modulation transformer RCA 901769-501, 500 watt

[mario_puzos]

i am pablo from Argentina I have trouble with modulaciónn transformer uses 2 valves 813 to 2000 v plate and seeing red decided taking place a couple of 810 to 1500 v and-30v plate-grid and the result is the same the percentage of audio is very low, I wonder if the secondary display must be connected to an external source to the screens of the 813 rf? q satisfactoriamnete to work? normal valves take red? according to data from the primary is a secondary impedance of 5.5k N1 in the seats of the 813 kV rf 2 work with a consumption of 360 ma. I hope that some have experienced amateur radio forum with this processor and I know rca clarify how to connect with valves 810 and on screens rf a hug, LU1MEK



http://www.amwindow.org/tech/htm/modtran/rca.htm


http://amfone.net/Amforum/index.php?topic=23119.0

[w3jn]

Pablo - the transmitter in this article (Tom K1JJ's "Tesla 360") has been duplicated many times and works well.

http://www.amwindow.org/tech/htm/813/813.htm

[WA1GFZ]

What is the plate current when there is no modulation.
Every tube is a little different so grid bias may be set too far positive causing high no signal plate current. Try setting the grid bias more negative.
Check to make sure the tubes are not oscillating at a high frequency

[mario_puzos]

Pablo - the transmitter in this article (Tom K1JJ's "Tesla 360") has been duplicated many times and works well.

http://www.amwindow.org/tech/htm/813/813.htm

Johnny, ARTICLE OF TOM K1JJ LO ARME IN AS IS AS IS WHY DID THE TRACK THE QUESTION IN THE FORUM IS FOR SOMEONE TO WORK WITH THIS TYPE OF MODULATION TRANSFORMER RCA.

[mario_puzos]

What is the plate current when there is no modulation.
Every tube is a little different so grid bias may be set too far positive causing high no signal plate current. Try setting the grid bias more negative.
Check to make sure the tubes are not oscillating at a high frequency

WA1GFZ, the plate current with signal is over 300 meters. no plate current is 80 ma signal. according to the table http://tubedata.tigahost.com/tubedata/sheets/141/g/GL810.pdf GE, AT THE PLATE SHOCK INTERCONECT ANTIPARASITIC PC. .

[WA1GFZ]

Using 813 tube connect grid to screen and bias the tube as a triode.
The 810 has the same dissipation so I think you could run the same no signal current. 813 may work at a lower current if the plates of the tubes are getting red. Also you might put a small fan near the tubes to keep them cool. Look at the 813 rig here for schematic.

[K1JJ]

The plate current with signal is over 300 meters. no plate current is 80 ma signal. according to the table http://tubedata.tigahost.com/tubedata/sheets/141/g/GL810.pdf GE, AT THE PLATE SHOCK INTERCONECT ANTIPARASITIC PC. .

Mario,

The 813 modulator tubes (carbon plates) should not show red color on the plates. It will damage them.  If you need to lower the plate current idle, add some diodes in series with the filament lead center tap to ground. This will add some grid bias and cause the modulators to idle lower.  However, usually you can ground the filament center tap to ground and the idle is good at 2,000 volts. More than 2KV requires bias to keep the plates from getting red.

Also, if you are seeing very low modulation at full power, be sure the modulation transformer is not shorted or is bad in some other way.  Try another transformer for a test, if you can. Check your wiring and be sure to use a Heising reactor if required at the minimum inductance of at least 10 Henries. Keep the Heising blocking cap between 1 to 2 ufd maximum.  See the 813 circuit posted above for details.

Hope this helps.

73,

Tom, K1JJ

[w1vtp]

The 813 modulator connected as a triode (CG to SG) is basically a zero bias config...  This approach was recommended a very long time ago -- it's in the earlier Radio Handbooks and as Tom can affirm works very well.  

Power pentodes of lesser power would need to have about a 20K resistor connected to each control grid (the screen grids are direct connected to the AF drive circuit).[1]

At any rate resting current for the 813 should not be so high so as to "show color" in the plates.

Al

[1] Circuit diag. found on page 661 of 15th edition of Radio Handbook.

[Gito]

Hi Pablo

To used a Modulator transformer ,You must know the turn ratio of the primary winding against the secondary winding,
easy way to know it ,used a small  transformer like a 10v ac filament transformer ,connect it to the primary winding and measure  the voltage at the secondary winding.
If the secondary winding read 15 ac volt than the turn ratio is 10 : 15 that means 1 : 1.5 and the impedance ratio is 1 :2.25

I'm using 813 as triode connected  modulator ,on the contrary of all 813 triode connected circuit .I connected all grid together (G1,G2,G3)  and used it as the Control grid ,and I got a Zero bias Class"B"  Modulator with zero bias standing current and 2000 VDC on the plate.
I have used it for years and never failed.

