I have been in electronics since 1975, These videos and your knowledge is a tremendous asset for people who love electronics. I have a 1500 HF amplifier to repair, watching these videos gives me more knowledge to start the repair. Thanks Jerry

Paul I really like how you always make comment at the beginning and warning to those working on high voltage equipment. I don’t see very many doing that. To me, it’s a must do. I really like your style of doing things, it really helps a lot of new people getting into this field or hobby. Always safety first. Thumps up !!!

I wish I knew what he has forgotten. Excellent video. Great learning tool.

I'm been a radio ham for 40years. I had a TL922 for 25years without a hitch, orgianl Imac2X300Z installed. Sold it to me friend, he had it for 5years at least. He sold it to a University in AR USA. Sent it Fed Ex [Air] did not remove the tubes! Arrived in AR safe and sound. The university switched the TL-922 on, all fine. As far as I know, it's still working today!! Thanks for taking the time to provide these videos. You explain things very well. Keep up the good work MCL! Roger-G4SEF UK

Thanks Paul for a no-nonsense learning experience. The vid is packed with a lot of info. I had this issue in the amp last week. The arc shorted the Zener and C3. Since I have a 1A fuse in the primary of the filament transformer, it of course opened. I installed the IRFP27N60KPBF and also two diodes IN4007 in the Gate as you explained in the vid. I have a bias of 90ma in CW and 170ma in SSB. The voltage at the Drain is 6.3v idle and at TX it goes up to 7.4v. Works fine so far. Output on CW is about 600w, and on SSB peaks are over 1000w. I drive with 90w.

This is exactly the type of video we need..... common gear we use in the shack....... I really like all your stuff esp the home brew test gear ones

Another great video, always look forward to these.Thanks!

I was given a loan of one of these a few years ago when I very new to Ham radio. I didn't use it because I didn't have enough confidence to use such a high power device. After seeing your video I'm glad I was cautious as I'm fairly sure it was unmodified. This is certainly something people should be aware of when using newer transceivers with older generation amplifiers,

I was thinking about buying one of these amplifiers and I didn’t realize all the stuff with you explained but I don’t I have solid-state transceivers and I don’t want to mess so much so thank you for all the good information I enjoy watching you more

Mr. Carlson, you videos are so interesting, I lose track of time watching. Really appreciate you taking the time to make them and I find them very educational. 73 Brian

Hi Paul, what a great video! It reminds me that I had a repair to do 3 years ago where exactly this Amp killed a Transceiver. I did a very similar interface to yours and the radio works after that mod without problems. But I have to admit I have nearly forgotten about this problem. So very good that you did this video and put it back into focus for all of us! Thanks and 73 Peter

Thanks Paul , I am ready to build this modifications with this beautiful amplifier 👍

Your videos are just amazing! I have learned so much, so quickly. Thanks for sharing it will all of us.

Just found this video, after buying a TS 890 and having issues...THANKS! Most likely saved my radio, as I started having issues.

First class video! I really enjoy watching how you resolve issues.Keep the great videos coming! Tony

Never a dull moment Mr Carlson. Thanks for sharing your knowledge great video.

Great video. Nice to see a big power amp on the bench. We use Wenol to polish our table silver.

Thanks for another great video. As an old safety officer, thanks for the warnings. The voltages in these amps will kill, and strange things happen around HV. I enjoyed the video very much. Please keep em coming.

I fully enjoy all your videos Mr Carlson I watch a lot of repair videos on You Tube but for me you are the best of what you do your a very very clever man please keep sharing your videos.

Outstanding VIDEO! Please continue your outstanding work.

Smiling! Just starting watching your videos and enjoy them, also know the odds of you reading this on an old post are slim to none but sometimes you just got to confess to messing up to fell better. Smiling. I always thought the TL 922A was a good looking Amp. Little over a year ago I bought a ICOM 7300. I used the send jack on the back to key my Clipperton L. Well one day a friend of mine told me the keying circuit in the Amp was more than the keying circuit in the 7300 could handel. Been using it that way for over a year and seemed ok to me. So I built a external relay like they show in the manual and in the process I melted the farrite EP102 on the RF Unit Board B8306E, and the send quit working as one would expect. Wish I would have never done it. Radio still works on transmite great and pretty much everything else works, but the receive audio has a hollow sound, kind of like a weird filter or something hard to understand sometimes. I have reset it but no help, not sure what else I hurt to get that sound on receive but I did something. When you talked about the relay and tapping it to try and free ii up, I thought wonder if that could be a problem not letting it go back into full receive mode. The parts are so small, I suppose it needs to go back to Icom but waiting till after the Christmas shipping stops, people say thing get damaged more this time of year. 73 Ed

My TL922 just arrived FEDEX from Jupiter Florida. I have always wanted one of these. I am restoring a total Kenwood Station based on the 520S and have all of the pieces and extras. What a beautiful piece of cosmetic design as well as performance. The fact that I found this at the time the AMP came was fortuitous. (DA-DA-DA Twilight Zone Theme)

Really glad I watched this before I placed an offer for one on Ebay! Also good to bare that interface voltage in mind before I buy any valved amp.

