Valve (tube) radio question .....?

Question

I have a question about US-built valve radios.

I have seen a set with five 7-pin valves and I just want to know, how do you get an oscillator and mixer onto a 7-pin base?

In a British set, the usual 5 valves are: UCH81 oscillator and mixer, UF89 IF amp, UBC81 detector and audio preamp, UL84 audio power amp and UY85 rectifier. (Some makes used a power transformer and essentially the same valves but with the prefix E instead of U, and an EZ80 full-wave rectifier.)

The oscillator is a triode (3 pins). The mixer is a hexode or a heptode (6 pins either way, if g5 is joined internally to the cathode). With a shared cathode (-1 pin), the second and fourth grids of the hexode joined (-1 pin) and the oscillator grid joined internally to the third grid of the mixer (-1 pin), that still needs 6 pins for the signal connections.

Unless it was at the bottom of the heater chain, so one of the heater pins could be connected to the cathode, I can't see any way of getting an oscillator and mixer into the same valve.

Or were American sets built with the oscillator and mixer separate?

Answer 1

Edited...



These were called the "All American Five". A schematic I have in front of me for an old Motorola has:

12BE6 as the converter (osc+mixer) The osc uses only the cath and G1.

12BA6 IF amp

12AT6 Det-AVC-AF

35C5 Pwr amp

35W4 rect



Converter 12BE6 connections:

Cath OSC coil tap.

G1 Osc Coupling cap. Grid leak -8V

G2 + G4 (Connected internally) B+

G3 input RF + AGC voltage

G4 = Cath (suppressor)

Plate (output)

No heater / cathode connections.



I'd haf-ta' study it to recall how it works.. Sorry - too many years. I'll guess G3 OOPS I MEAN G2 acts as the plate for the osc... but the real plate may as well. Cath also common to both. You don't necessarily need unique electrodes for each function, obviouslly.



See also

http://en.wikipedia.org/wiki/All_American_Five



Cheers

Answer 2

The schematic of the AA5 (All American 5) is at http://frrl.wordpress.com/2009/01/22/long-live-the-all-american-five-or-recovering-a-piece-of-radio-history/ this one uses octal based valves (12SA7) but the theory is the same for B7G 7-pin based miniature valves (12BE6). The hexode mixer uses K, G1 and G2 as the "triode" Hartley oscillator and the top half of the hexode as the mixer, all done with 7 pins.

Answer 3

Additional information on U.S. tube (valve) numbers: First digits are nominal filament voltage. Last digit is number of active elements (filament counts as one). Letters in middle are arbitrary. The 5-tube radios I have seen have three 12-volt tubes, a 35-volt rectifier, and a 50-volt audio output. The filaments were in series across the AC line, and these add up to 121 volts, approximately the U.S. line (mains) voltage.

Answer 4

7 pins type electronic tube like 6BE6 was used as mixer and oscillator together. See this link.......



http://www.radiomuseum.org/tubes/tube_6be6.html

Answer 5

Start with this http://www.radio-electronics.com/info/data/thermionic-valves/pin_connections/tube_connections.php

or rather end with that after picking a part number from

here

http://en.wikipedia.org/wiki/List_of_vacuum_tubes

or here

http://en.wikipedia.org/wiki/Tube_socket#Miniature_7-pin_base

and perhaps hook up with ham radio guys of a certain age