59 Bassman into 5G9

Little Ricky

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I recently picked up a relatively cheap 59 Bassman RI, that was apparently in a flood. The plywood on the bottom of the cab is delaminating and the blue alnico speakers are a little rusty, even though they seem to be above the watermark on the cab, so they’re probably just exposed to moist air.
Anyway, it works fine and sounds good. I mainly bought it for the speakers.
I’ve had a hankering for a 5G9 for a long time, partly because it’s described as a “baby Bassman”, but also because I like bias vary tremolo.
So I was wondering, could the cathode follower be taken out and replaced with dual triode 5G9 tremolo? Instead of a baby Bassman, I’d have a big daddy Tremolux, with 6L6’s and a 410 cab.
I’ve also heard that despite the similarities on paper, the 5G9 isn’t actually a baby Bassman, perhaps due to the lack of CF, or maybe the dual triode trem robs a gain stage?

So my questions are:
Is this a viable conversion? It could be similar to a 6G9-a, minus a triode gain stage, or minus the quad inputs if I used the normal channel triode to boost the bright triode (or just jumper them).
What is the difference between a dual triode tweed-era tremolo and a single triode tremolo? I read something about a buffer…

I realize that despite its rough condition the BMRI might be best left unmolested, but let’s do a mental exercise, if you don’t mind. Thanks in advance for your help.
 
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printer2

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Hope the flood was with clean water.

Anything is possible depending on your skill level. Will you be redoing the circuit or using the current board?
 

Little Ricky

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I’d
Hope the flood was with clean water.

Anything is possible depending on your skill level. Will you be redoing the circuit or using the current board?
No idea about the history, the seller said he got it in an estate sale.
I’d put in a completely new board.
 

NTC

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You could wire up the preamp more like a blackface so you still had bass, mid, and treble. Second channel volume and presence could become speed and intensity (or you could move the controls around for convenience) . You would still have the tone control with mid scoop, but it would sound more blackface. Only one channel. The Tremolux with a single tone control has a LOT more mids. Great if you like that (I do) but it will be more picky about pedals.

I have a "5F11" that can run 6L6's and it does not have the cathode follower for the trem oscillator circuit. It works fine, but most folks will shy away from recommending such a thing. You didn't hear it from me.
 

King Fan

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I love my 5G9, but it isn't a Bassman, and I sure as heck wouldn't mod a 5F6a to get there. Even if you *could* add real trem without sacrificing any gain or any of your amp's other sonic qualities, you'd basically achieve a trem that, though nice, most folks couldn't tell from a pedal. My theory: Buy the pedal, leave the big guy alone. :)
 

Little Ricky

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I love my 5G9, but it isn't a Bassman, and I sure as heck wouldn't mod a 5F6a to get there. Even if you *could* add real trem without sacrificing any gain or any of your amp's other sonic qualities, you'd basically achieve a trem that, though nice, most folks couldn't tell from a pedal. My theory: Buy the pedal, leave the big guy alone. :)
I think this is what will happen, leave the BM alone or maybe just experiment with some minor mods.

How would you compare and contrast the 5G9 and Bassman, speakers aside?
 

tubeswell

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If you’re after the 5G9 mojo, you’d probably have more success if you built it with 4 x 6V6s. That way, the 5G9 bias-vary trem would behave better (more like a 5G9), and you wouldn’t have to change out the iron.

If you want to keep the 6L6s with bias-vary trem, look at the brown tremolux (6G9) or brown vibrolux (6G11).
 

King Fan

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How would you compare and contrast the 5G9 and Bassman, speakers aside?

From what little I know, the 5G9 is (in overly simple terms) cleaner and quieter than the 5F6a. Less gain? @tubeswell would know better -- he has a ton of experience here. Now a couple questions for you. Other than possibly trem, what are you looking for in the 5F6a? In what ways does it meet, or not meet, your needs?
 
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loopfinding

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the 5G9 has a totally different gain structure than the bassman. it's just an input triode stage into a tone control directly into the phase inverter. i don't think it's a "baby bassman" at all. you would lose a lot of gain.

if it were me, i would just convert the bassman into a single channel and run the input stage in parallel for lower noise and a little more gain. this is really easy to do, just disconnect the associated circuitry from the second input, and then jumper their grids and plates together. play around with the plate and cathode values. if you use the normal channel, then snip the bright cap across the volume pot. you can also omit that 270k grid resistor or mess with its value.

bassman-single.png
 
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Little Ricky

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I think I might try jumpering the CF/tone stack by lifting the V2A grid to the C8 coupling cap. I think I can do it with minimal surgery. This would keep the Volumes and Presence intact.
I was playing it with all EQ at max, which I guess is as close to a bypassed tone stack as I can get, and it was fine.

Normally I would plug into Normal 1 and max mids and presence with bass on zero and treble 0-5 as needed. This is on the neck p/u with guitar volume pretty low and guitar tone just a little open.
 

Little Ricky

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You could wire up the preamp more like a blackface so you still had bass, mid, and treble. Second channel volume and presence could become speed and intensity (or you could move the controls around for convenience) . You would still have the tone control with mid scoop, but it would sound more blackface. Only one channel. The Tremolux with a single tone control has a LOT more mids. Great if you like that (I do) but it will be more picky about pedals.

I have a "5F11" that can run 6L6's and it does not have the cathode follower for the trem oscillator circuit. It works fine, but most folks will shy away from recommending such a thing. You didn't hear it from me.
Have you ever compared your 5F11 to a Bassman? I think a YT video of a 5F11 clone is what started me down this rabbit hole. It was basically a clean sound but with lots of clear bass and thumping tremolo.
Compared to my Pro Jr, I like the BM because it has better ability to control the tone, and more bass on tap.

 

5F6Animal

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Best bet, Source Audio True Spring. Best Fender style spring reverb and tremolo you can buy.

All three spring sizes and all three tremolo types Fender used before 1965. Just be sure to get the external expression switch and turn on the function in the editor.

I’ve split and paralleled V1 in a Bassman and I don’t like what it does to the feel of the amp. Channel interactivity is important to the gain and tone of the amp IMO.

That being said, if you really want to have actual bias modulating tremolo, don’t be discouraged by me. It’s a fun thing to have.

Maybe build a Brown Deluxe?
 




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