Reversing Polarity Peaks

[ve8xj]

I have been following Georgio's latest project on the AGC for negative peak control with enthusiasm ,will have to give it a try some day. Looks simple enough.

My BC-610 seems to always have about 5-10% higher negative peaks. As read on a general radio 1931A Mod monitor. I have no scope unfortunately .I am working on that though.

I recently also bought a Audio All Pass Filter / Phase Rotator Module but have yet to build a power supply for it. TOO many projects.

The phase rotation switch on my Behringer T1952 pre-amp only provides  limited results unfortunately .

  Seems to me someone mentioned in a thread recently that simply reversing the plate leads or grid leads on the Mod tubes could have a reversing effect. But it seems to me that a push pull modulator circuit is a pretty balanced thing and this would have NO effect at all. But perhaps I am wrong .

  Does anyone have any experience or opinion on this?

Before anyone says just do it and find out . I first have to go into the Bc-610 and extend the plate leads to do so as they are not long enough.  I already tried the grid leads with no results. Extending the plate leads is not too big a job but would take a few hours at the least to remove the mod deck etc.

Is it worth the effort or should I try something else ?

Thanks in advance

Tim
VE8XJ

[W2PFY]

Seems to me someone mentioned in a thread recently that simply reversing the plate leads or grid leads on the Mod tubes could have a reversing effect. But it seems to me that a push pull modulator circuit is a pretty balanced thing and this would have NO effect at all. But perhaps I am wrong .

Yes it will absolutely change the phase if you reverse the grids. I never did it with the plate caps but it should be the same. Do not reverse both at the same time or you'll have the same phase relationship as before.

While I'm not expert at anything, I have been operating BC-610's for over 30 years and it has worked for me. Another way to do it is with a preamp that has a reverse phase switch on it.

You may also have a weak 100TH in there. The way I test mine is by lowering the bias on the tubes and run them at about 100 mills and observe the redness of the plates. They should have equal color. It one is more red than the other, the one with less color is the problem as it is not pulling the same plate current. Make sure you are using tubes with identical plate structures for this test.

After running this test, go back to the 40 mills of resting current.
  

[Todd, KA1KAQ]

If you do end up swapping the leads, it might be easier to do at the transformer due to the length issue you mentioned.

[W2PFY]

I already tried the grid leads with no results. Extending the plate leads is not too big a job but would take a few hours at the least to remove the mod deck etc.

This must be a later model with a potted transformer if you need to remove the mod deck to change the polarity?

What kind of a driver are you using to drive the 100TH tubes?

Can you ship it to New York state for me to look at it

[ve8xj]

Well I have tried about everything today. Got up the energy and no results !!

I have tried reversing the grid leads, NEG 100 POS 90

I have tried reversing the plate leads, SAME RESULTS ,reversed at the transformer with much contortion of limbs and neck.

I did do the bias test as you suggested and did notice a VERY slight difference in colour but not great . I am not running matching tubes ,at least in brand. One is an EIMAC JAN-100th ,the other an I.C.E JAN 100th though both plates have the same appearance and structure . I did recently have a matched pair in there but one of them has a grid failure. The two good ones I have for spare are  both different from the ones in the 610. But I did switch the one with the slightly lighter colour on testing with both of my spares but to NO results.ALWAYS HIGHER NEGATIVE  PEAKS. I'd pull out my hair if I had any.  

I'm not going to spend too much time on this one now but would love to eventually get those nice POS PEAKS .

Any chance it is the MOD MONITOR ?? General Radio 1931a

I have another solid state METRON Mod monitor coming in the mail should be here any day and I will then be able to do a comparison ,as long as it works. I know a scope is the best way to go but that might have to wait.

If anyone has any other idea what it could be in the mean time let me know.

[ve8xj]

I am using the 2A3's as the drivers for the 100ths . Haven't gotten around to playing with another Speech amp yet as we discussed in a former thread.

Yes the mod xformer is potted.

[W2PFY]

Well as you know, a scope is the best way to see the pos peaks but it will be interesting to see what you read on your new monitor??

[ke7trp]

Are you using your voice or an audio generator.  The mod monitor can also be out of adjustment. Mine has an alignment procedure. The best way is really an O scope.  However, If you do not have an O scope, You can use any PEAK reading watt meter.  The setting with the highest PEAK peak using your voice is the correct phase. 

