How about AM with a 3cx1500 ?

[KI4THX]

I hardly ever hear of anyone running this tube on AM, Is there a reason ?

Ive got a Henry 3K classic, 4200 on the plate....solid amp with the 1500 in it. Kind of an odd duck as the 1500 is laying horizontal in the RF deck. I think the Power supply is rated at 1.2A CCS (the amp weighs in at a little over 200 pounds). Should be good for legal limit AM just fine right ?

Just scratching my head as there doesn't seem to be many (if any) AM'ers using this tube ? Correct me if Im wrong please.

[flintstone mop]

My AL1500 amp uses the 3CX1500A7. There is a youtube video where a Ham (?) modified his AL1500 with two final tubes and was getting an easy 3kw out.
And I use my AL1500 in AM mode with my Flex radio doing the driving. Only need 15W to make legal limit AM. (After the usual linear amp tune-up)
Fred

[WD5JKO]

   I use the pulse version of this tube in a highly modified Dentron MLA-2500. This amp originally had a pair of 8875's. I use this amp on AM, but the negatives include: The 2+ minuet turn on wait, the gain is high such that I need a bigger attenuator (more DB's), the forced air cooling is loud, and HOT when running AM. This is a good shack heater in the winter. After a long AM transmission, you cannot turn it off until the cooling lowers the tube temperature to a safe value. A blown fuse or power outage during a long winded AM transmission would stop the forced air cooling, and the tube seal temperatures could go beyond ratings.

  All that said, these are excellent tubes, and the linearity and IMD from them is better then the glass tubes. It is still more convenient to use glass tubes such as 3-500, 811, or 572b since there doesn't need to be a roar of air, and no need to wait for the warm-up and cool down.

Jim
Wd5JKO

[W3RSW]

The dissipated heat's the same at a given output from a tube's plate if the efficiency is the same in class AB.   A room heater is a room heater regardless of perception. 

You want way less heat, then go class D or E.

Your 8877 is fine in class AB.  If your worried about loss of blower then mount a vane actuated Power shut down.  Hey, even a noise activated mike glued to the blower housing would work.  Oops, these have another name in motor service.  A simple relay and a couple of other components will keep the fan running for a while after turning off.

A bigger worry in most shacks in amateur service is total loss of house power.  ..you can dream up Tons of amp/tube failure scenarios but some power is required is required to alleviate most of them.

The 88 series, along with 3cx800's, etc., of oxide cathode tubes consume far less filament power than thoriated tungsten filament bottles such as a 3cx1200 (which seems to be a 3-1000 with no glass but with much better forced air cooling.  )

The blower in an amp along with any additional fan is as quiet (or loud)!as the quality of build, mounting, and bearings allow.  - usually a function of cost.
The blower noise from an AL1500 vs. an Alpha is almost unbelievable. ..mostly because of a simple piece of rubber and intelligent mounting.

Modern ceramic tubes have much longer shelf lives than glass bottles and do not have to be rotated in service.

Even with all those advantages, I still like to fire up the 813's mod by more big glass bottles.  - yeah, even those have an older, loud fan exhausting the cab because the benefits of additional cooling beyond natural convection sure can't hurt now that tube costs have soared.

Filament voltage in both types is fairly critical and should be close to nominal in amateur service.  I don't know how the Russians can certify their ceramic tube filaments for such a wide variation of service voltage. The true military application (what are amateurs in the USSR anyway?) is the dead giveaway I suppose. Just like a lot of Russian stuff ..takes a lickin' and keeps on tickin'. --Battery and gen set voltage expected to range from 12 to 14 or more volts.

[K1JJ]

     All that said, these are excellent tubes, and the linearity and IMD from them is better then the glass tubes. It is still more convenient to use glass tubes such as 3-500, 811, or 572b since there doesn't need to be a roar of air, and no need to wait for the warm-up and cool down.

Jim
Wd5JKO

Hi Jim,

Tell me more about the "cool down"  requirements and reasons when using indirectly heated cathode transmitting power tubes...

I have a few in service here and use a delay timer for filament operation. For shut down, I manually let the fan run a while after turning the filaments off.  

Is there a special reason for turn-off / cool-down precautions that sets them apart from directly heated filament seal precautions?

T

[Jim, W5JO]

Modern ceramic tubes have much longer shelf lives than glass bottles and do not have to be rotated in service.

Tell me more about this, I have never heard it before.

[KD6VXI]

Modern tunes will be killed much more quickly than convection cooled glass anodes by design.   I've burned up more than 1 8877 in a three holer in the 80s by losing all AC.   Never had that problem with a 500Z.

