DIY PTP JCM800 in an old Laney- low volume issue

[Kapo_Polenton]

Voltages on preamp tubes seem in spec, 397 plate voltage, new power tubes biased up properly. However, I get low volume ugly fizzy distortion and for the life of me I can't figure it out. Retraced the circuit for continuity and to ensure what needs to be grounded runs to ground. Any ideas? How could I determine whether or not my transformer is on it's way out? thanks metrolites!

Just to add to this, how does one diagnose a bad / failing resistor ? Visually or by other means? I'm assuming if my voltages are good on the preamp tubes then I don't have issues with a resistor..

[Haze13]

I've built JCM 800 and my Plate voltage is 470... It's 70s volts more than you have. Are you shure that the voltage that your power transformer gives is what you need? Check the B+ from the start... What is the model of your Laney? And photos... and photos... photos.

[ivan H]

Hi, years ago I had an old 30 watt OT fail due to one half of the primary going open circuit & it produced pretty much those same symptoms, much reduced volume & a very nastily distorted sound. Checking for this is pretty easy, just measure the DC resistance from the center tap to the plate lead on both halves of the primary. If one half is open it'll read nothing on that half. But,, if u've got voltage on all output tube plates its not that. Good luck with. Cheers