If you have a Nems Clarke 120 series Field Strength Meter or any instrument that uses the 67.5V “B” batteries Bafaro Engineering has a replacement module that will allow you to run your vacuum tube instrument from eight “AA” batteries. The eight “AA” batteries will deliver 67.5V regulated at up to 17mA – this is better than the original “B” battery. The module is the same size as the original battery except for the output terminal strip on the top of the unit. The module has been tested in a Nems Clarke 120B and it does not affect the meter reading. The boost supply is isolated from the case of the unit and will not disturb the bias network used to set the gain of the tubes used in the Nems Clarke 120 series meters.
ONLY INTENDED FOR THOSE EXPERIENCED IN HIGH VOLTAGE CIRCUITRY!
This preamp has the same volume, treble, and bass controls as the original. The band width of more than 80KHz at -3dB from 2KHz and boost & cut of more than 9dB are provided with the original controls. The connectors are gold plated for the best reliability. If the controls in your guitar are noisy you can send me the complete assembly with the mounting bracket and I will clean or replace the Potentiometers. The board is made of G10 fiberglass epoxy for best reliability. The connectors are the same Molex connectors used on the original board that I worked from.
This relay is used in the MULTIVAC model AG6 or AG800 vacuum packing machine. This module will time for 1650msec with a 270K resistor between pins 6-7 or 7-8 and then turn on the relay which has a single pole double throw output. This is made to run from 220VAC 50 to 60Hz. The edge connector is an 11-pin circuit that will fit in the original socket. The power transformer and 5W Zener regulator should be able to withstand short term transients better than the original MULITVAC voltage dropping circuit. Testing has shown that the timing is within 3% of the timing original time delay relay.
The BE5080-1718A lamp replacement module is designed to replace the lamp module E1 in the HP4800A Vector Impedance Meter. The BE5080-1718A should also work in the HP8640A/B option 1. Although it has not been tested in the HP8640A/B option 1. The E1 module is in the negative feedback path of the Wein Bridge oscillator. The purpose of E1 is to regulate the negative feedback in order to keep the overall loop gain of the in the range of linear operation; This is the range of signal output in which the sine wave is pure and not clipped by running the output stage of the amplifier into saturation or cutoff. The lamps do this by changing resistance in response to the signal level coming from the output of the oscillator.
This change in resistance is highly dependent on the temperature of the tungsten filament of the lamp. This temperature coefficient of resistance is nonlinear so this makes it a good control device. This lamp in the negative feedback path was used in the first HP product, the HP200A Wide Range Oscillator. This was the subject of William Hewlett’s master’s thesis.
Since the lamps originally used are no longer available, a newer control device was sought. The Junction Field Effect Transistor (FET) has variable resistance characteristics that can be made to control the lower half of a voltage divider network inserted into the negative feedback path.