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I had been admiring this radio cab, for close to three years:
When I was looking through the pictures, I realized that I hadn't taken one of the front panel. Will try to do so, soon.
The radio cabinet was in an antique mall, about an hour and a half from home. Get there about once a year. And, it was always there. The radio chassis was built in several sections, and had been cannibalized quite a bit. Probably half of it was gone, as there were empty places on the platform that had something mounted to it previously. So, I made them a very low offer, and they took it. As this was man-day (wife had other more important things to do), I asked Don (music leader at our Church) to go with me. We loaded it on the truck, and while we were wrapping it up and tying it down, the store clerk told me that an elderly couple had a couple boxes of tubes that they had just tried to sell, but couldn't. I walked over to their car and looked them over. They had about 150, by their count. And, a rather thick book of old radio schematics. So, we bargained and I carried those away, also. I believe that I got more tubes than they figured.
Anyway, to preserve the look of the front panel, I plan to only have a volume pot (with power switch), a bass pot, and a treble pot. I've been playing around with octals for awhile, mainly because that's what I have the most of. As I only have a few of the 12A_7 series tubes, I decided to dig through the 'non-standard' tubes that I have, to see what I can substitute in place of them.
I've made an initial schematic, modeled after the '59 Bassman. Not that I wanted a Bassman. It was just a simple one to start with. I substituted a Baxandall tone stack in place of the Fender, to eliminate the Mid pot. I also added a Master Volume that will go on the front. The two volume pots in the pre-amp will go on the back of the chassis. I also added a 5G9 Tremolo to the schematic, as I wanted some form of effects built into the amp. Those controls will go in the back, also. I haven't assigned component labels or values, though the power supply shows labels. I pulled it over from another drawing, and neglected to remove them.
So, here's the first draft of the schematic:
Not a very good graphics print from ACAD, so I have included a high resolution PDF print of it.
In the drawing, I put a pot in place of the typical 220K resistors for biasing. I figure a 500K pot to balance the bias for mismatched tubes, and a 10K to set the bias for both, down at the power supply. I would like input as to whether anyone has done this configuration of biasing before. And, please advise me as to a better way, if this one is impractical.
I have a new chassis that Terry Naugler, of Seaside Music, built for me. I had him make it to be large enough to cover the entire platform, with plenty of clearance for the pots up front. I had to resist the urge to just fill up the chassis. I will leave it mostly empty. This will allow plenty of separation between the power supply and the amp.
I plan to have one of the local furniture shops refinish the cabinet, as I haven't done anything like that since I was a kid.
This will be a slow process for me, as I haven't been getting in much shop time. But, the temperatures are getting very moderate, and my metal shop is more comfortable to work in, if I open the doors. Rains from the hurricane have prevented that, lately. I don't mind, though. Earmuffs take care of that. Please look my schematic over, and comment. Thanks.
Jack
When I was looking through the pictures, I realized that I hadn't taken one of the front panel. Will try to do so, soon.
The radio cabinet was in an antique mall, about an hour and a half from home. Get there about once a year. And, it was always there. The radio chassis was built in several sections, and had been cannibalized quite a bit. Probably half of it was gone, as there were empty places on the platform that had something mounted to it previously. So, I made them a very low offer, and they took it. As this was man-day (wife had other more important things to do), I asked Don (music leader at our Church) to go with me. We loaded it on the truck, and while we were wrapping it up and tying it down, the store clerk told me that an elderly couple had a couple boxes of tubes that they had just tried to sell, but couldn't. I walked over to their car and looked them over. They had about 150, by their count. And, a rather thick book of old radio schematics. So, we bargained and I carried those away, also. I believe that I got more tubes than they figured.
Anyway, to preserve the look of the front panel, I plan to only have a volume pot (with power switch), a bass pot, and a treble pot. I've been playing around with octals for awhile, mainly because that's what I have the most of. As I only have a few of the 12A_7 series tubes, I decided to dig through the 'non-standard' tubes that I have, to see what I can substitute in place of them.
I've made an initial schematic, modeled after the '59 Bassman. Not that I wanted a Bassman. It was just a simple one to start with. I substituted a Baxandall tone stack in place of the Fender, to eliminate the Mid pot. I also added a Master Volume that will go on the front. The two volume pots in the pre-amp will go on the back of the chassis. I also added a 5G9 Tremolo to the schematic, as I wanted some form of effects built into the amp. Those controls will go in the back, also. I haven't assigned component labels or values, though the power supply shows labels. I pulled it over from another drawing, and neglected to remove them.
So, here's the first draft of the schematic:
Not a very good graphics print from ACAD, so I have included a high resolution PDF print of it.
In the drawing, I put a pot in place of the typical 220K resistors for biasing. I figure a 500K pot to balance the bias for mismatched tubes, and a 10K to set the bias for both, down at the power supply. I would like input as to whether anyone has done this configuration of biasing before. And, please advise me as to a better way, if this one is impractical.
I have a new chassis that Terry Naugler, of Seaside Music, built for me. I had him make it to be large enough to cover the entire platform, with plenty of clearance for the pots up front. I had to resist the urge to just fill up the chassis. I will leave it mostly empty. This will allow plenty of separation between the power supply and the amp.
I plan to have one of the local furniture shops refinish the cabinet, as I haven't done anything like that since I was a kid.
This will be a slow process for me, as I haven't been getting in much shop time. But, the temperatures are getting very moderate, and my metal shop is more comfortable to work in, if I open the doors. Rains from the hurricane have prevented that, lately. I don't mind, though. Earmuffs take care of that. Please look my schematic over, and comment. Thanks.
Jack
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