Thanks, 2005. I taught Math and Science for 16 years, and became acutely aware of the necessity to explain things in a clear, understandable way if you really want to convey knowledge. Talking down to an audience, or over their heads is a complete waste of time for all involved. I really appreciate your comment and your subscription to my channel.
Another great video from you. This repair was a total labor of love. One can really tell you care about preservation of guitar history. This little Supro was lucky to have ended up in your hands.
Thanks, Brad. It's obvious that you're a Supro fan :) I had never seen a vintage guitar amp this small (or cute), so I couldn't resist "going the extra mile" to restore it. As a bonus, it ended up sounding a whole lot better than I expected. Also, when I sell it, I can ask a real high price......because it's the same brand as the amp that Jimmy Page once used :))))
Greetings, F86. My electronics knowledge was self-taught over the past 35 years or so, working on radios and jukeboxes initially and more recently on amplifiers. I was a middle school math and science teacher for 15 years, so I guess the flair for teaching developed then. Thanks so much for your kind words. I sincerely hope you enjoy the rest of my videos.
You're welcome, Ron. I am flattered that you would take the time to watch all the videos, and I really hope you enjoy them. Best of luck with your own amp project.
I love little amps like this, especially old ones. Maybe because I’m little, and old 😂. Thank you so much Uncle Doug. I’m re-viewing all your videos for, I don’t know, the tenth time. I have to review everything you’ve taught me just before I return to my basement workshop every fall for my winter hobby of tinkering with amps.
Uncle Doug, you are the most informative person on the internet for tube amp knowledge. The other thing is your dry humor just cracks me up all the time, and I know I have told you that before, but you make me laugh a lot.
Once again Uncle Doug to the rescue, I Recently picked up a decent amount of old wooden radios, hoping to turn a few into small desktop amps, And sure enough, I have a little CL-543 which has that complement of tubes and a 50z5 rectifier and a handful of 120vac to 120vac transformers. Doug you and your channel are a fountain of knowledge.
Thanks for posting this site. The Supro student lap steel guitar they have for sale is probably just what this little amp was made for.....the wood color is similar and the Supro ID tag is identical. Very interesting.
The thing is, my knowledge of electronics is on a reasonably comfortable junior or novice scale but I am certain that I am picking up all kinds of knowledge slowly just by osmosis, as Uncle Doug’s humorous narration and confidant knowledge make these the most entertaining guitar amp tech videos I’ve ever seen.
21:28 'I don't think it's gonna put Fender out of business.' O the sweet irony seeing as they bought Gretsch. That is a great little amp, and you definitely gave it a new lease on life it deserved. Thanks Again Uncle Doug. Been learning a lot watching your vids.
You're welcome, Paul. Actually I notice that Supro is undergoing a strong rebirth, with all sorts of newly-designed, excellent amplifiers on the market. I wish them great success.
@@UncleDoug I have mixed emotions about new and revamped Supro. I've been hearing things about the new Jimmy Page Supro they reissused, and they've got none of the old Valco ptp wiring, or feel to them apparently. I think it's the folks at Pigtronix that revamped them, which is fine. Again, good to see them come back in what ever form, but wish they would have kept the old Valco standards. But anyway, you keep fixing em, I'll keep watching. :)
Thanks, Frank. I was with David when he took the SVT apart and I couldn't believe how hard it was to disassemble.....what a repair-man's nightmare !! It reminded me of old cars that were so poorly designed you had to pull the engine to change a spark plug. This is why I stick with simple vintage amps.....so much more fun to work on.
More fun! I have an almost identical Natco projector suitcase cab like yours. Another Bell & Howell as well. I know that some are made of metal. Nice long leads in projector cabs too. All coiled up neat with a reel and soft red material, lol. Good to see these videos!
Thanks, BT. I too was impressed by how good it sounded.....especially considering the limitations of two tubes and a 5" speaker. I'm glad you liked it.
12SK7 is a remote cutoff pentode commonly used for RF and IF amplifier in radio receivers. It was designed to work with the AVC circuit. The 12SJ7 is a sharp cutoff pentode which is much better for audio gain service.
Very nice. Just today I was searching the web for schematics of an amp with no PT. Should have known you would have one. At the risk of sounding like a broken record, thank you so much for the time and effort you put into these videos. I have attended much training in motor control electronics (forklifts) and have never experienced a better instructor. Now that I no longer work I needed some kind of gearhead hobby and vintage amps seem to fit the bill.
