The AM Forum

Hi I've got a heathkit apache and am wanting to do the turbo mod to the modulation transformer.  I've been doing a good bit of research on it but there isn't much out there.  The most info I found is here http://amfone.net/Amforum/index.php?topic=18449.0  down the page tim gives some more info on some other steps including how to find the right phase when moving the tap to one of the plates.  I'm still a little sketchy on exactly how this mod works but I know everyone that has done it has been very happy with the results.  When he says to remove the bottom of the secondary he is talking about the side closest to the 500 ohm tap correct? Also Tim states the rectifiers MUST be solid stated and I understand this is much more efficient and will get rid of the voltage drop across them but I want to leave it all tube.  I guess for now I would be ok just doing the transformer mod and later I could change the values to what he recommends as im know he knows what hes talking about but I would like to crunch the numbers myself so I know why I'm making these changes

One thing for sure, make sure you change out the coupling caps in the audio chain from 500 pF to .05 uF to get rid of that "scratchy apache" audio.

If I followed the Trons text, the circuit change will be shown in the attached image. I admit I'm having trouble following what he wrote. The schematic shows the primary is 11000 ohms P-P, and secondary is 3000 ohms. This is almost a 4:1 impedance step down ratio which is huge. Tim says the turbo mod changes the impedance ratio to 1.5:1 (or turns ratio of 1.22:1). Big change.

So guys, did I get the image correct? The "This", and "Or This" represent just 1 wire after finding proper phasing.

Jim
WD5JKO

It took a little brain power for me to figure out what Tim is saying about the turbo mods.

BUT he gives a reasonable explanation how to find the proper phasing

Here is a link from the AM WINDOW
http://www.amwindow.org/tech/htm/dx100.htm

And this one for using a power transformer as a mod transformer. He talks about getting the phasing correct. I did not disassemble the transformer.
http://www.amwindow.org/tech/htm/tvtomod.htm

Solid state will stress the components with more HV. What do you get?? Another 15 watts???
The DX 100 will make 125 Watts.if it is feeling good.

DO NOT overdrive the grids of the 6146's

Based on my understanding of the mod, the drawing is correct.

yep i did the w3scc audio mods.  I've gotten good reports but I do have clipping before I get to 100% modulation and I am checking this on a scope, so I figured I would do this mod also.  Thank you for your help and the drawing.

If I understand, these are the results?  (assuming 600V B+, I missed where Tim said 800V). Fantastic.

1. It's easy to see the original mod transformer ratio does not give much headroom. Cheezy to have done that on purpose!
2. The Turbo connection gives 30% more modulation voltage going positive. (Tim said 125%+ positive)
3. Instead of PEP power being 4x the 100W carrier (2x the DC volts), it would be 7X (2.67x the DC volts) ??.
4. Tune to 175mA in the PA instead of 250mA to prevent saturation.
5. Was any mod to the tank necessary for the higher voltage/lower current?


The waveforms and voltages have been fixed in the drawing

You could even go a little further with this and mitigate the transformer saturation concerns by adding modified heising.  No ???
I asked Tim this a few years ago on 40M, didn't get a response from him (bad condx) I guess.
Has anybody tried the Timtron Turbo (autotransformer) ckt. together with modified heising???  Surely this was done in past years when more of these rigs were used, just haven't heard too many super-modified 100 watt class boatanchors on these days...

Jim

Even without the mod, with any transmitter, if you are stuck with one good modulator tube and one weak one, put the weak one in the side of the pushpull circuit that generates the negative peaks.

If trial-and-error by simply swapping out the tubes doesn't give a clear result (oscilloscope required), try temporarily removing one tube at a time to see which one generates the positive peaks and which one the negative. You will still get some positive or negative peak on the side with the removed tube (since the transformer can't pass DC), but that side will show up as highly distorted when viewed with the envelope pattern.

I was able to increase positive peak capability with the Gates BC1-T from 110% positive to over 130% positive that way. I could tell no difference whatever in the negative peaks whether the the weaker or stronger tube was on that side.

