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| Light Bulbs and LDRs in Audio Oscillators |
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| Zenith:
The thermistors for this purpose I've seen were marked ITT, (which was a UK electronics company) and either R53 or RA53. They were in a glass envelope with getter which was maybe an inch by 3/8ths and was wire ended. They also came in a smaller envelope, about 1 inch by 1/8th sometimes marked ITT, sometimes completely unmarked. The bead is tiny. Until about 15 years ago they were stocked by RS Components and cost about £6. There was a similar one ,it may have been the RA43, but the 53 was always recommended for oscillators. They both suddenly went off the market. The usual places which stock hard to find vintage components such as obscure transistors and diodes, don't seem to have them. It's worth looking out for vintage equipment which is completely beyond repair and selling for pennies or being thrown out. Here there was an Open University oscilloscope and function generator, very low spec and now rarely seen, but it did contain an RA53 thermistor. Then there's ebay. Years ago I fixed a Far Eastern made audio signal generator which looked as if it was intended for school and hobbyist use. It had surprisingly low distortion. It had thermistor stabilsation but the thermistor was like an AC126 transistor, that is in a TO1 can. I don't know what modern cheap Chinese audio sig gens use for stabilisation. Best of luck with your efforts to make one. That shows dedication. |
| chris_leyson:
Then there is the Meacham bridge stabilized oscillator published in the Bell System Technical Journal in 1938. https://ia801604.us.archive.org/21/items/bstj17-4-574/bstj17-4-574.pdf Maybe Bill Hewlett got the idea for the stabilized Wien Bridge oscillator from Meacham's work. https://en.wikipedia.org/wiki/Wien_bridge_oscillator. Also, for best spectral purity and lowest phase noise the oscillator needs needs to be amplitude stabilized and linear, I think Ulrich Rohde mentions this in "Communications Receivers" 1st ed but then again it might have been Manassewitsch in "Frequency Synthesizers Therory and Design". Amplitude stabilised oscillators are always good whether RF or audio. |
| Benta:
Yes, the R53 and RA53 are classics for oscillator stabilization. SeanB, instead of leaving them in a box, I'm certain you can make a handful Rands selling them. |
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