QST article on tube life and filament voltage questioned

[WU2D]

Transmitter in a cat food can - BRILLIANT!

[k4kyv]

Despite what Tom says, I don't see safety as an issue in the QST article. The writer covers that pretty thoroughly:

...let me caution you.  High voltage is dangerous, and may be lethal. Meaning it probably will kill you - switch to safety!  If you are not familiar with working around high voltage, get help from someone who is.

...I unplugged the power cord and removed the cover... with the use of my meter's clip leads connected to the two black leads  from the  filament choke.

Keep one  hand in your pocket.

...plug the amplifier back in, and place the POWER switch to ON.

With an insulated rod, depress the INTERLOCK switch and measure the filament voltage...

Release the INTERLOCK switch, place the POWER switch to OFF, and unplug the amplifier.

Wait at least ½ hour before touching anything in the amplifier... Using an insulated tool, carefully short the plate cap to the chassis...



That looks to me like he covers safety precautions pretty well.  I would say his recommendations are a little over cautious as far as the half-hour wait.  If the rig is unplugged, the HV is shorted out with the jesus stick, and then re-shorted out before touching anything associated with the HV, plus checking the voltmeter reading, I'd say it is safe to proceed.  If there is an open bleeder, chances are the capacitors won't discharge enough in a half hour to make them any safer to touch.

That doesn't mean that I don't have other issues with the article.

[W0BTU]

Anybody see this? http://www.eham.net/ehamforum/smf/index.php/topic,77559.0.html
Interesting, the discussion that Tom had with the ARRL about that article. Page down to Reply #10. Wow.

[Opcom]

It would have been far simpler to have added an expanded scale filament voltage meter to the front panel (or added a function for it to an existing meter) and just used a variac on the amplifier, for cryin out loud. Oh I'm sure that would have deprived someone of a few watts. I read the article but was shocked at the wad of wire. Its not a professional way to do that. It is something I might do in the field, but I can't imagine why.

I think I figured this whole thing out. It is the October issue and therefore a Halloween Horror Story to frighten engineers and technicians!

[KM1H]

That thread on Eham is amazing! JI holding court with his usual collection of groupies with a few others thrown in. As JI pretty much gets laughed off forums he keeps moving down the ladder.

.........and when we are all done, in amateur use, tube failures are almost never end of life emission failures. Even if we ran 5.5 volts.

Pure BS. He has his head wrapped around a Chinese 3-500 and totally ignores the many decades of US built tubes that seem to run forever when treated properly. Even an Eimac 3-500Z needs to be regettered regularly by getting the anode up to a bright red or dark orange color. With the hundreds of SB-220 and other 3-500 amps Ive repaired or converted to 6M since the 70's Ive seen far more simply weak tubes than outright failures.
The Cetron 572B, 813, 4-250/400, 4-1000 and others are more examples.

This isn't even a gray area. The article is absolutely useless technically, and the article tells people to remove a cover and activate HV by holding an interlock with an insulated rod.

I read the article the day QST arrived and did a double take and just considered the source and the publication. As far as the interlock goes I just use a clip lead to bypass; you cant do much of anything with the cover off such as looking for a gassy tube. If Ameritron had used the type of interlock that the plunger could be pulled up to lock and activate it would probably be safer than jury rigging.
Anybody that has worked on amps for a long time has developed their own ways to stay alive. Ive managed since 1956.

Virtually no tubes in amateur service just "wear out" from hours. They are either overheated, or have defects or failures that cannot be controlled

.

Same BS JI is famous for

Interesting replies, thank you.  RCA did note that if emission were to fall off after a period of operation at full
specs, the tube could be rejuvinated by running the filament at 12 volts for several minutes with no other voltages applied.

Not just RCA but the groupies have limited reading experience.

I just have not seen amateur service tubes well past infancy that are emission depleted.

Enough already, we already know your experience is limited to a small low end company that has a long history of design issues and failures.

http://www.g8wrb.org/data/Eimac/care_and_feeding_of_power_grid_tubes.pdf

JI then tries to marginalize the above. Anyone with a basic reading ability can see that Eimac has set the guidelines for long life yet our favorite bozos jump on the term theoretical.

That thread has played its course, no real engineer would bother joining it. And JI has shown his true side..its all about the money

Carl

[DMOD]

If I ever get to meet W8JI, I'll have to ask him who pissed in his Wheaties!

Same here. He seems to have some technical expertise, but I find him very acerbic in some of his responses, especiallly if your response is not how he would have expressed it.

I know of one occasion when a person on QRZ asked about the choice of impedance matching networks for a particular application and a number of repondents including myself answered.

Since my response was not how Tom "JI" would have expressed it, it was criticized and we had a short exchange. I had given in my references many Broadcast texts about Impedance Matching Networks but he never repsonded to, nor apparently looked at those texts, but always pointed to his website.

  
Phil - AC0OB

 "My political ideal is democracy. Everyone should be respected as a person and no one should be deified." A. Einstein.

[Rob K2CU]

Just wondering if anyone has ever determined if input drive power contributes to filament heat in directly heated cathode (filament) tubes such as the 3-500Z? With the filament power at a nominal 70W or so, and drive power in GG service at 80W, where does the 80W of power go? I am sure that much gets dissipated in the grid, but all of it? 

[k4kyv]

Just wondering if anyone has ever determined if input drive power contributes to filament heat in directly heated cathode (filament) tubes such as the 3-500Z? With the filament power at a nominal 70W or so, and drive power in GG service at 80W, where does the 80W of power go? I am sure that much gets dissipated in the grid, but all of it? 

