Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jojokeo on October 25, 2015, 02:19:58 am
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I have this MOTS Magnatone amp above. It came to me in a round about way and has been sitting for several years collecting dust waiting for a little TLC. Another thread here got me looking at it again. I went onto Magnatone's website & there is no schematic. It does however list these as supposedly having 2 6V6s but mine does not? Since it may have been worked on by someone else at some point I don't know if this amp should even be single ended or pushpull as I've read it should?
The tubes in the sockets are: 5Y3 6V6 6SL7 6SJ7 6J7 This doesn't really seem correct w/ the info available? Anyone know anything about different versions of these?
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Here's another similar one that Bill Creller restored back in 2008. Yours will be slightly different since the first tube in yours has a grid cap. It's such a simple straightforward little amp that I doubt you'll have any problems even if you don't find the exact schematic. Take a look at the OT wires. They will quickly tell you if it's push/pull and which tubes are the output tubes.
I think Bill also had a thread on the forum about his 195.
http://home.comcast.net/~seluckey/amps/pila/pila.htm (http://home.comcast.net/~seluckey/amps/pila/pila.htm)
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maybe the amp is a PP with 2 6V6's and someone stuck a wrong tube from a radio in the other 6V6 socket..
however, if you find under the hood that all sockets are wired correctly, and that there is no PI, and the OR is an SE..... it might be original.
magnatoneamps.com is my website, and I made that chart. It's important to point out (and I should do so on that table) that it was not from an authoritative source that I compiled that data. It is based on observations of amps that I have found on auction sites and websites over several years. I listed those tube compliments but not at the exclusion of others.
They changed tube line-ups quite a bit in those days. you'll see elsewhere on the list tube line-ups changed for the same model number.
I'd do some close examination of your example, it might be the original line up. (1) going from PP to SE is no small task, it's easier to find an SE amp, or if replacing broken parts, its easier to find a PP OT, or another 6V6.
if the OT has a date code that's near the other date codes, and if all the solder joints and components look the same, or close to it., its probably original. and given that the modification would have probably had to have happened a long time ago, you gotta ask, 'who would go to all that trouble?'
Also, the -5 in M-195-5 means 5 tubes. (like -4 in M-194-4 and -3 in M-197-3...)
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Here's another similar one that Bill Creller restored back in 2008. Yours will be slightly different since the first tube in yours has a grid cap. It's such a simple straightforward little amp that I doubt you'll have any problems even if you don't find the exact schematic. Take a look at the OT wires. They will quickly tell you if it's push/pull and which tubes are the output tubes.
I think Bill also had a thread on the forum about his 195.
http://home.comcast.net/~seluckey/amps/pila/pila.htm (http://home.comcast.net/~seluckey/amps/pila/pila.htm)
What a great restore job. Steve I didn't realize at first that I was on your site - love it every time I venture onto there. It's a little gold mine of info. The Li'l Maggie is what I've wanted to put together since last year when I got a few of those original dog bone varistors straight from the source. Nice gentleman too. I didn't realize he put them in matched pairs and when I got them I re-measured them all and messed that up. Ooops. He was terrific (talked for over an hour on stuff) and sent all new pairs, lesson learned. Is that chassis the same one Doug sells for the 6V6 plexi & SG made cabs for? I was planning on using 6AQ5's for mine but maybe why reinvent the wheel and go with the 6GW8's since you did all the heavy lifting already? Probably about the same power I suppose and save an extra tube for the pi?
On the amp, yes I was thinking the same thing on the OT but the speaker has been replaced and no old-style field coil type of set up? Okay, I took a couple more photos and the OT is definitely SE and everything "appears" stock to this point. It has stamped numbering of 72365 on the side (maybe stancor?). Strange that this circuit is given the same model number as the pushpull amp circuits?! Also the 6F7 tube's plate wire is going through a pre-made hole in the chassis too (like it's meant to be there).
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maybe the amp is a PP with 2 6V6's and someone stuck a wrong tube from a radio in the other 6V6 socket..
however, if you find under the hood that all sockets are wired correctly, and that there is no PI, and the OR is an SE..... it might be original.
magnatoneamps.com is my website, and I made that chart. It's important to point out (and I should do so on that table) that it was not from an authoritative source that I compiled that data. It is based on observations of amps that I have found on auction sites and websites over several years. I listed those tube compliments but not at the exclusion of others.
They changed tube line-ups quite a bit in those days. you'll see elsewhere on the list tube line-ups changed for the same model number.
I'd do some close examination of your example, it might be the original line up. (1) going from PP to SE is no small task, it's easier to find an SE amp, or if replacing broken parts, its easier to find a PP OT, or another 6V6.
if the OT has a date code that's near the other date codes, and if all the solder joints and components look the same, or close to it., its probably original. and given that the modification would have probably had to have happened a long time ago, you gotta ask, 'who would go to all that trouble?'
Also, the -5 in M-195-5 means 5 tubes. (like -4 in M-194-4 and -3 in M-197-3...)
That is awesome that this is your site T! So far and until I take it apart, it appears to be all stock. This is a weird circuit for what it's supposed to be, or at least labeled as? When I get a chance I'll just make a schematic as it sits. If you would like it for your site then terrific, one more for the collection. My main interest in this amp was the crazy MOT finish and more importantly for me, the 6SJ7 & 6J7 pentodes and octal tubes.
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Is that chassis the same one Doug sells for the 6V6 plexi & SG made cabs for?
No, but Doug's chassis would work fine. My chassis is 1/2" longer and came from Watts (http://tubeamplifierparts.com/guitar-amplifier-chassis-enclosure-project-box.html#!/Project-box-outward-lip-12-5-x-6-5-x-2-5/p/14331153/category=3023208).
Also the 6F7 tube's plate wire is going through a pre-made hole in the chassis too (like it's meant to be there).
The 6F7 is a triode/pentode. The cap on top connects to the control grid of the pentode section. Wires for a plate cap would have an insulator over the cap.
You may want to price some 6GW8s before you commit to them.
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> The 6F7 is a triode/pentode.
Mic should have more gain than Inst.
The Wolfgang Iden schematic will not do that.
Maybe they realized that the 6SL7 was not doing justice to the Mic input, and changed from triode-triode to pentode-triode to get more gain for Mic with very little other change.
> Strange that this circuit is given the same model number as the pushpull amp circuits?!
Strange but strange things happen. They may have had a contract for a specific model number (not specific guts). To expedite delivery they used different guts with the appropriate model number. Happened a lot in radios. Woolworth orders 50,000 of radio model B-28, you don't have that many B-28 parts on hand, you put a B-27 or B-29 chassis in a B-28 case and B-28 tags, ship 'em out.
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Happened a lot in radios
and cars!