This radio has been recapped and all out of tolerance resistors replaced. It has about 6 feet of wire remaining of the original antenna. The radio aligned ok, but does not receive stations unless the antenna is touching metal od some sort...such as the vent hood over the range top, which is stainless steel. I added length to the hank, but that didn't help. I'm not real savvy on how the straight antennae are supposed to function. Could someone help me diagnose this please?

Stan, here's the schematic: http://www.nostalgiaair.org/PagesByModel/623/M0016623.pdf

I wouldn't expect this 4-tube set (including the rectifier) to be very sensitive. It has just one IF xfmr.

Still, something doesn't sound quite right here. I suggest going over the RF section (the ckt around the 12SA7) carefully. Check all the coils for continuity. Also, check the IF alignment of T1.

:Stan, here's the schematic: http://www.nostalgiaair.org/PagesByModel/623/M0016623.pdf
:
:I wouldn't expect this 4-tube set (including the rectifier) to be very sensitive. It has just one IF xfmr.
:
:Still, something doesn't sound quite right here. I suggest going over the RF section (the ckt around the 12SA7) carefully. Check all the coils for continuity. Also, check the IF alignment of T1.

Guys,

I agree with Doug that this set isn't that sensitive. The service data rates the sensitivity at 1400 KC at 500 microvolts. Might trying another known good 12SA7 for kicks.

Radiodoc

Doc's idea about the 12SA7 is perhaps a long shot, but worth a try.

Stan, can you just permanently hook up the radio to your range exhaust hood? :>) Just kidding, sorry.

If the place you live in has metal siding, try hanging your wire out the window. Years ago many houses had very long wires strung outside for antennas. Sometimes they were strung from gable end to gable end, tree to tree, house to garage, wherever they could hang a real long piece of wire. In the very early days, some people would even clean their antennas daily. They felt that the corrosion on the wire would block the signal. Now with more local and higher power stations you don't need a very long antenna (even though longer usually gives better reception unless the wave length is exceeded, which would be hard to do on the AM band).
If you can get a length of wire strung outside, your reception should improve. Metal siding blocks reception. Also devices such a computers, dimmers, certain battery chargers and various other electronic devices make noise which can block reception or make what you receive very distorted. Using an outdoor antenna can reduce the effect of this noise too. It is also possible that you have a problem with your radio's antenna input circuitry "BUT" you said you can get reception if you connect to various metal objects so I don't suspect that at this time. Some may think this is silly but you can use a metal slinky for an antenna. It acts as a inductor so when it is stretched out the effective length of the antenna is longer than if you would use a straight piece of wire of the same length. I hope this helps and I am sure there are more people on this site with good advice.
MRO

I agree with everyone on the antenna subject. Many of these low tube count radios won't pick up a single thing unless a rather long antenna is attached. When hanging your antenna, DO NOT make any right turns, and DO NOT fold the antenna back on itself. Any wire that runs at a right angle or in the opposite direction will pick up signals out of phase with the rest of the wire, and this will cancel out some of the signal.

A small right turn, curve, or fold back of no more than 10% of the full antenna length is permissable near the radio in order to bring the lead-in wire to the radio.

Thomas

:I agree with everyone on the antenna subject. Many of these low tube count radios won't pick up a single thing unless a rather long antenna is attached. When hanging your antenna, DO NOT make any right turns, and DO NOT fold the antenna back on itself. Any wire that runs at a right angle or in the opposite direction will pick up signals out of phase with the rest of the wire, and this will cancel out some of the signal.
:Wow...this radio has the antenna tied in a knot at the rear opf the speaker frame (to hold it in place) and then soldered to the antenna terminal. Sounds like a problem! Will advise results...thanks to all respondents!
:A small right turn, curve, or fold back of no more than 10% of the full antenna length is permissable near the radio in order to bring the lead-in wire to the radio.
:
:Thomas

Tied in a knot isn't going to affect anything. You can coil the wire around a few times and stash some of it inside of the radio cabinet, and it probably won't have much of an affect on reception. It's just that when you string up a 25 foot wire, and then fold half of it back on itself, or perhaps wind the wire all the way around your house (not gable end to gable end, but all the way around 4 sides), you make a very inefficient antenna.

