17-07-2017, 06:26 AM
Greg.
The point you make about the loading of the tank Q reminds me of the "uncle Clive" circuit that is used in the supergainer IF amplifier that was in that vintage homebrew transistor radio that I was trying to recreate, and failing.
In the original set, the transistor was an OC170, and would have had a hard job to be more than an hFE of, say, 80. In my recreation the transistor I used was a BC559c, with an HFe of 600. With the old Mullard alloy drift transistor the stage gain was much more reliant upon the regenerative feedback, however, when the silicon transistor version was made, the gain was already quite near that required for the stage to drive the audio amp, and as the regenerative feedback is less, then that explains why the stages BW is wide as the feedback level is not there to "Q multiply". Its difficult to prove that that is what's happening as the circuit inherently applies AGC action on strong signals, so that increasing regeneration only appears to narrow the bandwidth on the vintage version, and put the circuit into oscillation on my version.
Cheers Pal!
I've just realized that no one here is likely to know WTH I'm talking about! (This was all posted on another forum). So I'd better add an attachment of the circuit I'm referring to. It's a very nineteen fifties diagram complete with dots and jogs
Andy
The point you make about the loading of the tank Q reminds me of the "uncle Clive" circuit that is used in the supergainer IF amplifier that was in that vintage homebrew transistor radio that I was trying to recreate, and failing.
In the original set, the transistor was an OC170, and would have had a hard job to be more than an hFE of, say, 80. In my recreation the transistor I used was a BC559c, with an HFe of 600. With the old Mullard alloy drift transistor the stage gain was much more reliant upon the regenerative feedback, however, when the silicon transistor version was made, the gain was already quite near that required for the stage to drive the audio amp, and as the regenerative feedback is less, then that explains why the stages BW is wide as the feedback level is not there to "Q multiply". Its difficult to prove that that is what's happening as the circuit inherently applies AGC action on strong signals, so that increasing regeneration only appears to narrow the bandwidth on the vintage version, and put the circuit into oscillation on my version.
Cheers Pal!
I've just realized that no one here is likely to know WTH I'm talking about! (This was all posted on another forum). So I'd better add an attachment of the circuit I'm referring to. It's a very nineteen fifties diagram complete with dots and jogs
Andy
