zeh
Active member
Hi there,
iam trying to build my first tube amp and iam having some issues.
if i only connect the power tube and plug in a test signal from my signal generator directly into the grid of the power tube, i hear output on the speaker, if i crank up the voltage to about 4-5V it starts distorting, i think this is normal behaviour since the powertube gets overdriven at this voltage.
if i only connect the input stage (1/2 12ax7, the unused pins of the 12ax7 are grounded and the heater is only using pin 9 and 5, so only the first half should be used) i can measure a clean amplified signal after my coupling capacitor.
The issue is, as soon as i connect the coupling cap output to the grid of the powertube and increase the supply voltage, at some point around 150V, the signal on the grid of the powertube starts 'ringing' with some high frequency and the output is kind of distorted and the output power is also not very high. i have tried to simulate the project as good as i can using LTSpice, but since in reality always everything is slightly different, the voltages will not 100% match, i guess this is due to the series resistance of the power transformer which differs in reality, i tried different values, also measured the DC resistance of the power transformers secondary.
any help will be much appreciated, since i never built a tube amp i dont know how to proceed now, maybe you can guide me into the right direction.
at the test point i can measure about 5V AC, so the input signal gets amplified correctly, but ONLY if i disconnect R3 from the grid of the output tube.
in my simulation actually every looks totally fine and its working correctly. i also tried exchanging input and output tube and its the same error..
thanks and kind regards
chris
iam trying to build my first tube amp and iam having some issues.
if i only connect the power tube and plug in a test signal from my signal generator directly into the grid of the power tube, i hear output on the speaker, if i crank up the voltage to about 4-5V it starts distorting, i think this is normal behaviour since the powertube gets overdriven at this voltage.
if i only connect the input stage (1/2 12ax7, the unused pins of the 12ax7 are grounded and the heater is only using pin 9 and 5, so only the first half should be used) i can measure a clean amplified signal after my coupling capacitor.
The issue is, as soon as i connect the coupling cap output to the grid of the powertube and increase the supply voltage, at some point around 150V, the signal on the grid of the powertube starts 'ringing' with some high frequency and the output is kind of distorted and the output power is also not very high. i have tried to simulate the project as good as i can using LTSpice, but since in reality always everything is slightly different, the voltages will not 100% match, i guess this is due to the series resistance of the power transformer which differs in reality, i tried different values, also measured the DC resistance of the power transformers secondary.
any help will be much appreciated, since i never built a tube amp i dont know how to proceed now, maybe you can guide me into the right direction.
at the test point i can measure about 5V AC, so the input signal gets amplified correctly, but ONLY if i disconnect R3 from the grid of the output tube.
in my simulation actually every looks totally fine and its working correctly. i also tried exchanging input and output tube and its the same error..
thanks and kind regards
chris
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