Masco ME-27 Amplifier Part 1 Let's Take a Look
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- Опубліковано 22 чер 2024
- Masco ME-27 Amplifier on the bench for mods. This amp has been restored recently, but I am
not sure if it has been wired stock. The workmanship in this amp is first rate.
The 1st stages have been wired grid bias and this is not great for guitar.
The customer wants this amp to break up more.
It seems this amp may have been wired for a Harmonica player.
Let's take a look and get some ideas on the best way to mod this amp.
There are 2 slightly different versions of the Masco ME27 (and a ME27P-3 with a phonograph player mounted on top of the tube cage); I have the Sam's for both of these. Comparing the 2 schematics, the resistor and capacitor values are virtually identical but they do use different power transformers. From looking at the pictures in the service info it looks like you have the later version of this amplifier, with a transformer that is top mounted to the chassis with its bracket-feet while the earlier version has a rectangular cutout and the transformer lays down sideways into the chassis cutout. Nominal power input is given as 117VAC. DC working voltages are pretty close to each other, within 10 to 20 volts in most respects, except that the later version ---- presumably the one you have ---- runs the plate voltage to the 6SC7 phase inverter at 190 V, and the earlier unit at 160 V. The later version has 04, 8, 15, 70, 350 and 500 ohm outputs; the earlier version has 2, 4, 8, 15 and 500 ohm outputs. Neither unit has global negative feedback. Sams manual for the earlier (1952) unit is from Set 155, Folder 11; the later unit (1955) is Set 270, Folder 9. Hope this helps!
If you think this Masco amp has tubes that are unfamiliar to you, they made other models that used Loctal tubes, including 7C5 outputs which are basically a 6V6 but with short skinny pins and a locking base (and a 6.3V filament/heater, despite the tube nomenclature beginning with a 7)! I don't know if the 5V4 tube is original or was installed to replace a stock 5Y3 or 5U4 by the previous servicer (presumably to increase the B+ voltage), but anyway, the 5V4 is kind of like a baby version of a GZ34/5AR4, with an independent cathode, and therefore it usually has less voltage drop than a 5Y3 or 5U4, a slower rise/warmup time, and it can also handle a little bit more first-stage filter capacitance without arcing. If you want more voltage in order to increase the dissipation of the 6L6GC tubes, then you might actually want to use a GZ34, or even a solid state rectifier.
Hello. I saw the schematic for the the one with the Loctal tubes. There plenty of B+ on this amp. I don't want to bias the 6L6Gcs any hotter as the customer finds the amp to loud. Do you think it would be worth putting the 6L6Gs back in to it?
@@vintageguitaramp_guitarteacher it might be, but getting good 6L6G's could get expensive. 5881/6L6WGB"s, 23 watts/440 volts, might be a better choice ( if they're real 5881's, and not 6L6GC's in a short bottle). Or, try 6V6's if the B+ isnt excessive, and double up the speaker impedance (run 16 ohms on an 8 ohm tap). A 5Y3 or 5U4 could drop the B+ a little as needed.....
You've got a juicy piece of equipment there my friend. This is the same amp and model that Rhett Shull bought and demoed on his channel. Very cool Martyn!
Hello Ron, thank you. It's the first one I have ever seen. I will check out that video. Take care Ron.
Wow Martyn, I didn’t expect to see this one on your bench. You obviously have the bonez to make a wonderful minimalist type of design. I say keep it cathode biased on the outputs, and voice it with your ears and a guitar in hand, and it will sound great coming from your bench. I look forward to the conclusion and final design. Cheers my friend..!
Masco PA amps must be pretty uncommon in the UK!
It's the first one I have ever seen.
Hello David, thank you. What I ever i do, I need to get rid of some of the Bass. Take care David.
@@vintageguitaramp_guitarteacher , the phono input is probably voiced/eq'd to put back some of the bottom end that was eq'd out when the records were cut.
I recently found your channel and have been enjoying it very much. Amps like these are among my favorites and I think you did a great job with it.
Subscribed, and looking forward to the next one!
Hello, thank you. I am looking forward to modding this one. Thanks for watching and take care.
Can't wait to see how it comes out Martyn.
It's in the best hands for sure!.
Thanks.
Thanks Keiran. I will email you with a few ideas later. Take care
@vintageguitaramp_guitarteacher
I think your right identifying that first stage as the key to an overdrive sound, these amps are famous for that sound so it shouldn't be much of an issue modding it.
Thanks Martyn.
Interesting amp that one,loveley tones.Been trying to get my head around the DIY Layout app,its a handy tool for working out schematics.
Hello mate. There should be a bit more using of DIY Layout Creator on the channel. Speak soon mate.
Really enjoying the channel.
The harmonica player I work with collects these, and has a couple of the square dance caller models with built in turntables.
One of the more rare Canadian amplifier manufacturers Verlage used to take these power amps, add their own preamp circuit and Altec 15" speakers. They roar.
Hello. That's good info there. I thought this was more of a harmonica amp than a guitar amp. I will check out the Verlage amps. Thanks for watching and take care.
@@vintageguitaramp_guitarteacher, guitarists also say about Premier amps, "oh, those are Harmonica amps"; but I've worked on a couple and they sound great for guitar. Ry Cooder had a Premier 88N as part of his gig-rig when I saw him play a few years ago. Thats a very unusual amp for its time, with an engenious tone/eq stack. I watched a demo of an 88N on UA-cam recently.
