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Neither the 511 nor the 511A has a [[thermal cutoff]].   
Neither the 511 nor the 511A has a [[thermal cutoff]].   


===511A differences===
===511===
The 511 was produced with serial numbers 101 to 454.  The 511A has serial numbers 455 and up.
The original 511 was produced with serial numbers 101 to 454 (June 1947 – November 1948).  


The main difference between the 511 and the 511A is the power supply.
There are two power transformers, T1 and T2, both operating on 60 Hz mains power with their primaries in parallel.
 
In the '''511''', there are two power transformers, T1 and T2, both operating on 60 Hz mains power with their primaries in parallel.
T1 produces the CRT anode and cathode voltages, as well as various other regulated and unregulated voltages.   
T1 produces the CRT anode and cathode voltages, as well as various other regulated and unregulated voltages.   
The CRT cathode and anode voltages in the 511 are simply rectified voltages from the secondary of T1.   
The CRT cathode and anode voltages (+1500/-1500 V) are simply rectified voltages from the secondary of T1.   
The lack of regulation means that variations in mains voltage results in variation of deflection sensitivity.   
The lack of regulation means that variations in mains voltage results in variation of deflection sensitivity.   
The +275 V and + 475V rectifier circuits have choke inputs.


In the '''511A''', the CRT cathode and anode voltages are produced by a 2 kHz oscillator that is powered by the 511A's +225 V<sub>DC</sub> regulated supply.
===511A (SN 455+)===
This results in vertical deflection calibration that is independent of mains voltage.  Unlike in the 511, there are no chokes in the power supply.


The main difference introduced in the 511A is the power supply. 
The regulated positive supply voltages were lowered somewhat to +225 V and +450 V, with capacitor-input circuits (no chokes).
The CRT cathode and anode voltages are produced by a 2 kHz oscillator (a [[6AQ5]]) that is powered by the +225 V<sub>DC</sub> regulated supply.
This results in vertical deflection calibration that is independent of mains voltage. 
HV rectifiers are two [[1B3GT]] tubes producing +1500/-1500 V.
===511A (SN 1406+)===
Beginning with SN 1406, the 511A(D) gained a continuously variable sweep speed control, visible as a 2nd dial next to the "sweep speed multiplier".
===511A (SN 2406+)===
From SN 2406 upward, a dedicated calibrator stage uses one half of a [[12AT7]], V16.1, to clip a voltage derived from the mains transformer to a 100 V level divided from the regulated +225 V rail.
From SN 2406 upward, a dedicated calibrator stage uses one half of a [[12AT7]], V16.1, to clip a voltage derived from the mains transformer to a 100 V level divided from the regulated +225 V rail.
The HV rectifier uses two [[1V2]] tubes producing +1800/-1500 V.


===Delay===
===Delay===
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