Leave the dummy load on the green wire. Measure (recheck) the output voltage from green to ground (this is with a sinewave at the input). Take note of the voltage. Then, without changing anything, measure from the 4-ohm tap to ground. The voltage at the 4-ohm tap should be about 70% of what you're measuring at the green (8- ohm) wire. If you actually measure more voltage at the 4-ohm tap (about 40% more), then the two taps are swapped.Randall wrote:You know what? I asked myself the same question. I emailed Triode for the spec sheet and according to it, I am using the green wire for 8 ohms. How would I check to see if there somehow is a wiring color mistake? I ask because I am having the same approx. measurements on two amps built side by side with all the same components.Tillydog wrote:Apologies in advance for this...
...but are you *sure* you're on the 8 ohm tap? Everything looks OK to your power tubes, and that voltage swing would be roughly right for the 4 ohm tap.
Measuring output power
Moderators: pompeiisneaks, Colossal
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JazzGuitarGimp
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Re: Measuring output power
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
Re: Measuring output power
Measured the other OT taps, less on the 4 ohm lead, more on the 16 ohm lead. So, I guess I am resolved that these two builds are putting out about 10 watts clean, and there it is. They both sound good, so off they go!
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JazzGuitarGimp
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Re: Measuring output power
There is another possibility: Are you sure the output taps are 4, 8, 16 and not 2, 4, 8?Randall wrote:Measured the other OT taps, less on the 4 ohm lead, more on the 16 ohm lead. So, I guess I am resolved that these two builds are putting out about 10 watts clean, and there it is. They both sound good, so off they go!
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
Re: Measuring output power
Only as sure as the documentation provided by Triode, which shows 4,8, and 16.JazzGuitarGimp wrote:
There is another possibility: Are you sure the output taps are 4, 8, 16 and not 2, 4, 8?
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Andy Le Blanc
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- Location: central Maine
Re: Measuring output power
I think you might be looking at the wrong numbers.
Here's the thing... with your scope you ramp up the signal and look at the output form right... it clips and then you back it off until the form is clean.
All the data quantification's are for maximum power and minimum distortion.
But what your missing is the peak AF grid-to-grid voltage, this is the point where you start collecting data.
and you have two set of data you want to collect, the zero signal condition and the max signal condition, this peak signal grid-to-grid condition.
from the power out and the max signal plate current you get the max signal plate voltage.... W/Arms = Vrms
you get "effective load resistance" when you Vrms/Arms
the first steps toward finding load factor, gm and voltage amplification.
Now you also have to mind that there are clinical assumptions about the grid-to-grid signal that you need take in mind, equal magnitude and out of phase, and all of the phase inverter qualifications assume perfect voltage and current balance, and a pure sine wave etc... for your test conditions of the power side to be valid, I not saying that its impossible but you want to really work at a solid test bed to get good numbers to on your power side so you do need to Idealize you inverter as much as possible for AC and DC balance even if your not so picky when come to the final result, a couple extra trim pots in the circuits to get fine control for testing is all might take to realistic and valid test results.
Here's the thing... with your scope you ramp up the signal and look at the output form right... it clips and then you back it off until the form is clean.
All the data quantification's are for maximum power and minimum distortion.
But what your missing is the peak AF grid-to-grid voltage, this is the point where you start collecting data.
and you have two set of data you want to collect, the zero signal condition and the max signal condition, this peak signal grid-to-grid condition.
from the power out and the max signal plate current you get the max signal plate voltage.... W/Arms = Vrms
you get "effective load resistance" when you Vrms/Arms
the first steps toward finding load factor, gm and voltage amplification.
Now you also have to mind that there are clinical assumptions about the grid-to-grid signal that you need take in mind, equal magnitude and out of phase, and all of the phase inverter qualifications assume perfect voltage and current balance, and a pure sine wave etc... for your test conditions of the power side to be valid, I not saying that its impossible but you want to really work at a solid test bed to get good numbers to on your power side so you do need to Idealize you inverter as much as possible for AC and DC balance even if your not so picky when come to the final result, a couple extra trim pots in the circuits to get fine control for testing is all might take to realistic and valid test results.
lazymaryamps
Re: Measuring output power
Out of curiosity, I put the PI & output stage into LTSpice. I assumed B+ was fixed at 370V as measured above. I didn't model the preamp, but assumed a steady 2.5mA from B+3 in addition to the PI (this may be too much, as the other supply voltages have settled out a little below Randals measurements above, but the 6V6s are still driven into clipping).
Predicted quiescent conditions are:
B+1 (fixed) = 370V
B+2 (screen supply) = 322V
B+3 (PI / preamp) = 250V
Vk (cathode to gnd) = 20.8V - 270K shared resistor.
Maximum output with a 6k6 OT primary impedance at 400Hz is 14W (30V P-P across 8 ohm).
The supply voltages change to:
B+1 (assumed constant) 370V
B+2 (screen supply) 315V
B+3 (PI + preamp) 243V
Vk (cathode to gnd) = 25V
Drive at the 6V6 grids is 50V P-P, exactly as Randal measured above, which needs 54V P-P into the PI.
It's the 6V6s that clip first (in the sections I modelled).
Dunno if it is of any interest... (but I thought I'd post it anyway
)
Predicted quiescent conditions are:
B+1 (fixed) = 370V
B+2 (screen supply) = 322V
B+3 (PI / preamp) = 250V
Vk (cathode to gnd) = 20.8V - 270K shared resistor.
Maximum output with a 6k6 OT primary impedance at 400Hz is 14W (30V P-P across 8 ohm).
The supply voltages change to:
B+1 (assumed constant) 370V
B+2 (screen supply) 315V
B+3 (PI + preamp) 243V
Vk (cathode to gnd) = 25V
Drive at the 6V6 grids is 50V P-P, exactly as Randal measured above, which needs 54V P-P into the PI.
It's the 6V6s that clip first (in the sections I modelled).
Dunno if it is of any interest... (but I thought I'd post it anyway
)You do not have the required permissions to view the files attached to this post.
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martin manning
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Re: Measuring output power
martin manning wrote:So, with Vk at 21.7 and 270R that's 0.0402 A per tube, which is 114% of max... pretty hot! Vg2 to Vk is 309, and assuming an 8K load, the power output from the load line would be 18.3W. You won't get but maybe 85% of that (SWAG), so I would expect maybe 15W. 50V p-p ought to be enough to drive the grid voltage to zero...Randall wrote:My current V's at present line voltage of 120 Vac are:
B+ = 374v
Vp = 357v
Vp-k = 335v
Vsc = 331v
Vk = 21.7v
...With a 6k6 load you're down to 16.1W on the load line, guessing 85% of that would put you at 13.7.
Good stuff Tillydog, and even better, it seems to confirm my back-of-an-envelope estimate!Tillydog wrote:Maximum output with a 6k6 OT primary impedance at 400Hz is 14W (30V P-P across 8 ohm).