Can any of you guys help me identify the model number of this (AutoMatic Radio Mfg co.?)AirMaster radio?
It is BC/SW
The big oval dial has a sailing ship on it and country names on the SW band which covers 5.5-20 Mhz
The 2 pictures are on my page here:
www.pbpix.com/AirM-1.jpg
www.pbpix.com/AirM-2.jpg
The tube line up is:
Ballast K38B2, 25z5,6a7,6k7,75,43.
I cannot find any numbers on the chassis.

:Can any of you guys help me identify the model number of this (AutoMatic Radio Mfg co.?)AirMaster radio?
:It is BC/SW
:The big oval dial has a sailing ship on it and country names on the SW band which covers 5.5-20 Mhz
:The 2 pictures are on my page here:
:www.pbpix.com/AirM-1.jpg
:www.pbpix.com/AirM-2.jpg
:The tube line up is:
: Ballast K38B2, 25z5,6a7,6k7,75,43.
:I cannot find any numbers on the chassis.

It also has a 5U5 tuning Eye tube.

Have this same radio but as a Simplex Model D. A schematic is available here but does not include the eye tube but otherwise quite usable. Link follows:

http://www.nostalgiaair.org/Resources/411/M0018411.htm

Richard

Wow,..Richard.. Thanks!!
That sure seems to be it.
I would NEVER have known it was "Simplex" otherwise... there was just no clue...
I am so pleased now... and greatful too for your astute & quick assistance! ;-)

:Have this same radio but as a Simplex Model D. A schematic is available here but does not include the eye tube but otherwise quite usable. Link follows:
:
:http://www.nostalgiaair.org/Resources/411/M0018411.htm
:
:Richard
:

:Wow,..Richard.. Thanks!!
:That sure seems to be it.
:I would NEVER have known it was "Simplex" otherwise... there was just no clue...
:I am so pleased now... and greatful too for your astute & quick assistance! ;-)

... oh and by the way... mine has a small nameplate on the wooden case in the front under the dial that says: " AirMaster."
I forgot to indicate that before. Does yours also say that? Or does yours say "Simplex" ?
:
::Have this same radio but as a Simplex Model D. A schematic is available here but does not include the eye tube but otherwise quite usable. Link follows:
::
::http://www.nostalgiaair.org/Resources/411/M0018411.htm
::
::Richard
::

::Wow,..Richard.. Thanks!!
::That sure seems to be it.
::I would NEVER have known it was "Simplex" otherwise... there was just no clue...
::I am so pleased now... and greatful too for your astute & quick assistance! ;-)
:
:... oh and by the way... mine has a small nameplate on the wooden case in the front under the dial that says: " AirMaster."
: I forgot to indicate that before. Does yours also say that? Or does yours say "Simplex" ?
::
:::Have this same radio but as a Simplex Model D. A schematic is available here but does not include the eye tube but otherwise quite usable. Link follows:
:::
:::http://www.nostalgiaair.org/Resources/411/M0018411.htm
:::
:::Richard
:::
Glad to be of assistance. Seeing the photos was key. Mine has the Simplex plate on the front and rubber stamped "Model D" on the chassis and the speaker. Ordinarily Airmaster should have been made by Automatic so not sure about the Simplex connection. The Mallory Radio Encyclopedia does list the Simplex model D with the 6G5 eye tube but apparently Rider never published a schematic since the column was left blank. Only the eyeless version was published by Rider (Simplex 7-1). Did look in Mallory at Automatic and Airmaster but the 6D6 tube kept showing up instead of the 6K7 in the tube lineup. Merry Christmas!

