Update: Keith graciously, most carefully packed and sent me the 561B with the audio band 20Khz type PSA-021 Nelson-Ross Spectrum analyzer and other Tek plug-ins.
In exchange I offered to get it going and share findings with this forum. A walk through and photos follow. Enjoy!
561B Tektronix Scope
This is a nice scope. A mid 1960s design, 10Mhz rated with a high serial number of later manufacture. Perfectly suited for audio-band work. Compared to the 580s I’ve been working on this is a charm. Seems so compact, uncluttered and nice lines too!
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SOP for older equipment means cleaning and spraying the switch controls in the mainframe and plug-ins with (DeOxit) before use. Turned out this unit was pretty clean with only a slight dust coating (not usual!). Decided not to variac or reform the mainframe caps for several reasons; including that it had recently been powered. When switched on both LV and HV power-supplies were found regulating and in tolerance. The calibrator had spot-on voltage for all ranges and needed no adjustment. It also provided a perfect 1khz square wave with great symmetry (oh how I wish the big 500’s had a calibrator frequency adjust!). A promising green dot appeared in view.
Tektronix Type 2A60 Amplifier
For the 561B in the spectrum analyzer configuration, the 2a60 sits in the right-hand slot and used as a sweep horizontal amplifier. It’s driven by a 1.8v sweep signal coming from the PSA-021 horizontal output via BNC connection. The first order of business was calibrating the sweep to fit the 10cm display and to start at the left-hand lower corner. Getting it to do this took quite a bit of fiddling and was very time-consuming. I suspect this will be required every session. For Tektronix, the type 2a60 is a minimalist single trace dc-1Mhz amplifier though is entirely suitable for this application.
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Nelson-Ross PSA 021
For those unacquainted with a spectrum analyzer here's a little primer: it looks like an oscilloscope but instead reveals discrete frequencies that make up a composite signal. Specific frequencies are cast in relative strength (amplitude) along the Y -(vertical) axis. The different frequencies are shown spread across the frequency domain (instead of the time domain) on the X-(horizontal) axis.
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Approaching this was at first daunting without a manual.
While I had experience with a spectrum analyzer before, its been awhile and I was not entirely familiar with the NR control operation or nomenclature. However I was able to get response by fiddling around and using a HP 204c oscillator as a source. After awhile I figured out most controls. It has two basic spectral modes: Full scan (where the full 20khz spectrum is represented across the display) and Variable Dispersion (where the center frequency is selected and scan width is determined with the “dispersion” control). It offers two horizontal sweeping modes: Automatic (with horizontal sweep speed control) and Manual (operator turns the knob/ dot moves). These as well as the attenuator and IF amplifier controls all seem to work – though need calibration.
Initially I didn’t understand the purpose of the zero balance controls. Through internet research the manual for the Nelson Ross 001 and 011 predecessors was found . These have many of the same features and components but were made to fit the bigger 530/540 series scopes. Given this, I suspect the zero balance controls are equivalent to mixer controls described there and used to minimize the local oscillator bleed-thru seen on the display’s left hand side. I tried the suggested procedure though the results were not terribly impressive (and the documentation hints at this). Incidentally – unlike the 001 & 011, the 021 has its own sweep generator. The former used the 530/540’s sawtooth output as sweep driver – while the 561B, which is essentially an X-Y display, doesn’t offer.
The photo below shows the spectrum using the scope’s 1khz calibrator square wave. The odd harmonics separated by 2khz are clearly visible. Bleeding from the local oscillator is somewhat rampant in the 2 left-hand divisions. As mentioned above this unit needs calibration and can be seen as compression across the spectrum. Fiddling, I suspect it is ranging across 23khz instead of 20khz – which is why the grid lines don’t line up. The Center Frequency and Dispersion controls also needs adjustment. At this point it would be extremely helpful get hold of a manual/ or some calibration instructions specific for the 021 which I’ve not as yet been able to find (assistance appreciated!).
File comment: A difficult photo shot. The 561B is stocked with P31 phosphor so not much persistence for slow speed spectral analysis. To get this a Canon A720 was set on aperture priority and perched on a music stand. Not the best - I have to get a tripod.
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This PSA-021 was manufactured about 1970 though its design is contemporary with the Singer-Metric (panadapters) of the 1960s. I suspect units like these found home in medium and small businesses. It was probably displaced by the HP3580a when it debuted in 1973.
All-n-all this is a pretty neat setup and well represents the technology of it’s time. I have a bit more fiddling to do and things to check out – will be fun!
And my very best regards!