A cute little amp. A lot of work went into the radio-like cabinet originally. Designed to look at home in the home. What was it designed for? Leo was just taking his 1st steps towards turning the music industry upside down and inside out, so it wasn't for him. The existing jazz boxes with added pickup didn't need an amp for home noodling... Impedence matched for a magnetic transducer, though. Thank you, Doug, on behalf of guitar nerds everywhere.
Thanks for another great video and I love your dry sense of humor especially when describing an amp in the first look at it, and what others have done to it, or its general condition . Good luck at Wimbly stadium.
Hi Uncle Doug & Rusty, I have a 1945/6 Crosley 'American Overseas' model 56TC, wood cabinet radio that has some similar tubes as the Supro. It has the 50L6GT beam power tube, a half wave rectifier the 35Z5GT and a 12SQ, SK, and SA7 tube compliment. The 12SA7GT is a pentagrid converter, I'll have to research that. Still collecting parts for the 5F1 Champ, I have a new Jensen MOD series 8"-20 watt, 8 ohm speaker, and some jacks, pots, etc. for the build, can't wait to start it. I hope doing good, Take care, C.
+Cass Virgillo Cass, it sounds like the Crosley is a series-filament circuit (no power transformer) and therefore not a great candidate for parts donor or conversion to guitar amp. Good luck with your 5F1 Champ project.
excellent excellent video, a 10 out of 10. Love the way how you explain to make the chassis safe. I had the same concern about the tubes being too close to the speaker magnet, but you did a really fantastic job on refurbing that.
This one is by far my favorite video from Uncle Doug. The utter simplicity of this amp is simply amazing and yet it produces great tone with even the tiniest of speakers. The Stewart amp could not achieve that even with three times the cone area.
@@UncleDoug hi Uncle Doug, I have a question this guy did put a three prong plug on an amp very similar to my Lifco model 801 could you give a look and let me know if it's the way to do it. woodeso's guitar mods is the site. You can maybe bring light not just to me but others who are wondering about this mode. It'll be generous of you to give it a look and maybe leave a comment. Be certain it'll be very appreciated. Finally I'm glad you're doing well.
@@gerardcousineau3478 Gerard, I have demonstrated repeatedly in many videos exactly how the 3-wire cord should be installed. Rather than simply repeating myself, please watch one of these videos and see if your cord is installed in the way I demonstrate.
you done a Wonderful Job ;-) ..and can tell the Amp feels better looks better and Sounds Better, Your truly an " amp doc " !! ..Love the "Natco" Vintage speaker at 20:58 I have a smaller one with a Jensen 10" with the leather corners.. This amp knew where to go and so glade you fixed her up, you did a Great Job :)
Thanks so much, B2. It's nice to know that someone else understands the pleasure derived from restoring something that has been abused and damaged back into its former, good condition. I really appreciate your input :)
The flow of electrons into the tube can be disturbed by the proximity of a magnet strong enough, this can cause red plating. That's why the speakers in cathode-ray tube TV are shielded.
i LOVE this little amp. love the simplicity. im also beginning to love the tone of a pentode preamp. i want to make one of these and put it inside a 30s tombstone radio cabinet w/a 6". i think that would be appropriate since so much of this design comes from tube radios, especially the power scheme. if i want more drive, put a boost pedal in front of it.
The 12SJ7 is a sharp cut off pentode. The SK is a remote cut off used for RF/IF amplifier service to accommodate AVC. The Selenium rectfier should be replaced by a silicon diode.
Greetings, HB. This amp would not be hazardous, as I explain in the video, but I would be very nervous about contact with a different untested, series-filament chassis. As a rule, I don't buy or work on them. Thanks for your input :)
I actually tried it, Ben, and the increase in volume and distortion wasn't a whole lot greater than at 7 or 8. I think the preamp tube was saturated and couldn't drive any harder. The response to input is definitely non-linear at higher volume settings.
This is the ultimate night stand amp! I’d rather have this to play myself to sleep while writing the next “Satisfaction” than any modeling amp! Just don’t spill your beer 🍺⚡️
Uncle Doug, I believe that is what is called a "labour of love" - to put so much work and care into such a small and simple amp. It's what separates the hacks from the true Professional such as yourself. Flattery not intended, just the truth!
Thanks so much, Stony. I have a whole house full of such "labors of love"......neat old devices that I have spent way too much time and money on trying to rescue from previous mistreatment. It's the best way I know to show respect to these historical, wonderful old gems.