I did some online searching, and "Verlage" weren't built from Masco amps, they were modded/rebuilt *Fanon* amps. The Tone Lizard, Jedistar and Fenderbronco websites all have info on Verlage and other obscure Canadian amplifiers. Never seen a Verlage, and I've only seen a couple Fanon P.A. amps, at least one of which was Japanese made as I recall.
@@vintageguitaramp_guitarteacher, PS, the Fanon/Verlage amps had one particularly oddball tube, a 6CY7....
Hmm... the 6SC7 got me thinking and so i checked the early tweed deluxes, 5A3, 5B3 and 5C3 and sure enough they have a 6SC7 as V1 and it is wired with grid leak bias via a 5M resistor. Is the phase inverter a cathodyne? (I think you said it was wired as a triode) - which would be very 5E3... Interesting stuff.
Obviously what to do to it depends on what the owner wants. I'd be tempted to go for a 5A3 deluxe which are great sounding amps. Not sure about the grid leak bias though, might want to change that to cathode biased and I'd consider using different values of bypass caps to get different tones for each triode. Obviously it probably needs smaller coupling caps too. Interested to see what you do with it though!
Grid leak bias can rock! It’s a whole different sound! Before you decide to rewire that first stage, have a look at the supro 1690T Coronado schematic traced from multiple examples of the amps by Eric Kettenburg. That’s the Jimmy page/Zeppelin 1 amp that Mitch Colby cloned for the Sundragon. Grid leak bias first stage into cathode bias 6L6GB output section. Try larger value plate (360k+) and grid leak (6.8M) resistors and much smaller value couplers. If you need a copy of the schematic, just let me know where to send it.
Hello. I have just looked at the Supro schematic. It's not a million miles from what is already in this Masco. The main difference in the Masco is high value coupling caps. .1uf going in to the output tubes. And the same on one of the triodes on the first stage. It looks an interesting does the Supro. Thanks for watching and take care.
@@vintageguitaramp_guitarteacher exactly! Your best bet may be to attempt to limit bass right at the input by experimenting with small value input capacitors between the input and the grid of the first stage, and maybe try to squeeze a little more gain out of the first stage by experimenting the plate load and grid resistor network. There’s math you can do, but sometimes experimentation can bring surprisingly pleasant results. Good luck. Excited to see where you take this one.
Early in the video when you said "6L6GC", my first thought was, they are the wrong tubes. I would probably try to find a pair of 6L6GBs to avoid stressing the output transformer too much if in the future someone tried to bias the amp too hot.
Hello Michael. Although they are GCs, they are only biased at 18 watts. I don't if I would gain anything putting the GBs in it. I could bias GBs a bit cooler. The Guy wants it to have a bit less volume.
Good job tracing out circuit .
Looks like someone has one
Ive got a selmer truvoice same sort of era 6l6 valves havent a clue whats going on in it but the bass moves the floorboards..cant find any info ..great toons 😊
Thanks Paul. I need to loose some of the Bass on this one. Speak soon mate. Take care.
Masco was short for Mark A Simpson Company, of Long Island New York. Many of their small PA amplifiers are famous for use as harmonica amps in pretty much stock form. Sam's schematics posted service information for many Masco models and so that's where I would look if you have trouble finding a reasonably accurate schematic for it. Unfortunately somebody still owns the publishing rights to Sam's and so you might not necessarily find one for free online. PS, im old fashioned, and no longer have a full-size computer anyway, so I draw out schematics by hand, with pen and paper, and Whiteout! I've only watched the first minute of the video so far so we will see how you do! ( And by the way, British finger picker Martin Simpson used to play an acoustic slide guitar instrumental titled Masco Blues but I have no idea what the Masco in the title of that song refers to or where the song came from; it appears to be a traditional that he learned from somewhere else. You can find a video on UA-cam of him playing It).
Some good info there. The owner is tracking down a schematic for it. I await your judgement on my schematic drawing skills lol. Software to the rescue!!!!!!!!!!!
@@vintageguitaramp_guitarteacher , I'm not a judgmental guy by nature,, and instead I try to be merely helpful.. By the way there are plenty of short playing demos of these amplifiers on UA-cam but I didn't find one single deep dive into the circuit, nor improving it for guitar or harmonica.
Watching how you go at aroiund 16:00, the 6SC7 has a common cathode for both triodes, they're tied together *internally*.
Hello. Yes I saw that on the data sheet. I forgot to mention it. But hey would be tied together anyway in grid bias, so with that in mid I forgot to mention it. It will become more important in part 2 though. Take care.
@@vintageguitaramp_guitarteacher , A 6SL7 with rewired socket might be more appropriate if you need a tube with separate Cathodes so that you can voice the input channels differently. Also worth noting that Brad's guitar garage drew up a schematic today for a Little Walter amp with 6SC7's, based on a tweed Princeton.
Hello. That defiantly is worth noting. I will have a look that. Thank you. Take care.
@@vintageguitaramp_guitarteacher, I am unlikely to ever give you a hard time about your tech work, and I'll *never* have anything bad to say about your playing skills, which are first-rate.....but the word is definitely, not "defiantly". It's okay, blame auto-correct, or blame me for being an anal-retentive stickler for accurate spelling --- and if I make a mistake like that you have permission to give me heck! Fair is fair...