Ive seen a tall literature that states the 3CX1200 is the "solid state"  3-1k.  Orr calls it the same in his write up and construction article for a 3 or 4 - 1000Z amp.   With small changes,  a 1200 fits and works fine business.

--Shane
KD6VXI

[Opcom]

A small UPS dedicated to the blower would be the cheap seats for enforcing a cool-down when power disappears. A 100-300W inverter and a gel cell could be put in service for this function with a minimal space requirement and lowest cost.

Alternately, a bottle of compressed air or nitrogen as some people use for various purposes in their workshops, could be pressed into emergency service at the expense of some complications and a length of 1/8" line. An air ejector the same diameter as the blower air path could work to entrain a large low speed airflow through the tube cooling path without blocking it. The bottle would stay where it is, but the other things like a thermal control valve and a couple of solenoid valves would have to be built into the amp, and are not so tiny. Better for larger amplifier cabinets than compact desktops. Air ejectors need not be large or heavy: http://www.zex.com/zx/zex-ejector-air-amp-3-00-in-diam-4-ft-hosehtml/ Just presenting alternatives and possible experiments.

A guess as to why post-operation cooling is recommended for some indirectly heated ceramic power tubes could be related to the amount of thermal energy stored in the mass of the heater-cathode structure. It could continue to heat the tube body long after filament power is removed, and so, overheat the tube components if the heat is not removed by air flow.

[KI4THX]

Thanks for the replies gentlemen. I never thought about the effects of loosing blower power when hot when I made this thread. It has been very enlightening !

[kb3ouk]

As far as dealing with blower noise, I always thought this might be worth giving a try: take a second mic and set it near the transmitter where the only thing it is picking up is the blower. Combine this audio with the audio from the main mic, but have the blower mic 180 degrees out of phase, that way the only audio that can be heard is what isn't common to both mics.

[WD5JKO]

Hi Jim,
Tell me more about the "cool down"  requirements and reasons when using indirectly heated cathode transmitting power tubes...

Tom,

  I am not a tube designer, but I'll take a crack at it. I think the main issue is "radiation cooled" (internal anode - glass) versus "conduction cooled" (external anode). With a glass tube, the radiation of IR energy drops really fast when power is lost, and the plate has little thermal mass. The biggest concern is the plate seal to glass at the top. With external anode tubes, the plate has a lot of thermal mass, and the plate seal around the tube has a large area. The insulator instead of glass is either ceramic or beryllium oxide (BeO).
Therefore, a loss of cooling with a 4cx250, or 8877 can do more damage to the tube, than it would a 3-500, or 572B when the tube had been dumping significant power prior to the loss of cooling.

  You mention "indirectly heated" versus "directly heated". I'd like to hear from some of the heavy hitters on tube design how those differences factor in.

  If I got this wrong, remember I said I'm not a tube designer. I did however have the privilege working with Joe Cecil (w5riq) who was a pioneering Physicist in the field of ion implant. Joe designed several "ion sources", both hot cathode, and cold cathode. I used to watch him wind filaments around a threaded bolt, and spot weld the ends to the posts. Joe used to elevate his body to 40KV to debug the control electronics while the source was running. He had a "special" chair.  

  As a side note, BeO is a powerful carcinogen. Breaking BeO, makes tiny airborne particles, and if inhaled create a long lasting irritation. Sometimes transistor heatsink insulators for TO-3, and TO-220 are BeO. BeO is an excellent thermal conductor, and also a very good electrical insulator. Ceramic on the other hand is a crappy thermal insulator and an excellent electrical insulator. BeO has advantages. Does the 8877 use BeO? Machining BeO is best done under water to eliminate the airborne particles.

Jim
Wd5JKO

[WQ9E]

Jim,

Thanks for the advisory note on BeO; it is something a lot of us are aware of but some of the newer folks who weren't active in electronics during its heavy use as an electrically insulating thermal link during the 1970s and 1980's may have little knowledge of it.  Beryllium Oxide is very safe when properly handled and extremely dangerous when mishandled and it only takes a minute amount of liberated material for harm to occur. 

In addition to machining it is easy to crack a BeO link through excessive mounting stress.  Surfaces must be flat with no significant imperfections and excessive fastener torque will easily crack the material.  Dropping or improperly packed/handled equipment containing BeO is another common way to get into trouble with this stuff.  Cracking/fracturing it will liberate dust. It is a very useful material that is quite safe when treated properly but it requires more cautious handling than a lot of what we use.  Trying to machine BeO in a home workshop is an excellent way to expose your entire family to a material which is both a carcinogen and in larger amounts leads to heavy metal poisoning if the cancer doesn't prove fatal first.

