Hotrod Bassman50 do-up

[tubeswell]

Got an earlyish* Jansen Bassman 50 carcass on tardme which has been sitting around in my to-do pile for a couple of months now. Its in a pretty banged-up state and looks like the internals got cooked at some point.

(*before they introduced a separate screen winding on the PT, but still with the MV)

The carcass is in such a mess that it pretty much needs to be deconstructed and reconstructed. Everything inside is caked in rust, and it is minus the OT so it seems like a waste of time pursuing a restoration, cos I wouldn't get the original sound out of it anyhow. The PT seems to be good to go with the winding leads recovered

I've still got a few Basil Padgett-wound 40-50W OTs in my stash (that I got him to make for me before he gave it away), but I've splashed and ordered a Heyboer OT and choke with a view to turning it into a 6G6B blonde bassman circuit (seeing as how it still has the tapped treble pots) unless there's any screaming objections.

Anyway its my summer project for this year so ding dong.

[Kris]

awesome,as a fan of the bassmans from way back ive always wanted to see a "hot" version of one,one with a bit more filth!

[Anvil Amps Alan]

Will watch this project with interest.
I have a Bassman 5/ 25 chassis in less corroded condition, minus the OPT and can cap.
Don't know what I will do with it yet, I only have one suitable Basil OP Transformer left
I am contemplating building a Marshall Major soon using some Gunn 200 iron I have to hand.

[tubeswell]

Spent a couple of hours deconstructing the thingy. There were a few mustard caps worth salvaging including 4 x .1uF 400V 2 x .056uF 400V and a few other odd sizes. Ah the smell of 50-year-old solder! The faceplates cleaned up alright with a bit of hot soapy water.

I've just got to take the old tube sockets out and clean out the rust

[StrummersOfThunder]

Great project! Looking forward to following the thread!

[elams1894]

Nice work! Does it have an old voltage doubler PT? I have a few of those voltage doubler Power trannies hanging around but have not yet used them in a circuit. Looks a cool project!

[AiRdAd]

Looking forward to seeing the progress on this!

[Bg]

New chassis or decorrode?

[tubeswell]

Wired brushed it and primed in the end. Bit of progress today. PT tested good. Voltage doubler* and primary done.
(*its a very early Bassman 50 circuit - used a voltage doubler to get the ~500 B+)

[tubeswell]

Bit more yesterday. Wired in the heaters with a humdinger and heater elevation (taken from the voltage doubler bleeder network). Its got a 12V heater winding (so I picked up a couple of 12V lamps from the Lamp Man at the top of the Plimmer Steps). Had to make a voltage doubler for the bias supply as well (as a conventional bias circuit didn't cut the mustard). Put some bias test points in using spare TP terminals of different colours I had lying around. Put an in-line HT fuse after the standby switch, and made the standby 'soft start' with a 47k 2W bypass. Screen supply wired in. (The screen filter caps have parallel balancing resistors underneath each cap). I used a 4k7 screen dropper like the original Bassman 50 circuit. I have a couple of chokes that would work in this amp but a resistor is less hassle. I think I'll try 3k3 unbypassed screen resistor for a bit of screen compression (or maybe not). I might shuffle the filter caps around a bit more yet - starting to look like a birds nest.

The Basil-esk OT tested at 3k2 PrZ when I heated it up with a bit of Vac yesterday. I was banking on it being 4k or so, but I can double the load if I need to run 5881s or 6L6s. But as it is, it'd work well with EL34s or KT77s. I had to modify the end bells to get the leads popping out the bottom (instead of the sides).

Hopefully I can re-use the old pots without too much hassle. I will bang some new jacks in tho'.

[tubeswell]

Nice work! Does it have an old voltage doubler PT? I have a few of those voltage doubler Power trannies hanging around but have not yet used them in a circuit. Looks a cool project!

Yeah it needs voltage doublers for the High Tension and the bias supply. (HT winding was 244 VAC, bias winding was 34 VAC. -with a dummy load on the heater winding) With the doublers, the HT hits 695 unloaded and the bias goes up to -79.

Its evolving organically and out of spare parts I've got lying around so its nothing like your beautiful works of art I'm afraid.

[StrummersOfThunder]

Looking good! I love the smell of solder!

[tubeswell]

shuffled the screen supply caps around for more space and wired the inverter (using the salvaged mustard caps) and the OT secondary in. The sprague atom in the pic is leftover from elsewhere and may not last. Waiting on some 600V caps to come in, but could feasibly continue to use stacked 450V caps as I have a bunch of 47uFs. Time and patience will tell.

[tubeswell]

Bit more progress this last week

[druz15]

Holy crap that is a tidy build