The AM Forum

Here is my new toy.  Going to use it with the Globe king 500C.  Should be fun!

Anyone ever use one?

nope. Thats the first commercially available unit (not a homebrew) I have ever seen. Glad a gangsta got it. I posted it in the ebay section.  :D

I've been watching it on ebay and it shows that it didn't sell???

The owner is a good friend and elmer, I went over and he said it did not sell... So I purchased it from him. 

Its a good working unit complete with cover. I need to get Shielded HV wire somewhere to hook it up. I guess spark plug wire will work..

Also..  They dont want you to run it with a Tetrode with a seperate Screen supply.  My Globe king 500C has a seperate 400 volt screen supply.  Screen current runs around 30 to 40 MA depending on how I load it.

I have figured out I need 35K at 56 watts for the screen Dropping resistor.  To go from 1800 to 400 volts for the screen:


1800 volts (might be more like 2000 as I am solid state and have not measured the actual voltage.
400 volts needed at 40 MA

I came up with 35K at 56 watts.   Sound correct? 

If I could just find an adjustable 75 watt resistor, I will be good to go!  THen, Just attach it inline with my B+ lead and off to the 4-400 screen.  I can fine tune it to 400 volts in my situation.  I will just yank the Screen supply Rectifier tube and leave the rest there so it can be changed back later.  Simple and I get a modulated Screen :)

Anyone have a big adjustable resistor lying around???  I am dieing to plug this thing in and give it a go! 

This unit is rated for the 1kw broad cast rigs.. Its the larger of the two they made so I have no worries there! I am even going to leave the 866s in it so it glows blue sitting there next to the king!

Clark

I would use RG8X for shielded HV wire unless you have some old shielded military spark plug wire. RG8X should be good for better than 25KV. I forgot how that thing is supposed to work?  Anywho, it looked very nice.

Ok. I have RG8X. That will work out nicely.. I attached the PDF document on the original post if you want to see how it installed ect.. THis one is a commercial built unit but its identical to that article.

I just need to find a tapped/variable resistor now!

Clark

Let's sing the "Shaft" song. That's gonna be a mean mutha...........shut yo mouth!!

Good find. It should really wake up the bands

Fred

I had the idea of using a large variable resistor for the screen dropper.  That way, I can attach a Volt meter to the screen and adjust it for my actual B+. 

I called W0VMC Robert and he said he probably had the resistor I need... So thanks to Robert!

I do have two 20Ks at 100 watts.  I could series them for 40K, Drop it in and test it out. 35K to 40K is what I need at 56 to 60 watts.  I think the ultimate would be to have the adjustable one from Robert so I think I will wait.

ITs going to be a big change getting the King setup with modulated Screen and plate. Then with the UM unit hooked inline it should be fun:)

I just wish I could get a little more B+ on the 4-400!   1800 Volts is just not enough to really fire things off. But hey.. Its an old Globe king...

When I find time to get the Big rig working, this is going to get interesting. That unit has two 810s running up at 2600 volts with two 4-400s.  I will make up cables so I can use the Ultra mod unit with that machine also!

I would like to hear from people that have used these or have listened to them. 

Clark

  "" Ok. I have RG8X. That will work out nicely..  ""

Just to make sure.........


Don't use pl259's fer the HV connectors......



klc

Nooooo!

Do NOT use foam coax of any kind! RG-8X included!

It does NOT have near the voltage rating of solid poly coax. It's only good for 300 volts, max!

And don't use PL-259s, either! They're only good for 500V, max.

Use RG-213 solid poly coax and leave at least 2" to 3" of uncovered shield at each end for a good 'crawl'. RG-8 and RG-213 SOLID poly are good for maybe 13 KV.

DO NOT even try using RG-8X foam. Or any other foam coax, for that matter! Solid poly is the only way to go.

Please! I don't want to see you smoke it out! Or hurt yourself.

I have built several ultra-mod units...One is currently use in my big rig. You are talking at least 2x to 4x your static PA plate voltage if it's working properly. WAY more than 300V. Maye 10x that!

