Loctal Tubes

[benman94]

There was a tremendous advantage to the Loctals that I don't think any manufacturer really explored: compared to an equivalent octal, the parasitic capacitance between the various electrodes was much smaller. I think the reason for this is obvious however; much smaller 7 and 9 pin miniatures came along that were even better in this regard. Still, in the handful of sets that used an octal triode for the local oscillator, the equivalent loctal tube would have likely been more stable at higher frequencies.

[jr_tech]

Originally Posted by benman94

There was a tremendous advantage to the Loctals that I don't think any manufacturer really explored: compared to an equivalent octal, the parasitic capacitance between the various electrodes was much smaller. I think the reason for this is obvious however; much smaller 7 and 9 pin miniatures came along that were even better in this regard. Still, in the handful of sets that used an octal triode for the local oscillator, the equivalent loctal tube would have likely been more stable at higher frequencies.

Digging through my box of loctals, I found a stubby double triode (7F8) which has the triodes lying down, nestled between the pins connected with very short wires to the tube elements. I'm quessing that this was done to minimize capacitance. Odd coincidence, the tube is branded "Silvertone".

jr

[wa2ise]

Originally Posted by benman94

... compared to an equivalent octal, the parasitic capacitance between the various electrodes was much smaller. ...

Also the loctal tube has a metal base that should help act like shielding between say the control grid (input) and the plate (output) to avoid an IF stage from oscillating. Assuming the socket's metal snap-in grip is grounded.