Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Opry Audio on June 29, 2019, 05:03:59 pm

Title: Kent Trem Tone conversion
Post by: Opry Audio on June 29, 2019, 05:03:59 pm

I’ve been asked to make one of the worst amps ever made into something decent.. I installed an isolation transformer with a bridge rectifier and a fuse, and recapped the amp. I’ve attached the schematic, I’m reading 350v on the B+ line which is way too high for this amp. The 50C5 can only take 120v on the plate maximum. Any suggestions on how a power supply for a line derived amp should be rebuilt? Here’s the schematic https://el34world.com/charts/Schematics/files/Kent/Kent5999.pdf

Title: Re: Kent Trem Tone conversion
Post by: sluckey on June 29, 2019, 06:14:46 pm

Quote from: Opry Audio on June 29, 2019, 05:03:59 pm

I’ve been asked to make one of the worst amps ever made into something decent.. I installed an isolation transformer with a bridge rectifier and a fuse, and recapped the amp. I’ve attached the schematic, I’m reading 350v on the B+ line which is way too high for this amp. The 50C5 can only take 120v on the plate maximum. Any suggestions on how a power supply for a line derived amp should be rebuilt? Here’s the schematic https://el34world.com/charts/Schematics/files/Kent/Kent5999.pdf

Why would you put a bridge rectifier in this amp?????

My suggestion is to remove the stuff you put in the amp. Then fix the amp in it's original configuration. Once it's working, then put an isolation transformer between the wall outlet and the AC plug on the amp.

DO NOT PUT A BRIDGE RECTIFIER IN THIS AMP!

Title: Re: Kent Trem Tone conversion
Post by: PRR on June 30, 2019, 12:07:58 am

> I’m reading 350v on the B+ line which is way too high

I strongly suspect you have connected the iso transformer for 240V not 120V.

> I’ve attached the schematic

Of a plan that worked. Would be better to show what you *built*.

But I'm agreeing with Sluckey. It is "possible" to use a FWB, but that puts heater-cathode voltages at-odds. Use the original plan. The 47r 3W(5W) resistor _IS_ important!! With any modern single rectifier you can raise 60uFd to 200uFd and cut ripple. Simulation says 160+V no-load, about 140V with normal load. The 50C5 plate -is- rated 150V. I do suspect this amp over-ran the tubes, but 50C5 are cheap.