That makes total sense...    I guess I will just use Copper center spark plug cable.. I dont want to run RG213 sized coax to and from this unit.. Heck it has unshielded wire on it from the factory.. About 18 Gauge!   

Are we in agreement that Spark plug cable will work?   Henry has the larger diam stuff at a decent price.. I can just order 10 Ft of it and be done.

Clark

outdoor neon wire is cheap and good-sized guage.

theres a guy on ebay selling RG400 teflon double shielded silver braid jumpers. Rg 58 size but lots better voltage breakdown and shielding. do a search on rg400, you'll find him.

derb,  Send me the item number.   I got lost in the search. 

Clark

Hate to rain on your picnic, but you will most likely be disappointed with the results unless you substantially beef up the G-K modulator.  Ultramodulation works on the assumption that you have enough undistorted audio power available to modulate up to about 150% or more in the positive direction.  With an unmodified G-K you are lucky if you can achieve 90% positive or negative.

Of course..

I have that covered Don.  I can go 125% now :)

Its a toy.. I will play with it. If i dont like it, I will not use it... Either way, I will have fun!

Clark

http://cgi.ebay.com/RG-400-Silver-Plated-Shield-Coaxial-Cable-Up-to-12Ghz_W0QQcmdZViewItemQQ_trksidZp3286Q2em20Q2el1116QQhashZitem45ecf7f719QQitemZ300328417049QQptZLHQ5fDefaultDomainQ5f0QQsalenotsupported

not the same guy I got mine from, but the length is 3 ft, about what you need.

I you dont like him, look for others.

You can get 6 foot pieces of h.v. wire from rf parts

http://www.rfparts.com/hvconnector.html#wire

I've wondered about 100 v. 130%.  I can go up to 130% and I prefer to do that but I've read that guys using the older rx that don't have product detectors get distorted audio.  When I get my outboard plate supply built I should be able to run a 350 w. carrier at 100% but I'd still rather run around 300 w. at 130%.

Rob

You're right Rob,
130% Positive is about the max before a receiver starts distorting.
During the wild experimental days, before the 1500 P.E.P. fiasco, the ultramod and a P.E.P of 5kw was an outrageous signal. There was a thread recently here about a Ham who had a room for a very big transmitter using ultra mod.

Fred

UGG, Me not know that  ???

How does this differ from the three diode keep alive circuit by WA1QIX?

With good, undistorted audio from mic to modulated stage, you don't need any kind of negative peak clipper or negative cycle loading to achieve 130% or so. Most human voices are naturally asymmetrical.  Just make sure the audio polarity is correct so that the peak with the greater amplitude excursion goes in the positive direction.

Steve's circuit and negative peak limiters are best used to protect from occasional breaks in the base line on negative modulation peaks.  This can potentially destroy modulation transformers and cause splatter, although I have never noticed a tremendous amount of splatter from slight overmodulation on occasional negative peaks if the signal is otherwise clean.  Most  heavy splatter comes from the speech amp going into oscillation, rf parasitics in the modulated stage or distortion/self-oscillation in any leenyar that follows.  Even with gross overmodulation, more splatter is likely to come from spurious distortion products that originate elsewhere, than from the overmodulation itself.

If the transmitter flat-tops on positive peaks, that produces exactly the same kind of splatter as overmodulation on negative peaks.  A large percentage of slopbucketeers do that every time they use an amplifier, particularly since modulation monitor scopes have become virtually nonexistent within ranks of the "new" amateur community.

That could acount for slow sales of $1 CRTS at the hamfest.. If someone is too ignunt to build a modulation scope.. probably too ignunt to adjust the SSB leenyar correctly and too cheap to buy a scope as well.

I agree. I am shocked to see so many hams not using scopes.  I use the Yaesu YO-100s on alot of my AM stations and some of my SSB stations. Its a nice compact easy to use Scope.

