Got a Bassman Ten in today for service. Appears to be from early 1976 (transformers and pots date to late ‘75).
Customer said it sounded funny. I’ll be doing a cap job as well as reverting it back to stock 100%.
It looks like a screen resistor blew at one point and was replaced, and the bias circuit looks like a small mess, somebody moved the bias and rectifier board. And I’m not sure what’s up with the yellow leads coming off the PT going to the small tag strip.
I’m having a tough time finding a layout for this amp, please tell me it exists somewhere?
Last edited by Yoda on Thu Dec 07, 2023 3:20 am, edited 3 times in total.
The Bantam Bass-Amp has a layout that is similar to the Bassman Ten. The Bassman Ten is SS rectified and has a master volume, but the pre-amp is about the same.
Bantam Bass-Amp CFA7003 Layout.png
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I guarantee you that due to heat that PI decoupling cap up against that 10 watt resistor has drifted in value greatly.
Those amps had a oscillation problem hence the ciramic caps off of each output tube and all the wound up white wire around each harness.
The to eliminate the problem and clip out those caps move the PI decoupling caps right to each output tubes grid terminal.
This technique helps you to get the potential troublesome grid wires as short as possible, and is a technique that can be used and more over should be used throughout a amp.
Output tubes do not have a heck of a lot of gain by design, but this can really help out in the preamp sections, and especially if you have a problem with gain stage interaction.
You may need to try each cap installed one way ( flipped ) if there is still a light oscillation issue.
If the amp is being used for bass only then these two small ciramic caps can stay in.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
It also turns out that Bantam Bass schematic posted above is s much better match for the Bassman Ten. In fact the main difference really is the rectifier section which unfortunately is the section I need the most LOL. But this is great because with that schematic and various pictures of original Bassman Tens online I have a good idea of where the rectifier board and its wiring should be moved to. The preamp side of the Bantam Bass appears to be a dead match.
The customer wants to use this amp for both guitar and bass, I believe bass on one channel and guitar on another though not at the same time.
Transformer bolt should not be used for mains ground. Drill a hole near where the mains enters the chassis, use a ring lug, bolt it down there. Nice looking amp...LOL! Good luck with it.
Something concerns me about this amp !
That filter cap that blew up even before it did such should have been pulling enough extra current to pop the amps fuse.
Was / is the fuse in the amp the called for rating?
Have you had the amp powered up yet and is the PT ok?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
