need some help😩
Currently building my 70' slp clone.
Channel 1(v1a)works fine.
channel 2(v1b) on the other hand has high pitch squeal and hum when rolling the volume from all the way off to on, also causing the power tubes cathode current to spike (already blown a set of el34s)
(Note power tubes bias is currently set at 10ma for testing)
Have had the preamp tubes in and out so hopefully it's not a bad tube.
Checked connections from inputs to the grid of v2 all seems to be ok.
Only changes I have made is the coupling cap on v1b is a 0.022uf like v1a
And a master vol after the tone stack.
Any help is much appreciated 😀
Currently building my 70' slp clone.
Channel 1(v1a)works fine.
channel 2(v1b) on the other hand has high pitch squeal and hum when rolling the volume from all the way off to on, also causing the power tubes cathode current to spike (already blown a set of el34s)
(Note power tubes bias is currently set at 10ma for testing)
Have had the preamp tubes in and out so hopefully it's not a bad tube.
Checked connections from inputs to the grid of v2 all seems to be ok.
Only changes I have made is the coupling cap on v1b is a 0.022uf like v1a
And a master vol after the tone stack.
Any help is much appreciated 😀
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The circuits for V1a and V1b are so similar it's hard to see what would cause that, except a miss-wiring, or a bad V1 tube.
Marshall had this problem. The cure is a grid stopper 47k directly on pin 2 of V2A, add 220p across the anode load 100k resistor Pin 1.
Part 2 of ECC83s have slightly higher gain and less noise than part 1 for some reason, only known to Mullard, the valve designer of the ECC range.
The stage is probably suffering from parasitic oscillation.
Part 2 of ECC83s have slightly higher gain and less noise than part 1 for some reason, only known to Mullard, the valve designer of the ECC range.
The stage is probably suffering from parasitic oscillation.
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