C

At one time neon signs used Packard 440 spark plug wire. Belden still sells it in 25 foot spools. I bought my last spool at Napa.
Shielded is best so good soild dielectric 1/2 inch coax is good RG213 or RG11 gith plenty of spacing between the end of the shield and center conductor. A few inches will be fine. Strappers would use RG393 or RG141, RG400

Thanks alot!  I will call napa

Clark

Operating phone without a monitor scope is like driving at night with your headlights turned off.

Does anybody actually run upside down modulation?  Plenty of us run greater than 100% positive peaks.  I do in just the way Don mentioned, by taking advantage of the asymmetry of my voice.

But is there anyone actually on the air with downward modulation, reverse carrier control, upside down modulation -- 1500W carrier when silent, modulating downward?  Does it drive receivers nuts in practice or not?

Jon

sure would clear the channel but you need a rig with the BAs to do 1500W CCS

I don't know why anyone would want to put crap like that on the air.

I have an ultra mod deck I made 20 years ago, 3 diodes, resistor, power supply.
I had reports I was real wide when it was in circuit so I removed it and put it away.
The circuit shunts the excess audio into the resistor and allows the low voltage supply to power the final, but i suspect its not a smooth transition, maybe like a square wave?

I think one would be much better off running some low level compression and keeping the audio below 100% negitive, you have a much cleaner signal that way.

Brett
 

Need manual or more info on the hookup of my UM unit.  The Wires where cut on it.  I have three Shielded wires.

One white that hooks to the junction at the first Filiment Transformer in the unit
Another White that hooks to the junction on the Second Filiment transformer in the unit.

One Red wire that runs to the bottom of a Tube. Marked 2E something.. Cant read it. 

Anyone have the manual?  I have a Downloaded copy of the article for the unit but it does not show three wires..


Clark

Ok.. I understand that the 866s are diodes.  I understand that the B+ out of the modulator is sent to the UM unit. I understand it limits the peaks and then sends the voltage on to the final.  What I dont understand is that the UM unit has Two whites and a Red wire. Then, I have the shields for each.

Clark

Maybe I missed it but who is the manufacturer of this thing?

Correction.. I Have been looking over the schematic and opened the unit.


The TWO white wires go to the 866s at the Filament transformers.

The RED wire runs to the Resistor stack.   

Three wires total.

The unit is a commercial grade product.  It was made by UM.  It is for 1KW Class Broadcast rigs. 

UM company.  Red bank NJ.  Model UM4-B.  Serial number 1501

Clark

The schematic does not show that.. Or maybe I am blind..

Ok..  I understand that the white wires INTERCEPT the RF B+ out of the modulator deck and to the RF deck.  The RED just goes to the HV source that is NOT RF.  For example, The Feed from the Power supply to the INput to the Mod deck.


Clark

I got it..   My mind would not let me figure this out.   What got me was the RED wire on the resistor bank. That one connects to the B+.   The Whites, carry the RFB+ from the mod deck TO the RF deck.. I worked it all out.  I will have it hooked up in a day or two.

Clark

Hi


  Comparing the two circuits  D1 is V1,D3 is V3 ,D2 is V2.

V4,V5 ,6AF6G is part of the indicator when the circuit begins to limit the negative cycle of modulation.

In my opinion,The White cable ,which is written as " connected to mod.amp plate"  must be connected  to the Final amplifier Plate (RF final) like in the "Three diode negative peak limiter."

The other White Cable ,is used when you like to By past this circuit,(negative peak limiter),maybe manually  or with a switch  .interchanged(the two white cable) its connection to the Final Amplifier Plate (RF final).

Gito

Hi

 Sorry ,the white wire that is connected to T1 (filament transformer) is connected to the Modulation transformer, like the circuit diagram,The White cable connected to T2 (filament transformer)is connected to the Final RF tube,

The modulator can has its own B+ or.if the B+ is the same (only one B+),Connect it to the CT of the modulator Trafo (modulator side.) inthis case connected in parallel with the red wire .
Don't connect it to the white wire.

Gito   

Thanks for making that Diagram for me. I really thank you for that...

I labled them White 1 and white 2.

