Or, for the purist, a capacitor can be added in parallel with the resistor in the feedback path of the op-amp to implement a low pass filter. The heater circuit can power the DV-3 at its spec'd current (though at the low end of its adjustment range). The manufacturer of this system uses a Hastings meter but has apparently removed the 115 VAC input circuitry and powered the low voltage electronics directly which includes a zener regulator and a 500 Hz oscillator (two transistors, toroidal transformer) to drive the tube from a 9 V battery (pushbutton activated so as not to run the battery down too quickly!) - I added an input for an AC adapter since portability isn't a major concern for home-built lasers and replaced the pushbutton with a good old toggle switch! A photo of this unit is shown in Hastings SV-1R TC Gauge Readout. After calibration using my DB-18 which is the reference tube for the DV-5, it now tracks my NV-8B (DV-8) readout fairly closely which gives me some confidence that both the readouts are accurate and the reference tube hasn't leaked too much. However, the DV-5's voltage is much lower so the adjustment range may not be adequate (but a 1k ohm "I Adj." pot or additional series resistor would take care of that).
For campers who live in warm climates or those who take their gear seriously and want to invest in a sleeping bag made for the cold and another made for the warmth, this is a great choice sure to last for years to come. You should also make sure the engine is cold before you start -- spark plugs can get very hot! The DV-6M uses a much lower power heater, has slightly better sensitivity below 20 milliTorr, and a somewhat faster response than the DV-3M (which is no longer manufactured), but is otherwise similar. The bones were not regarded as holding a particular power derived from the hero, with some exceptions, such as the divine shoulder of Pelops held at Olympia. I'd have almost thought they copied the power supply, oscillator/driver, and sense amplifier circuitry from SG-TC2 except that the NV-100 predates it by many years. When I acquired this unit, I thought it used a DV-3 tube because that's what the SV-1 uses according to my chart from Hastings. Hastings VT-5B control unit for the DV-5M TC gauge tube. I have confirmed that the DV-6M is compatible with my home-built control unit requiring only adjustment of the heater current and atm offset.
However, there is a resistor of about 15 ohms in series with the DC output of the TC gauge tube (pin 7) which results in the 10 mV meter movement actually requiring approximately 14 mV for full scale deflection. For tubes other than the DV-3, the meter reading for the "Iset" position of the Meter Select switch won't be exactly full scale but can be recorded as an aid in initial calibration. This might be bad for TC gauge tubes other than the DV-100.) See that schematic in the Hastings NV-100 Operation Manual. Since constructing SG-TC1, I have acquired a variety of Hastings TC gauge tubes including two new DV-6M tubes for less than half the usual price. There is no "AC Null" adjustment - if the number of turns on each half of the windings of T2 are equal, the only ripple at the output of the op-amp will be due to the unequal resistances in the two halves of the TC gauge heater.
The initial setup procedure for SG-TC2 is almost the same as for SG-TC1 but the "I Adj." adjustment consists of two parts: "I Coarse" (the voltage regulator) and "I Fine" (formerly "I Adj.", front panel). An IC regulator (LT1084) provides stable 9 VDC from an 11 to 15 VDC source. 5.1 VDC sources for the op-amp since the oscillator voltage was somewhat marginal. The simpler approach of using a pair of blocking diodes would have dropped the battery voltage by 0.7 V which would greatly reduce its useful life; using the switched contact on the adapter jack would not permit selecting between the regulated 9 VDC and beauty uniforms battery. Others I've obtained used, but working, include a pair of DV-4AMs, a DV-5M, and another DV-3M. I obtained a third apparently new in box DV-6M along with my CVT-26 (see below). A shorted cap is apparently a common failure with this design as one of the other units I obtained using this approach had had its cap replaced in the past. The family units have an interconnecting door to a twin studio unit. Hastings VT-6B control unit for the DV-6M TC gauge tube.
