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07-17-2020, 05:40 AM
Thanks, Nauta.
Some interesting observations: this build is very prone to severe oscillation problems. Preamp tubes are poorly decoupled: V1 (two stacked gain stages) and V3 (reverb recovery + gain stage) are on the same supply node. I don't have spare electrolytic caps at the moment but I did notice that probably the oscillation is directly caused by a nasty ground loop from both RCA reverb jacks grounded at the chassis. Isolating them keeps the tubes from oscillating and it's a quick fix for the problem, but the voltage supply line should still be upgraded.
One of the original EL34's that got battered so much made the carbon comp screen resistor start smoking yesterday. Glad I noticed that before it burst into flames.
Some interesting observations: this build is very prone to severe oscillation problems. Preamp tubes are poorly decoupled: V1 (two stacked gain stages) and V3 (reverb recovery + gain stage) are on the same supply node. I don't have spare electrolytic caps at the moment but I did notice that probably the oscillation is directly caused by a nasty ground loop from both RCA reverb jacks grounded at the chassis. Isolating them keeps the tubes from oscillating and it's a quick fix for the problem, but the voltage supply line should still be upgraded.
One of the original EL34's that got battered so much made the carbon comp screen resistor start smoking yesterday. Glad I noticed that before it burst into flames.
