Monthly Archives: November 2013

Restoration

The Scott 222C Restoration, Part 2

Welcome back! You can find Part 1 here.

When I left off, the chassis had been gussied-up and the transformers were re-painted. Before I reassembled it all back together I thought that having the bare-chassis, free from the all weight added by the transformers, would be the best time to electrically refurbish the amp. Charles Hansen ran some excellent articles about completely-redoing a 222C in AudioXpress, and Craig Ostby of NOS Valves was always willing to lend his knowledge.

 

Clean!

Clean!

 

And here it is! All I have to do is test everything…

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Construction Toys In The Attic

A PCOXO Calibration Source

I have a 1GHz universal counter and a 5MHz function generator as well as an ancient RF generator, but I don’t really do a lot of super accurate frequency stuff to warrant a Rubidium standard (yet). In early 2012 I threw down an offer of $10 on a Bulova PCOXO-HP02 oscillator, and accepted the counteroffer of $12.50.

The Bulova PCOXO-HP02 oscillator

The Bulova PCOXO-HP02 oscillator

Now I needed to figure out how I could use the thing.

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Repair Restoration

The Mono Pioneer TX-8100 Problem

A couple years back my then-girlfriend said ‘hey, you fix stereos–I want a stereo!’ And so a Christmas gift was born.

I found a Pioneer QA-800A quad amplifier with a bad channel and lots of DC offset as well as a matching tuner, a Pioneer TX-8100 with a few bulbs out. Both were sold as-is and that was fine with me! I picked them up from the post office and set to work.

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A Mystery!

My HP oscilloscope has a curve tracer function… ?!

This is a ‘built for Amdahl’ HP 1725A oscilloscope.

I bought this ‘scope maybe six+ years ago but just last year I noticed that there’s a curve tracer function tied to the intensity knob. The back states it’s an option ‘H01,’ which does not exist in any HP literature, and I couldn’t get any info from HP / Agilent. As far as I can tell there are no curve tracer specific inputs (option 101 includes the 1607A logic-state analyzer inputs), but if you look at the first photo, this was a unit built for amdahl.

 

Front of my oscilloscope, showing the 'pull for curve tracer' text

Front of my oscilloscope; ‘pull for curve tracer’ text on topmost knob, in the centre

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