Great looking amp i have a 30l-1 to scarred to connect it to my 7300 even with the relay kit i got of ebay i will keep it matched for my kwm-2 just too much voltage on the relays,was offered one of these tl-922,s at a ham fest THE GUY TOLD ME IT WILL MATCH UP WITH NO RELAYS TOO A 7300, LUCKY I WATCHED YOUR CHANNEL.thanks a bunch.

Very good video - very instructional for me as I just got my 922a and replaced the Dead Filament Transformer.

Amperex tubes!! Good job, great information. I had my sb 200 tube Filament shorted and blew the grid caps and bandswitch contacts bad. Parted it out...

Those tubes look like something out of a science fiction film from back in the 40's Completely awesome.

These are the two "Must Have" mods for any of the 3-500Z equipped HF Amps. Well researched and well written, Paul. I've used optocouplers for this in the past, but I like the MOFET idea also. It may even be a bit more robust. This appears to also give you a Zero Signal Anode Current (ZSAC) turning the tubes off between words in SSB. This lowers overall temps in the amp by a bunch, and this amp needs all the cooling help it can get! Great Job, Paul! Jim

I use an Ameritron ARB-704 to handle the T/R switching. It is a nice little interface between old HV T/R systems and new 12VDC radios. People bring me tube amps that are HV T/R switched so I like having a external box to protect my radio. The TL-922 power switch gets pitted badly. I tore it apart and flipped the contacts around to use the new end. I bought my amp used. The tuning caps had the edges melted! I had to grind off the melted and mushroomed aluminum ends. Then clean all the mess I made up. I have modified my TL-922 for full QSK operation. New biasing, true grounded grid, etc. Works well.

About the most complicated thing I've done in this domain is replace some parts on my pinball machine's power supply board to correct a condition of no voltage on the -100v rail, and I had some help with that. That being said, I find your videos quite informative and entertaining. Cheers!

Absolute genius, thanks for sharing...

I've got several tube type RF linear amps of which the TL922A is a favorite. I believe some of the best mods are: [A] Vacuum Relays for the RF input and RF output with 12VDC coils. [B] 1Amp fast fuse on the HV DC (Plate B+) just ahead of the Plate chokes. [C] "Hairpin" VHF chokes for parasitic suppression on each tube Plate. [D] A 3" Cooling fan inside the XFMR side of the fan-box situated to draw heat from the power supply and especially its' transformer. I regularly use a clean-dry paintbrush and vacuum cleaner to remove any dust from the amp, especially the RF Pi network components. I'm able to regularly obtain 2.1KW PEP from my TL922A in SSB mode but, I like to use it at no more than about 1.8KW PEP to improve longevity. BTW: I'm an equipment engineer from the semiconductor industry and own & operate a technology business that rebuilds electron microscopes and X-ray microscopes for industry, having a customer base around the globe and the US.

Very Interesting and Informative. The methods and steps you show can be applied to all manner of fault finding/repair so I'm particularly keen on learning the process you follow - and hopefully fix simple faults with my old radios! I have an old Yaesu amp 2100Z - one of the most popular amps ever produced. There are a heap of safety mods for this amp and a video regarding doing these would be highly useful and watched by many. Thanks from South Australia

Hi mr Carlson many years ago I had the similar problem with my yaesu ft 2100 amplifier ,fortunately all I had to do is purchase a relay box from yaesu The box is called FRB-757 and I have never had any problems with relay switching since you always make very informative interesting video,s thanks again . Keith vk4ckc.

Great information presented in a manner easily conducive to learning, as always. Thanks for another great video.

Good to see someone who really knows what they are doing around this stuff! There's a lot of pseudo techies out there who really don't have a clue. Great video!

Great video as always, Paul. I built a similar "soft key" circuit for my SB-220. One thing, though if I may. The 3-500Z is the name for the original tube with the standard plate. The graphite plate tubes are 3-500ZGs. Just for clarification for those who are tube shopping. Thanks!

