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Barryg4 · 23rd May 2017, 9:08 pm

This may be of interest to builders of the VT1 The oscillator in mine varied from 100mV to about 160 mV on warm up. Looking at the oscillator circuit I was puzzled by the inclusion of D6 - it was not needed for the phase shift oscillator to function. Warming it caused the oscillator output to increase quite considerably, so I decided to remove it. This improved the regulation but it was still not satisfactory. I then decided to reverse this diode and found that my oscillator did not vary at all from the 100mV setting even from a cold start.

23rd May 2017, 9:08 pm	#1420
Barryg4 Retired Dormant Member Join Date: Apr 2017 Location: Kidderminster, Worcestershire, UK. Posts: 5	Re: The "Sussex" Homebrew Valve Tester. This may be of interest to builders of the VT1 The oscillator in mine varied from 100mV to about 160 mV on warm up. Looking at the oscillator circuit I was puzzled by the inclusion of D6 - it was not needed for the phase shift oscillator to function. Warming it caused the oscillator output to increase quite considerably, so I decided to remove it. This improved the regulation but it was still not satisfactory. I then decided to reverse this diode and found that my oscillator did not vary at all from the 100mV setting even from a cold start.