possible using the power feed of the lathe on a low thread pitch. But mainly, I would make some bobbin endflaps with spacers to place the windings better at the edges, preventing new turns from slipping off.

I must say I never thought I’d wind transformers, having assumed it to be a more complex process. But it’s actually very straightforward and requires only a bit of basic ingenuity. And patience...

Member Comments:
Add A Comment
 
New Life for an FT-101E Power Transformer Reply
by N1JAO on March 12, 2017 Mail this to a friend!
Thanks for posting this! Such detail and a fantastic looking finished product.

Bravo!
 
New Life for an FT-101E Power Transformer Reply
by KC8Y on March 12, 2017 Mail this to a friend!
Boy, does that bring back my memories :) Nice article; I didn't perform that many major changes to it.

That rig was my first major investment in radio; loved that radio
 
New Life for an FT-101E Power Transformer Reply
by K8AXW on March 12, 2017 Mail this to a friend!
As another said, "Boy, does this bring back memories! Many years ago I decided to build an 8 digit frequency counter based on a construction article in a QST magazine.

It was my first attempt at working with digital electronics; my first modification of an existing project going from Nixie tubes to 7-segment readouts; my first attempt at making my own PCBs; the main board had to be a double-sided board which used 26 TTL chips. It turned out perfect.

And since I was poor as a church mouse, I found it necessary to wind my first transformer because I couldn't afford any available commercial unit. The transformer rewind was an education in itself. It worked perfect as well. Over 30 years later it still works with no heat and no hum.

Thank you for the very interesting and well written article; the proof that homebrew is still alive and someone still has the stones to attempt such a project as this. It gives one a great feeling, doesn't it?

And finally, thank you for bringing back happy memories of another era of my life.
 
New Life for an FT-101E Power Transformer Reply
by KD5FPO on March 12, 2017 Mail this to a friend!
The FT-101 was my first big-rig too. I loved it so much that I still have it.
 
Great Stuff…! Reply
by VE3CUI on March 12, 2017 Mail this to a friend!
Kudos & congratulations BOTH, John, on an excellent article, & a successful "fix" for your dilemma there…

VERY WELL DONE.
 
RE: New Life for an FT-101E Power Transformer Reply
by WB4ILP on March 12, 2017 Mail this to a friend!
Hi John,
Very nice article and Thanks for posting. I'll never throw away another transformer. I love buying junk consumer electronics at yard sales for a buck or two
to salvage components. I can't wait to rewind a transformer for a project.
Jim WB4ILP
 
RE: Great Stuff…! Reply
by KB6QXM on March 12, 2017 Mail this to a friend!
Even though I have owned over a hundred radios in my life, I would have to say that the Yaesu FT-101B was one of my favorites. I had the radio in Pristine condition with the external VFO, 2-meter transverter and the Speaker/Phone patch accessories.

The only thing I was missing was the 6-meter transverter and the frequency counter accessory.

Nice radio! Good looking radio, well functioning radio. I miss it!

I have owned the predecessor which was the FT-DX100, which was nice, but did not measure up to the FT-101 series. I still own a FT-757GXII, but it is a different radio, different technology and a different era.

SDR for me from now on.

73
 
New Life for an FT-101E Power Transformer Reply
by AA4LR on March 13, 2017 Mail this to a friend!
Inspiring!

I have a 25 A power supply whose transformer developed a hum and eventually gave up the ghost when the primary winding opened. I've idly given thought to trying to re-wind it. After reading this, perhaps I will.

I have fond memories of the FT-101EE, as I borrowed one from a friend for a few months back in 1982. Somewhere along the line, I managed to obtain one that sorta works on receive, but transmitter operation is intermittent. I think the main T/R relay is shot, and apparently these units are no longer available.
 
New Life for an FT-101E Power Transformer Reply
by KB2DHG on March 13, 2017 Mail this to a friend!
WOW! GREAT ARTICLE! I love my FT-101EE and now I know there is someone out there that can repair the transformer if mine should go! wink wink nudge nudge...
But really, I commend you in this endeavor, Nice to know there are still some true HAM's around!
 