For some reason this wild but kinda classy little amp really speaks to me. It did look like a rats nest but Doug nailed that restoration. I looked for other demos of the amp after seeing this and none came up, but man it sounds good as is.
Thanks so much, Davo. The little guy is so small you could almost hang it around your neck with a chain....rapper style :) Rusty and I are glad you liked it ^. .^
Hi,long time sub,1st comment.Love your work and just had to say what a fabulous job.Beautiful restoration and long needed safety work on a potentially dangerous build and it does sound fantastic.Thank you Uncle Doug.
what a speaker stash that yielded that LIttle Gem (for never was the term more warranted!) Actually looks like it came from near Wembley... or the UK,. generally.
Yes, it was secretly removed from George Harrison's speaker cab during an intermission, smuggled out of the country in a fruitcake tin and sold to me at a flea market in Juarez, Mex.
@@UncleDoug OK when the millenials laugh this much, they type the letters RTOFL - but no word of a lie, Doug, I don't know what it stands for. PS incredible! we're now down to a 2-tube amp - which i guess you could carry from practice to gig, to be sat atop a singe 12 cabinet or similar,,already lugged to the venue
@@UncleDoug The 3x15 Kustom - with naugahyde - put that in your show rider, knowing the promoter won't find one - the Chuck Berry technique. Used here in Halifax Sept '74 when no one could find two Fender Dual Showman Reverbs & cabinets. I believe in torts this is called, a ding-a-ling..
This is so much better than the cheesy china made practice Amps sold today, and classy looking and warm sounding too. Would even make a great harp amp.
+David Salny Thanks for your kind words toward the tiny Supro amp, David. I agree completely. As small and simple as it is, I would definitely prefer it to virtually all of the small, modern amps currently sold.
Sounds amazing, even in the 5" ...in fact, that's where IMHO its charm is. Just wanna say, your restorative ethic has my vote all the way home. In fact I can't imagine any other POV. I'd like to hear some single high-ish guitar notes with the volume nearly maxed as in 'lead lines'... I bet it would sound really cool, daddy-o (as this thing is old enough to've been plucked by beatniks). thanks for another great video and... cheers
I'm always commenting too soon, as I do this and consider it important and pause the video, and typically as soon as I do, you'll say the same thing... but here goes! My house is quite old... but I find this in a disturbing number of places that I play, that the ground on the outlet is often not earthed... but floating around somewhere... early on in my gigging career, I found many places that I played, playing HECK with my amps and always carried a little outlet checker with me.... and for whatever reason, those grounds were nearly always OPEN... causing ground loops and mass carnage!! And one place that I enjoyed playing immensely had HALF the stage wired with the hot wire and neutral, BACKWARDS... CAUSING me to receive a full-on jolt of 120v to my lip! And another time, before they took my advice and had it wired to code, I was preparing to play my first song of the evening, talking to band members, and having lost a high E string at our previous gig, had about 6 inches of E string sticking out... as I talked to the guys before the song I thought someone took a picture of us with a flashbulb, but everyone's eyes got wide... and the distinct smell of ozone drifted into my nose... and the 6 inches of E string was now 3 inches after touching my vocal mic... that was the night I talked with management. And the next day bought a cheap little outlet checker... I have an old mic stand tube at the house, driven about 3 foot into the ground, and hard-wired to all of the audio circuits in the house, and all of the outlets with active grounds labeled as such... just a little PSA from the guy who probably has been shocked more than any of your other viewers, I'll wager! Lol.
And Uncle Doug does it again! Another great video :) This amp was a trip to see! Interesting series circuit. I've never seen an internal isolation transformer on an amp yet. This is a nice little practice amp; a lot better than the crap sold these days...It's funny, I watched David's latest video on the Ampeg SVT and I was cursed with one yesterday morning...Same issue as his...My girlfriend said, yesterday was the first time she heard me swear while working on an amp (LOL) I enjoyed this video.
Thank you Uncle Doug for all the time and effort you spend putting your content-rich videos together. I am trying my hand repairing a mid-60's series filament amplifier. What are the advantages and disadvantages to using in an isolation transformer for the mains inputs rather than the simpler approach you've taken? What was your decision process not to use a transformer for this Supro? What input did Rusty and Jack have for the design choices?
You're welcome, Kevin. I personally have never used an isolation transformer on any amp, series filament or not. To me, grounding the chassis seem like a foolproof way to eliminate the shock hazard, and it allows the amp to remain original looking, without the need for any additional bulky electronic components.
