Good Morning!
IT has to do with how the AM Regulator can also be a power switch for SSB modes.
How that works is by using two Transistors - TR52 and TR54
One works for FM and SSB modes - it turns (mutes) off audio by shuniting it to ground (TR54)
TR52 - keeps AM out of your FM mode - but ALLOWS for Carrier to be adjusted as if it was AM - this keeps the Final and Driver from overheating - FM mode is pretty hard on devices and consumes to the most power in the radio for that mode. Bandwidth is needed so you set up AM and FM modes with AMP VR13 for carrier - when in FM mode or SSB, the AMC amp TR53 is pretty much disabled.
TR52 works as a means to BYPASS any envelope developed in TR 51 and TR50.
So the battery voltage supply - is from the MODE switch routings to the various switches that turn on or off the AM Regulator sections for Audio or Envelope - SSB (TR52 and TR54) mode allows for full rail voltage, but in FM mode you don't want that on this design. (TR54 only)
IT has to do with how the AM Regulator can also be a power switch for SSB modes.
Good morning, another doubt I have. Later I will check previous answer when at home. How 12.5 volts in tr51 base is achieved? It is. Another voltage is under the specification, but I can't see in schema how 12.5 volts can be generated...
How that works is by using two Transistors - TR52 and TR54
One works for FM and SSB modes - it turns (mutes) off audio by shuniting it to ground (TR54)
TR52 - keeps AM out of your FM mode - but ALLOWS for Carrier to be adjusted as if it was AM - this keeps the Final and Driver from overheating - FM mode is pretty hard on devices and consumes to the most power in the radio for that mode. Bandwidth is needed so you set up AM and FM modes with AMP VR13 for carrier - when in FM mode or SSB, the AMC amp TR53 is pretty much disabled.
TR52 works as a means to BYPASS any envelope developed in TR 51 and TR50.
So the battery voltage supply - is from the MODE switch routings to the various switches that turn on or off the AM Regulator sections for Audio or Envelope - SSB (TR52 and TR54) mode allows for full rail voltage, but in FM mode you don't want that on this design. (TR54 only)