RE: New Life for an FT-101E Power Transformer Reply
by K3LRH on March 13, 2017 Mail this to a friend!
Very nicely done, John. Congratulations and thanks. 73
 
RE: New Life for an FT-101E Power Transformer Reply
by ZS1ZC on March 14, 2017 Mail this to a friend!
Thanks, it was a worthwhile venture. Happy to share the experience.
 
RE: New Life for an FT-101E Power Transformer Reply
by ZS1ZC on March 14, 2017 Mail this to a friend!
I'd happily help out, Lou, but you'll find the postage to me and back is a bit dear... :-)
 
New Life for an FT-101E Power Transformer Reply
by W3TTT on March 14, 2017 Mail this to a friend!
Thanks for the post - I am book marking this for future reference.
Joe W3TTT
 
RE: New Life for an FT-101E Power Transformer Reply
by ZS1ZC on March 14, 2017 Mail this to a friend!
Thanks, Joe. I reckon there's a wealth of experience out there - the guys just need to write it up. Now with digital cameras and cellphones it's easy to make a record of the work.
 
RE: New Life for an FT-101E Power Transformer Reply
by K4KRW on March 15, 2017 Mail this to a friend!
Thanks for documenting this and posting it. Very interesting.
 
New Life for an FT-101E Power Transformer Reply
by KB3SID on March 15, 2017 Mail this to a friend!
Great work not sure if I could pull that off. I have the FT-101zd and was wondering if you or some of the readers know off online instructions on how to replace the caps as you did for your transceiver.
 
New Life for an FT-101E Power Transformer Reply
by KB3SID on March 15, 2017 Mail this to a friend!
Great work not sure if I could pull that off. I have the FT-101zd and was wondering if you or some of the readers know off online instructions on how to replace the caps as you did for your transceiver.
 
New Life for an FT-101E Power Transformer Reply
by KB3SID on March 15, 2017 Mail this to a friend!
Great work not sure if I could pull that off. I have the FT-101zd and was wondering if you or some of the readers know off online instructions on how to replace the caps as you did for your transceiver.
 
New Life for an FT-101E Power Transformer Reply
by KB3SID on March 15, 2017 Mail this to a friend!
Great work not sure if I could pull that off. I have the FT-101zd and was wondering if you or some of the readers know off online instructions on how to replace the caps as you did for your transceiver.
 
New Life for an FT-101E Power Transformer Reply
by KC8YXA on March 15, 2017 Mail this to a friend!
Very good Info I often wondered i I could redo a transformer. But after seeing and reading about it I found That I will send it to the a Pro.
 
New Life for an FT-101E Power Transformer Reply
by KE4ZHN on March 16, 2017 Mail this to a friend!
Nice work! It's not often you see anyone rewind their own transformer. Congratulations on breathing life into an old classic.
 
New Life for an FT-101E Power Transformer Reply
by N6AFV on March 16, 2017 Mail this to a friend!
That is amazing work, and shows technical ingenuity at it's best. Congratulations!
 
New Life for an FT-101E Power Transformer Reply
by KG5RJS on March 19, 2017 Mail this to a friend!
You lost me at "I have a lathe."

Seriously though it's nice to see vintage radios restored and kept on the air.
 
New Life for an FT-101E Power Transformer Reply
by G4DWV on March 25, 2017 Mail this to a friend!
Hi John (ZS1ZC),

Thank you for a fascinating article. Once I have written this I will download it for local storage.

Kudos+++ for even attempting to do such a project* and getting so far with it.

*It was only the other day that I was watching one of those YouTube vids that show people doing things amazingly quickly; like packing playing cards into boxes, cigarettes into boxes, chopping things etc. Once of the things was a room of girls winding transformers (amazingly quickly, natch) by hand.

Mni tnx es 73 de Guy G4DWV/4X1LT
 
Email Subscription
You are not subscribed to discussions on this article.

Subscribe!
My Subscriptions
Subscriptions Help

Other Radios Articles
Can We Have a Quiet Shack?