I bought a well used 200CDR back in 1971 from Eli Heffron's in Cambridge. i got it cheap because the output was pulsating - clean but the output was not steady. I pulled off the case and found it had a pair of 6V6 output tubes, those were supposed to be 6F6. The Rp of those two types is very different so I picked up a pair of 6F6's and all was well. The 6S6 bulb was dibe and the unit had very low distortion. That oscillator has been on my bench for 50+ years and has never given me a lick of trouble - not bad for the $30 i paid for it way back then.
Love these Wien Bridge Oscillators, I have made a 1Khz fixed version made with an op amp and a 12v bulb with a low distortion better than 0.01 % I bet Dr Hewlett would like to have seen it, great video !
Nice equipment! I like to tap on the glass (or metal) envelope of the tubes when doing short tests. I've found quite a few bad tubes with intermittent shorts that way. Also, I like to shake metal tubes, and if the sound like a salt and pepper shaker, no since to test. Take care.
9:44 It looks like your oscillator is relaxing too quickly, so I guess it's a carbon composite that has "shrunken" a little. Edit 13:00 Ok, I was wrong. What an interesting failure mode!
This was a low distortion design (VERY low for the time) the SG505 from Tek does beat it out with a slightly newer unit. the HP 200 was HP's first product and what started it all. This is the low frequency variant of the first revision being the 201 There is a wide band variant of the 201 the CD which is currently on my bench and in service as one of my test oscillators. The 201C had a lower top frequency but the output was WAY higher at 3 Watts.
@@ZenwizardStudios For those interested the technical article co-authored by Hewlett relevant to the HP 200 series is in IRE Oct 1939 Terman & Hewlett’s oscillator article, pgs 649-655. There'a an HP200J with original manual on the bench here beckoning for its refurb. Extended very low frequency range. Intended for mixing with various low frequency oscillators to generate sea-state waveforms in analog computation work. As you say, high quality design and construction.