[K1JJ]

OK on the thermal precautions, Jim.    I will be even more aware of my external anode 8877 amp as it cools down.  Yes, the radiation-cooled 4-1000A certainly radiates heat better.

Quick story about a tube cooling disaster:  About 20 years ago I ran a conservative homebrew 3CX-3000A7 linear amp.  A bunch of us were on one night rag chewing - making long transmissions.  I usually wear headphones to monitor, so cannot hear the blower noise very well.  After a long xmission, I smelled a strange metallic burning odor.  I looked behind the linear and saw the 3CX-3000A7 anode glowing red! It was so hot that the steel? anode plate metal was heated enough to prossibly deform.

I turned the rig off and watched the glow slowly dissipate. I could feel the heat on my face. It turned out that the air ducting from the blower had fallen out and was blowing air on the floor. What a JS artist I was!

As the tube cooled down I heard a faint "pop."  Later, I turned the filament on and got a bright flash. It failed. The seal went bad.  It was a new Svetlana tube - what a heartbreaker.

Since then I use electronic kiln temp sensors and alarms that monitor all my amplifiers for heat. I watch them like a hawk.  Good lesson.

Another instance:  Back around the same time I left the filament of a 3CX-2500F3 on all night without air by mistake.  In the morning, I could see the weeping of solder coming out of the filament lead junctions to the tube. Amazingly, the tube was OK and I used it for a few years afterwards.


I now have digital / alarm temperature readouts in front of me for all power amplifiers. The only way to go.  The mechanical air shutdown fail safes are a good idea too.

T

[W3RSW]

JJ, What a rugged tube that 3cx2500 was. --Always listen to your advice and construction exploits.    prodigious!

Btw, curious.
What are the actual stats on BeO poisoning and deaths from heat sinks, the manufacturer , usage, and modification thereof? I'm not aware of any tubes that used the material other than as an external heat sink link, a coupler between the tube anode and a copper spreader, thence to aluminum radiator with fins. Yes Eimac manufactured or sold the couplings complete with part no. -- I'm Not sure if they actually made them or outsourced them. That would be a place to look for actual stats.

Also what are the real stats for same from PCB's? Deaths or poisonings?  There is a school of thought, a rapidly buried minority, that claimed that the xylene carrier in ARCLORs testing was the actual carcinogen.  I was involved in PCB identification in natural gas pipeline liquids, oils entrained mostly from high temp. Compressor lubrication oils, mainly attributed to Texas Eastern in "our" system at the time. ( -R.S. Wilson, PE, now retired.)

I mentioned this nagging doubt before in this forum but that was years ago. Why even pertinent now you might ask?

Entire industries were created to stop the PCB diaspora partially economically offsetting the mega-billions spent to alleviate same in the Electric, gas, RR/trucking and transportation utilities? Not so much (except legal) to stop the BeO scare.

But closer to our hearts, I think the loss of the 8873, the 8560, etc. along with unborn brothers was a disservice to the art. Class AB excess efficiency dissipation is the same for a device, say 40 to 50% regardless of solid or hollow state. .. And with lower IMD using tubes. Oxide cathode tubes require low power filaments so not much disadvantage there either.

Only now are SS devices approaching properly designed and operated tubes in distortion products. Yeah, they'll surpass tubes now with predistortion feedback but a good generation or two of alternate technology has been lost.

Sometimes I feel like I've stepped off my time line back when Colliers Magazine displayed Von Braun's magnificent baby space station followed by a glorious, great and spoked double wheeled station tended by upper stages of monster rockets, the stepping stones to Mars.

Litigation, short sightedness and rampant reallocation of resources has give us a zillion lesser stars, most now shrapnel  instead.

[WD8BIL]

I think Gary WA1OXT used a pair of 8877s on AM a while back.

[Opcom]

Since then I use electronic kiln temp sensors and alarms that monitor all my amplifiers for heat. I watch them like a hawk.  Good lesson.

I now have digital / alarm temperature readouts in front of me for all power amplifiers. The only way to go.  The mechanical air shutdown fail safes are a good idea too.

T

Could you suggest a manufacturer or source for those sensors?