Richard

Thanks for the feedback Richard.
I've got this thing half re-capped now already thanks to that schematic source. I needed it mostly as the old paper covered caps in this thing (unlike wax covered)have the values faded off or obscred. They were printed on the body just under the outer paper wrapping which now obscures it. Some I can get through the paper to see but not all. So I really needed the schematic for reference. ... but humorously... the print is so small that even when I enlarge it it's hard to read too. For instance, is that a 3 or 5 K resistor on the 75-cathode to ground? and is that cap in parallel a 5 uf?.. or what?
My speaker has a field coil that measures 700 ohms and the schematic says there's a 500 ohm choke instead (not shown exactly as the field coil).
And what the heck is that other thing shown on the print right after the rectifier?...(An inductor in series with a .1-cap to B+)The schematic says 2500 ohm then FK20 ? (I think) after that.
Is that correct? What does that Fk20 mean? And what does this coil/cap thing do exactly, I wonder? I guess it's some type of filter but I haven't seen this across a choke before.
in any case...I haven't found this coil/cap thing in the circuit yet if it's there.
The speaker (6.5")sounds pretty poor. Garbled and distorted. It had a few tears that were glued and some that I glued, which helped, but still not as nice as a substitue one. I un-soldered the vc leads and jumpered to the 5" substitute and that sounds perfect... so..I don't know why now because the old one (now glued nicely around the rim and a few other spots) seems to be in reasonable looking shape? But sounds especially crummy when the tone control is on or near bass, where the substitute one (5") sounds fine there.
The speaker is Rola model F-8 or F5.
I don't have one with a field coil of that size here now.
The magic eye in mine is on the dim side but I don't see any action in there at all. Perhaps as I get the rest of the components replaced I may see it work better.

Peter: Chose to keep my radio completely original since it plays, albeit not real sensitive, very clean and just looks nice just the way it is with that outstanding oval dial.

May be able to help with some of the capacitor values from my set. Let me know.

:for reference. ... but humorously... the print is so small that even when I enlarge it it's hard to read too. For instance, is that a 3 or 5 K resistor on the 75-cathode to ground? and is that cap in parallel a 5 uf?.. or what?

Looking at my radio, it's a 5uf-25V cap and 5K resistor.

:My speaker has a field coil that measures 700 ohms and the schematic says there's a 500 ohm choke instead (not shown exactly as the field coil).

:And what the heck is that other thing shown on the print right after the rectifier?...(An inductor in series with a .1-cap to B+)The schematic says 2500 ohm then FK20 ? (I think) after that.
: Is that correct? What does that Fk20 mean? And what does this coil/cap thing do exactly, I wonder? I guess it's some type of filter but I haven't seen this across a choke before.

That should be the speaker field and should read near 2500 ohms. It is not part of the pi filter of the power supply so common on radios. The high 2500 ohm resistance is important to not put excessive load on the 25Z5 tube. The speaker field is separately excited by the 20uF cap across it. The 500 ohm choke forms the pi filter with the 20 and 4 uF caps. Choke is near the 25Z5 rectifier. The FK20 must be word FIELD, very pixellated. It is unfortunate the Simplex put 5 radio schematics on a single page. Sometimes have to get a local radio collector who has the Rider books to help clarify things. The .1uf cap and speaker field are tied to B-. The schematic uses intersections to denote a connection instead of a dot and tiny loops around lines to denote no connection.

:The speaker is Rola model F-8 or F5.
:I don't have one with a field coil of that size here now.

Don't see a speaker name on my radio. Field on mine reads 2300 ohms cold.

:The magic eye in mine is on the dim side but I don't see any action in there at all. Perhaps as I get the

It will take a fairly strong station to see any action on the 6G5 eye tube. Even in a healthy radio.