Red -  MOD deck B+ input connector.

White 1 -  RFB+ OUTPUT of MOD Deck connector

White 2 - RFB+ INPUT of RF Deck (4-400)

Clark

Sure!    I am making up RG58 Belden Poly coax runs for the three wires. Each one will have a Millen connector on it so I can plug this into the GK500C and plug it in to the Dual 4-400 box.  It will be easy to take pictures.

Clark

13KV from Beldens website.  Its poly with a High Dielectric.   Its NOT foam which is listed at .3KV


Clark

Clark

It,s the right way to Connect the negative peak limiter unit.

What makes it confusing ,is that in the diagram ,its is written that the white cable from T2 is connected to MOD.AMP PLATE ,

Actually it must be Connected to the PLATE OF THE FINAL RF TUBE.(Its the B+ of the Final RF tube)

Thanks

Gito.

Yes.. I was very confused..  Lucky for me, I have you guys and others to help me  ;D ;D

I think the Belden will be fine.  The stuff they used from the factory is much smaller with very little insulation.


Clark

The statement might be a reference to the practice of using unprocessed voice signals, which can be non-symmetrical in the voltage domain, and instead of phasing the mod to where the taller voice peaks point upwards, pointing them downwards and raising the carrier to the level where there is no negative overmod. It can work only if a person's voice wave is not symmetrical WRT peak levels.

It's been covered in writings and there is at least one members'? website showing this principle.
The summary is that one eschews processing and sets the big voice peaks to negative side of the mod and raise the carrier to avoid spaltter.

symmetrical voice normal use:
voice voltage peaks +2.00, -2.00 relative  level
carrier  = 375W
PEP=1500

non symmetrical normal use:
voice voltage peaks +3.00, -1.00 relative level
carrier = 187.5W
PEP=1500

non symmetrical inveted use:
voice voltage peaks +1.00, -3.00 relative level
carrier = 1312.5W
PEP=1500

this is what was being illustrated I believe. For those who have a voice that gives a fairly symmetrical voltage waveform, there won't be much difference. But for those who have large peaks one way or the other, they can either turn the mike polarity so that the 1500W PEP limit is hit when the high peaks are "up", resulting in having to reduce the carrier, or, they can turn the mike polarity around so the big praks point down, and run a thick carrier. It will sound the same at the other end, and there is not negative overmodulation in either case. The advantage is a more powerful carrier to get rid of noise in the over-the-air path.

Unfortunately those with a very unsymmetrical voice will always be faced with a modulation cycle "duty cycle" far away from 50% and the "volume" of the voice on the RX end will appear weak. So instead the best thing is to process the voice somehow either with a clipper, balanced compressor, or phase rotator, or a combination of various techniques.

Ok restoration and repair of this UM unit is complete. Bad tubes and caps.  Made a new harness out of Poly RG58 covered in a RGU braid.  I put millen connectors on the end so you can interface it with the King 500C. 

Fired it all up and found that the King cant make enough audio to see much action. I can adjust it to limit negs to about 95%. Positive is 100%.  No noticeable difference on the air of course. I need more audio power.  With out the unit, I can go 125 up and 125 down.. But with it, just wont make it. I can just start to see the Negs limited.

I wish I had the smaller unit they made. This one is made for the KW broadcast rigs.  Four 4-400s ect.. The 811s just cant kick it into action much.

It looks great, It fills the room with a nice Blue glow with super bright when I talk. A really neat piece of gear I will save for my Big rig... I am sure with the 810s into the 4-400s It will work a bit better.

Thanks for all the help on this project!

Clark

Since that unit is only supposed to work on negative peaks, I guess I wonder why it won't hit 125 percent with it inline on pos peaks?

Odd, but...  Maybe you should just do a 3 diode limiter, if you are that worried about your neg mod peaks???


--Shane

Or, I can study the schematic and try to figure what I need to change to get it to act at lower power..  I think Its just the lack of audio power shane. I only have about 350 watts of audio power.  If I had 600 then this would be loud as hell on the air.. But I dont.

