Toots for vk3kri@mastodon.radio account

Written by vk3kri on 2025-01-16 at 05:54

About 30 years ago I replaced the active part of the wein-bridge oscillator with an ne5534 using lamp amplitude stabilisation rather than the R53 thermistor.

The distortion from the oscillator itself dropped to 0.006% - which was a huge improvement, however I rather quickly

discovered the output amplifier that followed had distortion of its own of about 0.05%. And there it stayed until 2025.

[#]electronics #vintagetestgear

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Written by vk3kri on 2025-01-16 at 05:52

Having finished the new ad9833 siggen and measured its distortion (0.15%) I thought it might be time to turn my attention again to my vintage AWA G250 signal generator. From the date code on the Sprague tantalum caps it was built some time after the 37th week of 1966. So its not quite as old as Aus decimal currency, but certainly more than 55 years old.

The manual says its distortion was originally better than 46dB down( 0.5% !). Not Great.

[#]electronics #vintagetestgear

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Written by vk3kri on 2024-12-16 at 04:40

Seems to be a bit of a droop this afternoon...

Time looks to have drifted about 1.5 Secs since 10:00 this morning with frequency hovering below 50Hz

@xssfox

[#]hertzSoGood #hertzNotSoGood

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Written by vk3kri on 2024-12-08 at 09:16

So next Issue- The board with the AD9833 DDS and the MCP41010 digital pot looks like the diagram, without the bits in red. The board I received had a 10k feedback resistor around the AD8051 rather than the 5k shown. The sine and triangle wave from the DDS has a swing from 38mV to 650mV . Feeding 650 mV into a non inverting amp with gain of 11 will give an output of 7.15V - clearly not going to happen on a supply of 5V . Changing from10k to 5 k feedback results in no more clipping .

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Written by vk3kri on 2024-12-04 at 05:12

The optical shaft encoder was not without problems.

It turns out that the bearings are so good that an inbalance in the knob is enough to cause the knob to turn slightly when released in certain positions. The heavy side was opposite the pointer so it tried to turn the pointer upmost

Gluing a nut under the pointer side balanced the knob. Problem solved.

[#]electronics #diytestgear #siggen

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Written by vk3kri on 2024-12-03 at 05:01

I wanted to use an optical encoder of this type for the main control as I have used them before for a VFO and they are really nice. A ball race at each end make the action super smooooth. No clicky knobs here!

[#]electronics #diytestgear #siggen

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Written by vk3kri on 2024-12-03 at 04:48

Prior to actually drilling that case I prototyped the control part of of the generator, so there was at least a chance I'd end up with something working.

[#]electronics #diytestgear #siggen

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Written by vk3kri on 2024-12-03 at 04:42

An early stage of the homebrew AD9833 sig gen. Using an Arduino nano and an AD9833/MC41010 DDS/attenuator module. I plan to trickle out status reports in a non-linear manner....

[#]electronics #diytestgear #siggen

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Written by vk3kri on 2024-11-28 at 00:33

I ran out of 10n caps so I used some .01uF instead. #electronics.

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