5F6A Bassman Modification Webpage

[robrob]

I have a webpage dedicated to 5F6A modifications.

Sample 3-way feedback switch (5F6A - No feedback - JTM45)

[Tom Phillips]

I have a webpage dedicated to 5F6A modifications. Sample 3-way feedback switch (5F6A - No feedback - JTM45)...

Cool site. Thanks for sharing and welcome to the forum.

[Pdavis68]

Count me as a big fan of your pages. I want to build the micro bassman at some point. Awesome idea!

[pdf64]

Any 5F6A type tone stack becomes rather more flexible (and to me, user friendly) if the mid control is modded to a variable resistor, ie 'hot' and wiper terminals linked.
All the previous tone options are available but the range of the bass control is increased (at the CCW end), ie it becomes possible to achieve rather less bass heavy balance. Bearing in mind these were intended to be bass amps, this may be seen to make them more guitar friendly.

Great work with your site!
Regarding the note suggesting uprating screen grid resistors to 2-3 watts, my feeling is this negates the capability of these resistors to fuse in the event of some tube failure modes, which may allow fault current to flow for an extended period of time, potentially stressing PT / OT / choke; therefore my view is that it should only be done if suitable B+ fusing is also added.

[robrob]

Thanks pdf. I'll try the mid tone pot mod and I'll add a note about the fuse function of the 1 watt screen resistor.

[pdf64]

A flame retardant / proof MO type is a benefit for the screen grid resistor.
The fuel load of carbon types, and the stress of the application, can result in burn damage to nearby wiring insulation if there's a tube short.
It may be seen to be worth replacing old but still serviceable CC types for that reason.