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Thread: What Amp is This?

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    Twobie
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    What Amp is This?

    Hi Folks,

    I'm a guitarist and was fortunate to have a father who was electronics guru and who built me numerous guitar amps over the years. Sadly he passed away a couple of years ago.

    I'm currently trying to get one of the amps he built for me up and running (it's been in storage). Problem is, I can't remember what it actually is! It looks like an early type of Marshall - it has four inputs and the standard Pre/Master/Bass/Mid/Treble/Pres controls. However it uses two 6L6s for output which is more like a Fender (?). Also, it's got a tube rectifier.

    After going through a large pile of hand-drawn schematics I've come across what I think is the schematic for it. I've attached it below. I'm hoping someone here could look at the schematic and recognise it. A word of warning though, it could be a hybrid (i.e. Marshall-style input stage, Fender-style output stage).
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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Name:	6L6 Head Input.jpg 
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ID:	51905  

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  2. #2
    Old Timer Leo_Gnardo's Avatar
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    Looks mostly like a Fender 5F6A Bassman, same amp Marshall copied when they started making amps. What's kind of hinky and can't possibly be correct, the C and D connections between pre & power amp. Find a 5F6A schematic & have a look. If your amp works well & sounds good, that's probably the correct schematic.

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    Bent Member Chuck H's Avatar
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    The C and D connections look ok to me.?. And it does look pretty much like a 5f6a Bassman. Which is as good an amp as any guitar player needs. Or in many cases could want. No modern features, but the design pretty much benchmarks the wattage, headroom levels, overall tonal properties, etc. that has shaped most of the criteria for every amp since. A very good choice for the restoration.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Quote Originally Posted by Leo_Gnardo View Post
    Looks mostly like a Fender 5F6A Bassman, same amp Marshall copied when they started making amps. What's kind of hinky and can't possibly be correct, the C and D connections between pre & power amp. Find a 5F6A schematic & have a look. If your amp works well & sounds good, that's probably the correct schematic.
    I agree that it's based on a '59 BM, especially as it uses a 12AY7 at the input and (4) speakers are wired in parallel meaning low (2 Ohm) output impedance. I don't see anything wrong with the A, C, D connections, though it is not clear why the 2 drawings are split this way.

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    Old Timer J M Fahey's Avatar
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    Looks fine to me.

    Drawings could be split because he wanted 2 large drawings, which means split in 2 full pages, stapled to the wall while he built them.

    In any case, besides many other good things I am certain, he left you something very nice, certainly built with love, by which you will remember him.

    By the way, it has been said that "if there is just *one* Guitar amplifier left on Earth, it should be a 5F6 Bassman" ... and here is one extra proof:

    https://www.youtube.com/watch?v=vgqrOCUQzH0

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    Juan Manuel Fahey

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    Bent Member Chuck H's Avatar
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    You've posted that clip before. I love that guy! I've seen several of his demos. Very sincere and enthusiastic. Also, the kind of player who adjusts his technique to exploit each amps strong suites.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  7. #7
    Don't forget the joker g1's Avatar
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    And here is the Fender drawing to compare to:
    Attached Thumbnails Attached Thumbnails BASSMAN_5F6A.pdf  

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Twobie
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    Thanks for the help! I'm planning on building a cabinet for it. The front panel layout is more Marshall than Fender so it's probably going to look more like a Marshall!

    Cheers,

    Chris

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  9. #9
    Old Timer J M Fahey's Avatar
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    Original Fender Bassman had 4 speakers in parallel for 2 ohm total; Marshall typically had 16 ohm output, check what *you* have.

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    Juan Manuel Fahey

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    As mentioned above, the original schematic drawing shows a single OT secondary and 4 speaker jacks wired in parallel. If the actual amp is built accordingly, an output impedance of 2 Ohm is the most probable.
    Maybe the OT carries some brand name/type No. that could help to identify impedances.

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