New transmitter is up and running :)

[ke7trp]

It was a busy week. Lots of small issues getting this rig up and running. Tonight, we finally installed it and made a 75 meter am contact with the rig. 

The specs:

Class C AM transmitter.  Two 4-400a's with its own HV supply. Three voltage levels.  2300, 3000, 3500.  Big tank with 3 bands, 40, 80 and 160 with vac cap. Tuned input on all three bands. Full metering.

Modulator has its own HV supply running 3000 volts to two brand new 304 TL Triodes in AB2. Adjustable bias and full metering. Modulator takes 8 ohms in from a small mono TOA studio amp.

So far so good. Running the low voltage setting tonight and the rig seems stable.  Since I have 800 watts of audio power here, I can run 150% if I choose.  Tonight, I ran about 80 to 90.  The 304Tls sure look incredible with current on them. I got good audio reports. Running an MXL large diaphram condenser mic with NO EQ or processing right now. Here are a few shots of the Rig!

C

[ke7trp]

another pic showing the Transmitter stacked on top of the modulator.

I forgot to mention, the rig is excited by a Yaesu FT450 in CW mode.  There is a seperate Sequencer box that is keyed by a switch.  Then, the exciter, the Transitter and antenna is all keyed up at the right times.

C

[SM6OID]

Hej !

WoW ! That rig sure looks nice! Impressive!

[W3GMS]

Clark,
Congratulations on getting your big rig running.  It sounds like everything fired up real well.  By your photo's I think your Power Supply is external but I am not sure about that.  The photo's were a bit blurred. 
I am sure you will enjoy its operation!
Regards,
Joe, W3GMS

[WA1GFZ]

Beautiful job!

[W2PFY]

Great Job! I especially like the chicken wire viewing windows

[K1JJ]

Nice looking rig, Clark.  That pair of 4-400A's with 3500V, modulated by 304TL's will certainly put you into the "ChannelMaster" class in your area ....

Expect a lot more work to come, cuz it can take as long for shake down, adding improvements, as it took to build.  Have the local guys with Flex radios email you some hi-fi recordings as an initial baseline to work from.


Have you added negative feedback around the modulator/ driver yet?

T

[ke7trp]

Robert built the modulator.  The power supplys are seperate. The Mod plate Xformer is behind that Huge Reactor so you cant see it.  This rig is not power supply limited  

I cant turn the power up over the air since I am using a KW matchbox. I need to build a big tuner.  IN the dummy load it will carrier at full legal limit power.

 The heat from the modulators is outragous. I am thinking of ways to put glass in the front and duct the air out the back so its not blowing right on me as I sit there and talk.

The RF deck has a BC edge wound coil with Vac relays to switch band taps from the band switch knob. This way, We have no bandswitch to Zorch.  The tuned input has a roller and cap.

I got called into work so I cant fire it up on 40 meters today. Maybe I will try when I get home later.  This thing took 2 years to complete and lots of money. 

Next up is to make a plate current overload trip.  I have not needed it yet but the T368 has a neat system that kicks a breaker out the instant the plate current gets over a set limit. I would like to have that feature incase I have an accident and key up on the wrong antenna or no antenna.

[W3GMS]

Clark,
Build them big and run them hot.  Nothing like plenty of fire in the wire.
Have fun after your 2 year build cyle!
Regards,
Joe, W3GMS 

[KA0HCP]

What a beauty!

[W1UJR]

Very pretty indeed!

Love those big bottles!

[Steve - WB3HUZ]

NICE! We shouldn't have any problem hearing out here on the East Coast this winter.  Enjoy.

[W1ATR]

Nice Clark. Looks awesome and just the right size too.

There goes the heat load on your air conditioning lol.

[ke7trp]

Its has not been that bad so far.  Running on the low tap there is no extra heat on the 4-400 deck that I can tell.  The modulators do blow some hot air out if you get long winded.  Lucky for me, The weather has cooled off here. It was 80 most of the day. 

I think I am going to change the cooling around a bit though.  I want to put Glass on the front of each unit and isntall fans at the rear to blow the air out that way.  I might even run some duct work out the wall using a Dryer vent.

On the air now on 3870..

C

[K1JJ]

Clark,


Dryer duct can be noisy and less efficient for air flow due to the bumpy inside rib's air turbulance. It can also melt if you push it hard for exit air.

