Mighty Midget by General Electric Radio - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Neil Purling · 14th Jun 2016, 9:34 am

The overall appearance does look as if the company had bought in Surplus extension speaker cases and converted them. Obviously they were trying to provide a radio at a low price with reasonable appearance.
The simple scale must have been adequate when there were only a few stations on medium wave.
The radio does look better than the kit radios of the same period & the wooden case would have helped the sound too.

FERNSEH · 15th Jun 2016, 1:10 am

You don't need a reaction control when the detector is of the anode bend type.
The valve imposes little damping on the tuned circuit compared with the leaky grid type of detector which does because the grid and cathode function as a diode.

DFWB.

Mike. Watterson · 15th Jun 2016, 1:48 pm

Quote:

Originally Posted by FERNSEH

You don't need a reaction control when the detector is of the anode bend type.
The valve imposes little damping.

Why does that follow?
The Q of the tuned circuits will vary with frequency.
The losses are constant.
Thus without a reaction control, the performance is progressively poorer across the band, if at highest Q point it's not oscillating.

FERNSEH · 15th Jun 2016, 5:39 pm

Extract from Wikipedia on the subject of leaky grid detectors and the anode bend type. (US: Plate detectors)

Disadvantages:

One potential disadvantage of the grid leak detector is that the input impedance of the detector may be affected by the need to self bias the detector tube with grid current. Having the grid leak resistor, even in the Megohm range, shunting signal to ground loads the received signal. Although this may be mitigated to some degree by taking the resistor to the top of the tuned circuit (i.e. in parallel with the capacitor) and through the coil to earth, or by circuit design and component optimization, forward grid current will still load the input signal (and reduce the Q of the tuned circuit). Plate detectors have the advantage in that they isolate the detector load from the input circuit more effectively and may be employed where sensitivity is thought to be otherwise compromised by a grid leak or diode detector circuit.

DFWB.

Phil G4SPZ · 15th Jun 2016, 9:04 pm

For what it's worth, my experience when using the Pye Mite is that oscillation can be made to occur between the HF end of the medium waveband and around 900kc/s. Below that, and on long wave, the circuit won't oscillate at all. I'd not thought about it much, but this is probably due to the increased Q at the HF end of the band as Mike suggests.

ms660 · 16th Jun 2016, 8:22 am

I've built quite a few regens over the years, all required an advancement of the regen control towards the bottom end of the band to maintain the critical point just below oscillation, one way to offset that might be to have an RF stage with a high inductance primary in the RF amps anode circuit that self resonates (along with anode capacitance, stray C) below the lowest end of the band of interest which would help to make up for the loss of Q in the following grid tank.

I've never actually tried that method but some manufactures used it in superhets with an RF amp, it might complement an infinite impedance detector's lack of gain and at the same time help to make up for loss of Q towards the bottom end of the band?

Lawrence.

14th Jun 2016, 9:34 am	#21
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Mighty Midget by General Electric Radio The overall appearance does look as if the company had bought in Surplus extension speaker cases and converted them. Obviously they were trying to provide a radio at a low price with reasonable appearance. The simple scale must have been adequate when there were only a few stations on medium wave. The radio does look better than the kit radios of the same period & the wooden case would have helped the sound too.

15th Jun 2016, 1:10 am	#22
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Mighty Midget by General Electric Radio You don't need a reaction control when the detector is of the anode bend type. The valve imposes little damping on the tuned circuit compared with the leaky grid type of detector which does because the grid and cathode function as a diode. DFWB.

15th Jun 2016, 5:39 pm	#24
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Mighty Midget by General Electric Radio Extract from Wikipedia on the subject of leaky grid detectors and the anode bend type. (US: Plate detectors) Disadvantages: One potential disadvantage of the grid leak detector is that the input impedance of the detector may be affected by the need to self bias the detector tube with grid current. Having the grid leak resistor, even in the Megohm range, shunting signal to ground loads the received signal. Although this may be mitigated to some degree by taking the resistor to the top of the tuned circuit (i.e. in parallel with the capacitor) and through the coil to earth, or by circuit design and component optimization, forward grid current will still load the input signal (and reduce the Q of the tuned circuit). Plate detectors have the advantage in that they isolate the detector load from the input circuit more effectively and may be employed where sensitivity is thought to be otherwise compromised by a grid leak or diode detector circuit. DFWB.

15th Jun 2016, 9:04 pm	#25
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Mighty Midget by General Electric Radio For what it's worth, my experience when using the Pye Mite is that oscillation can be made to occur between the HF end of the medium waveband and around 900kc/s. Below that, and on long wave, the circuit won't oscillate at all. I'd not thought about it much, but this is probably due to the increased Q at the HF end of the band as Mike suggests. __________________ Phil Optimist [n]: One who is not in possession of the full facts

16th Jun 2016, 8:22 am	#26
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Mighty Midget by General Electric Radio I've built quite a few regens over the years, all required an advancement of the regen control towards the bottom end of the band to maintain the critical point just below oscillation, one way to offset that might be to have an RF stage with a high inductance primary in the RF amps anode circuit that self resonates (along with anode capacitance, stray C) below the lowest end of the band of interest which would help to make up for the loss of Q in the following grid tank. I've never actually tried that method but some manufactures used it in superhets with an RF amp, it might complement an infinite impedance detector's lack of gain and at the same time help to make up for loss of Q towards the bottom end of the band? Lawrence.