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I'll try to keep this as short as possible. A year or so back I picked up an old Selmer Treble and Bass 50 MKIII head. It was something of a basket case but with the help of many here I got it all sorted out and it sounds beautiful. I had to completely toss all of the internals. Completely renovated the board, rewired to MKII circuit but retaining the diodes for rectification. All new pots. So really, all that is original are the transformers, the board itself (just the board, not the components) and the choke.
Fast forward to now, I wanted to make a copy. Got the transformers and choke from Mercury as they're the only co. out there (of whom I'm aware...) who make copies. I used the same pots and jacks as the original renovation, same components etc. Basically, everything is the same except for the transformers and I've actually shortened some of the lead dress over the original (those were pretty badly laid-out). I'm using the same preamp and power tubes in both amps. I amp a/b comparing them through the same cab/speakers with the same guitar/cord. Even the same wall socket.
SO WHY DOESN"T IT SOUND THE SAME?
It's got the same basic sound, don't get me wrong. It sounds like a Selmer. The power transformer is putting out 1 volt less B+ as compared to the original, so all of the voltages within the amp are the same and I've got them both biased the same. I've double-checked all cap and resistor values. The main differences between the two, to my ear, are: (1) The new amp is darker: the original has a high end chime like ringing bells, very sparkling, very Vox-y, while the new amp is lacking this. (2) The new amp has more gain and/or crunch on tap; when I crank up the treble channel to 10, with the same tone control and volume settings on both amps, the new amp sounds like a Marshall and it is noticeably dirtier than the old amp. To get the same level of dirt out of the old amp, I need to jump the channels.
The only difference I must own up to is the choke: Mercury does not make a specific choke replacement, however I did measure the old one about a year ago at 9.xxx henries. However, I forget the DC resistance. I got a 10H choke from Mercury which looks close, although the old one is a little (just a little) bigger. Mostly it's the coil that's a bit larger. I don't think this would really make such a noticeable difference, though, would it?
I think the culprit here is the output transformer. Mercury's copy looks pretty identical. I can't tell you what transformer exactly is on my old amp, as it's filthy and there is no mark or sticker anywhere on it. All I know is that it's whatever Selmer happened to be using that month. Again, at the least the two look basically identical. So, can the OT alone *really* make that much of a difference? I've replaced toasted OTs on old amps before with modern replacements, and never really noticed such a dramatic difference.
Any thoughts appreciated.
Fast forward to now, I wanted to make a copy. Got the transformers and choke from Mercury as they're the only co. out there (of whom I'm aware...) who make copies. I used the same pots and jacks as the original renovation, same components etc. Basically, everything is the same except for the transformers and I've actually shortened some of the lead dress over the original (those were pretty badly laid-out). I'm using the same preamp and power tubes in both amps. I amp a/b comparing them through the same cab/speakers with the same guitar/cord. Even the same wall socket.
SO WHY DOESN"T IT SOUND THE SAME?
It's got the same basic sound, don't get me wrong. It sounds like a Selmer. The power transformer is putting out 1 volt less B+ as compared to the original, so all of the voltages within the amp are the same and I've got them both biased the same. I've double-checked all cap and resistor values. The main differences between the two, to my ear, are: (1) The new amp is darker: the original has a high end chime like ringing bells, very sparkling, very Vox-y, while the new amp is lacking this. (2) The new amp has more gain and/or crunch on tap; when I crank up the treble channel to 10, with the same tone control and volume settings on both amps, the new amp sounds like a Marshall and it is noticeably dirtier than the old amp. To get the same level of dirt out of the old amp, I need to jump the channels.
The only difference I must own up to is the choke: Mercury does not make a specific choke replacement, however I did measure the old one about a year ago at 9.xxx henries. However, I forget the DC resistance. I got a 10H choke from Mercury which looks close, although the old one is a little (just a little) bigger. Mostly it's the coil that's a bit larger. I don't think this would really make such a noticeable difference, though, would it?
I think the culprit here is the output transformer. Mercury's copy looks pretty identical. I can't tell you what transformer exactly is on my old amp, as it's filthy and there is no mark or sticker anywhere on it. All I know is that it's whatever Selmer happened to be using that month. Again, at the least the two look basically identical. So, can the OT alone *really* make that much of a difference? I've replaced toasted OTs on old amps before with modern replacements, and never really noticed such a dramatic difference.
Any thoughts appreciated.
These amps were not high-dollar amps, so I'm guessing that possibly they went the jtm45/100 route and used an undersized choke that dropped inductance as the current went up. I guess the basic question is, can it *hurt* anything to hook up this 5 pound Hammond beast the proper way (OT after choke) and see what happens?
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