In GG service, much of the driving power is passed on through to the output, to combine with the tube's output.  I recall the FCC defined input power to a GG amplifier, as the DC input to the final plus the DC input to the driver stage.  The load through the tube acts like a swamping resistor that helps maintain a constant load on the driver stage, reducing distortion, so that the class-B GG circuit results in a cleaner signal than does the conventional grid-driven circuit.

[KM1H]

I believe the FCC went to the additive feedthru power awhile after they went to 1500W out as a few hams were really pushing it with some of the old bottles that needed 300-500W of drive. There were some other tricks they used to interpert the regs.

The earlier amps were always advertised as 1000W CW or 2000W PEP INPUT. Flip the CW/SSB switch for an extra 3dB on CW

Ive had forum battles with JI going back to the mid 90's as did many others. He was always right even when the CE of several other commercial and ham amp companies with much better reputations, Eimac engineers, and EE Professors said otherwise. His web site is regularly changed without attribution when he is forced to recant. It still has plenty of BS on it and not just on amps.

[k4kyv]

I believe the FCC went to the additive feedthru power awhile after they went to 1500W out as a few hams were really pushing it with some of the old bottles that needed 300-500W of drive. There were some other tricks they used to interpert the regs.

With the output power definition, transmit power is the total rf power input to the antenna.  It doesn't matter whether some of that power comes from the driver stage or all from the final.  That was one of the arguments the feecee used when they proposed the change.

But they shot themselves in the foot with output power by adopting the bogus one-size-fits-all p.e.p. definition (feecee magic), which allows some modes to run more actual power (up to 6 dB) than others, plus probably the majority of the "question pool" community has little clue what p.e.p actually is other than "that what the meter says".

[KM1H]

If I ever get to meet W8JI, I'll have to ask him who pissed in his Wheaties!

More likely in his scotch

[K5UJ]

Thanks Carl and Don for the technical comments; they have been very educational for me.  For one thing, I got in a dispute with Bob K4TAX over something a few years ago (long since forgotten by me) but I remember his giving his power with the additive feedthrough method (g.g. amp) and I thought he was nuts.  Well it turns out I was the one who was an idiot.  I owe him an apology.

[K1JJ]

The feedthrough power of a grounded grid amp is probably the closest thang we get in this whirl to a "free lunch."

Besides the addition of drive power to the output, that power also acts as regenerative (negative) feedback to make the signal cleaner. Just like an unbypassed cathode resistor used in an audio amp.  Very stable config, used extensively at VHF for voltage amps too.

Of course, the downside is that the GG config is harder to drive than a grid driven stage, but WTF. The grid driven stage would also be harder to drive if some RF negative feedback was introduced, so there...

I love GG for linear service, as do the Eimacs of the whirl as shown by their tube designs.

T

[k4kyv]

Wonder if anyone has ever tried push-pull grounded grid in a class B modulator.  It would take more driving power (at least 50 watts of audio to drive a modulator for a KW), but maybe you could use a large class AB1 power amplifier, like a quad of 6L6s or larger in push-pull/parallel, without worrying so much about the internal (plate) resistance, and the coupling between windings of the driver transformer wouldn't be such an issue.

It seems like such a simple solution to a long-perplexing problem, but I never have heard of anyone doing that, so is there some drawback I am overlooking?

[W2VW]

Wonder if anyone has ever tried push-pull grounded grid in a class B modulator.  It would take more driving power (at least 50 watts of audio to drive a modulator for a KW), but maybe you could use a large class AB1 power amplifier, like a quad of 6L6s or larger in push-pull/parallel, without worrying so much about the internal (plate) resistance, and the coupling between windings of the driver transformer wouldn't be such an issue.

It seems like such a simple solution to a long-perplexing problem, but I never have heard of anyone doing that, so is there some drawback I am overlooking?

I did. In 1995 and 6 I had a 4-1000 modulated by a pair in cathode driven audio service. Used 1:1 mod iron @ 6 KV. It was a kluge and I didn't have the test gear to prove it's worth.

[kb3ouk]

you would be feeding the drive audio into the filament.  running ac on filaments would probably introduce hum, have to have dc filaments.

[W2VW]

you would be feeding the drive audio into the filament.  running ac on filaments would probably introduce hum, have to have dc filaments.

2 seperate fil transformers. Feed center tap of each with audio. The audio transformer "secondary" center tap is the cathode return to b-.

Mine was not that simple because there were not too many off the shelf several hundred watt 4 ohm to 60 ohm center tapped transformers available to me at the time. I landed up using more transformers than a KA2DZT transmitter!

Today, I'd just grab a core from Antec and mod it. 

[kb3ouk]

oops, class B needs two tubes, i was thinking of it being single ended for some reason, which makes me wonder, could you have a grounded grid single ended audio amp, and in that case would it need to have dc fed filaments?

[k4kyv]

Single ended class B works for RF leen-yar service because the fly-wheel effect of the tank circuit fills in the missing half of the rf sine wave.  For audio, it has to be push-pull in order to accommodate both halves of the audio waveform, above and below base-line.

[kb3ouk]

so it couldn't be run as another class? like a regular class a audio amp can be single ended.

[KM1H]

Some very early receiving tube manuals listed single ended Class B specs. Dont remember distortion details.

[WA1GFZ]

Dave,
I just bought a 1KVA Antek power transformer for my HPSDR final. They make very nice stuff.