By offering the ultimate, virtually zero-resistance, path to earth ground, it only makes sense that the pesky electrons, lazy opportunists that they are, would follow that path rather than the relatively high-resistance path offered by our body, especially if we are not grounded. Granted, since we would form a voltage divider (us and ground), there might be a slight sensation of electrical flow, but it would serve more as a warning than a threat to our health.
Lov your work! Awesome. I would like to see you take on a big tube amp. With say 6 or 8 out put tubes that has issues. Like a dyno test of a genus. Thanks!
@@curtismuma1931 I don't see that happening, Curtis. I doubt that anyone would want to pay the shipping cost for the head and three speaker cabinets.....and I would definitely not want to have to lug them back to FedEx when the video was done :)
@@UncleDoug i agree too heavy to ship. Just a pipe dream. 435 watts of tube power wow. Alot of people have never heard of this amp. There is one for sale in my sound room. m.facebook.com/groups/537776489920188?view=info&refid=18&ref=bookmarks
the 5-inch speaker is basically an open back mid-range, similar speakers were used in numerous Magnavox and Motorola Hi-Fi consoles back in the 1950s. if I remember correctly, alnico five actually refers to the way the magnet metals are alloyed, the ratio of one to the other, or the number of medals in the alloy, or something like that. some alnico magnet formulations, in addition to Aluminum, Nickel and Cobalt, also had some copper, but I don't remember what the fifth metal could be.
How did I miss this episode? I have to admit that I had no hope for this economy -class Supro. However, my doubts were dashed by your understanding of circuit design. You made a potentially dangerous design in to a safer, logically sound amplifier. The restore of the cracked wood was well done; considering how poorly protected the original finish aged. This adventure was well executed, dear uncle. I need to traverse your entire catalogue of videos for any other I may have missed. Stay safe!
Americans really need to get their power plugs together. In Australia, even with a two wire plug, you still can't plug the thing in backwards. Also the plugs don't lose their grip on the socket! I can be a pretty old school person when it comes to electronics, despite my age. That said, this amplifier even made me a little uncomfortable right from the start with the lack of safety. Good job at whipping it into shape! Sounds nice.
I saw another channel refurb an old Magnatone 107... with the 50L6... I was quite impressed. I love the idea of building NEW versions of "oddball" amps. Too many things have the same tube compliments. It's fun to see the look on someone's face when they expect you to tell them it's a 6V6, or an EL84.. and 50L6 is the answer instead. It appears that one could re-create the Mag Starlet 107 amp with 100% new parts, at a cost of less than 200$. I wish I had a stash of stuff like the amp veterans... but I'm still the amp apprentice. It's quite impressive at how much volume and tone you can get with a "nothing" circuit.
I agree, DK. It's like most modern hot rods.....featuring 350 Chevy crate engines.......boring and redundant. I too like to see some creativity in circuit and cabinet design. I also wonder why the 6F6 tube, so popular in radios, is so rarely seen in guitar amps.
There's lots of stuff that is to wonder... like the PCL86 tube. You could make a 1 tube amplifier..... talk about a little tiny practice amp. Some guys have made hifi amps out of them...
freak55beat Greetings, FB, and thanks for the kind words. I agree that a FWBR would be an improvement over the Selenium Rectifier, but I tend to not alter vintage amp circuits, especially when the existing parts are fully functional. This is a series-filament circuit, so the heaters (and 300 Ohm 10W Resistor) take their appropriate operating voltage from the 120VAC wall receptacle supply, with the sum of their voltage drops equal to the input voltage. There are no power or filament transformers.
Hi Uncle Doug! Great informational video and I love those tube amps too! But I don't see why you say this little amp is a death trap. You had mentioned that it does not use a power transformer, but it does indeed : for the B+, and thus the B- can be connected directly to ground and still be isolated from the power line. Connecting the tube heaters in series is not dangerous; and the schematic shows no direct connection between the power line and ground. BTW I used to work on Marshall amps many years ago and remember fuses wrapped with foil and smoked transformers ;-)
Greetings, WG, and thanks. I agree with everything you said, and tried to make these exact points in the video. If I failed, then I apologize. The title had two parts, the first part (about "deathtrap") was intended to be ironic, and the second part (about "safe little tone monster") was, in my opinion at least, reality. Re the "modification" of fuses, my favorite is the tale, probably apocryphal, about the guy who substituted a .22 caliber bullet for a fuse in his car.....which led to all sorts of unpleasant surprises. Let's hope no one follows suit in their amp :)) Thanks for your input.