Thomas

:Tied in a knot isn't going to affect anything. You can coil the wire around a few times and stash some of it inside of the radio cabinet, and it probably won't have much of an affect on reception. It's just that when you string up a 25 foot wire, and then fold half of it back on itself, or perhaps wind the wire all the way around your house (not gable end to gable end, but all the way around 4 sides), you make a very inefficient antenna.
:
:Thomas

:Tied in a knot isn't going to affect anything. You can coil the wire around a few times and stash some of it inside of the radio cabinet, and it probably won't have much of an affect on reception. It's just that when you string up a 25 foot wire, and then fold half of it back on itself, or perhaps wind the wire all the way around your house (not gable end to gable end, but all the way around 4 sides), you make a very inefficient antenna.
:I untied the knot, straighten out the wire and it seems to work better. The wire is only 6 ft long. When I touch the end, reception improves significantly. How long should the wire have been on this redio? 20 ft? Thanks!!
:Thomas

Ok. The knot really shouldn't affect anything, though. I would bet money on that. Perhaps because the knot was holding the antenna close to the speaker's metal frame (which is electrically out of phase with the antenn), this reduced reception. If you tie a knot in the antenna wire all on its own, though, it isn't going to affect recteption.

The antenna should be at least 20 feet long. 6 feet isn't going to do much, but should pick up some stations. If it isn't, then your radio needs aligning.

Thomas

:Ok. The knot really shouldn't affect anything, though. I would bet money on that. Perhaps because the knot was holding the antenna close to the speaker's metal frame (which is electrically out of phase with the antenn), this reduced reception. If you tie a knot in the antenna wire all on its own, though, it isn't going to affect recteption.
:
:The antenna should be at least 20 feet long. 6 feet isn't going to do much, but should pick up some stations. If it isn't, then your radio needs aligning.
:
:Thomas

:OK...now for some education. The 20ft wire transformed into a coil in later radios and reception improved. Could you explain the principle of why please?

I'm going to try to advoid technobable in this explination so here goes.
The coil combined with capacitance forms what is called a resonant circuit. That circuit will be most sensitive to a certain frequency (center frequency). It will also respond to frequencies above and below that center frequency (very loose definition of bandwidth). A radio with more stages of these resonant circuits will have more senstitivity to that certain frequency and the bandwidth will become narrower (called selectivity). An antenna has a resonant frequency. A certain length antenna will respond better to frequencies that are the same wavelenght or fractions of that wavelength. The wavelenght for the AM band at the lower end of the dial (550kc) is 545 meters long. That is the full wavelength of the alternating current signal as it travels from the transmitter through the air. At the upper end of the dial (1500kc) it is 200 meters long (650 feet). With todays high power and close proximity stations you don't need to have a full wavelength antenna. Usually just a random length of wire will do. On some old radios I used to install a ferrite loopstick internal antenna. This was a coil of wire with a ferrite slug you could move in and out to tune it. This combined with a capacitor made resonant circuit that I could tune to a desired station. This is not the entire description of tuned circuits. You may want to lookup parallel and series resonant circuits, capacitive and inductive reactance, real length versus effective length antennas by use of inductance and capacitance. I am sure there will be others with helpfull explinations.
MRO

:Very interesting...makes sense and I will do more research to try to learn the principle. In the meantime, I just soldered the antenna wire to the range hood. Trying to explain to the wife... ;>)

:I'm going to try to advoid technobable in this explination so here goes.
:The coil combined with capacitance forms what is called a resonant circuit. That circuit will be most sensitive to a certain frequency (center frequency). It will also respond to frequencies above and below that center frequency (very loose definition of bandwidth). A radio with more stages of these resonant circuits will have more senstitivity to that certain frequency and the bandwidth will become narrower (called selectivity). An antenna has a resonant frequency. A certain length antenna will respond better to frequencies that are the same wavelenght or fractions of that wavelength. The wavelenght for the AM band at the lower end of the dial (550kc) is 545 meters long. That is the full wavelength of the alternating current signal as it travels from the transmitter through the air. At the upper end of the dial (1500kc) it is 200 meters long (650 feet). With todays high power and close proximity stations you don't need to have a full wavelength antenna. Usually just a random length of wire will do. On some old radios I used to install a ferrite loopstick internal antenna. This was a coil of wire with a ferrite slug you could move in and out to tune it. This combined with a capacitor made resonant circuit that I could tune to a desired station. This is not the entire description of tuned circuits. You may want to lookup parallel and series resonant circuits, capacitive and inductive reactance, real length versus effective length antennas by use of inductance and capacitance. I am sure there will be others with helpfull explinations.
:MRO

I wonder what the calculations for resonance would be for a range hood and a hank of wire........
MRO

Regarding loop antennas, they aren't really more sensitive than a good long wire antenna. Your radio just isn't that sensitive. All of my long wire radios out-perform any of my loop antenna radios unless I put a long wire on the loop. A loop antenna will out-perform a long wire radio with its coil exposed and no wire connected to the coil. Zenith Wavemagnet radios are incredibly sensitive, though. They can out-perform just about any radio, and the portables are often amazingly static free. My 6-G-601 can pick up stations static free in a fluorescent illuminated steel building. There are some places where it doesn't work very well, like in commercial buildings with commercial style computers. It still out-performs most other radios.

Thomas