GE A-66 new refurbish job

[de.facto7]

Thanks for the tip on the I.F. I'll get on it.

The gruff sound I will also check. It's hard to tell but it may disappear at very very low volume, like less than 10% volume. It seems to clear up for a moment or so though when I do that tap thing on the 6J7. That is why I think it is in the radio somewhere. It also reduces a bit after the radio has been on for 30 or 40 minutes.

I just looked at the speaker and I don't feel anything rubbing or see any tearing. But I did notice that the hum is 2 fold; there is a hum that follows the volume control and another that does not. The hum that follows the volume sounds like the kind of sound you get when you drive too close to a power line except there aren't any motors, florescent lights or power cords or line in the way. The one at the speaker is always humming and at the same volume whether the pot is up or off.

Thanks Reece.

[Reece]

Sometimes hum is due to heater-to-cathode partial short in the output tube. Usually that gets worse when it heats up rather than better. Maybe try a new tube. There will usually be a little hum with your ear right at the speaker but should not be objectionable at normal listening levels.

Is any of the hum tunable, that is, more when you're on a station than when in between stations? That volume controllable hum may be from electrical interference. Light dimmers, dusk to dawn lights, garage door openers, computer power supplies, almost any plug-in wall charger, can produce nasty stuff. You can put a portable radio in between stations and probe around your house and yard to sniff out sources. Even your neighbors' devices can cause this. Sometimes a different location for the radio helps, or a "real" outdoor antenna.

[de.facto7]

Ok... snooping here... I found that if I touch the uninsulated wire that goes from the R.F. broadcast coil to a Bus switch to the braid of the trimmer to the top connection of the 6A8 tube... all problems cease. The reception is 100% improved, the volume comes up which means I can turn it down and all gravel is non existent. I can touch either side of that switch and it does the same. This only happens when I touch it. If I put a wire between... no change. If I put a resistor between... no change. If I am holding a wire and touch it it fixes the problem... point, it only happens when my person is in contact. not ground, not antenna... just me. I guess the 6A8 likes me.

[Reece]

Not sure I'm following because I don't see any braid specifically on the schematic, and don't think the wire to the top cap is shielded (which would be a type of braid), BUT: try connecting a ground wire to the G terminal. If you don't have a dedicated ground temporarily connect it to the center screw of an outlet cover.

Edit: found the braid etc. on the pictorial

[de.facto7]

Thanks!

Stupid question... what's a G terminal?

[de.facto7]

I think you mean a ground on the radio chassis. Anyway, the upper frequencies improve greatly. I completely loose the low ones when I do that grounding.

[Reece]

This radio is just being difficult, isn't it? With the ground, what happens with the hum or roughness?

[de.facto7]

Both disappear in the upper frequencies, but the lower frequencies also disappear. I have to turn down the volume on the higher frequencies but I have to turn it to maximum to even hear the lower ones in the distance. Without the grounding, both ends are even but the volume must be turned up. Then I have a rough sound which touching the 6J7 fixes for a moment. Touching the 6A8 or those mentioned places underneath fixes everything throughout the AM freq.

Make any sense?

[de.facto7]

On the thought of I.F and Oscillator adjustment, You know I cannot tune in the Bureau of Standards time signal on either of those frequencies or anywhere near them using my digital SW receiver on which I get a lot of things. I have never been able to pull that in. If I can't get it on my digital, I surely can't rely on it for the GE radio.

Also, If anyone has a schematic for making a test oscillator, I'm sure I can throw one together.

Thanks!

[Reece]

If you can find a suitable station near 15 Mhz on your digital, note the frequency displayed and just shoot for that to align the G.E.

As to the strange R.F. behavior of this set: I wonder if an RF/Antenna coil is open or shorted. The fact that the trimmer is all the way tight and won't peak could also point to this. An open antenna coil can cause a hum and poor tuning. They are often fine wire and over the years corrode or snap at the terminal. See L1 through L4 on the diagram. Their approximate resistances are shown, are they close to that?

[de.facto7]

Here's L-1 through L-4 respectively: 29.5, 8.2, 2.9 and .55

L-4 seems like the only one that is a bit off. It should be more like .015

The scheme says respectively: 29, 8, 2.5, and .015

[de.facto7]

Well... I think I figured it out, although I don't really know exactly why what I did worked.

It seems to have been an antenna issue. I added a wire between the antenna terminal on the inside to the center pin on the bus that controls where the antenna is connected. That center pin is the braided wire that leads to the tuning cap on top on the side that is NOT connected to the 6A8 tube. All the unevenness between the ends on the bands and the volume issue as well as the gravelly sound are no more. I have too many channels now. They are everywhere. On the SW side, everything is clearer but if I add a ground from the chassis to the radiator in our house, I can hear Voice of China if there is such a thing... It's amazing! I have to remove the ground though if I use the AM band or I loose my lower half of the radio channels.

Now, just because it works, doesn't mean it right. If this is a bad idea, please let me know. I'm just futzing around. It would be nice to know what I did here. It's not a wire that existed before.

Thanks everyone.

[de.facto7]

Now wait a minute... it's on the schematic. But the solder terminals have never been used; they were completely clean...

[Reece]

Not following exactly: can you mark up a piece of the schematic on N/A to show what you added?

[de.facto7]

hare ya go...