Whew!
Richard

Wow!... thanks Richard!!!!!
It pays to ask questions... lol
Thanks for the cap & resistor values... I had already kinda guessed that it was probably a 5uf @ some low voltage and so I substituted it with the smallest electrolytic I had here..a 22uf @ 25v.. and it's working fine.
But here's the good news categories... the choke and the speaker!!
Thanks... this thing was re-wired screwy.. and that's why I was a tad misled & confused. The 700 ohms I measured was the primary of the audio output xformer.
So now I was able to un-wire the speaker terminal jumble and now I get 2600 ohms on the field and 700 on the audio primary.
Well the choke was not here (missing in action) and the field coil was wired in it's place. So I dug up a 300 ohm choke from an old fried chassis, and wired the whole thing back to original layout. It worked! And I see that the B+ went up at least 20 volts or so too. The plate of the 43 is now right on @ 95v.
But the best part is that the speaker that was sounding so crummy and kinda garbled is now sharp crisp and clear!
I noticed a slight ac-hum though that was not here before... so since the new choke is only 300 ohms not 500 I thought maybe I ought to kick up that 4 uf cap and added 33uf... which helped a good deal but not totally so I then replaced the 20uf with a 68uf. (I'll trim these both out to optimum values later)
Now the speaker sounds as smooth as silk... and great, even as I turn the tone control well into bass.
Richard, without your help identifying and interpreting the schematic's hen-scratching ... I probably would have canned that speaker and used a PM with a resistor replacing that choke. But this is much better!
YI know you know how good it feels to solve these little mysteries.. right?
Especially when the pay-off is a beautiful sounding radio doing what was designed to do...
Ahhh...simple pleasures! lol
Thanks, Richard. I owe you one!

:Wow!... thanks Richard!!!!!
:It pays to ask questions... lol
:Thanks for the cap & resistor values... I had already kinda guessed that it was probably a 5uf @ some low voltage and so I substituted it with the smallest electrolytic I had here..a 22uf @ 25v.. and it's working fine.
:But here's the good news categories... the choke and the speaker!!
:Thanks... this thing was re-wired screwy.. and that's why I was a tad misled & confused. The 700 ohms I measured was the primary of the audio output xformer.
:So now I was able to un-wire the speaker terminal jumble and now I get 2600 ohms on the field and 700 on the audio primary.
:Well the choke was not here (missing in action) and the field coil was wired in it's place. So I dug up a 300 ohm choke from an old fried chassis, and wired the whole thing back to original layout. It worked! And I see that the B+ went up at least 20 volts or so too. The plate of the 43 is now right on @ 95v.
:But the best part is that the speaker that was sounding so crummy and kinda garbled is now sharp crisp and clear!
:I noticed a slight ac-hum though that was not here before... so since the new choke is only 300 ohms not 500 I thought maybe I ought to kick up that 4 uf cap and added 33uf... which helped a good deal but not totally so I then replaced the 20uf with a 68uf. (I'll trim these both out to optimum values later)
:Now the speaker sounds as smooth as silk... and great, even as I turn the tone control well into bass.
: Richard, without your help identifying and interpreting the schematic's hen-scratching ... I probably would have canned that speaker and used a PM with a resistor replacing that choke. But this is much better!
:You probably know how good it feels to solve these little mysteries.. right?
:Especially when the pay-off is a beautiful sounding radio doing what was designed to do...
:Ahhh...simple pleasures! lol
:Thanks, Richard. I owe you one!
... as a follow up:
I decided to toss the choke completely as it's a bit hard to mount. And although I don't know the actual reactance of the original choke, I experimented with a 560-ohm 2 watt resistor which seems to do the job swimingly!
(17v drop x .03 amps = .5 watt x 3 safety factor = 1.5 watt)
... and the 68uf and 30uf caps used with it in pi-formation seem to be the best as I start to notice a little hum again when I try to reduce them.

My Eye tube still doesn't do much but sit there looking pale green like it's gonna puke... but if I ind the strongest station and grab the short piece of longwire- antenna with my hand ... which really brings the staion in booming... I can notice just the slightest lack-luster motion in there...
Again.. we'll see if cleaning up the rest of the components at the RF end will help.

Peter: That's wonderful news! You have overcome a heck of lot to bring it this far. Suspect most would have put it back on the shelf to be forgotten. You have turned the onion into a orchid! You know your way around electronics very well. Seldom one gets such good news after giving some advice.