I would like to report that I used the turbo mod with heising on an Elmac AF-67 and it was unbelievable modulation. The turbo autotransformer was a power transformer from a stereo tube amplifier (4 ea 6L6's and two 5AR4 rects) and about 20HY of choke.
Got about 120% pos peaks and freq resp. down to a clean 40hz..top end died out around 5kc.
The mod tubes in the Elmac were 6550's.

I fed the grids of the modulator tubes with a backward connected output transformer driven by a pretty nice audio amp with microphone input.

FRED

I think my waveforms are wrong because when the modulator tube plate that is also driving the low end of the mod trans. secondary goes close to zero, the secondary will also have a negative voltage on it, in phase, and go below zero. But there were diodes mentioned, so..

So that tube, which has its plate connected to the low side of the transformer secondary, is the one responsible for the negative peak, and that side of the transformer is also the side with the excess DC.

Would it help to double up on the other tube to lessen the imbalance on the transformer current? Because the other tube is making the positive peak, would adding another in parallel with it help?

well I know my hookups are right but when I went to tune everything up I'm having a problem setting the modulator tube bias.  I would increase it slowly and it would jump to 100ma then I'd decrease it down to 50ma sometimes when I would get to 50ma it would fall to zero if I had it just a tad above it would stay.  Then when I go back to standby then transmit it would be zero.  I figured it was the touchy 10k variable.  I replaced it with another and same problem.  I'm gonna take another look tomorrow I hope I don't have any major problems.  I hadn't used it for a while before the modification but it worked fine last time I used it...

I was looking at the schematic a little bit more.  I think it must be a bad solder joint or a problem with the .2 ohm sensing resistor in the cathode.  Maybe it's making close contact and when it gets to a certain voltage it is flowing current.  Either that or a tube problem is all I see it could be.  I guess I'll try swapping one of my spair el34s (take out my 2 more expensive ones in there) and see if I can turn it up to 25ma without a problem.  Then I'll have to take it back out of the cabinet and do some closer inspection if that is not it

I went and stuck one cheapo el34 in there and I'm getting similiar results.  I slowly turn the modulation current adjustment up and all of the sudden shot to 40ma.  Keep in mind this is one tube.  So I guess I need to touch up with the soldering iron or replace the .2ohm resistor it must be one of those things.  Cheap fixes are ok

Could it be a sudden ultrasonic oscillation? It might not show up through the mod iron or be heard, except to be indicated on the current meter. When fiddling with it, are the VR tubes in the PA screen regulator staying lit? What happens to the B+ during these two states? Is it possible to use a scope to look around the modulator? What about R28 and R29? Just thinking of things that can cause two states as you describe it is one or the other, even it if seems unrelated there may be some kind of link.

If we are attempting to use a few extra turns (like a 500 ohm winding) on one side of an symmetrical turns side to get a asymmetrical boost for more positive going stuff. We should keep an eye peeled on any negative feedback for this feedback can easily make asymmetrical, symmetrical.

Eee gads my end results are from what cumulative steps ?    


Roger OM my Modulator tubes here are a 50C5 in the neg side and a 811A in the positive side.   

Hi

Maybe some RF is feed back/come into the audio modulator,and rectified it/as an audio signal ,and if the phase is right,it becomes a positive feed- back,and the modulator tube will oscillate .

By swapping the plate wiring at the tube sockets ],changing the plate wiring from tube socket A to tube socket B,and the wiring from tube socket B to the tube socket A,making the rectified audio signal become a negative one.
and the modulator tube won't oscillate.
Just a though

Gito.N

I agree with Opcom and Gito...........remove the negative feedback and start from scratch to see if sudden jumps stop.
Why only one tube in the modulator?
And what is a .2 ohm sensing resistor??? in  a tube circuit??? Something for solid state circuits.

I'll check out those things.  .2ohm resistor is just a meter sensing resistor for plate current.  That is what they used from the factory.  I had to replace one in the rf section when I first got this thing and fixed it up thats why I was suspect.  Maybe I should have a shielded wire going from where I made the connection from the 500ohm tap to the plate.  It is kind of a long path...

