Zenith 707 - Rewind an Output Transformer & Change the Turns Ratio

[@TheRadioShop]

Don, you are the master of transformer rewinding. Great video as always my friend.

[@RestoreOldRadios]

Thank you Buddy. I don’t have it mastered yet, but I have found them to be rewarding when things go as planned. Hope you’re doing well. Best, Don

[@jimnewman5596]

That was a great video on matching the speaker impedance to what the tube likes, great craftsmanship on the output transformer Don.

[@RestoreOldRadios]

I appreciate your feedback Jim. Hopefully others will find it easy to follow as well. Best, Don

[@greggsvintageworkshop8974]

Brilliant Don, simply brilliant! Excellent, detailed and amazing attention to detail.

[@RestoreOldRadios]

Much appreciated Gregg. Thanks for watching. Best, Don

[@hestheMaster]

You made that transformer rewiring look deceptively easy. I guess that must come from a lot of practice on doing it right the first time. Steve

[@RestoreOldRadios]

Thank you Steve. I’ve done a few and with the secondary accessible, it went as planned for a change. Best, Don

[@saturn5tony]

Wow I never imagined repairing my own xformers Don, man that was great!

[@RestoreOldRadios]

Thank you Tony. It’s fun poking around in them; a learning experience for me too. Best, Don

[@neilwilder6744]

A tip: you can watch series at flixzone. Me and my gf have been using them for watching lots of of movies during the lockdown.

[@giannilachlan9081]

@Neil Wilder yup, I have been watching on flixzone for since december myself =)

[@rodrigoluka453]

@Neil Wilder yup, I have been using Flixzone for years myself =)

[@Backtothefutureradios]

Another great demonstration Don! Thanks for taking the time and sharing! Take Care-Larry

[@RestoreOldRadios]

I appreciate it Larry. I hope you are doing well and getting caught up on your rest and other... Best, Don

[@anthonycarulli6491]

Great work as usual! It amazes me how involved and in depth you get to a restoration. I do learn a tremendous amount from your videos.

[@RestoreOldRadios]

Anthony, much appreciated. Thanks again for reaching out. Best, Don

[@rciancia]

What a fine job and demonstration Don.... bravo !!!! Love it.. thanks

[@RestoreOldRadios]

Thank you Ron, I really appreciate it. Best, Don

[@fibberscloset498]

Very nice, Don. It's good to know that you can reduce the gauge a bit if necessary.

[@RestoreOldRadios]

Thank you. I hope it works out and sounds okay when I get it back together. Thanks again for watching. Best, Don

[@sissonscott]

Great work, enjoyed the video as usual.

[@RestoreOldRadios]

Thank you for watching and your feedback. Best, Don

[@K1ZEK]

Very nice job, thanks for taking the time to make a video. 73 Leo

[@RestoreOldRadios]

Leo, much appreciated. Thanks for watching and reaching out. Best, Don

[@KetkAiball]

Very good job Don, as always. Have a nice day. Ketk (From España).

[@RestoreOldRadios]

Ketk - thank you my friend. Best, Don

[@waynethompson8416]

Very much appreciated the video! I still don't understand the bit about the calculations for impedance and turn ratios, but maybe if I watch it several more times I will. I have been wanting to create some Toroid transformers...both for power and for audio output.

[@cjay2]

Wayne, the impedance ratio is the square of the turns ratio. So he worked backward from the requirement of the vacuum tube - 6000 ohms, and calculated the impedance of the loudspeaker as well. Therefore he knew the impedance ratio needed. The square root of that gives the required turns ratio. Just not sure why he is changing anything if the speaker and the transformer are original. I probably missed something.

[@RestoreOldRadios]

Wayne - thank you for watching. Cjay's reply is spot on, so you can see how I backed into the numbers. I don’t think the output transformer is the OEM part and had been replaced at some point during its life. Best, Don

[@VintageElectronicsGeek]

Impressive Don! You should market and sell the turns ratio device...Id probably buy one. :) ~Jack, VEG

[@RestoreOldRadios]

Thank you Jack. It’s an easy build and takes a couple of hours; would make for a fun summer project. Best, Don

[@kenf8563]

Very impressive, Thanks for sharing.

[@RestoreOldRadios]

Thank you Ken. I appreciate you watching and reaching out. Best, Don

[@tinkeringwithelectronics]

One thought comes to mine......."Mr. Wizard"!

[@RestoreOldRadios]

LOL - far from a Wizard, but it was cool to be successful re-engineering this one. Thanks again Josh. Best, Don

[@dhpbear2]

Be kind - rewind!

[@RestoreOldRadios]

Good one. Hopefully it will work out and if not, I’ll pull out the universal... Thanks for watching. Best, Don

[@olipito]

That was really cool!