As for the eye tube, believe the it will take -18 volts of AVC to completely close it. An RF alignment may be needed to get more action on the eye. This is not a super-duper high performance radio to begin with. So don't expect it to perform like a radio with twice the number of tubes.

Those hum problems can be tough. Not sure what more to say. Thomas D. had a lot of good ideas in another posting on this.

Congrats!
Richard

Hi Peter

As others mentioned be sure you have a good negative AVC voltage on pin #3 of the eye tube. For this you need a strong station, good alignment and maybe antenna?

Your eye tube will have a resistor between pin #2 and #4. It's often built into the tube socket and 1 meg. If this resistor has increased or opened you won't have much eye movement. The resistor can be replaced.

Voltage on pin #4 controls brightness. Ideal is 250 volts but as eye tubes age they dim. You can increase voltage on this pin to brighten up the green.

Norm

:Peter: That's wonderful news! You have overcome a heck of lot to bring it this far. Suspect most would have put it back on the shelf to be forgotten. You have turned the onion into a orchid! You know your way around electronics very well. Seldom one gets such good news after giving some advice.
:
: As for the eye tube, believe the it will take -18 volts of AVC to completely close it. An RF alignment may be needed to get more action on the eye. This is not a super-duper high performance radio to begin with. So don't expect it to perform like a radio with twice the number of tubes.
:
: Those hum problems can be tough. Not sure what more to say. Thomas D. had a lot of good ideas in another posting on this.
:
:Congrats!
:Richard

Hi

Just noticed something.. If your radio follows Simplex Model D it only has a half wave rectifier off the AC line. With this circuit about the best eye tube voltage you could expect would be 125 volts. This may be enough for a new tube but as they age tubes dim.

If this is your circuit building a voltage doubler for the eye tube will bring up brightness.

Norm

:Hi Peter
:
: As others mentioned be sure you have a good negative AVC voltage on pin #3 of the eye tube. For this you need a strong station, good alignment and maybe antenna?
:
: Your eye tube will have a resistor between pin #2 and #4. It's often built into the tube socket and 1 meg. If this resistor has increased or opened you won't have much eye movement. The resistor can be replaced.
:
: Voltage on pin #4 controls brightness. Ideal is 250 volts but as eye tubes age they dim. You can increase voltage on this pin to brighten up the green.
:
:Norm
:
:
::Peter: That's wonderful news! You have overcome a heck of lot to bring it this far. Suspect most would have put it back on the shelf to be forgotten. You have turned the onion into a orchid! You know your way around electronics very well. Seldom one gets such good news after giving some advice.
::
:: As for the eye tube, believe the it will take -18 volts of AVC to completely close it. An RF alignment may be needed to get more action on the eye. This is not a super-duper high performance radio to begin with. So don't expect it to perform like a radio with twice the number of tubes.
::
:: Those hum problems can be tough. Not sure what more to say. Thomas D. had a lot of good ideas in another posting on this.
::
::Congrats!
::Richard

Thanks for the encouragement.
Puting it back on the shelf would never be an option for me.. lol.. unless I had to wait for parts maybe.
I figure there is no problem that can't be overcome eventually. It just takes time to figure it out and parts. What else is there? It worked once before .. and as long as I have that schematic and enough parts..eventually it's gotta work. No?
Last week I had a Howard 901-B with both IFs shot. The first one had an open secondary and the 2nd IF had both windings open.
I saw an article posted here somewhere about by-passing open IF windings with a resistor. R-C instead of L-C .. but you then have to couple across the coils with a capacitor too.
So I tried it and it worked... but very broadly tuned.
But it did work.
Then I saw a Howard chassis for sale... so I bought it to get the IFs out of it. But while waiting a few days for it I decided to experiment. So I took the IF cans out of an old Zenith 6d525 that was in a fire...
Boy those IF cans were blackened and burned... wires all fried going in and out. But I ohmed them and they were good.
Took the cans all apart, gently glued around the sagging coils then I re-wired in new leads etc. Then I by passed some extra components in the 2nd IF that the Howard IFs didn't have. I was lucky that the can mounting holes lined up closley too. Well to make a long story short... it worked great!. I re-aligned the IFs and the RF.. And now that lil' bugger plays so beautifully!
So I know that if there's a way.. I'll find it. But I can't do it without input from guys like you who steer me in the right direction and clear up my confusion when I'm lost.

