My new toy. Ultra modulation unit

[ke7trp]

Ok. I will try to take a picture this morning. I have negative peaks. Its just difficult to modulate it and take a picture. I even used the Trapazoid. Seems to be be fine. 

There are two big resistors.  You can use one or both.  Both measure 10.2K  I used one.  Then, you have a tap.  My King is 6000 ohms.  Maybe I need to add another resistor to get the overall down to 6k?   

Clark

[ke7trp]

Yeah.. Your right.. Its early and I have not had my coffee.. LOL.. I figured that to be 9k.  Its a 10K resistor with the tap set to -1 so about 9K now.

Clark

[ke7trp]

Here are some pics..  Unmodulated carrier.   Then a Tone from voice on mic.  Real hard to do.   I dont have a Sig Generator handy

Clark

[N3DRB The Derb]

if you r gonna hammer on he 811's replace em with 572'b's. they each have 4 times the plate dissipation of a 811A. it wont raise yer power too much but the tubes will take heavy use much better.

[ke7trp]

I have twenty 811s and no 572Bs.  Let em Cook.. I dont care

I did Recordings this morning through a monitor reciever.  I read a page in a book with the unit out of line and the unit inline. The recording shows a big difference in loudness. The RMS meter is showing much more with it on. The plate current kicks up when I talk. Its working. 

The Eye tube does not work. It stays full on all the time.


Clark

[ke7trp]

It sure sounds loud and clear on the air.  I can see the limiting.. Just not much more then what the scope shows. Eye tube does not work but its just for setting it without a scope. I will use it until the Big box is done, Then I will move the UM unit over to that box.

Clark

[N3DRB The Derb]

Let em Cook.. I dont care

scope pattern looks good, but i see some triangular looking stuff leading up to the peak of each wave.

not quite enough audio to really make that munky swing is my technical diagnosis. 

Go ahead and use it!

[ke7trp]

What you are seeing there is my DBX peak limiter in my audio rack.  To protect the mod iron, I have it set to clamp just the tip off of peaks.  I can turn it off and its just round.  But I tend to run it on all the time. On the air, You cant hear it working and I figure it is easier on the Mod deck.

Clark

[N3DRB The Derb]

yah keep it on. nobody will ever know. Congrats. 

[ke7trp]

Yes..  I set the resistor for 9k.  Thats what the book lists for 811s at 1500 volts.  It works and loads like normal.  Except I have much more AVG power when I talk. The plate current rocks forward.  If I had a couple 572Bs, A big Mod tranny and a 2500 volts. I would probably have enough to really kick it in. Hower, Its an old Globe king 500.  I dont intend to go that far with it.

Clark

[Opcom]

There's the audio. With a human oscillator, the wave is probably good. Lots of beef up at the top of the modulation peak, less, and more pointy, at the downward end where the machine is doing its work. It looks like it is working gracefully. Would be interesting to see the action with a sinewave, or better a triangle since it makes straight lines. If that sort og generator happens to be handy some time. Also, the eye may not do much in the absence of a much bigger modulator. Look at the resistors values there. OTOH maybe it flashes only when the machine is overpowered and "loses it" so to speak.. If that is possible. I don't think you can hurt anything with the system.

[ke7trp]

Yeah.. I agree. The Eye tube is setup for a KW broadcast rig. So considering that.. I wont even touch it with my volted 811s.

It sure works..   I used it for a few hours today on 40 meters..  350 watt carrier with 450 RMS on the bird when I talk. It hits 500 RMS if I do a steady tone.  Lots of AVG.   Listeners report that I am LOUD but yet somehow Clear.. LOL   Just what I wanted.

I talked to the man that purchased this unit brand new in 1957.  He used it on various rigs over the years. He said the pictures and the sound really brought back memories.

The old 866s glow really nice...  It turned out to be a nice old Vintage station.

