[MRCA] DC-DC Up Converter

[Ray Fantini]

Imagine it would. The first incarnation of that power supply had a series pass transistor powering the filament string with about a dozen components, but at the end of the day that entire regulator was all  just a dropping resistor supplying a constant current load and decided that a regular old resistor would do the same thing. The trick is the voltage drop acrost the resistor. All the tubes on the DAG draws 500 mA at 1.5 volts so the dropping  has to dissipate 10.5 volts and at 0.5 amps that has that resistor producing 5 watts of heat! A proper engineer would never waste so much power generating heat and would use a switching regulator as opposed to generating so much waste but using 7 aH SLA batteries who cares? On the GRR-5 you would have to work backwards figuring the tubes current drain and the appropriate dropping resistor.

Ray F/KA3EKH


From: comcast <kg2bz at comcast.net>
Sent: Friday, September 12, 2025 10:22 AM
To: Ray Fantini <RAFANTINI at salisbury.edu>
Cc: MilRad <milrad at comcast.net>; Mark K3MSB <mark.k3msb at gmail.com>; Milsurplus List <milsurplus at mailman.qth.net>; mrca at mailman.qth.net
Subject: Re: [MRCA] DC-DC Up Converter


Ray. would that circuit work to power a GRR5 receiver ?  do you have to be careful about the voltage drop for the 1.5v side?  Jeff
Sent from my iPhone


On Sep 12, 2025, at 9:22 AM, Ray Fantini via MRCA <mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>> wrote:

Just finished a DAG radio direction finder using this same converter. Its providing 90 volts and replacing a B battery. Built a small box that takes the output of a twelve volt SLA Battery and provides 1.5 and 90 volts for the direction finder. Found that the inverter was fairly quiet but is almost completely lacking any output filtering. It also produced noise on the input buss to the battery but keeping everything in a meatal box and short it was not an issue. Regulation was ok but did notice there are some points where the PWM system on the board will produce weird noise at some settings. Think the little inverter is good for low power things like replacing B Batteries but would not trust it for things like 225 B+ supplies in a big radio.

Ray F/KA3EKH


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