Is my tube soft..... very funny .... the AMP tube....

[lonestarbandit]

Asked some people via PM but using it with my phone is well I screwed it up.
One person responded and then apparently I deleted their answer when responding with more specifics below and the other either didn't see, or couldn't be bothered with me, which I also understand completely but I still don't want to waste 300 bucks if no improvement will be gained by a new tube. But if my numbers are soft it would "behoove" me to replace and have a "spare" on hand. Tube is older Eimac I believe based on design, I saw no lettering.

Test equipment

Yaesu FT 710
AL80A 1x 3-500z
MFJ 826B on peak setting
Dosy TC 4001 P on pep setting
MACO VQUAD beam as Max2000 omni gives false power readings I believe possibly due to higher reflect, IDK.

(swr is similar to beam but reflected power w amp shows 45ish watts reflect vs 4.5 watts on beam yet Max2000 swr isn't high and beam power output shows quite a bit lower and these lower potentially more accurate figures are what I've posted)

Results

Yaesu SSB NO AMP / 116 MFJ / 80 dosy
Yaesu SSB AMP / 720 MFJ / 575 dosy
Yaesu AM DK / 35 MFJ / 30 dosy
Yaesu AM Modulation / 52 MFJ / 30 dosy
Yaseu AM DK AMP / 350 MFJ / 300 dosy
Yeasu AM MOD AMP / 475 MFJ / 325 dosy

I also just for test purposes did a one time basis turned down the yaesu and put my 2x Toshiba cobra amp inline @200 ssb Into AL80A hit just over 1k pep. This amp is not inline for use and was just a test. Other individuals results w a 3-500z achieved much higher output with much lower input so I am a little concerned.
Tube experts please help me out.

Thanks!

 

[lonestarbandit]

@nomadradio thoughts or opinion on above?

 

[nomadradio]

Running from 120 Volt circuit?

This is a famously-popular way to weaken the current output of the tube's cathode. This is the "soft" condition in question, when the tube's cathode saturates at a current level below what it should deliver.

Short version is that the tube's filament/cathode is an alloy of tungsten and thorium. The thorium content radically increases the output current per unit of surface area on the filament. Problem is that a line-voltage drop under load reduces the temperature of the filament. If the temperature falls enough, it screws up the thorium chemistry and reduces the peak current the tube can deliver, as if the filament were just plain tungsten.

Running from 240 Volts improves this in two ways. The voltage drop at the wall outlet will be half what it was on a 120-Volt circuit with the same size wire in the wall, since you draw half the current to get the same RF power.

Second way is the ratio of line voltage to the filament's 5 Volts. For every Volt of drop when running at 120, the 5-Volt circuit only falls half as far running at 240.

So, you should get one-fourth the filament-voltage "droop" from a 240 outlet as you would from 120 Volts.

I call this the 240-Volt double whammy.

And if you're like one customer who had his 120-Volt amplifier outlet six feet from the breaker box, you won't have this problem.

73

 

[lonestarbandit]

You are correct Sir. It is on 120v.
So given all the above, this tube is likely in full operational condition but unless 240 is used it will not achieve its full potential. Sadly if I had the amp 6 ft from the breaker box I would be relegated to either the laundry room or the garage.
Though the laundry DOES have 240....
Food for thought anyway. Thank you for the explanation.

73

 

[nomadradio]

Well, no. I don't think the reduced power is caused by low line voltage now. Pretty sure the tube is weak as the side effect of being operated from a wimpy 120 outlet in the past. Pretty sure low line voltage damaged the tube's cathode, made it "soft" as they say.

It really sounds as if the tube is weak. Sure glad I keep a one-tuber around to test them and find out. No other way but in a circuit that pushes the tube to full bore.

This is what we used to call "JB2000 syndrome". Along with solder melted from the two filament pins. The JB2000 was popular among operators who had no access to a 240 Volt circuit. Made the amplifier famous for wearing out a pair of Zs in under a year. It would operate from 120 Volts, but the filament voltage would sag under load, especially when it was being hot-rodded past the red line.

73

 

[lonestarbandit]

Oof. And replacing said soft tube would then take a new 300ish dollar Z and convert it into the same condition as the one I have presently if operated on 120.
I wonder how much it would cost me to take 240 round to the living room....
Given the operating conditions I laid out ...what would ballpark fresh tube do vs a fresh tube on 240 I realise the variables are immense just trying to get a feel for what this AL80A is supposed to be doing vs what it is.