[@RestoreOldRadios]

Thank you. All the best. Don

[@chetpomeroy1399]

The smaller gauge of the wire, to accommodate for the larger number of turns, might have little to no effect on the operating requirements of the audio output tube.

[@RestoreOldRadios]

Chet - I always value your feedback and taking time to share your knowledge and experience. Thanks again. All the best. Don

[@vladnickul]

what is that "aparatus" do you have a schematic /program for it? it looks miraculos!

[@RestoreOldRadios]

I assume you are referring to: Build a Transformer Turns Ratio Meter w/ Arduino kzbin.info/www/bejne/fKrHm5Ktjdeebrc If not, please let me know. Best, Don

[@tucker934]

I have a question, mind you I’m still quite new too this, but what about the frequency response of the coupling capacitor’s?

[@RestoreOldRadios]

Sorry for my belated response, I’ve been away from YT until recently. Capacitive reactance does come into play; check out the following site at: www.sengpielaudio.com/calculator-RC.htm You can use the online calculator to calculate Xc, which will calculate the AC capacitive reactance in ohms for any value capacitor based on the frequency of your choice. Hope this helps. Best, Don

[@tucker934]

⁠​⁠​⁠​⁠@@RestoreOldRadiosThank you Don! Hope all is well! enjoyed the video, and learning! Thank you for your time making this video, there really isn’t much out there showing this! Love how you tackle these quite complex issues you come across! All the best, Anthony

[@RestoreOldRadios]

@@tucker934 Anthony, thank you for your kind words. Seems like every project for me provides many learning or relearning opportunities. Thanks again and all the best. Don

[@tucker934]

@@RestoreOldRadios I’ve learned so much from You, and many Other’s! I’d say I’m very very new to workings on, “ I’d say these quite unique devices” there’s just something about electronics that I find quite unique, and vacuum tubes are that much more! I love solid state devices too! I restored my first AC/DC not to long ago, and repaired one that was already recapped a year before that! I’m only 24, and fell into electronics when I was 13 a long with many other different “subjects” like HVAC, and mechanical stuff. Your videos, and Many others Taught me how to be much SAFER!!! I can’t stress that one enough as I’ve been shocked by a charged CRT that I “assumed” was discharged correctly! And a few other devices that I learned the hard way you can’t just touch things with in! Thank You very much for your Work Don! Anthony

[@theoldbigmoose]

Don could you help me understand core stacking in the transformer? In power transformers, I see the E and I laminations alternated. In this audio transformer, they were not intersperced. Was there a gap between the E and the I section? All the best, Dave

[@RestoreOldRadios]

Dave - my knowledge is limited in this area as this was my first time rewinding a power transformer. There were no gaps between the E & I laminations other than me applying MG Chemicals 419D Acrylic Conformal Coating, Clear Finish, Aerosol to the laminations, which should reduce Eddy currents making the transformer more efficient by reducing losses. The overlapping of the E & I laminations should reduce flux leakage, again making the transformer more efficient according to the engineering white papers I’ve read. Sorry I can’t expand more beyond my response. Thanks for reaching out. Best, Don

[@theoldbigmoose]

@@RestoreOldRadios Thank you Don for the reply! Every little bit helps. I was going to ask on the conformal coating, so that was a great addition. Magnetics have always been a hidden art form to me! ... still learning though, after 3 retirements... 🙂

[@RestoreOldRadios]

Here’s a good read: worldradiohistory.com/UK/Bernards-And-Babani/Babani/118-Practical-Coil-Construction%20Bernards_60.pdf

[@theoldbigmoose]

@@RestoreOldRadios Thank you again Don, what a great resource! Those old handbooks are the best! I am going to read cover to cover over the Christmas holiday!

[@cjay2]

Don, just wondering why the turns ratio isn't already a good match for the tube and speaker. Did they miscalculate back then?

[@RestoreOldRadios]

Cjay - a great question. I’m guessing the transformer is a replacement and not the OEM. I looked around and haven’t found any other examples to validate my theory. If you run across something, please let me know. Thanks again for watching. Best, Don

[@cjay2]

@@RestoreOldRadios I would trust your guess that the transformer has been replaced, seeing as you measured the actual voice coil impedance, and the transformer isn't correct as measured. Rewinding the secondary and using the smaller guage was brilliant, and no one's gonna be playing that radio at a high volume anyway, to stress the smaller guage (besides the more efficient match anyways). All in all, it'll be a good restoration and an enjoyable learning experience for all.

[@jdmccorful]

For me, great math explanation. Thanks for the look.

[@RestoreOldRadios]

I appreciate your feedback John. Best, Don