[K1JJ]

Could you suggest a manufacturer or source for those sensors?

http://www.ebay.com/itm/New-PID-SSR-TEMPERATURE-CONTROLLER-FURNACE-KILN-OVEN-/230564150406?pt=LH_DefaultDomain_0&hash=item35aeb1bc86

Sure.   These kiln units are on eBay for between $25 - $40 each.   They have a probe that I mount a few inches above the tube airflow output.  Two display readouts.  The trigger temperature alarm digital readout can be set and it has relay contacts out.   The second digital readout shows the tube's air temperature in either C or F.

I have one on every amplifier. Nice Chinese unit. This one is available from San Francisco.

T

[pa0ast]

About berilium oxide:
BeO is carcinogenic and may cause chronic beryllium disease. Once fired into solid form, it is safe to handle as long as it is not subjected to any machining that generates dust.[9] Beryllium oxide ceramic is not a hazardous waste under Federal law in the USA.
http://www.inchem.org/documents/icsc/icsc/eics1325.htm gives more data.
Aprox the same danger as asbestos that can course cancer as well.

[Opcom]

About berilium oxide:
BeO is carcinogenic and may cause chronic beryllium disease. Once fired into solid form, it is safe to handle as long as it is not subjected to any machining that generates dust.[9] Beryllium oxide ceramic is not a hazardous waste under Federal law in the USA.
http://www.inchem.org/documents/icsc/icsc/eics1325.htm gives more data.
Aprox the same danger as asbestos that can course cancer as well.

Aluminum Oxide is used today for many of the same functions.

[Opcom]

Could you suggest a manufacturer or source for those sensors?

http://www.ebay.com/itm/New-PID-SSR-TEMPERATURE-CONTROLLER-FURNACE-KILN-OVEN-/230564150406?pt=LH_DefaultDomain_0&hash=item35aeb1bc86

Sure.   These kiln units are on eBay for between $25 - $40 each.   They have a probe that I mount a few inches above the tube airflow output.  Two display readouts.  The trigger temperature alarm digital readout can be set and it has relay contacts out.   The second digital readout shows the tube's air temperature in either C or F.

I have one on every amplifier. Nice Chinese unit. This one is available from San Francisco.

T

Wow, that is really slick and I see several kinds in the 'also' section.
It suddenly makes a great deal of sense on new projects considering the layout convenience of building equipment from parts, plus the cost of those ceramic tubes.

Do you use an exhaust chimney or does the air just come out of the tube and diffuse in the enclosure?

Had you seen anything like that able to take a passive infrared sensor for monitoring the anode or seal temperatures directly?

[K1JJ]

Opcom,

I use chimneys for all forced air tubes and sample the air above them.

For direct surface measurement, I wonder if one of those inexpensive laser temp guns could be run on DC (no batts) and stayed on all the time?  Aim one at the tube anode and mount it so the readout is visible.

There are probably other temp samplers out there, but I never looked into them.

T

[WD5JKO]

Looking at kiln heaters brings upon an affordable option for monitoring the air temperature. For an economical means to move the air, look at marine bilge blowers. Go to Epay and search for words in this text string: " IN-LINE BOAT BILGE AIR BLOWER". Neat stuff!

Jim
Wd5JKO

[Opcom]

Those PIR temperature guns do a great job and will run off DC. Just have to bypass the power switch to ON. They have no alarm output but it is possible on some of them to get at the display segments, so there's a low level digital output that could be converted to a digital number and used to trigger an alarm. That's more hackery than I want to get into. I'm not sure if or how they drift either, as there must be a reference inside to compare the sensor's output to, and those things are meant to work at more or less room temperature. If the PIR thermomoeter gets heated up inside the RF amplifier, the measured result might be skewed.

[K1JJ]

Looking at kiln heaters brings upon an affordable option for monitoring the air temperature. For an economical means to move the air, look at marine bilge blowers. Go to Epay and search for words in this text string: " IN-LINE BOAT BILGE AIR BLOWER". Neat stuff!
Jim
Wd5JKO

On eBay:

http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0.H0&_nkw=IN-LINE+BOAT+BILGE+AIR+BLOWER&_sacat=0&_from=R40

Vely, bery interesting, Jim.

I see there are quite a few different kinds.  I wonder how they work with back pressure?  Noise? Anyone have experience with these and could recommend one for a 4-1000A or 8877?

My goal would be to get a quieter unit compared to the common squirrel cage blowers.

T

[Opcom]

Not to disparage them but looking at the ones cited on ebay, most of those inline bilge blowers are really only ducted fans and would probably not make as much pressure as a centrifugal or squirrel cage blower. Pressure is important for external anode tube use. Takes some digging to find the pressure-volume charts.
https://www.google.com/search?q=12VDC+blower&source=lnms&tbm=isch