To used a modulator transformer ,You must know the Impedance of Your Transmitter,if You used Two 813 with 2000 v Plate voltage and load it to 300 ma than You got  6.3 K Ohm impedance.
When the Impedance  of Your Modulator tube ,for example 810 class B push pull has a impedance of 11Kohm.

So You must have a 6.3 to 11 impedance ratio than means !.7 ratio or the root of 1.7 than means about 1.3 turn ratio.

This ratio is the important thing.
You can used a 5 kohm to 8.5 kohm mod transformer .0r a 7 kohm to 11.9 Kohm . as long as the turn is right./impedance ratio is right
Of course a slight difference ratio can be tolerated ,maybe with a slight difference in output


Gito.N


  

[The Slab Bacon]

Just a thought: For a simple way to check the turns ratio for the transformer in question would be to simply put 120vac across the primary terminals and measure the voltage you get on the secondary and divide it out. This will tell you quickly what the turns ratio is and where you need to go from there.

If you use something precise like a DMM, you can tell quite accurately what the turns ratio is.


                                                  the Slab Bacon

[Gito]

Hi

You are right Slap bacon,I myself uses 110 V ac to check the turns ratio of my Modulation Transformer,since I build my own transformers ,and knowing there;s enough winding  in the Transformer( enough inductance) ,that' can handle this 110VAC.

Why I suggest to use a 10 VAC to check "unknown" modulation transformer,it is for savety  reason.
Since we don,t know  there's enough  Inductance or enough winding that can stand the 110 VAC .( ellimating the risk of "burning" the transformer)

Gito.N

[Opcom]

i am pablo from Argentina I have trouble with modulaciónn transformer uses 2 valves 813 to 2000 v plate and seeing red decided taking place a couple of 810 to 1500 v and-30v plate-grid and the result is the same the percentage of audio is very low, I wonder if the secondary display must be connected to an external source to the screens of the 813 rf? q satisfactoriamnete to work? normal valves take red? according to data from the primary is a secondary impedance of 5.5k N1 in the seats of the 813 kV rf 2 work with a consumption of 360 ma. I hope that some have experienced amateur radio forum with this processor and I know rca clarify how to connect with valves 810 and on screens rf a hug, LU1MEK



http://www.amwindow.org/tech/htm/modtran/rca.htm


http://amfone.net/Amforum/index.php?topic=23119.0

"I wonder if the secondary display must be connected to an external source to the screens of the 813 rf?"

If you mean the secondary output? There is a screen modulation winding/output on that transformer. Yes, put the secondary #2 in series with the RF tube's screens.

Another way to test the transformer is put a 5000-10000 Ohm resistor , 500 watts, across the secondary and see if you can develop the needed audio power.

[mario_puzos]

thank you all for answering my question, thank you kindly, there is a clarification that I want to make the processor I'm using an RCA type is above the primary impedance is 5.5 k ohms and the secondary is 5.5 osea k ohms is a ratio of 1 to 1 in 810 tubes I have audio working with 1,500 volts in the q plate according to the data sheet indicates GENERAL ELECTRIC plate to plate impedance of 6.6 k ohms so it should work fine, but Audio percentage is low and the valves in tune almost orange color in turn are blown by a fan, I have a couple radio frequency from 813 to 2000 v plate and a consumption of 360 milliamps. turn modulation transformer has a second child to feed the screens rf valves from a point source, but in this case I'm feeding the screens from the tension plate with a resistance of 21k ohms 200 w of dispacion.

[Gito]

Hi

Pablo,i'm confused when You wrote the tubes intune almost orange red? which tube is that the 813 or the 810,how do you used the modulation Transformer,direct coupling or with heising modulation.

Since it's a 500 watt modulation transformer,if You used two 813 with 2000 volt and loaded to 350 ma than the modulation transformer will be Saturated with a 700watt input (2000 X .35 ).(with direct coupling Modulation)
Since the Modulation Transformer is saturated ,You can not get a high modulation output .
You need at least  A modulation transformer with a 1500 watt rating.(with direct coupling)

And if You mean that the 813 that got orange color,than   it is something wrong with The 813 (RF) circuit or tuning..
With  350 ma and 2000VDC (2 x813) the tubes stay the same(black) even with full modulation.