A strip of paper soaked in contact cleaner is the best relay cleaner I've found. The paper falls apart before any metal is even scratched, but it will remove oxidation and carbon.

most hams don't like the 922 because they have a lot of problems,Myself,I fixed up a heathkit sb 1000 with a single 500z.I love it.Great video as always.73 from Ronnie.kn4u

Awesome job as usual. I was waiting for you to connect it up to your radio and give it a trial run.

Great info working on a 922 presently. Txs

Thanks for the info! Never know when it'll be needed!

I love my TL-922A........I pull cool air through it with an external blower mounted outside the shack to keep it cool and noise free in the shack.

Thanks for this video! I have 2 of these beauties and they have served me well but I think the bias mod is great, will apply it to both my units as the original circuit is definitely a weak point. Thanks for your time and dedication! 73, Rudi de ZS6DX

Thanks for Mr Carlson's Lab multiply video's on KZfaq

"Knocking on the side of a shorted transistor will not work as well"...ROTFL! You are a funny fellow Paul!

Wow you are the best. The way you explain things is so helpful. Please keep up the good works.

Thanks, I've worked on a few Heathkit amps and Dentrons and have heard a few Hams complain about trying to work on this Kenwood amp. Most of the complaints were that the components in this amp was cramped and hard to get to for servicing.

Hello I enjoy hearing your explanation is continuous and understandable and a lot of knowledge I just enjoy tagging you

Great video, however, I was hoping to see this product demod. It looks very cool. Thanks for your videos.

Love your videos. I am a safety Inspector for the mining industry and deal with high voltage daily.(12,470). I can't commend you enough about your safety warning. M a y I suggest a video just on safety when working on amps. Particularly making sure it is de-energized in case bleed resistors are open by shorting to ground. Thanks for your videos please keep them coming.

The TS-2000 Kenwood has an old style reed relay in the TX keying ciruit, so its not nessecary to do this modification, but having said this I did this many years ago so its done and forgotten about. Grounded grid, same as Heathkit, Collins, Drake, and several others. Also its has a tuned input design so you are tuning the input as you match the load and plate.

I use an old 9.6 volt Makita cordless drill with the torque setting turned way down, as low as it will go, on the high speed gear setting (to reduce the torque even more). It simply ratchets & rattles those set screws loose, without using very much torque, much like an impact wrench. It works a real treat doing that. It also does a great job backing roll pin punches that are jammed into firearms really tight, out of a gun without breaking the punch pin off. Just chuck the hex shaft of the punch into the drill, hold the chuck so it won't turn and let the drill rattle the punch, and it backs it right out of the gun. That was actually how I discovered it would work on those plate cap connectors on transmitting tubes, and it does,.... extremely well. Maybe use the pliers too, but there is so little torque when that setting is backed off as far as it will go. It is a very gentle but extremely effective very low torque impact type action. I have had to use it with screw terminals on Japanese made pressure sensors in process & automation instrumentation too. When those are assembled they use a constant velocity clutch actuated screwdriver, which really rams the screws in super tight. You can easily destroy the screws and damage or destroy a brand new $26,000 sensor.

Brilliant Video Paul. I just so happened to of acquired one of these amps for my TS-830S Station that I am building. Thanks for the priceless information.. VK4JK Jay Down Under.

your welcome, on a entirely different subject, your Firebird sounds unreal- that is music to my ears. great sound coming through your camera.

Incredible.!! Thank you

This seems like a very well built amplifier. Why did they not spring the extra money on good fans, or even a small blower? Even a small "computer" fan under the tubes inside the chassis blowing up through the pins should help them greatly. That's the way the PL175 A's (4-400's) are cooled in my Johnson Invader 2000. This video makes want to build an amplifier. You should do a video on how to place component on a chassis using a schematic without the project without it being the size of a refrigerator! It takes real talent to take what's on paper on bring it into fruition! Thank you! 🙌

Years ago I built a Heathkit SB220 amplifier. Things went well during the kit building. When I got finished with it, it was time to fire it up and test it out into a Heathkit Cantenna dummy load. I got plenty of RF through bands 80-15. On 10 meters I got only the power the Kenwood 820 put out and nothing more. I checked and re-checked all the wiring but gave up and took it to the local Heathkit store. The store manager told me to bring it back to the test bench for testing. The technician set it to 10 meters with a wattmeter to a dummy load. Instead of tuning up the radio in steps as you did in those days he cranked the radio up to 100 watts and started twisting the tune and load controls on the ampflier. The two 3-500Z tubes started to get red hot and then white hot, then the parasitic chokes on top started to smoke! I told the manager to have him stop as he was burning up the ampflier tubes. At that time they were $ 180 each! He told me the repairman knows what they are doing and we sell the kits in front and that is all that counts. After several letters and phone calls I got two new tubes and somehow they found what was wrong with the amplifier. When asked they did not know. I had build a number of Heath Kits and about half of them had mis-labeled capacitors or errors. It’s no wonder some people call them Greif Kits. I am still running the amplifier to this day and that was 37 years ago.

