Here in Australia we rarely see genuine tweed-era Fender amps. There was an embargo on imports from the USA for quite some time after WWII and we only got Fender imports starting in the early '60s. So you can imagine my delight when I went to Guitar Centre in downtown Manhattan a few years ago and saw a row of tatty old tweeds!
So it was really exciting and a little daunting for me when a guy I know brought around a 5F6-A Bassman for me to fix up. He only bought the chassis part - all the electronics - but no cab or speakers. He knew I had a Mojotone 4x10 cab that I had built a Bassman into a while back but had then put that amp into a 2x12 cab for another friend. So I sold him the cab and he brought around four ten inch speakers and the amp and I got to work.
Firstly I cleaned a lot of gunk out of it. I didn't want to make it look brand new but also didn't want it to burst into flames! So now it still looks impressively old but there's no greasy gunk to cause issues. Then I removed the (replaced) 120V PT. I just happened to have a Mercury Magnetics 8087 style PT with a lower B+ than stock. This suited the owner perfectly as he wanted to try and get it to break up at lower volumes than a normal Bassman and it does just that.
The OT and choke seem to be original - yay! The electrolytics had all already been changed but I rewired the caps in the doghouse because they had been replaced in the authentic '50s fashion, with the grounds soldered though holes drilled in the actual doghouse cover. I had always thought this was a dodgy way to ground some of the most important caps in the amp and recently saw a Psionic Audio video where he basically confirmed my fears. It's just a bad, noisy way to do it. So I made up a little tagboard and soldered all the caps to it with the ground being soldered next to the PT like they do in BF Fenders. As a result the noise floor is extremely low - a lot less noise than a RI Bassman. I'm quite proud of that!
I replaced the old worn out switches and wired up the speakers in authentic fashion with Switchcraft RCA plugs. Installed a 3-pin power cable wired to code with the ground being longer than the hot or neutral. The hot now goes to the fuse and then the On/Off switch. With the lower B+ PT I had to adjust the bias circuit a little to get it to bias but now it's biased at around 60% (my preference) with a pair of NOS USA small bottle 6L6s. The B+ is around 330VDC and it sounds better than I thought it would. It's still loud but not crazy loud - you could use it at a (loud!) pub volume with it cooking and not get into trouble too much with the sound guy. It's a little louder than I would play but blues guys seem to get away with it here...
The only real "mod" I did was to reduce the cathode bias cap on the first stage. Even with Bass on zero it was still really bassy so I swapped it out for a .1µF cap and the owner loves it. Now he can turn the bass down enough for his Strat to almost sound too thin - it gives him some leeway and will hopefully let him play a Gibson through it without it booming. I also used the more common 5F6-A tone stack of 250pF treble cap, a .1 and a .022 tone caps and a 100K slope resistor. The RI Bassman follows the original factory schematic but I've never seen a photo of an old Bassman with that setup.
What has struck me about this experience is that Leo knew a thing or two about amps! With the exception of the filter cap grounds the amp is very well designed to be very quiet. And the tone is just glorious. Detailed, complex yet clear, incredibly responsive and just beautiful. It really does sound impressive. I've never heard a RI Bassman sound as clear, punchy and detailed. Even when cranked the low end holds together impressively - no RI Bassman I have played does that. I'm not really a "vintage tone" snob, but damn this amp sounds killer!
And in all my excitement of course I forgot to take any photos. Sorry!
So it was really exciting and a little daunting for me when a guy I know brought around a 5F6-A Bassman for me to fix up. He only bought the chassis part - all the electronics - but no cab or speakers. He knew I had a Mojotone 4x10 cab that I had built a Bassman into a while back but had then put that amp into a 2x12 cab for another friend. So I sold him the cab and he brought around four ten inch speakers and the amp and I got to work.
Firstly I cleaned a lot of gunk out of it. I didn't want to make it look brand new but also didn't want it to burst into flames! So now it still looks impressively old but there's no greasy gunk to cause issues. Then I removed the (replaced) 120V PT. I just happened to have a Mercury Magnetics 8087 style PT with a lower B+ than stock. This suited the owner perfectly as he wanted to try and get it to break up at lower volumes than a normal Bassman and it does just that.
The OT and choke seem to be original - yay! The electrolytics had all already been changed but I rewired the caps in the doghouse because they had been replaced in the authentic '50s fashion, with the grounds soldered though holes drilled in the actual doghouse cover. I had always thought this was a dodgy way to ground some of the most important caps in the amp and recently saw a Psionic Audio video where he basically confirmed my fears. It's just a bad, noisy way to do it. So I made up a little tagboard and soldered all the caps to it with the ground being soldered next to the PT like they do in BF Fenders. As a result the noise floor is extremely low - a lot less noise than a RI Bassman. I'm quite proud of that!
I replaced the old worn out switches and wired up the speakers in authentic fashion with Switchcraft RCA plugs. Installed a 3-pin power cable wired to code with the ground being longer than the hot or neutral. The hot now goes to the fuse and then the On/Off switch. With the lower B+ PT I had to adjust the bias circuit a little to get it to bias but now it's biased at around 60% (my preference) with a pair of NOS USA small bottle 6L6s. The B+ is around 330VDC and it sounds better than I thought it would. It's still loud but not crazy loud - you could use it at a (loud!) pub volume with it cooking and not get into trouble too much with the sound guy. It's a little louder than I would play but blues guys seem to get away with it here...
The only real "mod" I did was to reduce the cathode bias cap on the first stage. Even with Bass on zero it was still really bassy so I swapped it out for a .1µF cap and the owner loves it. Now he can turn the bass down enough for his Strat to almost sound too thin - it gives him some leeway and will hopefully let him play a Gibson through it without it booming. I also used the more common 5F6-A tone stack of 250pF treble cap, a .1 and a .022 tone caps and a 100K slope resistor. The RI Bassman follows the original factory schematic but I've never seen a photo of an old Bassman with that setup.
What has struck me about this experience is that Leo knew a thing or two about amps! With the exception of the filter cap grounds the amp is very well designed to be very quiet. And the tone is just glorious. Detailed, complex yet clear, incredibly responsive and just beautiful. It really does sound impressive. I've never heard a RI Bassman sound as clear, punchy and detailed. Even when cranked the low end holds together impressively - no RI Bassman I have played does that. I'm not really a "vintage tone" snob, but damn this amp sounds killer!
And in all my excitement of course I forgot to take any photos. Sorry!