Gito

[The Slab Bacon]

Pablo,
         Are the plates of the modulators turning red? Or is it the RF finals? If the modulators are getting red, you have a serious bias problem. If it is the finals, you either dont have enough bias to get them down into class C, or a serious plate tank problem. Either it is not tuned to resonance, or it is loaded too heavily.

Graphite plate tubes (810s, 813s, etc.) are NOT suposed to get "red in the face" running them that hot will usually damage the tubes.

Also if you have it loaded so heavily that the plates are red, tne modulator may not have enough grunt to modulate it fully. The same goes if you dont have the finals biased far enough down into class C.

If the modulator tubes are getting red, and the resting modulator plate current is way high, you probably dont have enough bias for class B operation.

Either way if you are pulling way too much current on either or both windings, you could also be saturating (magnetizing) the transformer core to the point where the voltage wont swing. You may end up also needing to add a Heising reactor and blocking cap to keep some of the unbalanced DC off of the transformer.

                                          
                                                               The Slab Bacon

[mario_puzos]

[quote author = link = topic = Gito 23872.msg176128 # msg176128 date = 1272019906]
¡Hola

Pablo, estoy confundido cuando le escribió los tubos intune casi rojo naranja? que es que el tubo de 813 o 810, ¿cómo hacer que utilizó la modulación del transformador, acoplamiento directo o con Heising modulación.

Puesto que es un transformador de 500 vatios de modulación, si ha utilizado dos 813 con 2000 voltios y se carga a 350 ma que el transformador de modulación será saturado con una entrada de 700watt (2000 X .35). (Con acoplamiento directo de modulación)
Dado que el transformador de modulación es saturada, no se puede obtener una salida de modulación de alta.
Necesita al menos un transformador de modulación con un número de vatios de 1500. (Con acoplamiento directo)

Y si te refieres a que los 813 que tiene el color naranja, de lo que es algo mal con el 813 (RF), o la sintonía de circuitos ..
Con 350 ma y 2000VDC (2 puntos X813) los tubos permanecen igual (negro) aun con modulación completa.

Gito


[/ Quote]

gito hello, step aa explain that I colored valves are those of the modulator, the 810, the transformer is connected without jet maybe that is then saturating the core with the cc.

[mario_puzos]

Pablo,
         Are the plates of the modulators turning red? Or is it the RF finals? If the modulators are getting red, you have a serious bias problem. If it is the finals, you either dont have enough bias to get them down into class C, or a serious plate tank problem. Either it is not tuned to resonance, or it is loaded too heavily.

Graphite plate tubes (810s, 813s, etc.) are NOT suposed to get "red in the face" running them that hot will usually damage the tubes.

Also if you have it loaded so heavily that the plates are red, tne modulator may not have enough grunt to modulate it fully. The same goes if you dont have the finals biased far enough down into class C.

If the modulator tubes are getting red, and the resting modulator plate current is way high, you probably dont have enough bias for class B operation.

Either way if you are pulling way too much current on either or both windings, you could also be saturating (magnetizing) the transformer core to the point where the voltage wont swing. You may end up also needing to add a Heising reactor and blocking cap to keep some of the unbalanced DC off of the transformer.

                                         
                                                               The Slab Bacon
You may not have enough bias for

hello slab bacon, I will explain that I colored valves are those of the modulator, the 810, the transformer is connected directly to reactor has not maybe that is then saturating the core with cc.las valves are successful for a couple of a transformer driver EL34

[W1RKW]

Anyone know what this transformer was used in?  What is it's audio quality?

[mario_puzos]

HELLO BOB, this processor has been used in any transmitter am CAR TYPE O RCA BTA-250 BTA-500 were searching COLLEAGUES INTERNET IN PICTURES THAT HAVE RESTORED THIS TYPE OF TRANSMITTER but found none of this specification RCA 901 769 501 500 W,
PABLO LU1MEK

[Opcom]

thank you all for answering my question, thank you kindly, there is a clarification that I want to make the processor I'm using an RCA type is above the primary impedance is 5.5 k ohms and the secondary is 5.5 osea k ohms is a ratio of 1 to 1 in 810 tubes I have audio working with 1,500 volts in the q plate according to the data sheet indicates GENERAL ELECTRIC plate to plate impedance of 6.6 k ohms so it should work fine, but Audio percentage is low and the valves in tune almost orange color in turn are blown by a fan, I have a couple radio frequency from 813 to 2000 v plate and a consumption of 360 milliamps. turn modulation transformer has a second child to feed the screens rf valves from a point source, but in this case I'm feeding the screens from the tension plate with a resistance of 21k ohms 200 w of dispacion.