In fact even as we speak (lol) I have a new wrinkle with this AirMaster that I'll need to tackle before trying to get that Eye tube going.
About 4am I was feeling so proud of all my progress and I turned it off for a while to read my email and go to bed...lol
But just before going upstairs I turned it on again to enjoy it a little... but there was no joy. lol
Only a.c. hummmmm strongly behind the audio. It was not there when I shut it off. So I guessed there must be some extra load somewhere somehow... like maybe the field coil leaking or something. So I've been troubleshooting for hours and things are getting a bit better but not totally.
First I increased the filter caps a bit and that made it quiet but I didn't want to leave it that way as it had been fine before. So I took out the extra caps and tried puting back the 300 ohm choke which also helped a bit but not perfectly. The hum was now not so bad but there was distortion and loss of volume. The distortion was kind of like waterery background and whishing shissing behind everything.
I had finished all recapping already so I couldn't hope it was just a bad paper cap.
Well afer many tests and swapping.. I'm now at this point.
I have removed the field coil speaker for now and am using a similar sized PM.
Each time I turn it on it is loud but then the volume starts dropping off slowly.
I step by step (testing in between) replaced all the components in the output amp section as these old funny looking canoe-shaped resistors were all way out of tolerance. So everything in that circuit is replaced and close to schematic values. like where it has a 700 ohm cathode resistor.. I used a 680 ohm carbon composition. And the 300ks were replaced with 330ks etc.
But altough the B+ is rather steady at 111v... the amp still fades away... like an old soldier..
So there's a leak here somewhere. The cathode voltage says it should be 15.5v I think.
I do get close to that on power-up...like maybe 16v or so.
But as it gets warmed up that voltage slowly keeps rising to like 16.85 and up to 17v.. and the volume gets softer....
I changed audio output transformers 3 different ones to see if any were leaky... no difference. I removed the .05 tone cap from the plate. No difference.
I replaced the cathode capacitor. Not it.
I removed that cap... still the same thing.
The cathode voltage keeps rising and the plate voltage keeps dropping.
The cathode starts out at about 16 and creeps up to 17 or so very slowly. The only way I can keep it stable is to ground the grid pin 4.
i can't seem to figure it out.... maybe i'm over-tired.
Been up all night now... and it's 2:30pm now.. lol
There's only a few components in this circuit.
Any ideas you guys?

I'm going to go to bed for a while and see if that helps.. lol

Hi

Grid #1 voltage is rising in relation to cathode of your output tube. This causes the tube to draw more current lowering overall voltage. Measure voltage between grid #1 and cathode.

Problem is usually caused by a leaky coupling cap connected to grid #1. It can also be caused by grid resistor going up in value. This resistor should be limited to 470K. Some manufacturers used higher values. A gassy/leaky audio output tube can also run away with current.

