Install a phase invertor trimmer?

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stelligan
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Re: Install a phase invertor trimmer?

Post by stelligan »

talbany wrote: Wed Aug 16, 2017 4:26 am There are many ways to go about balancing out!.. quickest and easiest method I have found is this one. :D Originally posted by Gil Ayan a way's back..

Tony
I may have to get more scientific and try this. Thanks!
talbany
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Re: Install a phase invertor trimmer?

Post by talbany »

stelligan wrote: Wed Aug 16, 2017 12:07 pm
talbany wrote: Wed Aug 16, 2017 4:26 am There are many ways to go about balancing out!.. quickest and easiest method I have found is this one. :D Originally posted by Gil Ayan a way's back..

Tony
I may have to get more scientific and try this. Thanks!
Sure thing :D ..A couple things you guy's can do to better set up the amp to speed things along is to add a switch on the back or bottom of the amp that is called a Bias/Balance switch where if you already have the bias test points in the cathodes. Then wire up a DPDT switch that ties off both cathodes on each pair on each side of the 1 ohm resistors.. It also helps to go through and find a PI tube that is already fairly matched on both sides of the PI (with 10k balance pot I get about a 7-8V swing from 0)..
After that it's simply a matter of setting the front end flipping the switch and injecting the signal, dummy load and zeroing the thing out..My SSS is set up with the switch and balance pot on the back of the amp (w/lock down pot) don't even have to take the amp out of the cab to bias or balance works great and is really convenient :D Yes I am Lazy!! :lol:

Good Luck!..Tony
" The psychics on my bench is the same as Dumble'"
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erwin_ve
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Re: Install a phase invertor trimmer?

Post by erwin_ve »

talbany wrote: Wed Aug 16, 2017 4:26 am There are many ways to go about balancing out!.. quickest and easiest method I have found is this one. :D Originally posted by Gil Ayan a way's back..You can download some kind of free signal generating software on your laptop/Tablet or they may have an app for it if you don't have a generator.(I made my own cable Min to 1/4 straight to front of the amp).A meter screwdriver and a couple alligator clips..You will have to have the 1 ohm resistors in the cathodes and matched output tubes since we are balancing current draw on the tubes on each side of the OPT primary (in relation to Gnd).BTW IMO..As long as you have a fairly well made (newer) output transformer I wouldn't worry too much about the winds being too out of balance there.After I get everything set up it only takes about a min or so to set it using this method..I have a 100W power resistor for the load and when I am done the resistor a little warm..The more you do it the quicker it becomes so I don't really worry about cooking my test load
Good Luck and Thank You Gil!!


1. Tie together the cathodes of the power tubes that are in phase with each other (i.e., the tubes that have their plates connected to the same B+ wire coming off the OT's primary).

2. Connect a digital multimeter set to DC Volts (yes, DC!) to each pair of cathodes, and set the scale to millivolt's. You will be measuring the voltage difference between the two pairs of cathodes.

3. Inject a 1 Vrms 100 Hz signal into the amp. I keep the amp in clean mode with the preamp volume turned down low and the tone controls where I normally set them (it will not matter much where you set them anyway, all I try to do is to not overdrive anything).

4. With a load connected to the speaker jack, set the output level (master volume) to the point where the amp dissipates about as much power as you think it dissipates when you normally use the amp. My rule of thumb is that at gigs I may be running at 50W tops, so into an 8-ohm load I will have a 20 Vrms output (P = V x V/R, so V = SQRT (PxR) = SQRT (50 x 8.) = 20). If you play your amp at lower volumes you may want to shoot for say 20W, which translates into 12.7V, etc. The output level will change the results/readings.

5. The multimeter's reading should be on the order of a few milivots. Turn the PI trimmer until the reading is 0 mV; 0 may go by quickly, so look for the reading to shift from + to - or vice versa. When 0 is reached, each pair of cathodes is at the same voltage with respect to ground and the two sides are therefore balanced. If the reading doesn't cross over, try another tube in the PI slot; it could also mean that your power tubes are not matched.

This method does not take into account any further imbalances introduced by the OT but has, per my experience, consistently yielded excellent results. I hope it works for you too.

Tony
The 20Vrms output maybe a good benchmark. When scoping and measuring things In noticed lower and higher output result in different outcomes for the balance. So that may explain some of the bloom. Perfectly balanced at gig volumes at pick attack and then as the output drops the amp gets a little off balance generating more overtones(2nd, 3rd?).
Does this make sense?
talbany
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Re: Install a phase invertor trimmer?

Post by talbany »

erwin_ve wrote: Thu Aug 17, 2017 11:57 am
talbany wrote: Wed Aug 16, 2017 4:26 am There are many ways to go about balancing out!.. quickest and easiest method I have found is this one. :D Originally posted by Gil Ayan a way's back..You can download some kind of free signal generating software on your laptop/Tablet or they may have an app for it if you don't have a generator.(I made my own cable Min to 1/4 straight to front of the amp).A meter screwdriver and a couple alligator clips..You will have to have the 1 ohm resistors in the cathodes and matched output tubes since we are balancing current draw on the tubes on each side of the OPT primary (in relation to Gnd).BTW IMO..As long as you have a fairly well made (newer) output transformer I wouldn't worry too much about the winds being too out of balance there.After I get everything set up it only takes about a min or so to set it using this method..I have a 100W power resistor for the load and when I am done the resistor a little warm..The more you do it the quicker it becomes so I don't really worry about cooking my test load
Good Luck and Thank You Gil!!


