Barbouri's Electronics Projects
Restoring vintage electronics along with designing and building new circuits. One eye looking into the past, the other looking into the future.
Electronic projects that I work on in my spare time.
After the restoration of the Nakamichi 620 amplifier last year, it had been working great for 6 plus months. Then one day I turned it on and there was no sound output. Luckily the speaker protection circuit did it’s job and no speakers were damaged. The right channel had it’s output shorted to B+ (53 volts).
I finally decide that I had pushed my luck far enough with my battery backed NVRAM in my Tektronix TDS 380 oscilloscope. The specifications for the Dallas Semiconductor DS1644-120 Timekeeping RAM state that it is good for at least 10 years at 25°C, and mine had just turned 28 years old.
I decided to take a gamble on purchasing a Power Designs Inc. TP330 triple output power supply. It was a bit rough looking with a bunch of stickers on the front panel, but no scrape marks from past sticker removal visible. The seller stated that the bottom analog meter was non-functional, but the output terminals measured voltage that changed with the voltage knob.
I was generously donated three Nakamichi BlackBox series units, by the same person who donated the “System One” rack from a previous post.
The units were in great condition, and more than likely could have been used as-is. They also surprisingly came with their original owners manuals, which usually get misplaced or lost over the years.
I did not take any pictures of the initial refurbishment of the Nakamichi 610 control preamplifier as it was mainly cleaning and capacitor replacement. But as soon as I thought the work on all the components of the System One rack had been completed, one of the dB meter lamps failed in the 610 preamp.
Included in the rack of Nakamichi “System One” equipment I recently acquired was a 600Ⅱ two head cassette console. This is the same rack that was involved in a building fire and the previously repaired Nakamichi 620 amplifier.
I was kindly donated a Nakamichi “System One” rack of audio equipment recently. Overall the equipment was in good shape, but had been in a building fire and suffered from significant smoke damage. There was not any detectable heat damage and only minor water damage.
After successfully repairing the 610 FM Tuner / Preamp I decide to tackle the model 620 audio power amplifier next.
I managed to snag a Monroe 430 calculator that was in good condition and a reasonable price. The Monroe 430 is 14 digit four-function calculator with memory, percent, and a few other extras. I have worked on a model 425 and 420 in the past so I kind of knew what I was getting into, especially the lack of documentation.
Welp, another calculator tale of woe. This time it is a Monroe 650 calculator found on eBay. The 650 is the top-end model of Monroe’s 600 series calculators. It is a 16 digit Nixie tube display calculator with addition, subtraction, multiplication, division, square root function, and two memories. It operates in fixed decimal or floating point modes, and has 5 changing indicators spaced every increment of the base-10 exponent of three from the decimal point.
The price was right and included free shipping.
The APF Mark XII (12) is an interesting calculator. It is based on the Cal-Tex Semiconductor Inc. CT5005 FlexiChip, which was developed in 1972. The calculator is a four function with separately addressable memory register, all on a single IC.
A recent addition to the desktop calculator collection is the Canon Canola L100A desktop 10 digit gas discharge display calculator. This unit was purchased as a working calculator, and was in good shape except the heavy yellowing of the beige upper case..
It wasn’t the exact calculator that I was looking for, but the purchase was well worth the price paid for it. The model 425 from Litton Monroe is a 12 digit Panaplex display with memory calculator.
I decided to see what I could do about the temporary modification to the Burroughs C 3207 multiply key indicator, before it became a permanent modification.
Another nice calculator find for the collection is my CS-2115. It is a 12 digit calculator with a vacuum fluorescent display, memory, and several extra functions.
Well I just finished working on the APF Mark 1 calculator so I wasn’t looking for another calculator project right away, but I stumbled upon this Burroughs C 3207 calculator with several issues for a price that was too good to pass up. And it’s a vintage 14 digit Nixie tube calculator Built in late 1969.
The newest addition to my small calculator collection is an APF Mark 1 desktop unit. I found it on Ebay a few dozen miles from where I live. As usual it was untested, as it did not have a power cord, and other than being dirty it looked in good condition.