Norm

:Thanks for the encouragement.
:Puting it back on the shelf would never be an option for me.. lol.. unless I had to wait for parts maybe.
:I figure there is no problem that can't be overcome eventually. It just takes time to figure it out and parts. What else is there? It worked once before .. and as long as I have that schematic and enough parts..eventually it's gotta work. No?
:Last week I had a Howard 901-B with both IFs shot. The first one had an open secondary and the 2nd IF had both windings open.
:I saw an article posted here somewhere about by-passing open IF windings with a resistor. R-C instead of L-C .. but you then have to couple across the coils with a capacitor too.
:So I tried it and it worked... but very broadly tuned.
:But it did work.
:Then I saw a Howard chassis for sale... so I bought it to get the IFs out of it. But while waiting a few days for it I decided to experiment. So I took the IF cans out of an old Zenith 6d525 that was in a fire...
:Boy those IF cans were blackened and burned... wires all fried going in and out. But I ohmed them and they were good.
:Took the cans all apart, gently glued around the sagging coils then I re-wired in new leads etc. Then I by passed some extra components in the 2nd IF that the Howard IFs didn't have. I was lucky that the can mounting holes lined up closley too. Well to make a long story short... it worked great!. I re-aligned the IFs and the RF.. And now that lil' bugger plays so beautifully!
:So I know that if there's a way.. I'll find it. But I can't do it without input from guys like you who steer me in the right direction and clear up my confusion when I'm lost.
:
:In fact even as we speak (lol) I have a new wrinkle with this AirMaster that I'll need to tackle before trying to get that Eye tube going.
:About 4am I was feeling so proud of all my progress and I turned it off for a while to read my email and go to bed...lol
:But just before going upstairs I turned it on again to enjoy it a little... but there was no joy. lol
:Only a.c. hummmmm strongly behind the audio. It was not there when I shut it off. So I guessed there must be some extra load somewhere somehow... like maybe the field coil leaking or something. So I've been troubleshooting for hours and things are getting a bit better but not totally.
:First I increased the filter caps a bit and that made it quiet but I didn't want to leave it that way as it had been fine before. So I took out the extra caps and tried puting back the 300 ohm choke which also helped a bit but not perfectly. The hum was now not so bad but there was distortion and loss of volume. The distortion was kind of like waterery background and whishing shissing behind everything.
:I had finished all recapping already so I couldn't hope it was just a bad paper cap.
:Well afer many tests and swapping.. I'm now at this point.
:I have removed the field coil speaker for now and am using a similar sized PM.
:Each time I turn it on it is loud but then the volume starts dropping off slowly.
:I step by step (testing in between) replaced all the components in the output amp section as these old funny looking canoe-shaped resistors were all way out of tolerance. So everything in that circuit is replaced and close to schematic values. like where it has a 700 ohm cathode resistor.. I used a 680 ohm carbon composition. And the 300ks were replaced with 330ks etc.
:But altough the B+ is rather steady at 111v... the amp still fades away... like an old soldier..
:So there's a leak here somewhere. The cathode voltage says it should be 15.5v I think.
:I do get close to that on power-up...like maybe 16v or so.
:But as it gets warmed up that voltage slowly keeps rising to like 16.85 and up to 17v.. and the volume gets softer....
:I changed audio output transformers 3 different ones to see if any were leaky... no difference. I removed the .05 tone cap from the plate. No difference.
:I replaced the cathode capacitor. Not it.
:I removed that cap... still the same thing.
:The cathode voltage keeps rising and the plate voltage keeps dropping.
:The cathode starts out at about 16 and creeps up to 17 or so very slowly. The only way I can keep it stable is to ground the grid pin 4.
:i can't seem to figure it out.... maybe i'm over-tired.
:Been up all night now... and it's 2:30pm now.. lol
:There's only a few components in this circuit.
:Any ideas you guys?
:
:I'm going to go to bed for a while and see if that helps.. lol
:
:
:
:
:
:

Peter: I've seen the 75 tube become weak and distorted after 5 mins of operation. Kept cranking on the volume knob as the radio warmed up. Saw this on a Walgreen and American Bosch radio recently. The diode section remains normal, its the triode section that goes limp. Showed up nicely on a scope. With another 75 tube, the volume and fidelity has been fine ever since. Worth a try.

