I just bought a Philco model 38-12 and tried it out without an antenna. Pardon my ignorance on radios, but I noticed that just touching the top of the 6A7 tube greatly amplifies the radio reception. If not touched, the radio is very weak. Does this indicate a problem?

:I just bought a Philco model 38-12 and tried it out without an antenna. Pardon my ignorance on radios, but I noticed that just touching the top of the 6A7 tube greatly amplifies the radio reception. If not touched, the radio is very weak. Does this indicate a problem?

Dear Gary:

An outside antenna or just a longer wire connected to the antenna post on the back of the receiver should help. Does it work better when you just touch the antenna input with a finger??? Let me know

Henry Heuver

Gerry,
I had the same response on an old TRF, with an external wire antenna connected. A cupped hand around the first RF tube raised the volume. I tried disconnecting the antenna at its terminals, and winding multiple turns of the wire around the tube, but didn't get the same results. My antenna is not a complex assembly, but a simple horizontal "V" attached to the underside of my garage ceiling. About 50 ft of cheap #20AWG hookup wire, with a drop at both ends. Even stranger, I had 2 old TRF's at the time and both connected to the drops while I was testing only 1. After realizing that both were connected, I unhooked the unpowered set, and the volume level on the active one dropped. The unpowered set was obviously acting as an impedance termination for the wire, and improving the antenna performance.
marv

:I just bought a Philco model 38-12 and tried it out without an antenna. Pardon my ignorance on radios, but I noticed that just touching the top of the 6A7 tube greatly amplifies the radio reception. If not touched, the radio is very weak. Does this indicate a problem?

Since the terminal on the top of the 6A7 tube is connected to the control grid that is normally connected to the antenna circuit of the radio, it would only seem logical that you would improve radio reception by touching this terminal or by placing your hand near this terminal when no other antenna has been connected to the radio. Your body makes a fine antenna, and touching the antenna circuit control grid with your finger connectes you, the antenna, to the antenna circuit, feeding the signal received by you through your finger and into the control grid. It is best, however, to never connect an antenna directly to the grid cap of the 6A7 tube, or, for that matter, any other RF amplifier tube. There are special circuits between that grid terminal and the normal antenna connection that allow efficient and balanced reception at all parts of the dial, be they simply a tuning condenser and antenna coil, or an RF pre-amplifying stage accompanied by another tube. That said, only connect the antenna to the antenna terminal on your radio as instructed by your radio manufacturer for your particular model. No physical or electrical harm is done by connecting an antenna to the grid cap of the 6A7 tube, but proper radio performance cannot be achieved in this manner.

Thomas

Hi

Also check continuity of both windings of the coil connected to your 6A7. An open coil will cause a similar effect.

Norm

:Since the terminal on the top of the 6A7 tube is connected to the control grid that is normally connected to the antenna circuit of the radio, it would only seem logical that you would improve radio reception by touching this terminal or by placing your hand near this terminal when no other antenna has been connected to the radio. Your body makes a fine antenna, and touching the antenna circuit control grid with your finger connectes you, the antenna, to the antenna circuit, feeding the signal received by you through your finger and into the control grid. It is best, however, to never connect an antenna directly to the grid cap of the 6A7 tube, or, for that matter, any other RF amplifier tube. There are special circuits between that grid terminal and the normal antenna connection that allow efficient and balanced reception at all parts of the dial, be they simply a tuning condenser and antenna coil, or an RF pre-amplifying stage accompanied by another tube. That said, only connect the antenna to the antenna terminal on your radio as instructed by your radio manufacturer for your particular model. No physical or electrical harm is done by connecting an antenna to the grid cap of the 6A7 tube, but proper radio performance cannot be achieved in this manner.
:
:Thomas