a timtron turbo mod question

[NR5P]

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

[W4AAB]

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.

[WD5JKO]

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

[flintstone mop]

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

[Steve - K4HX]

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

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

[NR5P]

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.

[Opcom]

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

[Jim KF2SY]

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?

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

[k4kyv]

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.

[flintstone mop]

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

[Opcom]

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 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?

[NR5P]

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...

[NR5P]

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

[NR5P]

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

[Opcom]

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.

[K1DEU]

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.   

[Gito]

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

[flintstone mop]

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.

[NR5P]

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...

[NR5P]

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.

[flintstone mop]

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...

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.

[WD5JKO]

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.

  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

[NR5P]

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. 

[WD5JKO]

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

[NR5P]

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.