A 1948 Supro with some fuzz and speaker heat issues
I have a question for you. Recently, I was given an old Supro amp. As far as I can tell it’s a 1948 model, all-original except for the power cord, which I replaced. There are no model numbers on the amp. Of course, it’s an all-tube amp, with what appears to be a 10" speaker, two inputs, an on/off toggle switch and a 2-amp fuse. When I turn on the amp, it fires fine and sounds pretty good. After it’s been on for about 10 minutes, it starts to lose a little volume, but the sound just gets better … sort of a nice fuzzy, bluesy sound. I noticed last night that the speaker frame was getting hot (after about an hour of playing). Is this normal for an old amp like this? Is it okay to use it without fear of it “blowing up?” The amp is in excellent condition except for the handle. Any idea what the value of this amp might be? Also, I was thinking of replacing the transformer with one of the new ones on the market. Would it be worth doing? Thanks for your time, and I hope you have a great day. Love your articles in Premier Guitar.
I don’t know that I’ve ever worked on that particular model amp, but from the research I’ve done it looks to be a very cool amp. It seems that there are quite a few different versions of the amp, but the common thread appears to be a bottom-mounted chassis with inputs and controls accessible from the lower rear. The speaker is mounted above the chassis and could have been either a Jensen or a Rola, the latter of which came in PM (permanent magnet) or field coil versions. I’d have to assume that the field coil version would have been the earliest version of the amp, as the field coil speaker predated the PM speaker. (Just FYI, in a field coil speaker, the magnetism needed for the operation of the speaker was generated by running the B+ (high voltage) of the amp through a coil on the rear of the speaker, essentially turning it into a large electromagnet.) The tube configuration in these amps seems to change as well. While all of the versions utilize a 5Y3 rectifier tube, the preamp section consisted of either a single 6SL7, or a 6SC7 along with a 6J7. Also, from the information I’ve seen it’s possible that the amps were built using either a single 6V6 for the output stage, or two 6V6s in a parallel single-ended design. That’s it for the history of the amps. Now let’s get to your questions.
You mention that the amp loses some volume and starts to sound a bit fuzzy/bluesy after approximately 10 minutes of operation, and that the speaker frame was getting hot. Remember that the speaker is mounted directly above the entire chassis. On that chassis are the mains transformer and anywhere from three to five tubes, with an output stage running in Class A mode. This in and of itself is probably enough heat to warm the speaker frame, but excessive heat could be the tell-tale sign of a problem. The symptom of the amp dropping in power and becoming “dirtier” is a somewhat typical sign of an output tube that’s shorting internally once it gets nice and warm. This produces a substantial amount of extra heat that would add to the warmth of the speaker frame. There may be, however, an additional cause.
If the speaker is of the field coil variety, the excessive current that the malfunctioning tube is consuming is being pulled straight through the coil windings on the rear of the speaker. This may not only cause the coil to produce additional heat, but could be bad for the longevity of the coil as well. It can also cause the mains transformer to run warmer than it typically would. With that diagnosis in mind, I would suggest replacing the 6V6 output tube(s) and see if the performance of the amp is improved. If it continues to lose power and become buzzy, I’d have it looked at by a local tech to see if the filter caps need to be changed. The only reason I wouldn’t tell you to just have them replaced is that you mentioned the amp was almost 100 percent original. Since it’s functioning rather well, replacing the caps may reduce the value of the amp on the vintage market—should you, of course, decide to sell it.
Which brings me to your question regarding the replacement of transformer(s). While there appears to be replacement transformers made for these amps, and installing one could improve the sound of the amp, the vintage value of the amp would be compromised. The decision should be based on tone vs. value. If you plan on keeping the amp and making it the best it can be, I’d say go ahead and try it. In my opinion, you’d probably get a bigger bang for your buck by replacing the speaker— almost always the weak link in older amps. Just remember, if the speaker is the field coil type, you’ll need to install a choke to take the place of the magnet winding, as it’s an integral part of the power supply. I hope this will help you make your Supro amp super.
Jeff Bober, Godfather of the low wattage amp revolution, co-founded and was the principal designer for Budda Amplification. He can be reached at firstname.lastname@example.org.
Kick off the holiday season by shopping for the guitar player in your life at Guitar Center! Now through December 24th 2022, save on exclusive instruments, accessories, apparel, and more with hundreds of items at their lowest prices of the year.
We’ve compiled this year’s best deals in the 2022 Holiday Gift Guide presented by Guitar Center.
Looking for a compact, “noiseless” way to plug in and play guitar? Check out the brand-new Gibson Digital Amp, available only in the Gibson App.
The new Gibson App simplifies the learning process and brings guitar playing to life for the current and next generation of guitarists in a modern, comprehensive, and intuitive way. The Gibson App is the place to take your guitar playing to the next level. New to the Gibson App is the Gibson Digital Amp, the ultimate starting amplifier for beginners and a flexible amp on-the-go for intermediate players and pros to get their sound anywhere. The Gibson Digital Amp is an accessible amplifier for both acoustic and electric guitars, and is currently available for Apple/iOS users--an Android version will debut next year.
Use the Gibson Digital Amp’s jamming guide to get started and transform your sound with built-in effects and pedals, jam to backing tracks, or use it in lessons and songs. The Gibson Digital Amp only requires your phone, and wired headphones for the best playing experience, no cables are needed. The amp features 3 acoustic mic presets, 4 electric amp presets, and 6 effects pedals.
