How to fix repair Vintage Magnatone tube guitar amp power supply hum

This amp came to D-Lab electronics via mail. Complaint, dead, no power, fuse good. It had been at a shop in another state and verdict, bad power transformer. Well, good thing the fellow sent it up here for a 2nd opinion. Turns out the real culprit was a bad power switch! Of course the amp had other problems to tackle. The repair turned out well and this classic amp will live to see many more years of service. They sure don't make things with this quality anymore. I really enjoyed the project. A very retro looking piece of history. If you have something like this gathering dust in your closet, get it boxed and shipped to D-lab! Hope you enjoy the video.

[@edcataldo7019]

Enjoying videos from D-Lab is never in doubt

[@mikehenshaw2986]

Terry, thank you so much for doing such a wonderful job with this amp for such a reasonable price! Played the amp today for the first time. The sound was absolutely beautiful! I normally use a Klon-style overdrive with my Vox tuber, but today I ran the guitar straight in to the amp at first-- and the sound was so freakin' incredible I never even thought about the pedal! It was an all-around great experience dealing with you-- you are truly one Mag-nificent dude!

[@mikehenshaw2986]

OK. Just can't stop gushing about this amp (and Terry's work!). You get a tiny bit of hum when you first turn on the amp-- for about 10 to 15 seconds as it powers up. Then it goes dead silent. This with the volume 2/3 of the way up. It was so quiet the first time I played it, that I thought the amp had died until I hit the strings of my guitar! It's 5 a.m.-- I've got to put it down and go to bed-- thanks so much, Terry!

[@bucyruserie1211]

@@mikehenshaw2986 They are great little amps when operating correctly...I owned the same one from 1982-88, I never used a pedal except a wah or flanger. I fried the original speaker, then blew about 4 more ceramic replacements until I found another alnico 8" out of a hammond organ, that one sounded great and held together as well. Enjoy it, as any new amp that size is total junk....

[@DragonCrestPC]

Terry you're just too cool.

[@kevinmiller4486]

Never trust what other people have checked. That will bite you in the rear every time. My two cents. Love your videos.

[@74dartman13]

Amazing job! It's crazy how some repair shops misdiagnose things. That may have ended up on the scrap heap if the owner had taken the other shop's word!

[@timridley1]

That's a beauty, I have a rebuilt Magnatone Varsity Aqua, it has some hum, but I think it might be the transformer that I have to use here in the UK to step down 240-110V.

[@islanderwinder]

Love the old tube amp videos ,Keep it up Terry!!!

[@sammyrussell936]

CHEERS TERRY !!!

[@Cavemannspace]

Another fun to watch amp video. Keep 'em coming. Cheers.

[@onemanswrld]

What a cool amp...nice repair...thanks for the video and knowledge Terry.....

[@jwl9286]

A magnificent repair indeed! I enjoyed it too! Thanks

[@johnstrunck3659]

Classic D-Labs! Stay cool Terry!

[@martinreid1740]

I really enjoy your videos, entertaining and educational. Great stuff.

[@rohnkd4hct260]

got to love that old stuff. Wiling to bet the last "tech" figured the customer would not pay the bill and he told him not worth fixing.

[@sam127001]

I enjoyed this - just recently discovered your channel and am hungrily watching all of your videos. Keep it up !

[@BrianWCole]

Just watched this in preparation for working on an 1962-ish Magnatone MP-1 with only stated problem of 'blowing fuses'..Thank you for this informative, well-paced, and well spoken job. As a former military 'instrumentation mechanic' and a musician, I have happily fallen into tube amp repair jobs in my 'retirement'....and really love it!...Got a classic Variac, but no audio generator yet, but I've worked on Musicmans, Old Gibsons and Silvertones. Anyhow, thanks again. Brian Lompoc, CA

[@d-labelectronics]

Hi Brian, I was stationed at Vandenberg AFB for 8 yrs. We may have bumped into eachother. If your looking for an audio generator, I have a nice VIZ analog solid state unit that is perfect for amp repair, could make you a nice deal on it.

[@anthonywatson754]

Thanks, Terry! Enjoyed the video.

[@ferraridinoman]

Great Work Young Tel!! Could only be bettered by your mentor Young Eli!

[@startend7196]

Terry you are an artist!!!!

[@tracyc7813]

It's nice to see your videos again. :o)

[@RobertKohut]

Well that was a switch, but you capped it off in the end, and with a bit of resistance, in the end we can be in accord......LOL Nice!! (A switch, a capacitor, a resistor and a power cord) (for the less inclined)...LOL

[@egorreshetnikov3864]

Cheers!

[@mobicus1]

Good stuff! Thanks for another great video.

[@kane100574]

I love those Magnatones... I haven't the slightest idea why. They call too me though! lol

[@douro20]

Either that cabinet is solid Pearloid or it's the thickest Pearloid I've ever seen. Never seen an old aluminium can bulge like that.

[@buildstoys]

Great job Terry. I would have liked to seen your test steps to determine adding the grounded AC cord. Has that perhaps been shown in a previous video?

[@sarcophagist4097]

It is show ar the end of the first video on the "Chicago 51" he did last year.

[@buildstoys]

Thank you. Here's the link for anyone looking: kzbin.info/www/bejne/fGrEnKSfmaieocU

[@GertjanRoossien]

Cheers Terry!!!!!

[@nationalduo4945]

Great channel…

[@bijouxbijouxbijoux]

Another great video Terry ✌️ question : do you often see Bad power transformer?? That must be pretty rare seeing how robust they were built isn't it?

[@eugeneeaton7262]

Great video!