I'm sure it is oscillations now.  I was trying on 40meters when having the previous problems.  I went to 80 meters and I can adjust it to idle at 50ma (with both tubes in, I was using one electro harmixox tube after the problems as not to destroy my mullards).  But on 80 meters if I increase the mic gain modulator current shoots up.  BTW I have done the w3scc mods on amwindow so my front mic gain control is actually my gain control and my mod current is adjusted now behind the key jack.  It worked fine after this so it must be something I done now.  I'm confused about switching the wiring in the tube sockets and how that would help?  I think the next thing I am going to do is drill a hole so I can shorten the path from the 500ohm tap to plate as short as possible does that sound like a good idea to try? 

I do have a scope and could check for oscillations I guess but I don't want to have to buy another set of tubes!  I unkey as soon as I can.

oooops my bad...........geesh.......YUP I remember .2 ohm metering......thanks

If there is oscillation with just one modulator tube , then it may still be negative feed back or your audio equipment is getting trashed with RFI........especially consumer type EQ's. and unbalanced audio.

  Nathan,

   Others have said to remove negative feedback. I looked at the W3SCC mods, and there is no NFB there, nor is there any in the original TX1 design. Did you add NFB? If so remove it for now.

http://www.amwindow.org/tech/htm/w3sccmods.htm

   Are you sure you got the turbo mod phasing correct? Did you try it both ways using just 120vac across the mod transformer primary, rig floating on bench electrically, and with 120v in get ~ 100v out with meter hooked to CT one lead, and mod B+ the other lead? There might be a typo in Tims instructions. (Tim says: "You can disconnect the centertap of the primary for this test if you would like.").  If you disconnect the CT as he says you can do, then you lose your referencing to the B+ line.

  One other thing, try removing the 12BY7 driver. With that out, the EL-34's won't get any drive, so the bias pot should show smooth control so long as the mod tubes don't sing (oscillate).

Jim
WD5JKO

I'll try removing the driver next.  I've only done the w3scc mod and turbo mod.  I also have not added any NF.  I did check the phasing both ways I connected 120v across the modulation tubes(primary of transformer) and jumpered the center tap to each plate.  One I got 98volts on(thats the one I permanently connected) the other read much lower I can't remember now what it was. 

  When you said center tap above you meant 500 ohm tap right?  ;)

Jim
WD5JKO

yes sorry i meant the 500ohm tap.  Also I have no audio equipment just a d104.  but before when I was adjusting the mod current bias and I had mic gain down and the current was jumping up nothing was hooked to the mic input. 

Well I rerouted the wire the way I should have to begin with.  Shortest run possible and it has fixed the oscillation problem.  but now don't have any modulation when I increase mic gain.  It's easier to figure out atleast, I replaced the 12ax7 and the 12by7 in the audio chain as a quick check and it's something else.  I sure have learned alot working on this thing.  If only it weighed 10lbs instead of 100

just an update with a dmm I checked across the grids with the el34s unplugged and getting about 2 volts a/c while talking in mic on the meter.  I know it's not the most accurate way but tells me there is audio getting there.  It doesn't surprise me as I didn't mess with that part of radio.  Gonna do some more rechecking of what I wired.  I really wanted to get on the air tonight with it!

I have double and triple and quadrouple checked using an ohm meter and looking at the wiring in the radio to make sure the wiring I did was correct and it appears to be.  I guess I need to check again using the 120v method that I have the correct plate connected to 500ohm tap, but I was careful in checking that and was happy that it was the tube plate that was easy to get to when I checked so it wasn't a problem getting the soldering iron in there.  tubes are idling correctly now and appears that modulation is getting to them.  I'm beginning to run out of ideas here.  I checked the screen and plate voltages on the el34s also and that is fine.  and grid dc is also good.

Does the modulator cathode current kick up when you talk? If not do the cathodes find ground through the metering circuit and 0.2 ohm resistor? Or maybe it is modulating fine, but the meter does not move..If all that checks out, all I can say is reconfigure back the the last known working condition, i.e. remove the turbo mods..

I'm beginning to think there is more than a typo or two in that mod. as stated.