1. Tie together the cathodes of the power tubes that are in phase with each other (i.e., the tubes that have their plates connected to the same B+ wire coming off the OT's primary).

2. Connect a digital multimeter set to DC Volts (yes, DC!) to each pair of cathodes, and set the scale to millivolt's. You will be measuring the voltage difference between the two pairs of cathodes.

3. Inject a 1 Vrms 100 Hz signal into the amp. I keep the amp in clean mode with the preamp volume turned down low and the tone controls where I normally set them (it will not matter much where you set them anyway, all I try to do is to not overdrive anything).

4. With a load connected to the speaker jack, set the output level (master volume) to the point where the amp dissipates about as much power as you think it dissipates when you normally use the amp. My rule of thumb is that at gigs I may be running at 50W tops, so into an 8-ohm load I will have a 20 Vrms output (P = V x V/R, so V = SQRT (PxR) = SQRT (50 x 8.) = 20). If you play your amp at lower volumes you may want to shoot for say 20W, which translates into 12.7V, etc. The output level will change the results/readings.

5. The multimeter's reading should be on the order of a few milivots. Turn the PI trimmer until the reading is 0 mV; 0 may go by quickly, so look for the reading to shift from + to - or vice versa. When 0 is reached, each pair of cathodes is at the same voltage with respect to ground and the two sides are therefore balanced. If the reading doesn't cross over, try another tube in the PI slot; it could also mean that your power tubes are not matched.

This method does not take into account any further imbalances introduced by the OT but has, per my experience, consistently yielded excellent results. I hope it works for you too.

Tony
The 20Vrms output maybe a good benchmark. When scoping and measuring things In noticed lower and higher output result in different outcomes for the balance. So that may explain some of the bloom. Perfectly balanced at gig volumes at pick attack and then as the output drops the amp gets a little off balance generating more overtones(2nd, 3rd?).
Does this make sense?
Having the honor of working with Jack Pearson the one thing I've noticed is his ability to make just about any note sustain and bloom (sometimes into feedback) at will on just about any note, (even on an amp that was not obviously perfectly balanced) .. I asked him one time how he was able to pull that trick off..He said if I attack at just the right volume (Vrms) at just the right note (frequency) I can get it to do it..Some notes I have to attack them differently to find that spot..Jack generally keeps a light consistent touch when he plays (consistent Vrms output) .One other thing he mentioned was some notes bloomed and some notes were more consistent than others (generally the 1st octave of the guitar)..He also mentioned that he could get our amps that were balanced to bloom with little effort.
Erwin yes so judging by what Jack was telling me was that Vrms at the input plays a role along with frequency!!!.Not exactly sure what would be the benchmark for the 2 but would obviously pretty cool to find one that was right in that sweet spot if there is one, since the 2 are constantly changing... More math and testing would need to be done :D :D
Thanks!!
Tony
" The psychics on my bench is the same as Dumble'"
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erwin_ve
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Re: Install a phase invertor trimmer?

Post by erwin_ve »

talbany wrote: Fri Aug 18, 2017 4:24 am
erwin_ve wrote: Thu Aug 17, 2017 11:57 am
talbany wrote: Wed Aug 16, 2017 4:26 am
The 20Vrms output maybe a good benchmark. When scoping and measuring things In noticed lower and higher output result in different outcomes for the balance. So that may explain some of the bloom. Perfectly balanced at gig volumes at pick attack and then as the output drops the amp gets a little off balance generating more overtones(2nd, 3rd?).
Does this make sense?
Having the honor of working with Jack Pearson the one thing I've noticed is his ability to make just about any note sustain and bloom (sometimes into feedback) at will on just about any note, (even on an amp that was not obviously perfectly balanced) .. I asked him one time how he was able to pull that trick off..He said if I attack at just the right volume (Vrms) at just the right note (frequency) I can get it to do it..Some notes I have to attack them differently to find that spot..Jack generally keeps a light consistent touch when he plays (consistent Vrms output) .One other thing he mentioned was some notes bloomed and some notes were more consistent than others (generally the 1st octave of the guitar)..He also mentioned that he could get our amps that were balanced to bloom with little effort.
Erwin yes so judging by what Jack was telling me was that Vrms at the input plays a role along with frequency!!!.Not exactly sure what would be the benchmark for the 2 but would obviously pretty cool to find one that was right in that sweet spot if there is one, since the 2 are constantly changing... More math and testing would need to be done :D :D
Thanks!!
Tony
Thans Tony, interesting about Jack Pearson's viewpoints.(love his playing!).
One thing I noticed on all Ods builds so far: they easily go off between F# and A,(92,5Hz-110Hz hello!) with different guitars.
Testing, math: lack skills on the math side. You just reminded me how to calculate Vrms to Vpp :D
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dragonbat13
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Re: Install a phase invertor trimmer?

Post by dragonbat13 »

Hey, I thanks for all the info!

Im still new to all this, so I got a couple more basic questions. During searching around for more info on phase inverters, I noticed sometimes there was a capacitor between the junctions of the coupling caps and the plate load resistors. Is this called a "fizz cap" and what does it do? EDIT: I have since found out something about this. High frequency noise being canceled out between the out of phase signals.

Another thing I read about was using a metal film for one plate resistor and a carbon comp for the other. If anything it seems interesting to try. Is there any capacitor type that should be used for the capacitor between the two points mentioned above? What about the resistors?

I am ordering polystyrene caps for the bright cap and the treble cap for my amp from justradios.com and wanted to know if there was any other special caps I needed, such as that cap in the phase inverter.
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