Richard

Well... isn't strange?
I'm sure all of you out there can see the dandruff flying around as I scratch my head raw!!
I am befuddled though pleased.. .. mixed emotions you'd call it.
I was so puzzled over this 43 amp problem that I was up all night Christmas Sunday and didn't hit the sack till 3pm on Monday afternoon.. slept till 10pm.. stayed there and didn't get up till Tuesday 9am!
Today I got to read all the advice you guys left for me.
I tried the measuremens Norm suggested and found from ground reference the cathode at +16v and the grid at +.5v and referenced from the cathode the grd was -15.5v and seems to stay in that relationship as the cathode voltage rises. It goes from about 16v when 1st turned on and drifts upward to about 18v after a few minuets. next:
I tried to see if the coupling cap from the 75 was at fault by changing it. Same thing. So I disconected it from the 75 and watched the cathode of the 43 continue to climb still. So since the output amp stage is isolated now ...I figured the previous stage or that coupling cap are eliminated. Especially as the cathode voltage continues rising after turn on even with that cap disconected.
Richard suggested that the 75 tube may be the culprit but I couldn't see how since I had that stage disconected yet the cathode still drifts higher...
So I just continued on and tested and checked and scratched my head all afternoon.. all to no avail.
THEN... (through some devine providence I assume)... my luck started to change.
I have 2 tube testers here. An old 1948 model Precision 10-20 and an EICO-666.
While in the flurry of trying various things on Monday morning after I 1st noticed that hum...I took out the Eico-666 to test the 25Z5 rectifier tube and figured I check the others too ...but they were not listed on the roll chart. Not the 25Z5 or the 43, or the 75.
So I dug out the Precision 10-20 tester.
That showed the 25Z5 as good. When I checked the 43 all showed good.. and the 75 was showing wierd erratic bad readings all in the "replace" zone... but since it was a 'working' tube I felt I needed a comparison... which I pulled out of a nice (working) Philco 38-12 sitting around here.
The 75 from the Philco was showing great.. all in the grassy-GREEN! The Triode section read "good" as did both diodes... so I couldn't figure out why the other 75 from this set should read so badly since it was "working" in the set...The needle wouldn't even move. Jumped a bit that's all..strange.
Well ... so who am I to doubt science!!?? lol
So I put THAT other, good "philco" 75 into the AirMaster and went along my merry way.
That's when I later concentrated less on hum problems and more on the dying volume problem.
In the heat of things Monday morning I thought the tubetester quit on me too as the meter stoped moving even for "line-check" and I made a mental note to think about that another day.
So today while ripping that apart..and finding nothing wrong... I realized I had the first rotaing knob in "resistor" position where the meter is diabled... lol
What I dunce I felt like. Just a knob in the wrong position!!
Well... ok.. I've done dumb things before.. like starting the car and pressing the garage door opener, out of habit, even when the door is open... and seeing it close as I try to drive out!

So... here's the devine providence part:

I figure now is the time to test that darn 43 tube again.
Well it checks fine. So I get the original 75 laying around on the bench and sure enough it still shows erratic bad. So I pull the other 75 back out of the Airmaster to compare again... and sure enough it is 'peachy-keen' in the green.
I just couldn't believe that that old, original 75 could read so bad inasmuch as it had been working.
(Now this is also the tube I had to re-solder on the grid cap too.)
Anyway I stuck it back into the Airmaster just to confirm that I wasn't crazy and that it HAD really been working before. So sure enough.. it works just like before.. so much for that erattic tube tester reading.
So I go back to my output amp de-bugging.. but suddenly.. everything is fine...!!! the volume stopped drifting away.
Richard was right... it was that Fr*@iggin 75!!!!!
What?
How can this be.?????????????
The good reading tube causes volume drifting down to nuttin... and the BAD reading tube workes just fine???

Oh woe is me.. I'm sooo confused ... head sore from scratching... but happy it's working.

Hi Peter

Good to hear you found a 75 problem. Just for an experiment try resoldering the tube pins and top cap. See what happens.

