Building tube amps (whilst waiting for thesis comments)
Posted: Wed Jan 21, 2015 9:11 pm
Pics of a build underway here at present
I got an old Jansen Bassman 50 Carcass of local website auction a couple of months back. Here's how it looked then.
Then I gutted the chassis (salvaging some mustard caps in the process), and wire-brushed all the rust of the the chassis
and primed it with rust guard
Then I rigged a dummy load (8 paralleled 64R 10W resistors to give a draw of 1.5A on the 12.6VAC heater winding) to test the original PT
And tested the HT winding too (It needs a voltage doubler - The original Jansen Bassman 50 was built with voltage doublers everywhere)
The I wired in the heaters and built the voltage doublers for the HT and the bias
Then I wired in the screen supply node (using a 4k7 screen-supply dropper) (I decided later-on not to go with an unbypassed 3k3 screen grid - too much screen current feedback)
Then I wired in the inverter (but later I ditched the Sprague Atom cap shown here in the mock-up (see later shots)
How it looked after I changed the inverter supply cap to 2 x 47uF 450V in series (and began to mock-up the pre-amp)
Here's where I'm up to at present ('61 bassman normal channel wired in and bass channel partly wired in - I ran out of salvaged mustard caps at this point dammit)
I got an old Jansen Bassman 50 Carcass of local website auction a couple of months back. Here's how it looked then.
Then I gutted the chassis (salvaging some mustard caps in the process), and wire-brushed all the rust of the the chassis
and primed it with rust guard
Then I rigged a dummy load (8 paralleled 64R 10W resistors to give a draw of 1.5A on the 12.6VAC heater winding) to test the original PT
And tested the HT winding too (It needs a voltage doubler - The original Jansen Bassman 50 was built with voltage doublers everywhere)
The I wired in the heaters and built the voltage doublers for the HT and the bias
Then I wired in the screen supply node (using a 4k7 screen-supply dropper) (I decided later-on not to go with an unbypassed 3k3 screen grid - too much screen current feedback)
Then I wired in the inverter (but later I ditched the Sprague Atom cap shown here in the mock-up (see later shots)
How it looked after I changed the inverter supply cap to 2 x 47uF 450V in series (and began to mock-up the pre-amp)
Here's where I'm up to at present ('61 bassman normal channel wired in and bass channel partly wired in - I ran out of salvaged mustard caps at this point dammit)