 

[KneeBiter]

Oof. And replacing said soft tube would then take a new 300ish dollar Z and convert it into the same condition as the one I have presently if operated on 120.
I wonder how much it would cost me to take 240 round to the living room....
Given the operating conditions I laid out ...what would ballpark fresh tube do vs a fresh tube on 240 I realise the variables are immense just trying to get a feel for what this AL80A is supposed to be doing vs what it is.

On SSB with strong tube full drive 700 to 950 out depending on band.

 

[nomadradio]

The one bit of advice I have for running one of these from 120 Volts is to position yourself on the right side so you can see the yellowish-white light from the tube's filament.

Tune up the amplifier as you would normally. Now key it, modulate and watch the color of the filament light. The color of a piece of hot metal tells you the temperature. If you can see the filament's light dim at all, or change color towards red, this is the danger zone. Won't hurt it a few times, but the cumulative effect over weeks or months will be for the tube to become progressively weaker. It's that drop in temperature under load that causes the premature wear.

And if you see no change at all, you're good to go. Means your AC outlet is close enough to the breaker box to prevent major "sag" in the line voltage under load.

73

 

[lonestarbandit]

Awsome info ty Sir I will give it a shot.

 

[linearone]

Asked some people via PM but using it with my phone is well I screwed it up.
One person responded and then apparently I deleted their answer when responding with more specifics below and the other either didn't see, or couldn't be bothered with me, which I also understand completely but I still don't want to waste 300 bucks if no improvement will be gained by a new tube. But if my numbers are soft it would "behoove" me to replace and have a "spare" on hand. Tube is older Eimac I believe based on design, I saw no lettering.

Test equipment

Yaesu FT 710
AL80A 1x 3-500z
MFJ 826B on peak setting
Dosy TC 4001 P on pep setting
MACO VQUAD beam as Max2000 omni gives false power readings I believe possibly due to higher reflect, IDK.

(swr is similar to beam but reflected power w amp shows 45ish watts reflect vs 4.5 watts on beam yet Max2000 swr isn't high and beam power output shows quite a bit lower and these lower potentially more accurate figures are what I've posted)

Results

Yaesu SSB NO AMP / 116 MFJ / 80 dosy
Yaesu SSB AMP / 720 MFJ / 575 dosy
Yaesu AM DK / 35 MFJ / 30 dosy
Yaesu AM Modulation / 52 MFJ / 30 dosy
Yaseu AM DK AMP / 350 MFJ / 300 dosy
Yeasu AM MOD AMP / 475 MFJ / 325 dosy

I also just for test purposes did a one time basis turned down the yaesu and put my 2x Toshiba cobra amp inline @200 ssb Into AL80A hit just over 1k pep. This amp is not inline for use and was just a test. Other individuals results w a 3-500z achieved much higher output with much lower input so I am a little concerned.
Tube experts please help me out.

Thanks!

You shouldn't need 200w to get 1000. Thats a poor amplification factor. Usually 75-100 ish should get you there.

 

[lonestarbandit]

You shouldn't need 200w to get 1000. Thats a poor amplification factor. Usually 75-100 ish should get you there.

Yes Sir, I thought not myself. It does seem the general consensus is I'm a little soft but would that be 100 in @120 that does it usually or @240?

 

[linearone]

Yes Sir, I thought not myself. It does seem the general consensus is I'm a little soft but would that be 100 in @120 that does it usually or @240?

But are you measuring pep?

 

[linearone]

This was on 120v.


This is on 120v

 

[lonestarbandit]

This is what both meters claim pep but as you can see they differ quite a bit from one another. My AM is significantly less as the yaesu only does 25dk and maybe swings toward 50 w mod. Judging with your videos and Nomads advice it would seem I am indeed soft. Bugger. Time for new tube I guess.

 

[lonestarbandit]

The one bit of advice I have for running one of these from 120 Volts is to position yourself on the right side so you can see the yellowish-white light from the tube's filament.

Tune up the amplifier as you would normally. Now key it, modulate and watch the color of the filament light. The color of a piece of hot metal tells you the temperature. If you can see the filament's light dim at all, or change color towards red, this is the danger zone. Won't hurt it a few times, but the cumulative effect over weeks or months will be for the tube to become progressively weaker. It's that drop in temperature under load that causes the premature wear.

And if you see no change at all, you're good to go. Means your AC outlet is close enough to the breaker box to prevent major "sag" in the line voltage under load.

73

@nomadradio I did not find any condition when tuned up where filament glow was even a little reddish. It remained a constant warm yellow/white glow with no dimming. I am fairly "close" to the mains in the garage, relatively speaking. The voltage meter on the front only flicks back slightly, not much at all, more like a twitch, under modulation.