I use flexible fiberglass 4.5" ducting that has a smooth inside. It costs more, but works really FB. Find it on the web. It is used for car ducting sometimes.

I have three rigs that suck air from the outside. This decreases the noise maybe 70% over having a blower inside on the chassis. When you have a long run of ducting, it is important to have a smooth inside ducting wall.

Mounted outside, you can use a big mo-fo blower.  I use a Variac to tone it down - and use a digital temp gauge to monitor exit heat. The temp gauge is on the web too.

T

[ke7trp]

Good idea.   This morning its been kind of nice. I woke up and it was in the 60s here.  Unreal. I cant remember the last time I felt this type of weather.  Going to fire it up on 40 meters a bit and make some calls.

[Bill, KD0HG]

Yes, I use glass for viewing windows. The days of needing extreme shielding because of TVI are over. Harris used plexiglass windows in some of their 1 KW rigs, which didn't last or stay transparent after a few years.

I assume you do have a fan or blower on the 304s. Put as much wind on them as possible, including the base. That's why the Johnson sockets for the 304s elevates the tubes, so air can circulate at the bottom and through the hole in the base. As old as they are, I've had several go gassy on me after running bright orange for a few months. Don, K4KYV has had problems in the past with their base pins getting so hot that they unsolder themselves.

I use a stack of two muffin fans for cooling, their combined height is just about right to cover the base pins to the plate cap. Not the quiet ones, but the industrial fans that really wail.

304s are made from a glass called "Nonex", which is similar to Pyrex but also is minimally expanding with heat, hence the name. When they're new, you can run them until the glass almost gets red hot, but a questionable practice when they're 70 years old. Pyrex won't begin to soften until it reaches nearly 1,500F.

[ke7trp]

I have plenty of airflow on them and there is no current when its not keyed up.  I am running them down so low that they do not get to hot.

The big issue now is I feel that I am getting to much radiation out of these viewing ports.  I am sitting in front of the rig. I noticed my right arm has some color to it. Its about 1 to 2 feet from the Tls when I sit and talk. Currently, we are using aluminum expanded metal over the ports.  What can I do to ensure I am protected?  Is this a concern or am I over acting?

I thought going down and getting some house screen and cutting some panels out to lay over the windows.

C

[W2PFY]

The big issue now is I feel that I am getting to much radiation out of these viewing ports.  I am sitting in front of the rig. I noticed my right arm has some color to it. Its about 1 to 2 feet from the Tls when I sit and talk. Currently, we are using aluminum expanded metal over the ports.  What can I do to ensure I am protected?  Is this a concern or am I over acting?

Interesting question Clark. I wonder if it's IR?

Some years back a ham in this area was running the more modern 304TL's with the plates that have a carbon coating on the anodes. He said he could get 30 percent more power out of the tube and he attributed it to the coating. Anyone agree with that finding? This is not a high-jack 

[ke7trp]

It may be just the heat.  My Arm is right there taking the brunt of the heat output.  It just got me worried.

Never seen the carbon coated 304s.  Mine are original NOS eimac tubes that say VT129/304TL.   They are just wonderfull to look at and make audio power I only dreamed about before. This is a huge step up over an 810.

C

[W2PFY]

Hi Clark, here is the type I was referring to.


http://cgi.ebay.com/NOS-GENUINE-EIMAC-304TL-POWER-AMPLIFIER-TUBE-L-K-/270634001477?pt=Vintage_Electronics_R2&hash=item3f030b2445

There are no plate fins on this type. I like the older type as they have a much nicer glow. I don't think these would like a yellow glowing plate color? Perhaps this type would emit less IR?

 

[ke7trp]

Its the IR that was getting my arm. I moved back from the rig.  I know a guy that has one of those carbon tubes. Maybe I will try to bid on this one and have a pair. I am told they do not Cherry up so they are not as near as cool looking. But can make more power.

I had my first failure today on 40 meters.  I started hearing a snapping sound in the RF deck.  I loaded up the deck higher and the snapping stopped. The it started again. I took a close look and found there was an arc about half way up the plate choke. It looks like the choke was sitting in a box of parts over the years and got some nicks and dents on it.

I plan on ordering the RF parts plate choke. Its 4kv, 1.5 amp and 225UH.  This one is out of a BC rig.  Robert said he would cover the cost of a new plate choke. They are $25 at RF parts. Anyone had any good luck with this unit?