[Gito]

Hi

Maybe i'm wrong.
In my opinion the negative peak limiter works like this,looking at the schematic diagram
The RF Amplifier Plate,got its B+ two ways ,first via the modulator transformer and V3 (866) and from R1 via V2 (866),but since the resistance (internal R) of the modulator transformer is small ,most of the plate current flows in it,

When the modulation goes negative ,with reference to the HV (B+,red cable) than V1 begins to conduct ,there's a current that flows in R1,but since the. R is high ,the current is small.

R 1 becomes a voltage divider resistor .With Red cable and white connection at the modulator trafo via V1 (866)

When  negative modulation goes more than 100 % ,the plate voltage can't go to Zero ,because there is   voltage from B+(HV) trough R1 and via the tap goes to V2 and the plate of Rf Amplifier,

This voltage is depended from the current that flows trough R 1,the setting tap point of R1(voltage divider) ,the current that flows from this tap via 866  to the RF amplifier plate.and the negative modulation percentage.

I think the Indicator (V4)works when the voltage at its heater is lower than than the plate voltage of V4.

There' another version of 3 dioda peak limiter By Steve Cloutier WA1QIX.

Gito


 

[ke7trp]

That sounds Right to be Gito.  I have seen the 3 diode limiter. It might work better..  I just wanted the old piece of gear working.

I wish, I could have more Neg peak limiting with it.  Right now, I have it working. But not enough Action on Neg peak limit

Clark

[Gito]

Hi Clark

In the 3 diode ...... by steve,
R1 is the Plate impedance of The RF Amplifier ,it makes more sense.since it 's the reflected impedance  that the Modulator impedance has,it depends on the turn ratio of the modulator transformer.

So R1 must be 6000 Ohm,in my opinion it can be used for any transmitter,since the secret behind it is ,having a  small B+ in voltage "stand by", which is supplied   from HV -R1 - tap - V2 - Rf amplifier plate, when the negative modulation hits more than 100 %,it depends on the tap  setting of R1.

again maybe I'm wrong

Gito

   

[ke7trp]

I set mine for around 9K.  I looked up the plate impedance of two 811s at 1500 volts which is what I have.


Clark

[Gito]

Hi

The impedance that the modulator(811) looks is depended  of the impedance of the Transmitter load ( since it's fixed load ),in this transmitter the Impedance is 6 kohm.,
the impedanceof the modulator is depended on the turns ratio of the modulator trafo.

If the turn ratio is 1 to 1 ,than the modulator tube has a impedance load of 6 k ohm,not the right load for 811(9 K ohm) ,but it works maybe with  reduced power .

if the turns ratio is 1.2 to 1 ,than it has 1.44 to 1 impedance ratio.
And  the transmitter  is 6 k ohm and the modulator is around 9 k ohm,the right load.

R 1  must has the same value as  Plate impedance of The RF Amplifier(in this case 6 K ohm).because it's in the transmitter circuit set.
and  it's  also the right impedance the modulator  looks into ,with the correct turns ratio of the modulator trafo .

in the tube manual 811 has an a need for 9 k ohm impedance load
but of course it can work with a 6 k ohm load or 10 k ohm load,but with reduced power ,or maybe  the auidio is not good.

if we used an audio tube amplifier that has an out put trafo with 6 k ohm primair and 4 ohm secundair for 4 ohm speaker .
the voltage turns ratio is around 39 to 1

Connect it with a 2 ohm speaker ,it works . But The tubes does, not see the primair (tube load) impedance as 6 K ohm anymore ,but 3 k ohm.
So it depends on the load,and the turns ratio of the transformer.
 
The closer the tap on R1 to V1 the more negative modulation can we get.
if the tap is connected to the plate of V1 , the negative peal limiter  does not work ,it does not limit the negative when it hits more than 100% 



Gito
 

[Gito]

Hi

 Clark ,how can the indicator (V4) always on,because if its on .it means  the plate voltage of V4/indicator is higher than the voltage at its heater voltage (at T2)
I don't know  the plate voltage (V 4 ) is  ,because the current only flows  when voltage(B-) at the heater ( T 2) is lower than the plate voltage.(V4/indicator)
That means the Rf final voltage is lower than the plate voltage of V4(indicator)?
The Rf final voltage get its voltage from T2,That's connected to V2,V3,V4, trough the heater power supply (T2)

yes there's only 3 wire from  this negative peak limiter ,but actually there's must be  a fourth wire ,that's the ground wire connecting this unit to the transmitter.
If not the  power supply of this unit is floating.