Switching at the audio rack should change the phase, There is no need to swap the grids or plate connection if you have the audio rack option available.
C

[Gito]

Hi

looking at the BC 610 schematic,it's a high level modulated transmitter,
than there's a current flow in the secondary winding of the modulator {RF tube side) ,the current that is taken by the final tube transmitter,so the mod.trans former is partly magnitizise  ,by a direct current (plate current).

I think when the modulation is positive,the current flow in the primary winding is in phase with the current flow in  the secondary winding ( RF tube plate current ) that makes  the modulation transformer saturated
.
On the negative cycle, the current flow in the primary winding is out of phase with the current in the secondary winding ,the mod.transformer  is not saturated ,giving a higher voltage output.

Gito.N


reversing the phase of the modulator primary ,i think don,t change the modulation ,since the positive peak is always in phase with the D.C  current flow in the secondary winding,Maybe reversing the modulator secondary winding ?

[k4kyv]

I wouldn't recommend reversing the secondary winding.  One end is designed to feed the rf final, while the other end is designed to connect to the +HV from the power supply.  The bottom (plate supply) end is not so well insulated as the end designed to supply modulated HV to the final, and has more capacitance to ground than the "top" end.  This is true for many, if not most modulation transformers.

[KF7JAF]

should I try something else ?

Thanks in advance

Tim
VE8XJ

Tim, have you tried swapping the tubes? If one is weaker, maybe that would balance things in the other direction, since changing the phase didn't seem to help any.

Just my two cents,

Dave

[The Slab Bacon]

Without a scope you are just wasting time. You cannot usually see the phase relationship with an analog meter! ! ! The inertia of the needle movement is just not fast or articulate enough to show it up. Short, sweet, and simple.

If you have a digital peak reading wattmeter with a "grab and hold" function, you might be able to see the difference.

Without a scope, you are just flying blind. (or as they say, pissing in the wind)

[WA1GFZ]

You need to make sure the AC line feeding the rig is up to the task. Also rig loading can have a big effect. Try reducing your power and see if peaks improve. Maybe your rectifiers are weak.
You really need a scope

[ke7trp]

peak voltage is what Drives the meter. It will read higher if the positive peaks are higher.  You can run an audio generator in, or just use your voice and toggle the audio polarity switch and see this on any peak meter. The difference will be clear. The correct phase will drive the meter much higher Frank

I agree on the scope.  I cant imagine not using one here, however, I understand that some cant afford one, or simply do not have one.

C

Without a scope you are just wasting time. You cannot usually see the phase relationship with an analog meter! ! ! The inertia of the needle movement is just not fast or articulate enough to show it up. Short, sweet, and simple.

If you have a digital peak reading wattmeter with a "grab and hold" function, you might be able to see the difference.

Without a scope, you are just flying blind. (or as they say, pissing in the wind)

[The Slab Bacon]

peak voltage is what Drives the meter. It will read higher if the positive peaks are higher.  You can run an audio generator in, or just use your voice and toggle the audio polarity switch and see this on any peak meter. The difference will be clear. The correct phase will drive the meter much higher Frank

I agree on the scope.  I cant imagine not using one here, however, I understand that some cant afford one, or simply do not have one.

C

Clark,
         If you were to use an audio generator for this test, you would not need a peak reading wattmeter to do it. Most audio generators put out something pretty close to a perfect sine wave,(at least they're supposed to.) so depending on the audio frequency used for testing, it will just show up as an increase of total output power. (maybe not exact P.E.P. but an approximation close enough to see if there is a difference.) And the inertia factor of the meter needle wouldn't be much of a concern,
so you dont really need a "peak hold" function with an audio generator.

But.........................

Here arises the issue: The human voice waveform (especially the male voice) is NOT symetrical. So in order to see the difference in output and the phase relationship, you need to have something with a a very fast rise time (scope) and/or a peak reading meter with a "peak hold" function. And I mean a real peak reading meter, not just one of those cheapies with a capacitor to slow down the fall of the meter needle.

With a scope this becomes obvious very quickly, if not immediately. Not to mention that with the audio phased incorretly, you get that funky "fishbone" pattern. Good scopes have gotten so cheap lately that it is very foolish (if you're serious about this stuff) to be without. W2XR has a nice little Telequipment (Tektronics) scope listed for sale here for $55. That is a good little scope, I have one and paid a lot more than that for it some years back. As cheap as they've become it is senseless to be without one,
It tells you so much instantly at a glance. Also if you have a good scope, you really don't need a peak reading wattmeter period.