Norm

:Well... isn't strange?
:I'm sure all of you out there can see the dandruff flying around as I scratch my head raw!!
:I am befuddled though pleased.. .. mixed emotions you'd call it.
:I was so puzzled over this 43 amp problem that I was up all night Christmas Sunday and didn't hit the sack till 3pm on Monday afternoon.. slept till 10pm.. stayed there and didn't get up till Tuesday 9am!
:Today I got to read all the advice you guys left for me.
:I tried the measuremens Norm suggested and found from ground reference the cathode at +16v and the grid at +.5v and referenced from the cathode the grd was -15.5v and seems to stay in that relationship as the cathode voltage rises. It goes from about 16v when 1st turned on and drifts upward to about 18v after a few minuets. next:
:I tried to see if the coupling cap from the 75 was at fault by changing it. Same thing. So I disconected it from the 75 and watched the cathode of the 43 continue to climb still. So since the output amp stage is isolated now ...I figured the previous stage or that coupling cap are eliminated. Especially as the cathode voltage continues rising after turn on even with that cap disconected.
:Richard suggested that the 75 tube may be the culprit but I couldn't see how since I had that stage disconected yet the cathode still drifts higher...
:So I just continued on and tested and checked and scratched my head all afternoon.. all to no avail.
:THEN... (through some devine providence I assume)... my luck started to change.
:I have 2 tube testers here. An old 1948 model Precision 10-20 and an EICO-666.
:While in the flurry of trying various things on Monday morning after I 1st noticed that hum...I took out the Eico-666 to test the 25Z5 rectifier tube and figured I check the others too ...but they were not listed on the roll chart. Not the 25Z5 or the 43, or the 75.
: So I dug out the Precision 10-20 tester.
:That showed the 25Z5 as good. When I checked the 43 all showed good.. and the 75 was showing wierd erratic bad readings all in the "replace" zone... but since it was a 'working' tube I felt I needed a comparison... which I pulled out of a nice (working) Philco 38-12 sitting around here.
:The 75 from the Philco was showing great.. all in the grassy-GREEN! The Triode section read "good" as did both diodes... so I couldn't figure out why the other 75 from this set should read so badly since it was "working" in the set...The needle wouldn't even move. Jumped a bit that's all..strange.
:Well ... so who am I to doubt science!!?? lol
:So I put THAT other, good "philco" 75 into the AirMaster and went along my merry way.
:That's when I later concentrated less on hum problems and more on the dying volume problem.
:In the heat of things Monday morning I thought the tubetester quit on me too as the meter stoped moving even for "line-check" and I made a mental note to think about that another day.
:So today while ripping that apart..and finding nothing wrong... I realized I had the first rotaing knob in "resistor" position where the meter is diabled... lol
:What I dunce I felt like. Just a knob in the wrong position!!
:Well... ok.. I've done dumb things before.. like starting the car and pressing the garage door opener, out of habit, even when the door is open... and seeing it close as I try to drive out!
:
:So... here's the devine providence part:
:
:I figure now is the time to test that darn 43 tube again.
:Well it checks fine. So I get the original 75 laying around on the bench and sure enough it still shows erratic bad. So I pull the other 75 back out of the Airmaster to compare again... and sure enough it is 'peachy-keen' in the green.
:I just couldn't believe that that old, original 75 could read so bad inasmuch as it had been working.
: (Now this is also the tube I had to re-solder on the grid cap too.)
: Anyway I stuck it back into the Airmaster just to confirm that I wasn't crazy and that it HAD really been working before. So sure enough.. it works just like before.. so much for that erattic tube tester reading.
:So I go back to my output amp de-bugging.. but suddenly.. everything is fine...!!! the volume stopped drifting away.
:Richard was right... it was that Fr*@iggin 75!!!!!
:What?
:How can this be.?????????????
:The good reading tube causes volume drifting down to nuttin... and the BAD reading tube workes just fine???
:
:Oh woe is me.. I'm sooo confused ... head sore from scratching... but happy it's working.
:

Peter: So glad you are getting your sanity back!

I'll have to try Norm's suggestion on resoldering the pins of those two 75 tubes of mine with emphasis on the triode pins, diode sectons were OK in the radios.

Congrats!
Richard