For now, I brushed on Corona dope over the spot.  THen took a sheet of plastic film and wrapped the choke around and pulled the plastic tight. This forced the dope into the windings of the choke. I applied more until it was level in that spot. Also found some other questionable spots so I decided to dope them up as well.  Lucky for me this case has a hinged top so it was a 10 minute job.  I let it Dry for an hour, The turned the filiments and blowers on. I hope it will be ok for tonight. I doubt it would even do this on 80 meters anyways.  So I might have to stay off 40 until the new choke is in. We will see how my Quick fix works!

Roberts going to make me a tuna.  A big one.  He has the parts and a spare HT32 chassis to mount the tuner in.  I cant have an open tuner here with the animals and curious people around.  The idea is to be able to open the hinged top of the HT32 case and gain access to the taps for the coil to change bands. This should cure my issues with teh KW flashing over.  I know why they call em Flashboxes now.  Even on low power, mine flashed over on audio peaks.

C

[K1JJ]

...should cure my issues with teh KW flashing over.  I know why they call em Flashboxes now.  Even on low power, mine flashed over on audio peaks.

C

Welcome to the wonderful, wild world of the living on the edge of wetness...

T

[ke7trp]

Ok. Corona dope fixed the plate choke for now.  The method I came up with really worked.  I used the plastic to inject the dope into the windings.  Going to replace it anyways.

Two KW matchboxes flashed over now. I used the T3 for a few years at full tilt and never had an issue. At the same power level this rig takes em right out. Must be huge audio peaks I cant see on the scope or meters going on. Really strange. If you get anywhere near 100% audio, BANG they flash over. 

My theory is that with the T3, You have a hard limit of modulator and cant go past that, If you turn up the gain, You just compress the signal so you end up with dense audio but hard limited at 100%.  With this rig and no limit of the modulator, any word spoken into the mic can shoot that peak way up there.  I guess I need to get a peak limiter going and hard set it to 1500 watts.  I bet the KWs dont flash anymore. I might try this today.

My brother gave me a Bird 500 watt Dummy load. Model 802.  I ran the rig into that dummy and finally had some time to listen to the audio and make a few adjustments. This bird load took the transmitter at 500 watts for 10 minutes before showing any sign of warmth.  I guess 500 watts is a rating for 24/7.  The transmitter sounds incredible. A huge jump up over the king and T3 that is for sure. The biggest thing I noticed is that I can now boost the lows with no huge current swings or distortion. Just smooth clear audio and as much as you want.

Initial testing is that at 500 watts carrier it will do 150% pos mod easy with a perfect wave form.  At 750 watts it is real happy to do about the same.. maybe 140%.   At 1000 watts the transmitter will do at least 120 clean.  At 1500 watts carrier you are down to 100% clean modulation.  I just start to see color on the 4-400s at 1200.  Thats about the limit of the 4-400s anyways.  Even at 1200 to 1300 you see forward on RMS meter.

 ITs nice to have a super power modulator   These figures work out perfectly as my modulator is currently set in AB1 and on paper it should produce 750 to 800 watts of audio. The only difference is that my wall voltage is high.  So we have an extra 200 to 300 volts on the mods and finals. So there you go...  Better performance then a BC Rig,  400lbs and a small foot print that fits into the avg ham shack with ease.

So the plan for this wonderfull sunday, is to get the rig up and running with a hard peak limiter if 1500 watts. I will be legal and I wont flash my Tunas over.  Thats all I want out of this thing, I cant run it higher on the air anyways, I dont want to tear up the bands or neighbors. Just want to get out there and enjoy myself with supa audio soundz.

C

[ke7trp]

Happy to report that the DBX 166xl tamed the beast.  I set the 166xl for very little compression. a couple DB.  Then I rotated the "peak stop" limiter control back until the rig would not go over 1500 watts on the bird in PEP mode. I ran the gain up so my avg is high but there is just a slip bit of action from the peak stop limiter.  I can scream or clap into the mic and it will not go past legal limit. The audio seems decent. The compression gave me some audio punch. The KW matchbox no longer arcs.  Now I can enjoy my new rig without worrying about flashing the Flashbox over or bothering the neighbors!

Hope to see some of you guys on 40 meters today. Will be on 7293.

Just goes to show you that you really need a peak limiter with this much audio power. Otherwise, Certain words will really spike the output.

C