[@jteichma]

Terry this is a great instructional video. Can you explain what you had to test on the power supply to know it was safe to add a 3 prong grounded cord?

[@jeffreyhaynes5774]

If you have ac leakage on the primary of the transformer to the chassis,adding a ground to chassis becomes a dead short across the ac power.Guess what ,boom.

[@johnbravo7542]

Thank you,that was great.

[@thats2kewl]

Hi, another great video! As another viewer commented, could you please describe what "buzzing out" the primary of the transformer really means/entails? Thanks!

[@vonzigle]

thats2kewl Usually, that means you’re checking the primary for continuity. As I recall, older continuity checkers (like for telephone circuits) would buzz instead of beep if you had continuity...

[@smstiao-tecnologia]

Nice job man !

[@z95m]

Nice job, Terry. Any idea when that amp was made? I'm guessing late 1940's or very early 50's just from the components used.

[@joeyvanostrand3655]

Prime canidate for the landfill.

[@dwightjt]

Nice work terry. Your a son of a gu Good very good electronics repairman. Give me a starting ball park figure on my Heath hot water 101 It only works on 80 and 40 meters. The other Bands nothing on receive hardly no transmit. 20 meters Is flaky on transmit Does receive not real Good. I'd love this thing to be working top notch. I have all the Right tubes in it and the power supply Needs new caps probly The ones on the radios Chassies circus boards?

[@squiertelecaster6854]

Great video, would you look at my Magnatone, I'm trying to date it, this one looks older.The chassis doesn't have the ears.

[@TheGalaxyhopper]

thank you.

[@stealyourfacekev]

I love your videos...

[@Dan79istheman]

ahhh Terry, Your humour is so bad it makes me laugh. ha ha. Great video as always.

[@dwightjt]

Me again the 101 heath you have to yell into the microphone just to get it to do 100 Watts on 80 or 40 meters it probably needs any electrolytic v the radios circuit boards to All I have here is a fluke volt ohm meter and a soldering gun well soldering guns and pencils if I can get it out to you would you be willing to take a look at it?

[@laranjiinha77]

Hi Terry, great video! Lovely! Have a question for you, I have a 2015 Maganatone Single V, second hand, the sound is great but the tremolo/vibrato and reverb is noisy when it's on, and getting reverb feedback at 12oclock. Do you have any possible clue why it's noisy and how to avoid feedback? Already changed one tube from the reverb channel, but still noisy and still getting feedback. Any help will be dry appreciated. Sent an email to Magnatone support but got no answer from them. Thanks 🙏

[@rciancia]

Very very nice job... Sometimes the easy stuff is the hardest to find :) Thanks Ron

[@sparkey1958]

been watching your amp repairs now for a while, i dabble myself, my question concern's final testing i can dummy load and scope a sign wave as you do, my problem is nothing beats hearing the sound quality, but my neighbours dont agree! is there a way to test the audio quality via a low level speaker while at the same time putting out the full output into a dummy load of the correct impedance...i have searched the internet for a unit or schematic of how to do this with no luck...thanks, bob in the UK

[@robertisrael338]

The one I have is very similar. Just different tubes, no power transformer and no pilot light. I'm assuming this is a late 50s to early 60s. Mother of toilet seat amp covering. This is an original varsity student amp.

[@goodun6081]

Robert Israel, if your supposedly "similar" Magnatone amp doesn't have a power transformer, then the only thing similar about it would be the look and style of the chassis and the cabinet. It sounds as if you have a "Starlet" or similar Magnatone (Magnatone put the Starlet name on several different varieties of transformerless amp with different tubes and circuitry and physical design); those were transformerless "AC DC" amps that only put out about 2 watts of power and can be highly dangerous to play because of the Transformerless design that actually can put voltage on your guitar strings as well as the amplifier chassis. To be safe, you really should get an isolation Transformer for your transformerless Magnatone. Or at the very least, plug it into a GFI adapter that will trip and internal breaker if it senses voltage on the chassis. A grounded cord and input AC wiring modified for safety purposes would be a good idea.

[@SwanseaTitanFan]

Terry, you should do a wine video.

[@roberthurless3295]

Another excellent video. Do you happen to know what the cabinet is covered with? And I love the construction grade plywood speaker baffle.

[@crystalturtle3033]

Cabinet covering is made of pearloid plastic otherwise known as "mother of toilet seat".

[@d-labelectronics]

Toil-la-tunes

[@tronics666]

How do you check the tubes and how do you check the power transformer for leakage to ground.

[@DeadKoby]

What's your solution for the failing insulation on the transformer wires? The technique I like is putting shrink wrap tubing over the top of questionable insulation.

[@eetechtom]

DeadKoby Shrink wrap will insulate some, but it’s not going meet the voltage rating of the original insulation.

[@RobertKohut]

Good one!! (Mag-nificant repair)

[@yeraydiazhurtado7640]

Nice man. Whats the Band in the introduction Music? Cheers! Yeray

[@tiki_trash]

It sounded like Joe Jackson to me.

[@blakejohnson7148]

Here's a dumb question....when you say you hoped that the problem wasn't a bad power transformer...would that have meant that the amp was not worth fixing at that point?

[@d-labelectronics]

Its still worth fixing. Higher cost due to the transformer, affects collectors value due to a different make being installed. So, I was hoping it was not defective.

[@blakejohnson7148]

I see...that makes sense...thanks for the reply!

[@medhawk4885]

Another great video........I learn alot here ~N4TYX~

[@Germinalx]

Acrosst?

[@greatreset3]

Wino? 😋