I live about an hour away from you, and I do have Monday off....


Jim
WD5JKO

I want to learn your methods to make that work! And here I just wanted to make a little more current available to the side that was short on magnetization. I obviously have no ambition!




If this is on that same TX-1 transformer, then by the specs shown in the schematic, putting 120VAC the whole pri. should make the whole sec. do 62.4V, and from the 500 Ohm tap to the hot side ought to be 37V, and to the cold side 25.6V.

So, 1/2 the primary being 60VAC, and adding the 37V coming from the 59% connection (500 Ohm to 'hot'), there is the 97v, same as your 98V. Perfect!




The post you made previously shows you had the larger amount of boost. If the tubes biasing and current is now behaving right, then the oscillation if that was the main issue seems to have been dealt with.

If all this is fine, are you not getting sufficient modulation now? If that is the case, the best thing to do might be to use a scope and look at the modulator plate (where the boost winding is connected) and note its most negative and most positive voltage when beeping a sine wave in there. Do the same at the hot end of the mod transformer secondary too.

With a B+ of 750V, you need +1500V peak to be delivered to the RF stage for 100% positive modulation. That is either stock or turbo'd, it does not matter. With the added 59% of your boost secondary there, it should add 460V to that and give 1960V peak.

To check it safely with a scope, just tack on a resistive voltage divider made of five  1M resistors, and tap the scope off the lowest one, so when you read 200V safely on the scope you know the circuit voltage is 1000V.

If RF is an issue to the measurements:
A small capacitor to GND cross that first resistor will help get rid of any RF messing up the measurement. Maybe 100pF or 0.001uF? Not too large though or it will load the voltage divider and throw off the measurement.
Or
Remove the final and put in a resistor equal to 750V/175mA (as Tim stated hopefully that's OK) 4300 Ohms @ (at least) 132W.

Just some ideas, can't swear by the outcome. More than once thougn a second pair of eyes on something was just what was needed when I overlooked something and could not figure it out.

Hi


I don't have the Heatkit apache schematic,but I have  the heatkit DX 100 (?)looking at the mod circuit ,the modulator tube is a push pull circuit which is drive by an inter stage transformer

Case 1 : with  a certain connection .the  modulator transformer has a current flow in phase with the current flow in the inter stage transformer.(output voltage in phase with input voltage}

  Case 2:when swapping the plate connection the current flow in the Mod.Trafo is 180 out of  phase with current flow in the Inter stage trafo.(output voltage is out of phase with the input voltage

In these two cases .the out put voltage in connection case 1: is 180 degree  againts the output voltage in case 2.

In case 1: an audio signal(x) is put into the audio circuit,audio -interstage transformer- modulator tube -transmitter---RF got into the audio circuit--rectified  --rectified audio + the original audio(x) ----input audio.

Since this audio signal are in phase  (rectified audio + original audio) than the audio amplifier began to oscillate

Gito.N

I'm going to reread over these last few posts and maybe do some checking tomorrow.  To answer wd5jko though it definately isn't modulating as I have the power meter inline also.  I appreciate your offer I've got some other things to do around here monday and hate to use up your day off. 

When I hook up the resistor chain to check with the scope I put them to ground correct and ofcourse it would be the one closest to ground to tap off of. 

But yes the problem now is I'm not getting any current at all when I talk into the microphone.  Seems to be idling fine at 50ma.

Well a little while ago I hooked up mod transformer the way it was(easy enough to do) to see if my problem is related to the mod. I still got zero modulation registering on the meter.  So I stuck in the extra el34 I have (only other el34 I have) and removed the mullards.  Then I tried again and I got slight modulation from the one tube when i turned up the gain I only had it idling at 25ma because of one tube.  Maybe there is damage to the tubes from the oscillation problems I was having. 

I did notice something I have not noticed before.  when I place the meter selector in rf final plate current or modulator plate current(even if the modulators are removed) after about 5 seconds the meters slowly go below zero and start lightly bouncing off below the zero.  Maybe this has been doing this all along and my bias I am adjusting is much lower that what I'm adjusting.  I can double check this easy enough with a seperate meter but for now need to find out whats going on with the negative charge building up.