Clark

Here is picture of it with me talking into the mic.  Its working.. But Not the action I want.  The resistor is a 10K. The tap is near the 866.  If I move the resistor tap like they say, I get lower audio pos and neg.  Maybe Try changing that resistor?


Clark

This must be working.. The Eye tube is not though.. Its nice and bright but it never changes from full on modulating. I will have to find out why.

I unhooked the unit.  300 watt carrier on easy tune up. Talk and get 325 RMS.. So a slight bump in RMS on the Bird.  Plate current stays the same with a slight wiggle down.

Hook up the unit,  Adjusted Tap to 6000 ohms.. Thats the plate load of my 4-400a.   Load to 300 watts on bird meter. Talk and it takes out the 500 watt slug hard to the side. Back it off a bit and it talks around 450 rms. Plate current jumps UP when I talk.  Scope is not showing Flat topping or over mod at 450 RMS when I talk.  Really clean looking.

The NEG limiter 866 glows bright as hell.  The Peak about half as much.  Maybe when I get on the air and they guys ask me to turn it down, I will know its working.  BIG increase in RMS talk power.

Clark

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

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

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

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.

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

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

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!

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

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

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

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.

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.

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


 

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

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

   

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


Clark

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
 

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

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

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

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

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

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

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

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

Hi

I still believe that R1 value  is the impedance of the Rf Amplifier'

When we used an solid state amplifier as a modulator which has a low " P to P" impedance ,maybe 100 ohm to modulate a 807 transmitter which has 600 V B+,and load it to 100 ma .it has a 6 k ohm impedance.

So when R1 must have the P to P value ,R1 = 100 ohm.

 when the white cable connection at the Mod.Trafo,with negative modulation hits /goes down to  Zero ,

V1 conducts ,so a current flows ,from 600V (B+)  trough R1 to Zero volt,that means  the current is 600 V divided by 100 Ohm is 6 amp,

So R1 must dissipated  600 X 6 amp = 3600 Watt?


Gito

hi

  V3 is the limiter part of this unit,when the white cable connection at the mod trafo hits zero volts.it stop conducting ,so when the negative modulation peak is lower than zero ,it can not get trough to  the Rf final ,
but when there is no voltage at the  RF plate ,nasty things happened .

It's where V1 gets into action,when the voltage at the white cable connection gets below its B+ V1 begins to conduct,There is a current flow from B + to this connection

the current flows from B+ trough R1 to the connection.
if we put the tap in the middle of R1 ,the voltage is half  from  B+ to this connection.

So the RF plate voltage gets its B+ from this tap ,when the plate voltage is 1000 v,and  the downward swing  is  minus 100 volt, the plate voltage gets minus 50 volt,and the upward swing  (positive modulation) is 100 volt ,and the down ward modulation is only  minus 50 volt.

so when you modulate more than 100 %   ,say with a 2000 v sine wave,

than the downward modulation ,will gets its peak minus 1000volt( B+ - 2000v = minus 1000v),but since there is a B+ supply that gets to the RF final from the center tap  of R1,where the voltage is minus 1000 V.
in that way the voltage at the RF final never gets negative.(B+ - 1000V= 0 V),the B+ in this case is 1000 V.

So the upward modulation in these example is 2000 v,and the downward modulation is  only minus 1000 V.And the downward modulation never goes  , below zero V
of course ,its only an example,

I believed ,how this unit works.


Gito

The manual states, R1 should be RF Deck impedance. This is 6K ohms period.  I set Tap so the overall resistor R1 is 6K.

I then set the middle tap on R1 as the manual states,  Near the diode.. No action. I moved MIddle tap in one inch inrements all the way up to the other tap. No action.. I lose mod and cannot hit 100% as I move away from diode with middle tap.

I have unhooked the unit and now get 125 UP and 125 down. MUCh more PEP.  I dont believe UM unit is in working order. I am going to test caps and such over the next few days and try again.  Its been 50 years since it was used and it may just have a bad Black capacitor or electrolytic.