The Gibson Digital Amp is the ultimate starting amplifier for beginners and a flexible amp on-the-go for intermediates and pros.
The Gibson App uses a unique two-way, interactive platform to teach guitar students how to do everything from playing their first note to shredding loads of songs. The Gibson App features interactive lessons with thousands of lessons and songs. Learn the songs step-by-step with video tutorials from superstar artists and pro guitarists in the “Gibson App Guide.” The Gibson App also includes the new Digital Amp, a built-in tuner, a metronome, Gibson TV, and new songs are added every week. New Gibson App Guides are added regularly and include Tommy “Spaceman” Thayer’s favorite iconic KISS guitar solos, Richie Faulkner’s (Judas Priest) “Guide to Metal,” Jared James Nichols’ “Guide to Blues,” CELISSE’s “Guide to Songwriting,” and more.
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Learn Guitar With The Gibson App
The Gibson App is more than a pocket-sized guitar teacher, it’s loaded with an archive of exclusive content and original programming from its premium and accessible award-winning online network, Gibson TV, featuring music icons telling their best guitar stories, with more episodes and installments added regularly. Users can watch Black Sabbath’s Tony Iommi share insights and tales from his decades-long career on the series “Icons,” dive into Joe Bonamassa’s assortment of legendary Les Paul guitars on “The Collection,” or see how Gibson’s iconic instruments are made in their Nashville factory from body to binding on “The Process.” There’s even a series called “The Scene” that focuses on backstage stories from hallowed music venues from coast to coast like The Troubadour and Grand Ole Opry.
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For more information, please visit gibson.com.
This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl and smooth sustain saturation when pushed into overdrive.
Belltone Guitars, as part of their Custom-Select System curated offering of pickups, has partnered McNelly pickups to create a one-of-a-kind retro-vibe P-90 pickup in the standard Filtertron size format. This pickup captures the clear, bell-like single-coil chime of a classic P-90 when played clean and retains the tight mids and articulate low-end vintage growl, and smooth sustain saturation when pushed into overdrive.
The McNelly P-90 Foil-Coil comes housed in a ‘raw’ nickel outer casing with a dull nickel foil face with metal mount screw gromets to complete the ‘new-vintage’ aesthetic, making it a perfect choice for your signature Belltone custom build. Available exclusively through Belltone Guitars.
Check out the Custom-Select System belltoneguitars.com to preview the McNelly P-90 Foil-Trons and all our standard and selectable components available to create your own signature Belltone. Then visit the Dream Lab on our website and select either model B-Classic ONE with its top binding or B-Classic TWO with its arm and body contours select your body color from our wide range of offerings, select your neck profile of either standard ‘C’ or thicker ’59 Round Back and either Maple or Rosewood fingerboard followed by your tuners, pickguard, and strings. Finally, review our curated custom-designed, and unique pickup selection to locate the McNelly P-90 Foil-Trons to complete your signature build.
Builds start at just over $2,300.00 with a custom case and shipping included.
For more information, please visit belltoneguitars.com.
McNelly P 90 Foil Tron video Sep27
Belltone P-90 Foil-Tron Pickup
DiMarzio, Inc. announces the Relentless P (DP299), the Relentless J Bridge (DP301), Relentless J Neck (DP300), and the Relentless J Pair (DP302) for 4 string basses.
DiMarzio, Inc. announces the release of the Relentless P (DP299), the Relentless J Bridge (DP301), Relentless J Neck (DP300), and the Relentless J Pair (DP302) for 4 string basses. The new Relentless P and Relentless J series pickups feature the Relentless cover designed in collaboration with Billy Sheehan.
As with the Relentless pickups, we removed all the hard edges from the standard P Bass and standard J Basspickups, and added an arch to the top of the pickups to bring the sensing coils and pole pieces closer to the strings. These improvements increase the dynamic range and make active circuitry unnecessary.
The Relentless P and Relentless J pickups incorporate Neodymium magnets and produce 70 percent more output than traditional passive pickups, and they’re dead quiet due to the incorporation of metal covers and foil-shielded cables. To dial in (or fine-tune) the individual string output, the Relentless P and Relentless J include eight adjustable pole pieces. These pickups also have a broad magnetic field so you can even bend notes without volume dropout.
DiMarzio’s extra shielding makes the Relentless P and Relentless J better for both recording and stage performances. We’ve mounted them onto robust .09375” thick circuit board base plates to eliminate the annoying protruding mounting screws — ultimately creating a more comfortable and consistent foundation to rest your fingers on.
The new Relentless P steps beyond the traditional P-Bass sound and can only be described as massive. It has more of everything: more volume, beefier lows, a growling midrange, and crispy highs with better individual string definition.
The Relentless J incorporates a new invention, (patent pending) parallelogram-shaped coils, offering an expanded mid-range punch, snappy highs, precise lows, and a new dimension to the sound of the Relentless series pickups.
Relentless P and Relentless J pickups will breathe new life into any bass, increase playability, and work well for any style of music from Motown to metal.
DiMarzio’s Relentless P, Relentless J Bridge, Relentless J Neck, and Relentless J pair are made in the U.S.A. and may now be ordered for immediate delivery.
Suggested List Price for the Relentless P is $169.00 (MAP $119.99).
Suggested List Price for the Relentless J Bridge and Relentless J neck is $155.00 (MAP $109.99).
Suggested List Price for the Relentless J Pair is $296.00 (MAP 209.99).
For more information, please visit our website at dimarzio.com.