Gito

[ke7trp]

Yeah.. See thats what I thought as well.. I thought the TAP on R1 sould be set to 6k for the king. The 4-400 is 6K ohm load resistance.

Then I was corrected by one of my elmers.  He said no.. it should be set to the modulator impedance. That is 9K according to my book.   I have it somewhere around 9K now.

I think what confuses me is that R1 is a 10.2 ohm resistor with both ends hooked up. Then we have the TAP.  The Tap should be set at 8k?

I will lower it down to see the effects.  From memory, The lower I got, The less peaks I saw on the scope. I will set it to exatly 8K now and try it out.

In the manual it states the eye will OPEN to 90 when you are overmodulated and it instructs so the eye opens to 45 degrees by setting R1.  My Eye tube is ON almost completely in a round circle and never moves.. I am confused as to what they mean by OPEN.



Clark

[ke7trp]

I will try it now.. Its warming up.  I will try 8K.

My tube has a slight section that is dark.  But just wiggles when I full modulate. It does not open much.


Thanks again!

Clark

[ke7trp]

I got it to 7.98K 

I forgot to add the Unit is grounded.. I made a harness out of three runs of Belden RG58 Poly (13KV). I then Used RG8 Braid slipped over the three RG58s. One side of the braid is bolted to the UM chassis, The other is bolted to the GK 500 PS Ground lug.

The Ends of the three HV lines use MIllen HV connectors. All heat shrinked and safe.

Clark

[ke7trp]

At 8K things changed.

I now have more neg then pos.  I calibrated the carrier to the scope exactly. Full modulated, The peaks almost hit the third line up and the neg goes to 4 lines down. I wonder if I should flip my Modulator caps? I dont think I can.. I might have to lengthen them.  Or maybe switch the Audio at the 1/4 jack?  I wonder if this is my problem?

The eye, Does not move at all.. Its sitting with a Slice dark and does not wiggle.

C

[ke7trp]

I flipped the 811 leads.. That problem went away. Now I have equal peaks pos and neg.  The Neg diode is lighting up more now. Peak power came up a bit.

I reread the instructions again.. They are telling me to set R1 to the RF amplifier impedance. NOT the modulator impedance. It states to find this by throwing an AM carrier at full power, Measure PLATE voltage and PLATE Current of RF amplifier. That is around 6K ohms for me.  I am going to try it down at 6K again.

Clark

[ke7trp]

Thanks alot!   

I made another mistake.  Remember. I am a young guy that is learning..

The overall Resistor is to much at 10.2 K.  I have the unused Second resistor (there are two 10.2ks in but only one used).

I will remove the Slide Ring from that and move the tap down to 7.5K for the overall resistor.  Then, I can set the Middle Slide adjustment to RF amp impedance of 6K.

Clark

[ke7trp]

Its 2000volts on the plate.  Under load its prob more like 1700.   The 811s have 1550 on them. Under load maybe a bit less but I am using a non stock Mod power trans  Current is 55 mils idle on the 811s. It runs them HARD. They glow red if your long winded.

I used a 6K ohm Plate load resistor when I checked and repaired the tank and PI.  Those knob postions are exactly the same when I put it into a 50 ohm dummy.  So 6K should do it for the RF deck.  I am going to heat up the iron now and add a spare tap to the load resistor at 8K.  Then I am going to set the middle tap to the RF decks 6K and give it a shot. Its not a huge change. Its set at 10.6 for the MOd and 6K for the RF deck now. I dont expect a miracle.. But I will try it!

Thanks again for all the help!

Clark