The AM Forum

After solving few problems with my card reader instalation, the photos of the "Lady in red" are here.
The new ones with reactors in place and power set over 7kw under carrier condition will be uploaded very soon.
For the main part I want thank all of you for the knowledge you provided to me through your threads.
For the difficult part I want thank Stu and Tom for the solutions and courage they armed me to walk the difficult road to high level am modulation.

The "Lady" is dancing almost every night with 82% efficiency and is waiting now the final touch-painting, knobing and wax shining...

A huge thank you
Stefano
 

few more photos

and more

BEAUTIFUL transmitter porn :)


Some reason I feel like I should shower :)


--Shane
KD6VXI

few more

I'll post the full schematic later...

the af supporters...

Very, very unique setup, OM!

Interesting on using a 5KW solid state audio amplifier to plate modulate the final. Where did you come across the mod transformer for those impedances?  FB on the 3-diode NPL.

Hope you don't have too many close neighbors in the 'hood... :D

It will be interesting to see the schematic when you post it.  Good job.

T

my 4CX3000A Afterburner

It's coming along pretty well, Frank.  Youse gots a good headstart on the Huzman. Now for the infrastructure wiring.


I will buy an apple crisp for the first one who joins me in the DX window with their finished amplifier... ;)

T

Frank where did you get that bandswitch?  I have one similar to it except mine is only one throw not three.  I think I have 8 or 9 poles on mine non-shorting.   ah, I bet you found it under a table at some hamfest  :D


Rob

I've been cutting strips of copper for the switch taps. Double 1/2 inch for each tap. common off the 4 switch commons 1 1/8 inch wide

A few more 4CX3000 porn shots. Nice job Stefano.

I built my switch from a bunch of parts. I just found silver button contacts for the commons. The silver plated ones worked fine for years but these are more HD. The hardest part is cutting that shaft, but my brother is a jeweler and took care of that. The front two wafers have dual contacts front and back. Learned the trick from a surplus switch from a mil rig. The rotors also have dual wipers to pick up the dual contacts. So I have 4 sets of parallel contacts to select coil taps. The third wafer is for padder caps on the loading cap. Loading cap is only 1400 pf so need more on 80M and 160 if I add some more L. 
Input circuit is a pi with 1000 pf variable at input and 2000 pf variable at the tube. L is a 10 uh variable inductor.
This rig was on the air with bread slicers but couldn't hack it.

WOW.  Talk about heavy artilary coming out.

Mike - quick comment. In picture one it looks like the copper tubing coil is using the vac variable as a main support. The glass/ seal can't take a lot of stress and strain before cracking. I've seen some vacs go that way. Consider using a pillar there with a more flexible copper strap jumper to the vac cap.

If I  am seeing the pic incorrectly, then never mind!  ;)

T

Thanks for the advice Tom. I'll get a post in the network next week. Hope we didn't hijack Stefano's thread.

Mike

Outstanding work, Stefano!  I take it you're using it on MF?

Yes, Stefano very nice job. 7 KV, wow!

Always a pleasure to look at those kind of equipments!

Thank you guys for the positive comments,

As you can see the system is just on the end of the experiments road and now I will start the final definition.
All wirings inside will take the clearest way, the aluminums will come out and have the proper painting and the knobs will be changed to the same style.
The amp is working with 5kv full load plate voltage at 1.4A-1.6A, -150v fixed bias to grounded (not in series) 5.4k leak resistor at 70-90ma, 0-700v screen voltage at 140-180ma (overcurrent protector takes screen voltage away if more than 200ma).
Input is a linked parallel sircuit and output is a pi with 0-450pf/32kv vac cap, 24uh/60A and 0-2300pf/5kv vac cap.
The amp works even easier than the exciter does, no surprises at all, very stable and secure.

Frank, mine was easy because of one band use. Am very jealous of your band switch.

Opcom, learnt a lot from you,too.

Mike, very good job for low band, too.

w3jn, yes it is for mf 1.5-1.7 mhz.

Shane, hard core is coming soon, be patient.

Tom, the mod trans is a 120v/65A rms pri to 0-3500-4000-5000v/1.5A rms sec, insulated for 15kv. The Rmod= 5000v/1.4A=3571ohm so a 30:1 voltage/turns ratio will transform the Rmod to 4ohms, 30x30x4ohm=3600ohm.
I use the 0-3500v sec for the rf side and the 120v pri for the 4ohm bridged solid state output in mod heising with one leg of mod transformer sec grounded.
The af amp is an H class with 2 huge toroid transformers (60lb) for highest efficiency and less than 0.1% distortion. The sound is amazingly clear, the frequency response almost perfect from 40hz-7khz and the mod transf is singing like a good midrange megaphone.
Now I'm thinking to interupt a 4700uf/450v cap between solid state out and mod transf pri for keeping out any dc or strange feedback from the sensitive solid state amp. Any thoughts about that are welcome.

