HP 204c Oscillator

You should see 5Vrms output with an AC voltmeter if the output level control is advanced to max and frequency is set anywhere within the voltmeter's capability. If you have a small tube amplifier output transformer, you could use it as an ad-hoc speaker matching transformer. It won't be loud -- output power is only 10mW max.

Here's the manual: http://bama.edebris.com/download/hp/204c/HP%20204C.pdf
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