After further research last night, as far as I can tell there is no schematic for a MV equipped Bassman 50 and that it was a model only around for a couple years in the late 70's. Fun stuff!
I always thought that a cool idea for one of those amps would be to replace the existing master volume with a good sounding post phase inverter master. You see a lot of used Bassman heads that have had a Master volume added on, but this amp has one from the factory...just not a very good sounding one.
That “470” ohm resistor in the phase inverter definitely is a blue/grey/brown/silver to my eyes. That would be a 690 ohm 10%. I found a Bassman 70 Schematic that might help you piece together the master volume circuit.
Blue/grey/brown would be 680Ω. 690 was never a value for CC resistors of that era. 680Ω was probably a factory install. It's not unusual to find discrepancies on old Fender schematics. 470Ω was a more common value in the Fender LTP PI cathode circuit but the value is not critical.
That makes sense, especially considering how consistent they were. I always check the value by lifting a leg before actually removing as well, but for the cursory check I like to do this so I get more familiar with the amp(s).
After further research last night, as far as I can tell there is no schematic for a MV equipped Bassman 50 and that it was a model only around for a couple years in the late 70's. Fun stuff!
The “blue turds” are great once you get any DC leakage out of the board.
I always thought that a cool idea for one of those amps would be to replace the existing master volume with a good sounding post phase inverter master.
You see a lot of used Bassman heads that have had a Master volume added on, but this amp has one from the factory...just not a very good sounding one.
The 7025 tube you are hung up on is V2, not V3. V2 is in the Bass channel and only half the tube is being used. V3 is the Normal channel preamp.
That's a brave viewer!
I like to think what I lack in experience or theory I make up for in technical ability, actually giving a crap, and extreme transparency. Ymmv.
That “470” ohm resistor in the phase inverter definitely is a blue/grey/brown/silver to my eyes. That would be a 690 ohm 10%.
I found a Bassman 70 Schematic that might help you piece together the master volume circuit.
Blue/grey/brown would be 680Ω. 690 was never a value for CC resistors of that era. 680Ω was probably a factory install. It's not unusual to find discrepancies on old Fender schematics. 470Ω was a more common value in the Fender LTP PI cathode circuit but the value is not critical.
Thanks Matt!
Those 100K 1W resistors you were struggling with are fine. They all have other resistors in series/parallel that are making the meter read low.
That makes sense, especially considering how consistent they were. I always check the value by lifting a leg before actually removing as well, but for the cursory check I like to do this so I get more familiar with the amp(s).
also if i'm not mistaken the schematic states 20% tolerance unless otherwise stated. So 14 off 100 would be within tolerance.
@@mcascone The schematic states "All resistors 1/2 watt, 10% tolerance if not specified."