Thanks for the interesting video. Looking forward to more.

great video, thank you for the great video, wished you lived close to Chattanooga, i would definitely let you look at mine, Thanks again

Your videos are amazing, thanks.

Very nice work Paul.again

Another great Video Robert. Really enjoy them. Regards, Jim

LOL you ought to see my TL-922. I have the Trio version. ie., it has 28Mhz. I bought it used. The variable capacitor had melted ends. I actually had to use a Dremel to remove the mushrooming on the ends of the capacitor plates. Flash over is bad. Lost a tiny bit of capacitance. But it fixed that problem. I also now have full QSK with a vacuum relay. And blue LED lighting. Oooo.. Many other mods. Works great now.

Love my 3-500z's. I have a amp supply LK550 with (3) 3-500z's and a 1.75ccs peter dahl transformer. 65lbs of 3300 volts.

I used an optocoupler in my buffers to prevent damage in case of a short circuit

Very cool stuff! I always I find my self with a reading list every time you post a new video >_

Subscribed!!. Like the video format and love the detailed explanations. I came here merely on the back of some research into the TL922 before I buy. Already have a Yaesu FL7000 Solid state linear which is great for the 400w limit in the UK however as more transistor amps come to the market place the older Yeasu FL2100Z, TL922 and Heathkit SB220's valve amps which were very common years ago but expensive!, are making it to Amateur radio rallies and getting considerably cheaper. With that said the price of the 3-500z is still quite expensive (not as much as 2SC2652 Planar transistors however if they are not abused they should last 20 years and at about $1200 to replace all 4... the amp is pretty much written of if they all decide to fault at once!!!) hence looking at an alternative if my FL7000 bites the dust. I am leaning heavily toward the TL922 after this video. Thanks, its very well received across the pond.73 dit dit PS: the Motorola MRF448 is apparently an equivalent to the 2SC2652... however I think valve is still the way to go after seeing this video.

i always replace zener diodes over to 1n5408 then fuse bias to just over max plate current with a 50-100k resistor across the fuse holder .. this is usually fine for US tubes due to low bias voltage requirements .. but if using some of the Russian tubes there usually 30+ volts zener with a nice pass transistor like your setup cool video as usual

That's a lethal unit. WOW!

Thanks for sharing Carl!

I ENJOY WATCHING YOUR RESTORATIONS OF ELECTRONIC EQUIPMENT! HOW DO YOU MANAGE TO HAVE KNOWLEDGE IN EVERY FIELD OF THE ELECTRONICS WORLD. I MYSELF HAVE AN A.A.S. DEGREE IN ELECTRONICS, AND BEING 70, I HAVE EXPERIMENTED WITH ALL KINDS OF ELECTRONICS SINCE ABOUT 12 YEARS OLD. PLEASE GIVE ME MORE INFORMATION ON HOW YOU HAVE LEARNED SO MUCH ABOUT THE FASCINATING FIELD OF ELECTRONICS!

Nice job. Thanks for the video!

Really good stuff. Thanks for all the info. Carl

I love the 922s I have a amp supply LK-550 with (3) 3-500s

great stuff, thank you ...

Very well informed teacher, explained clearly. Hope to see more video's of the kenwood Tl 922. Thank You!! Awesome Job !

I like when you warn us about dangers. Please, colud you make a vid explaining ways to avoid risks, electric shock...preventive measures

Hi; My Name is Cecil AJ4MT is my call and have been an extra class operator for some time. And been an amp builder and repair tech for over 30 years. That amp was built as a companion for the Kenwood TS 530 and 830 both of which were tube type final radios. As a matter of fact all amps from the 60's and 70's all had 110vdc relays. they used the same 110vdc for the alc voltage as well. 12vdc relays didnt come on the market till about 1980. All 3-500z amps from the 6o's had 110vdc relays Heathkit Sb200,220,221 Kenwood 922 and 922A Yeasu FL 2100B Collins Amps Also Henry Amps easiest way is to make a slave relay from a 12vdc transformer a rectifier and cap and a 12vdc relay SPST have your radio key the 12vdc relay that brings in the 110vdc relay at least thats what I do

Boy that is a compact design, I would opt for a little more room in a case, no wonder it flashed over somewhere, and your right, I don't see how the tubes survive with that fan, especially with that RF capture grid right in the stream. The plate transformer looks really small, I wonder how much the voltage swings when during high plate current? Why would they use 116 volts on the amp relay? I bet that coil spikes pretty hard when it's cut loose and I see why you would use a zener to capture it? I'm going to hang on to that diagram, looks like this would work on any rig/amp as a clamp for the amp relay. Paul, thanks for this one...

