Applied Science over at YouTube has a great video about adding a capture capabilities to a vintage scanning electron microscope, including some great videos of that instrument in action. Check it out:
I’ve been trying to figure out if I want to bother repairing my old HP 1222A oscilloscope which I’ve been using as a waveform monitor attached to the scope ports of my Sencore PA81 Stereo Power Amplifier Analyzer. It’s been run hard over its lifetime from the looks of it, and the CRT is so dim now that with brightness turned all the way up to maximum, you can just barely see the trace if you shield it from external light. It’s an older model, from the late ’70s, but it makes a good audio scope.
While a replacement CRT seems hard to come by, I did stumble across an interesting solution for some of the later digital display oscilloscopes and analyzers: the Simmconn Labs NewScope modules! I’m not affiliated with them at all, but it looks like an interesting product that could preserve a lot of the highly reliable digital gear which just happens to be old and have worn out display sections.
They’re really interesting upgrade modules, which add color and clarity to the old display screens, and have some other interesting features like saving traces, etc. which may not have been available on earlier models. These come in several models, designed to work with:
- 3577A, 3577B Network Analyzer
- 3562A Dynamic Signal Analyzer
- 3563A Dynamic Signal Analyzer
- 8756A Scalar Network Analyzer
- 4145A, 4145B Semiconductor Parameter Analyzer
- 8566A, 8566B Spectrum Analyzer
- 8568A, 8568B Spectrum Analyzer
- 8567A Spectrum Analyzer
- 8753A, 8753B Network Analyzer
- 8757A Scalar Network Analyzer
- 8702A Lightwave Component Analyzer
- 8720A Network Analyzer
And some Tektronix scopes, too:
- TDS 520A 540A 620A 640A
- TDS 520B 540B 620B 680B
- TDS 520C 540C 580C 680C
- TDS 520D 540D 580D
- TDS 644A 644B 654C
- TDS 684A 684B 684C 694C
- TDS 724A 724C 724D 714L
- TDS 744A 754C 754D
- TDS 784A 784C 784D 794D
Worth checking out if you’re in the market!
Rain City Audio had an unusual project through the shop recently. It’s a Magnavox tube amp from the late 1950s. The owner brought it in reporting he’d purchased the amplifier, pulled from a damaged console stereo and modified to be a standalone stereo tube amp, from a Craigslist posting. After a scare involving un-inspected vintage equipment giving up the magic smoke unexpectedly, the amp came in for an inspection which turned up a few recommendations.
It’s a simple amplifier with a 12AX7 and pair of 6V6s per channel, using a 5U4GB rectifier tube. The chassis was thoroughly cleaned and polished, unnecessary parts stripped, and various jacks and controls were added to make it into a standalone product.
Underneath, the wiring was nice and orderly. The previous technician was a hobbyist who’d done good research, and the work which was completed was of surprisingly good quality. My only suggestion would have been to use shielded wire runs to the RCA jacks, but it proved not to be a problem in this implementation. The electrolytic filter, coupling and bypass capacitors (the 4-section can and two components below the chassis) were original, though, and that could cause a problem down the line.
The electrolytic capacitors in this amplifier hadn’t been replaced, but the paper ones had. In some later ’50s gear, it’s entirely possible the original filter capacitor can was still working, but it’s on borrowed time and should be replaced for sure. I soldered a terminal strip with a grounded lug to one of the can’s ground lugs to make a solid starting point for the can rebuild.
Attaching the filter capacitors, associated wiring, and dropping resistor to the terminal strip:
There were also two electrolytic coupling capacitors, 20 uF 25V capacitors, replaced with Nichicon Fine Gold 22 uF 63V electrolytics:
As well as a bypass capacitor, attached between the balance pot and ground. The old lugs for the replaced electrolytic can were cut off to ensure no connections could be made to them in the future.
While inside, I also touched up the solder joints for the new neon power lamp, which had broken free. Then, it was on to testing! This amplifier’s specifications are unknown, so it’s time to measure them.
Using the Keithley 2015 THD Multimeter, HP 3585A Spectrum Analyzer, and Sencore PA81 Stereo Power Amplifier Analyzer I made measurements of the amplifier’s characteristics. The channels are slightly different power. Measurable but not really audible. The amplifier measures about 10W per channel at 1.0V sensitivity. Output was highest into an 8 Ohm load, which means that’s the correct output impedance for the transformers.
At maximum output, volume control full clockwise, 1.0V input signal into 8 Ohms the amplifier produced 1.197% THD. While that sounds high, it’s not bad at all for the time and implementation. In addition, tube harmonic distortion is often considered pleasant to listen to, as opposed to the distortion generated by solid-state devices.
At normal listening volume of 5W, it was about 0.621% THD.
At 1W of output power, the amplifier produced 0.208% THD and at 0.5W it produced 0.129% THD. Driving very high efficiency speakers, this would be a low distortion hi-fi amplifier by standards even well into the ’70s or ’80s. The frequency response was “flat” +/- 3 dB from 70 Hz – 20 kHz.
Bass response in this case is almost certainly being limited by the amount of iron in the output transformer; with less iron, the core will saturate more easily and be able to transfer a smaller amount of lower frequencies. The coupling capacitors are sufficient value not to impact the frequency response in this case.
Overall, with a rebuilt power supply and new coupling and bypass electrolytic capacitors, this amplifier has been overhauled and should be reliable for a long time to come. It’s a little different looking, but it works well and sounds good – and that’s what matters!
Rayovac has been making batteries for over 100 years, and their batteries were commonly found in use with many types of battery-operated tube radios. Most commonly, radios would operate on 45V batteries with a tap half-way (for 0-22.5-45V). Two in series would give you 67.5V and 90V for bigger radios. This style has been out of production for many years, but Rayovac has a good modern replacement for the older Type 783 batteries, the 45V-HD.
It has connections for a modern connector as well as the old-style connections:
If you have a ’20s or ’30s battery radio, and want something more original than using a stack of 9V cells, this looks like a good bet!
I wrote about how the Keurig 2.0 single-serving coffee maker came crippled by built-in DRM, locking you into using only “authorized” coffee servings in the new version of the machine a few weeks back. Enterprising users figured out how to use some scotch tape and the top of a Keurig-branded pod over the sensor to fool it into accepting any coffee serving, but even still, that’s not the most durable fix. Water, steam and a flimsy piece of tape aren’t a great mix and the last thing you want is having to fiddle with tape and optical sensors first thing in the morning just to get your fix.
It gets even better, though: the Keurig 2.0 DRM Freedom Clip! The coffee masters over at the Rogers Family Company, manufacturers of fully biodegradable single-serving coffee pods, figured out the special color Keurig uses to authenticate the cups and produced a clip that fits over the optical sensor with that color on the top face. It clips right in, once, and stays there forever. And the best part?
That’s right: it costs NOTHING, not even postage.
You should probably buy some coffee from them for making this hack possible, but this is fantastic and definitely worth checking out.
Thanks, Rogers Family Gourmet Coffee!
Pekka Väänänen must have been bored over the holidays, as he came up with a fantastic and fascinating new use for an oscilloscope and a laptop: playing a round of Quake on his Hitachi V-422 scope in X-Y mode.
After some pre-processing, apparently it’s a playable vectorized Quake game with a very unique display. Never seen anything like this before! Lots more details over on his site. Check it out!