I'll be in the radio room throwing stuff and kicking radios

Ok I forgot and didn't have the ground attached to the chassis.  I think I am narrowing down the problem and things look better.  When I crack the mic gain all the way open I'm getting slight modulation on the current meter.  Must be something in the preamp sections.  Either with the 12au7 or 12ax7.  I've tried replacing the tubes earlier and no dice so gonna go through it maybe tomorrow and see if I can find where the problem is.

Great!!!  I found the problem the "spring" that is around the audio connection that is a shield was touching one of the heater voltage pins on the 12by7a.  I guess it wasn't causing enough of a short to blow a fuse but was drawing down on the transformer.  It supplies voltage to all of the audio tube heaters.  I hope I haven't shortened the life of the transformer.  These radios can sure take  a beating.  Im going to make the connection again now for the timtron mod and I will let you know results.  I guess I'll be on am this weekend.

Good! I hope that's all it was. I'll be happy for you anyway if it's got the turbo thing going.

Hi


This Turbo modulation troubled my mind ,with the original connection ,the voltage ratio of the modulation transformer is 627 : 1200  (1 : 1.9 },the impedance ratio is 3K to 11K.
 with the turbo connection the voltage ratio becomes (600 + 370) : 1200 = 970 :1200 = 1.237 ,the impedance ratio is 1 : 1.530.

Since the modulation impedance of the transmitter is 3 K . ( 750 : .25)
Than the reflected  impedance 1.530 X 3K = 4.593 K

The EL 34 operated  as modulator in the transmitter condition (original connection} ,has a 11K  impedance,the right load.

But with the Turbo Modulation  The EL34 looks at a 4.593 K load ?(reflected impedance) not the right load.

So this puzzled me? Do I missed something

Gito.N

 Not much Time for me. But I look mostly at magnetics and coils of wire with and without cores that may reduce the physical size of a coil. Unfortunately there are so many different cores that it is very difficult to find some material that collapses and builds up a near field with out adding distortion. Sometimes we want the field to be misshapen on purpose. Tubes and transistors are mostly current switches. And can be harmed by requiring them to exceed their heat dissipation or voltage max ratings. 73  John

So you want to discuss impeadence ?  Well you have Walt W2DU to guide you.

Hello Gito,

I apologize for these numbers because I had them wrong in the drawing due to not knowing the TX-1 B+ was 1500V. I replaced that drawing in the previous post, and here it is for convenience. I am very sure it is correct assuming "perfect" tubes (in reality the plate swing does not go to 0 on the modulator tubes because of their G2 voltage). But it is the turns ratios than matter.

I agree the original connection is 627:1200, or 783:1500. (1.044 or 1.045 for secondary to half primary)

I have to think about the impedance ratio in the turbo hookup but if the swing to the RF stage is the sum of:

0 to 1500 of the modulator tube,
plus
-462V to +462V,

then it is:
0 plus (-462V) to 1500V plus 462V
which is -462V to +1962V.

(diodes are assumed to prevent negative modulation beyong 100% from the previous article)

If the total winding of the primary is 11K, and the secondary is 3K (by the turns ratio or the specs) and only 59% of the 3K winding is in use then the secondary portion in use is 2500 Ohms.

There are issues with saying this because the windings do not stack impedances, only voltages, so it is easier to look at it from a voltage standpoint.

If the total primary has 1500V peak on it and the partial secondary has 462V peak on it
and
If the primary is 11K CT then, the signal ground is the CT, so that makes the primary impedance 2.75K to ground.

1962V / 1500V = 1.308 voltage ratio
1.308 * 1.308 = 1.711 impedance ratio
2.75K * 1.711 = 4.7025 K

I think our numbers agree closely enough (4.593K to 4.703K) about the impedance the RF stage should present, IF we want to see 11K CT at the modulator tubes.

It was said that the plate current had to be reduced to 175mA to avoid saturating the transformer due to DC imbalance.