Those are some massive tubes

very good, take your time! need you to keep on going hi.

tnx for the great info , very very informative for me ,many tnx agn ...

good thing about big tubes they warm up the radio room mite nice if you live in Michigan where it could be 30 below zero

Excellent video! I have to ask where you acquired such a depth of knowledge of vacuum tube circuits. I'm 64, so my early ham days were in that era. I haven't found many younger people who ever learned about this stuff. I love seeing the mix of old and new tech.

Nice video! Just as an aside. the "Z" in 3-500Z indicates that the tube is designed for zero bias (grounded grid) service. The Z was part of the original Eimac designation for the metal plate tubes. Some sellers designate their graphite plate versions as a "3-500ZG", and others (like the Amperex tubes you showed) just used the standard designation for their improved graphite plate version.

I really like your tips on the Keying circuit. Especially how you suggest an external circuit to interface the amp and transceiver. Very nice. I also like your Bias control modification circuit. Very nice. Have you considered using a dynamic circuit that can increase the bias voltage to cut the tubes off during the time between speech utterances then when speech returns, the bias would be returned to the normal Class AB2 setting? I think that could help to increase the lifetime of the 3-500ZG tubes. The existing ALC circuitry could be used to monitor the incoming RF during SSB transmission and with something like a comparator, the Bias voltage could be quickly transitioned between cutoff and Class AB2 with time delays so as not to cut off the beginning or ending of words. What do you think? Thank you so much for sharing your good work and ideas Mr. Carlson.

sturdy piece of equipment :-)

GROUND THE GRIDS . CHANG THE RELAY AND CHANG THE BAND SWITCH

Excellent thank you

Does a super job keep it up would like to know where you. Got your education very articulate. And extremely well versed.

Hi Paul: The designation "3-500Z does not indicate a graphite plate. Three dash 500ZG (3-500zg) indicates a graphite plate. Good video, & all your videos are first rate, Thanks for your efforts. I am subscribed to your "pay" channel.

I agree with Dave. I wish I knew what you forgot lol . so interesting

Sir! Your videos are ALWAYS first rate & this one is no exception. Permit me to disabuse you of a misconception. The "Z" in the tube type stamp on the envelope does NOT indicate a graphite plate. The graphite plate tube will be labeled 3-500ZG ....The "G" indicates a graphite plate. This is not a criticism, it is to avoid anyone buying a "Z" when expecting a "ZG". Cheers! Brian

another great video, thanks Paul. btw, is the key line interface you have there, good for between the ic746 and the yaesu FL2100b amplifier? cheers

Thank you again!

Just watched this for the first time Paul. Nicely done to bridge the gap on a few of the weak points in the design of this amplifier. Always liked the looks of the 922, but the cramped interior design is concerning, not to mention the high keying voltage. What were they thinking? As you mentioned, the designer's futile attempt at cooling the 3-500z triodes is weak, very weak. But as I recall, even the old Heath SB-220 utilized a similar fan arrangement instead of the recommended forced-air method of cooling. Of course that amp also suffered from under-cooled tubes. I guess the 3-500 tubes were much cheaper back then to replace. I was hoping you would measure the filament voltage with the tubes installed and drawing filament current. Most tabletop amps really do a good job of NOT delivering the correct filament voltage and offer the owner no means of adjusting that voltage for varying line voltages encountered. The owner of that 922 owes you a great deal of gratitude. Thanks, Joe W4JF

I would love it if you would make an audio amp with one of these tubes. Maybe run class A2 , so we can see how to do that. Thanks Duane

I heard ”Kenwood TL-922, eh?” every time. 😂🇨🇦

What do you have to say about strapping the grids directly to ground? Also what is your opinion on the hairpin type of parasitic suppressors on the plate circuits? I have done both and can see no difference but I don't have sophisticated instruments to check everything. I get very good reports on signal and audio using a Kenwood TS-520 with a MC-50 mike. Also I have only two good 3-500 tubes left. One is metal plate and the other is graphite but they are happy together and give me full output. Any comments? Thanks, KV4JT.