And for strangers in your shack when you are demonstrating your hobby, it adds a nice little bit of mystery and ombiance      

[ke7trp]

Ok good to know. I always use the audio generator to test the transmitter. Even with the audio generator one side will have more pos peak.   Then, When the scope is calibrated, I switch the audio rack using my voice. 

If you hold a tone with your voice...  ahhhhhhhhhhhhhh and flip the audio rack phase button, the Bird 43P goes 200 watts higher on the correct setting.  I confirm this by watching my 2245a scope.  Even if you dont have the scope, The setting with the highest peak output power will be the one with more positive peaks on the watt meter. I will take a video for you when the camera charges.

[W2PFY]

ahhhhhhhhhhhhhh

around here we say eeeeeeeeeeeeeeerrrrrrrrrrrrrrrrrrrrrrryaaaaaaaaaaaaa

[KB2WIG]

"  around here we say eeeeeeeeeeeeeeerrrrrrrrrrrrrrrrrrrrrrryaaaaaaaaaaaaa  "

Others say   STRAP .

[Steve - K4HX]

If one side has a higher peak when using a sine wave input, there is something wrong with the transmitter (or the sinewave generator has a problem).

Below is the FT-102 with a sine wave input - 100% positive and 100% negative modulation.

[ke7trp]

Here ya go.  Correct phase as shown with a peak watt meter.

http://youtu.be/aleWFlE2cuk

If you dont have a scope handy just use your meter until you get a scope.

C

[The Slab Bacon]

Here ya go.  Correct phase as shown with a peak watt meter.
http://youtu.be/aleWFlE2cuk
If you dont have a scope handy just use your meter until you get a scope.
C

That is because of the asymmetry of the human voice also there might be some phase shift error in all of the stages the poor audio has to make it through in the audio rack BEFORE it gets to the modulator. And Like Steve said, if there is a difference with a pure sine wave input, you have an issue somewhere, as the sine wave should be perfectly symmetrical.

In that case it will tell you which phase makes the most output, but not always which is the correct phase. (I have seen this myself) Sometimes the incorrect phasing will produce higher average percent (modulation density) and lower peaks. This will show up on any analog meter as a higher output. Also the meter will not tell you if you are over modulating, flat topping, distorted, etc.

Now............Lets add another ingredient to the mix...................
A descent used scope is a hell of a lot cheaper than a Bird 43 + the "peak reading" kit and a handful of slugs. Now, If you know what the operating impedance of the transmitters load is, a scope will tell you what the peak power REALLY is! A descent scope can be had nowadays for less than the cost of 1 slug, and it can do so much more. Years ago that wasn't the case, but now good used lab-grade test equipment is getting very affordable, and scopes are to the point where they will almost throw them at you. I saw an older Tek 545 with a handful of plug-ins on a hamfest table for $10 last year. I bought a good working and clean Tek 465 2 years ago for $50 or so.

[ke7trp]

You dont need a Bird 43. Any peak watt meter will work and almost every ham has a watt meter. Certainly, you will find a watt meter way before a scope in the avg shack

I just used a POS MFJ watt meter and it shows the same thing.  The higher then positive peak, the higher the meter will read.  Even the crappy Cross needle meter in my palstar tuner shows higher on the correct positive peak.

I still think you should always use the sig generator first to verify the transmitter is working as it should before doing anything else. The T368 would always have more neg peaks. We found it was the mod tubes. Once replaced, It equaled out and then I used my voice and scope to set the phase that had the highest peak. 

I already got a note from a view of my video.  He had a Valiant with a peak meter.  He swapped the plate caps and got an xtra 150 watts on the meter.  So clearly, his valiant was backwards to his voice.  He thanked me for the video. 

Happy hollidays every body!
C

[Steve - K4HX]

Yep, the accuracy of the meter is not important since it is a relative measurement. So, any PEP meter will work. I haven't tried it but you might even see a much more muted indication on a average reading meter (slight up-kick with the right phase or a larger up-kick).

[ke7trp]

Yeah.  Peak off, I can see big forward jump on the RMS meter when in phase.  So just about any meter would probably work.

C

[Jim WB5WPA]

What? No mention of monitoring using a Trapezoid pattern?

de Jim WB5WPA


Added: Like one of these:

http://www.youtube.com/watch?v=f38Pq-zaNpQ