Clark

doing some analysis on this unit's circuit, an interesting factoid was uncovered. On a given PA stage of 100W DC input at carrier level, equippped with a modulator of >1KW peak
power, and where the resistor tap was always adjusted so that with any given mod power of 100% or more (% deemed to be an additive voltage scale as seen on scope and therefore the SRQT of the power percentage. i.e. 100%=4x the peak power, 200% = 9X the peak power), the resistor tap is in the middle at 140% modulation (5.76 X the carrier level).

The only things changing were the audio power and the tap position required to keep the negative RF peak level at 10% of the positive RF peak level. It is amusing to note the near-complete waste of modulator energy during the negative going half of the modulation cycle. Not that it matters.

Normally I suppose the tap is to be set properly for where the modulator is maxing out, and at lower audio figures the data is different. It will be interestig to look into that and plot the currents and voltages over an audio cycle, but not now at 1 am.

Hi Clark
 
 I',m an old man, I overlook that you had the manual ( The Ultra Modulation System) posted on your article .

Reading it carefully,it stated that there' a voltage drop across this  diodes (866) ,it needs an additional voltage and there's also a voltage drop across the small resistance between the tap an resistor.

So the conclusion there's a" resistance "in this diodes ,so the plate voltage that gets to RF final is smaller(there's a voltage drop) than normal modulation,also  because this resistancei the modulation proses.the peak voltage is lower than normal modulation,

The modulator trafo turns ratio is the important part of the modulation ,it's not only the power of the modulator tube,that can create an high peak voltage.on the secondary part (transmitter part ) at the modulator trafo.
since the peak voltage at the primair modulator is limited  by its plate voltage.(modulator tube)

For example a  100 watt filament transformer, has an  10 volt output , a 1000 watt has the same 10 volt output

the voltage output  is not depended on the wattage of these transformers,but the turn ratio.
but of course with higher wattage we can used more tubes, but the voltage is the same.

When an high wattage modulator  that has more than enough power to drive an Transmitter with a modulator trafo not with the right turn ratio,even with full power it can not drive the transmitter for 100% modulation.
Because the peak voltage  at the transmitter can't reach the needed voltage for 100%  modulation

With a higher voltage at the 811 plate voltage  and the right turn ratio,we can get more peak voltages at the secondary (transmitter side ) modulator trafo.

Gito

Hi
Sorry,what i mean is an article from QST  October 1956 about " The Ultra Modulation System" as a PDF form 5610027(!) ,that Clark has attach  in His First "Question"

Reading this Articles,I think We don't need to have the "manual" to know how it works and how the schematic is.
The only thing that Confused me(for a while) is the connection of the white cable from T2.
The connection,it is written  to connect it "To Mod Amp Plate" giving the impression that it must be connected to the plate of the modulator tubes.

But actually it s must be connected to the RF final p;late circuit and becomes the B+ for the Final RF tube .

reading it carefully ,it is written...the value of R1 in ohms is the same as the modulating impedance of the RF amplifier.It CAN BE DETERMINED by dividing its plate current into the plate voltage.....(QST Oct 1956 page 29)

And sorry for my English,sometimes I did not write the right words to express my thinking.


Thanks


Gito

We all suffer from that problem, even those of us who have English as a first language!  ;D

Hi

Thanks Steve.
Carl,maybe the problem that You have in this unit is the 866 tube.I found an article more detailed from Hytron 866 it stated :

...(filament voltage)..the rated voltage of 2.5 volts under all operating conditions.The filament voltage,measured at the tube terminals,should not vary more than  plus or minus 5%,(0125 volt) from the rated value.

This tolerance should include the effects or regulation caused by transmitter-modulation load as well as the normal power supply regulation.
Less than the recommended filament voltage may cause a HIGH VOLTAGE DROP with consequent bombardment of  of the filament and eventual LOSS OF EMISSION.
Higher than the rated voltage will greatly shorten the life of the filament.

So maybe the tube (866) has lost it's emission or a drop in filament voltage.


Gito,