If you have a 1:1 ratio (total) and you have 1500VDC on the primary (modulator tubes), and 2000VDC on the secondary (RF amplifier), then there is a problem.

1.) To modulate a 2000VDC supply, you need 4000V peak to peak.
1a.) The RF amplifier supply voltage voltage must go from 0 to +4000V

2.) With 1500V on the primary you have 3000V peak to peak across the primary.

3.) the transformer is 1:1, so primary volts = secondary volts

3.) therefore the modulation of 3000 volts peak to peak (+/-1500V) will only take the RF amplifier DC supply from +500 to +3500V

So the modulation is not complete, and perhaps the modulator tubes are over-driven in the attempt.

Can you do either of these for a test:

A.) increase the modulator plate supply to 2000V
or
B.) reduce the RF amp plate supply to 1500V

If this is wrong, someopne point it out?

[Gito]

Hi

In my opinion a class B push pull amplifier with a 1500 VDC has more than 1500 vac output

A class B uses two tubes  in push pull .let say P1  --> CT of transformer<----P2,when there's a voltage swing between P1 and CT for instance 1000VAC than the voltage between P1 and P2 is 2000v,since the winding between P1 and P2 is twice than the winding of P1 to CT,("voltage step up transformer")
Since The modulation transformer has 1:1 ratio than there's 2000 VAC on the secondary  winding that's enough  to fully modulate the 2000 V 813 transmitter.
But maybe I'm wrong.

The theory behind this modulation with direct coupling system if the transmitter has a 2000 VDC loaded to 350 ma ,or 700 watt input, the modulator must supply a half of it,that means 350 watt output.

So the modulator transformer has a 700 + 350 =1050 watt,not including the loses in the modulation transformer.

When You used a 500 watt modulation transformer,it will be saturated with only the present of the current from the transmitter that's flowing in the secondary winding .

Since it is saturated ,when you modulate even with a high power modulator,there's no output or a little output audio, that's why there's little modulation on your 813 transmitter.

Try to used one tube 813 with 1250 VDC load it to 200ma ,that means a 250 watt input ,with a about  6 kohm impedance,since it's only 250 watt it won't saturate your Modulation transformer.

If the modulation transformer is not defect ,than I think the Transmitter will have a high modulation .

Or used "Heising " modulation sytem to block the DC current(transmitter) flowing in the Modulator secondary winding.(if You used two 813 with 350 ma loading)


Gito

[The Slab Bacon]

Pablo, Gito,
                Pablo states that the plates of the modulators are red. If this is the case, and they are red in the face (especially with no audio drive), you dont have enough negative bias on the control grids to get the tubes into class-B. If the tubes are drawing that much current idling, it will require much more drive to get the desired voltage / current swing needed for modulation. Unless you have a pair of tubes that are gassy and/or soft, you need to start off with more bias on the grids and work your way backwards from there. Also, it wouldnt hurt wo wring out the mod transformer and see what the actual turns ratio ends up being.

Patrick,
          figuring out what rating of turns ratio you need from a mod tranny has always been a pain in my ass! Different manufacturers rate them differently. Some mfrs rate them full primary to secondary, and some rate them half primary to secondary (center tap to flying end), and some are rated only by application. Also some mfrs dont tell you which way they rate them, so what you assume is 1:1 actually ends up being 2:1. That is why I ALWAYS wring them out with 120vac and see for myself, just to be sure. This will help save you from inventing new cuss words further along.

                                                          The Slab Bacon

[mario_puzos]

hello friends performed the tests I recommended on rca transformer will connect 113 v on the primary and reflected 110v secondary Realizing the test then the 110 v conctando reverse side and measuring from the middle toward the ends got 49 v 59 v realizing that there is an asymmetry which implies that the primary winding is punctured. for this reason the valves colors and not the power delivered to the secondary

[WA1GFZ]

maybe not. Try putting a load on the secondary. Say a pair of 100 watt light bulbs either side of center tap. A shorted turn in the secondary would have reflected a low resistance on the primary and would have blown a fuse.

[mario_puzos]

hello wa1gfz perform the following test series connect a 100W lamp with half of the winding which gives more voltage and brightness of the lamp was higher, then connect the side under tension and the luminosity was lower