The EL84¡¯s should be getting plenty of drive on their control grids. Go back along the signal chain from there to the multivibrator. On my own instrument, after power-on, sometimes it doesn¡¯t start until I switch back and forth between HI AMPLITUDE and FAST RISE. Seems like the multi needs a kick.
Dave Wise
From:
[email protected] <
[email protected]> On Behalf Of Stephen via groups.io
Sent: Tuesday, March 01, 2022 3:20 PM
To:
[email protected]Subject: Re: [TekScopes] Type 106 Saga (Again)
On Tue, Mar 1, 2022 at 11:26 PM, Albert Otten wrote:
Stephen, the ripple sizes in your pictures are only a fraction of what I see
in my working 106. Perhaps they are so small because the 4 tubes never
conduct.
Even with almost exhausted tubes you should get some output square wave.
I would measure the waveform at the grid line w.r.t. the DC cathode
voltage(s). And then consult Ia-Vg characteristics of the EL84.
Albert
Albert,
You¡¯re probably right. Hence the zero volt output measured on all 3. The question is why did they stop conducting all of a sudden, whereas the unit was working perfectly the day before, and had been for weeks.
I¡¯m pretty sure it¡¯s not the tubes themselves. Had it been the tubes, changing them would¡¯ve solved the issue.
It¡¯s kinda late in Europe, but tomorrow I¡¯ll check R55 and the voltages at the plates and grids.
Will report back then.
Thank you.