The RF stage then becomes 750 / 0.175 = 4286 Ohms instead of 3K.


mine:
11K / 4.7025K = 2.339
yours:
11K / 4.593K = 2.3949


750V @ 175mA = 4.286K

mine:
4.286K * 2.339 = 10.0249K plate to plate
yours:
4.286K * 2.3949 = 10.2645K plate to plate

So the EL34's will work harder, but a 10K or 10.3K plate to plate load should be OK.The load would be too light with the RF stage at 750V/175mA if not for the added winding. With the given winding it is a bit heavy by 8-9%, so let the tubes show some color maybe?

This brings up another point related to the reduced input @ carrier, unless I misunderstand it. The reduced input was to be arrived at by drive or loading changes.

the input will be 70% of the normal input.

The theoretical PEP available at 130% positive modulation would therefore be not 6.8x stock but 4.76x stock.

I think that is 118% positive modulation but not sure. There may be some tuning to help this, but the unbalanced DC thing is going to come back, and the plate to plate load on the modulators is going to decrease a lot if the stage is tuned back up. Tim said 125% mod worked, maybe there is a middle ground where it works best.

If there were no issue with core magnetization, some other issues begin to arise that have not yet been discussed:
-total current capacity of the power supply
-current capacity of the modulation transformer primary
-ability of the modulator tubes

So, the results will be interesting to see how well this works.

Hi


The way I see it,the voltage developed across The modified circuit  for the transmitter is the voltage  of the CT of winding of the modulator tube  + the voltage the primary winding minus the 500 tap winding.

750 + 462 volt = 1212 volt since the reference volt(B+) is 750 volt than the voltage developed across the transmitter is 750 + 1212 =1962 v  positive peak modulation
 and the the negative peak modulation is 750 - 1212 = -462 v.

since the AC voltage from the CT (B+)  to the plate of The RF Pa is always plus and minus 1212 v.

Than the turn ratio is 1500 : 1212 =1.237 or the impedance ratio is1.5317.

If we load the transmitter with 250 ma ,than the impedance is around 3 K ( modulating Impedance} Than the transmitter looks into a 1.5317 X 3 K= 4.5951 K.

Remember the the winding from the CT to the Rf Pa is a series Winding,and in phase

and CT is the reference point, so a positive swing across the modulator winding will cause a positive swing across the CT to the RF pa.windings.
A negative swing across the modulator winding will cause a negative swing across CT to the RF PA windings.

But of course I can be wrong

Gito.n

I modify and attach a picture ,that maybe more explaining ,sorry for my pictures ,I can't make good pitures

(perfect parts assumed and screen voltage issues ignored) I agree except that I believe the peak to peak voltage across the modulation transformer primary is 3000V. I believe this because I believe that the plate of each modulator reaches a 1500V peak voltage and each modulator plate swings from zero to 1500V. That is why I said 1500 + 462V.

I also add that it may be me who is missing something, so if so please point it out. I'm no expert on this stuff.


You can make good pictures on even the most backwards PC! (8086, CGA, mouse, pc-painbrush) --> The pictures were made with the Microsoft "paint" program to open the file with paint, save it, then save as PNG for small data size. The symbols come from the attached file. The file is ancient from a forgotten web page but has grown a little over two decades. (I sometimes wonder how others have grown their copies or forgotten them.) Just copy the components one at a time from the file and paste each to the new bitmap file (your good drawing), and use the lines to connect and draw the schematic. It is low tech but that is what was done, so looks OK.

Finally got it checked on the scope.  It definately helped out the peaks.  I'm getting right at 100% before it starts to clip.  I was getting about 80% before when this happened.  I do start to get clipping on the negative peaks at about 80%.  I was getting clipping there before the mod also.  People tell me I sound good just don't have the lows.  I've got 3 megaohms across the grid that the d104 looks into.  I've heard some people say the d104s do best into 10 megohms atleast.  Don't know if this would make a noticable difference or not.  Also may be to much across the grid and make the tube unstable. 

I don't understand why you are getting only 80% on the negative side. Are you using the 3-diode limiter?

sorry i worded that wrong.  When positive peaks are at about 80-90% some of my negative peaks are clipping. 