Stefano

that's a classic HI-FI transmitter, Mike

Hey might as well go to 600V on the screen and be THE channel master

I built the 5-gang ceramic-wafer selector switch for my antenna tuner array out of 4 or 5 of those switches, although it looks like mine may be the next size larger.  I re-stacked wafers and ceramic spacers, and connected two shafts together using an Oldham coupler (http://en.wikipedia.org/wiki/Oldham_coupler) since I couldn't get them to stay lined up perfectly over a full rotation.

Mine are each 10 position, non-shorting.  I soldered the wire directly to the tabs, using a big-ass soldering iron.  The wire is #8 stranded.  I stripped about 1" of insulation at the ends of the wires, fanned out the strands and flattened the bundle with pliers, attached the wire to the tabs by tightly wrapping some small gauge "copper zirconium" wire over the end of the wire and the tab to hold everything firmly in place, and then generously applied solder until the connection was well saturated.

Don, beautiful job; yes your switch is exactly like the one I have except as I mentioned earlier, mine is one wafer (does one use "wafer" to refer to these things?); I got mine by getting to a hamfest last Sept. at 6 a.m. and they were out on a table $2 each.  I got both of them with indexes.   I apologize for getting off into ceramic switches but I do not see these often and they go for obscene prices at $urplu$ $ale$.

rob

Hello Stefano, what country are you located in and is that transmitter made for the broadcast band in your country?

Who manufactured the modulation  transformer for you?

Perhaps some of these questions have already been asked and answered, but I'm old and ask questions more than once :D :D :D

Stefano,

OK on the 30:1 transformer.  So this is a 60hz power transformer being used for audio... interesting. I know some (including myself) who have used them for plate modulated tube service, but none yet for solid state audio.  Have you swept the rig for audio and checked results?   That will tell the story if you might need some feedback compensation to tailor the iron.  Otherwise, consider some negative feedback from the mod output to a low level audio stage to clean it up further.  With a big rig like this, your side products will need to be 10db cleaner than the average AM station on the air or they will complain. You know how that goes... ;D

 

T

Tom,

I have modulated the amp with the Yamaha and the result was excellent from fidelity and quality sides.
The ham society here in Greece found the sound more elegant and complete than the pll exciter with absolute linear amplification could do. Myself couldn't believe how smooth and sweet the voice came out from the monitor. I made the blind test between console's phones monitor and the phones monitor of the Lowe HF125 with 7khz & 10khz filters and 3 of 3 thought that the radio sound was the console sound. The chain was experimental without any processing just a mixer and a condenser mikrophone.
The thing is that with this amp - at 3200w bridged- I couldn't get more than about 75% modulation to check the sidebands for artifacts or for splatters. For the 3 nights of testing nobody complained about splatters but all said that I need 20%-30% more volume to modulate the huge carrier. The big amp will be ready next week and I'll test it further. I could also upgrade the transformation to 41:1 and get more audio from the mod transformer but I want stay closed to the right calculations so the truth is that I need 5000w af at least.
In here there are very powerfull linears with 4x15s that modulate 5-10kw at 130% without negative peak limiters and annoy at least 15-20khz left right. All that story is a local fest out of mf band that in Greece stops at 1602khz, then we start at about 1620-1720khz with nvis horizontal antennas for covering with 70-90 degrees take off and extreme power 300-400 miles max. It is however an elegant ham-pirate experimental community trying to mix rf power with modulation quality in a local race (Totally oposed to CBers, except power). The mod transf is not that simple as an ac hv transf but it is more closed to a pushpull output transf with 4 windings of primary between 5 windings of secondary. W2PFY, I ordered a 7kw pushpool output transformer from a company that used to make same transformers for valve B class amplifiers used for musicians in open area concerts. They did first time so heavy (360lb) but they had the know how from 1-2kw ones. They also made the 3 reactors (30H,10H and 2H).
I used to have big problem with the kick back of the reactor but Steve gave me the golden solution and now all are in right order. My only worry is how to protect the solid amp in case of smthing goes faulty...let's say if the driver dies or shut down during transmitting, the reactor will spark and the trancient will jump as a small in time but huge in energy spark on the sensitive solid state output...A capacitive coupling could help but I am not sure, does anybody have an idea if a series cap would help and what are the minus or plus for that?

Stefano

LOL.   Freebanding.  I love it.

Beautiful amp.  Good luck on getting the audio amplifier protected:  Maybe look at some of the car stereo schematics, they have some that are pretty much bulletproof.....  Shutdown works GREAT on them...  I've actually shorted out one channel of one of my amps with a pair of pliers, and the other 3 channels played just fine.  Pulled the pliers away and the 4th channel popped right back.

Just a though.

--Shane
KD6VXI