[dconant]

Well I have replaced the 6A8, 6K7 and 6F5 tubes three times. I have not tried heat or freeze spray. I'll give that a go before I start on the coils. For some reason I have got it in my head it is the 6A8 tube that is the problem but can't prove it. I'm gonna see if I have a radio with one and try that. I have sprayed the band switch. I will take it out and give it good look see and cleaning. The Z and G connection is bright and tight. I even removed the strap and it makes no difference in reception when it is playing properly. What doea that say?

Sometimes when I turn it on for the first time of the day and there is no reception I have let it set for a half hour being on reception does not return. Removing the ground wire from antenna G and replacing it bring back the reception. The A terminal remove and replace has no effect.

I will be working on the radio today.

[MrFixr55]

BTW, if you don't have freeze spray, get a couple cans of "air duster" from Staples. When you turn them upside down, the "Air" (actually a refrigerant) comes out as a liquid and acts as freeze spray.

[RodB]

Here's another thought. Have you checked the leaf springs that connect the tuning cap rotor to frame ground? I've had them produce some flaky symptoms when they have crud in them. We'll never know what fixes this problem.

[dconant]

MrFixr, I have freeze spray. Sprayed freeze spray everywhere and applied heat. I even sprayed freeze spray up in coils and heat. No change.

RodB, If you are referring to the forks I have cleaned between them and the frame with fine sandpaper.

I have disconnected the wave trap. I removed the shortwave detector compensator and wired the AM part directly. This disconnects the SW section and allows AM to continue to play. This way I can possibly ruled out those two items two items. I tried a fourth 6A8. Radio did its thing as soon as I turned on the radio after replacing the 6A8. So I guess I can rule out the 6A8. I have not taken out the band switch yet.

[DaleHCook]

I have two from Rich, the smaller and the bigger

I have one of Rich's large stands. I needed something which could handle my 1939 Howard 425-A. That 14-tube chassis is not only large, it is heavy.

I had only seen the inexpensive Howards before I saw the 425-A at an auction. It cost me $150, and was well worth it. The 15" Jensen speaker sounds amazing.

[dconant]

The band switch has been taken out and cleaned within an inch of its life. All nice and shinny and purdy now. Radio played on power up. We will see how this works out.

[MrFixr55]

I think that the only scientific explanation for the issue is demonic possession.

[dconant]

Still playing. I'll leave it play until bed time but as I have said before it has played all day.

[morzh]

I wonder if the oscillator just quits.

[Arran]

This is making me think that there may be something in the oscillator tank circuit that is acting up, but it was mentioned that most, if not all of the resistors have been replaced, as well as many of the molded mica caps. Has R1 and C4 been replaced or checked? They are on the cathode of the 6A8.
Regards
Arran

[dconant]

It did it s thing last night. Did a few voltage checks on the antenna coil. All were the same as when working except the one pin that connects to C2 (.05). Normal is -4.9 acting up is -3. Not a big difference but who knows. I did swap out with another new one.

R1 and C4 have been changed. All caps and resistors have been changed. Micas too. Just to make sure R1 (47mohm) is 47K and not 47 meg. I know M means K in these old radios.

Turned it on this morning with no reception. Replace C2 still no reception. Turned it off, disconnected antenna ground, turned it on and got reception. Funny how it always works after messing with antenna ground that connects to a rod in the ground.

Early on when messing with this problem when there was no reception I could get the squeal on a small transistor radio. So can the oscillator be messing up? I have not taken osc coil out yet. Maybe I should so I can have a look at it. Could that gimmic that is connected to the osc section of the tuner and wrapped around the antenna grid cap wire be messing up the oscillator? I had replaced both of those wires and may not have gotten the osc wire the exact length but they are in the same place.

I certainly appreciate you guys hanging in there with me.

Dan

[morzh]

If there is a squeal, the osc could be OK.
At any rate, I would not touch coils before I exhausted the freezer/poking.

Here's the thought train:

1) it quits after long time working. Implying, temperature could be at play.
2) What could temp rise do?:
a) cold solder spot disconnect.
- test: take a chopstick or a thin plastic rod, start poking (not too gently, a poke has to have physical effect) at every soldered cluster, every screwed lug connection, every grid cap, wiggle every tube, poke every knob....anything that is not the chassis itself, but soldered/bolted/etc, has to be wiggled/poked.
- test: same places, freeze spray (not too much, just cool it a bit, like spraying from short distance in 1/4 sec pulses).
b) internal tube electrode short.
- test: tap the tubes. Take the grid caps by the wire, try to gently apply rotating torque to it. Very gently, you want tension but not actual rotation. DO NOT use freeze spray, you might crack the tube.

3) You said Candohm is good. Candohms could go temporarily bad. Try to wiggle Candohm's lugs, use little Freezespray on it, measure the voltages during the "quit" period.
4) Simply wiggle the band switch knob lightly. Or try switching bands back/forth. Just for the heck of it, wiggle tone ctl switch.
5) last. Wiggle the speaker wires, the cable that goes to it. Tap the transformer, poke with the rod the wires that go into the field coil.

[RodB]

Are there any rivets holding terminal strips or lugs to the chassis? See if they are soldered to the chassis. One of my Philcos had that and it measured about 50k to ground.

[RodB]

I think you said you replaced the 6A8 grid cap wire. Maybe you should try a shielded wire. Speaking of shields, does the 6A8 have a tube shield? If so, measure the shield to chassis ground resistance and make sure it's zero.

[dconant]

Mike

1) It does not play at first power up of the day most times. Sometimes plays for over 4 hours without issues. So I guess that rules out temp.

2a) I have prodded, poked wiggled all connections and wire quite hard and gently. Will do again.
2b) No change while playing normally.

3) Voltages between quit and playing remain the same on Candohm. Freeze spray does not alter the reception. Voltages are -2.5, -4, -22 going away from ground.

4) Have done just that moving those control very slowly and rapidly.

5) I have just done that and no change.

I think the clue here is removing the antenna ground while powered on restores reception but I don't know what it is telling me.

Also I have stated before the AVC voltage does not vary much between strong and weak signal. Around -1.7 (strong) to -2.2 (weak). Is this a problem? Seems to me it is.

Rod

Yes there are rivet terminal strips and eyelets and I have run a wire from them to new ground connections with screw and nut. I have measured them all and they are at .4 ohms. My Fluke rarely seems to read below that.

Yes I replaced the 6A8 grid wire and cleaned the connector. The wire is about 5" long from top of antenna section of tuning cap to grid cap of 6A8 and has a gimmic wire on it from the osc section. So would the shield effectively disable the gimmic? The 6A8 is metal and yes pin 1 is grounded. The tubes shields are both missing with the 6K7 being the other one which has pin 1 grounded.