They are clipping at 0 volts not 80% just to clarify again.  No I'm not using a negative diode limiter.  Radio is stock except for the w3scc audio mods and the turbo mod.

Ok Nathan,

  Soo, I wonder what happens if you swap the wires going to the D104 mic element? It would be neat if you then could peak 120% positive when hitting 100% negative...

  Also try swapping modulator tubes in case one has more emission than the other..

Have a tone generator? If not here is a free PC based one, SigGenFreeWare:

http://www.dr-jordan-design.de/Downloads.htm

Jim
WD5JKO

Thanks no I don't have a tone generator except my voice I will give it a try.  The d104 isn't running into a balanced amplifier one end is grounded.  Would swapping the element wires still make some kind of a difference?

Nathan,

  The DR. Jordan tone generator will work with your PC. You just need to scale the voltage to your input with a voltage divider. If you get hum, use a cheap RS 600 ohm to 600 ohm audio transformer for isolation, or use a laptop running on batteries.

  Yes swapping the wires on the D104 will work with an unbalanced feed since the D104 element outputs are not referenced to ground until you hook wires to it.

Jim
WD5JKO

I think I will have much better lows now.  I did try swapping wires on the d104 element and didn't seem to help.  Neither did swapping the tubes.  I did swap the d104 head to a different one with a different element and wow when I speak lower they are up there with the highs now.  Before if I said a 2 and held it it would not be nearly as loud as a one.  Seems to be greatly different frequency response.  I haven't used the tone generator yet I will need to take the computer in there.  There definately seems to be something strange with the negative peaks.  When I hold a tone with my voice or speak normally I'm seeing bottoming out on negative peaks and 100% mod is maximum even when swapping tubes or element wires.  Maybe it would take a constant solid tone to get an accurate check.

   Yea, many of the old D104 mic cartridges are crapping out, and Astatic does not make them any more. After they get old, expect differences in them. Your transmitter issue limiting modulation peaks is interesting. Maybe try boosting grid drive to the RF final to see if that helps, and/or load the final amplifier lighter.

PS, for just sine wave drive, maybe extend the wires to remote a PC speaker over to your rig, and set speaker next to the Mic element. Somewhat crude I know..

Jim
WD5JKO

Heres what ive done now.  I switched the wires on this better cartridge and it seems to have improved positive peaks a tad over 100%and not clipping on my negatives at this point like it was.  I played a couple audio sine waves over the speaker into the mic but like with a 1000hz wave my modulation current is at 125ma (manual says don't go above on positive peaks) before I get to 100%.  And I am a little confused on exactly how to use a scope when monitoring voice.  sine wave is easy to monitor but when speaking or holding a tone with my voice the left side of scope is showing 100%and the right is much lower modulation.  I gues this has something to do with the sweep of the scope.  If I'm holding a tone I thought it would be even. 

The element that is not working as well is NOS It was in a box not used I got it a while back...Maybe there was a reason the factory didn't use it...

I still have two this old one I'm using now and another that I repaired with a razor knife, glue, candle wax and a lot of patience. 

  Nathan,

   With a sine wave drive, the tone is continuous, so the average level is higher. Therefore the modulator current will be higher. I wouldn't worry about going over 125 ma, but maybe limit it to 30 seconds or so. Do worry about going over 100% negative though as that unloads the modulation transformer, and modulator for the time period the over modulation exists. This is where the Apache clipper might help out if it is still in the circuit. Otherwise you keep the level down, or just use some form of high level clipper, or negative cycle loading circuit.



  I did the razor, and wax repair myself years ago. It worked! I made a post about it too, years ago on AMFONE..

Jim
WD5JKO
 

I did a sine wave test 400hz 1000hz and 2000hz just downloaded test signals off of youtube.  Couldn't get the program to play for some reason.  exactly 100% mod on 1khz and 2khz and less of course at 400hz.  This would be a much more accurate way to now swap tubes and see which gives me a little advantage.  thanks for elmering me you all have been a big help.  Monitoring on the scope I seem to be getting the 120% without clipping if I talk normally...

  Did you press the green triangle up by the '?', and uncheck the 'Mute' button?