Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Richs1979 on August 11, 2025, 06:52:11 pm

Title: New Hoffman Plexi build
Post by: Richs1979 on August 11, 2025, 06:52:11 pm

Hello again.
After a successful 1st build AB763 back in February, I was talked into building a Plexi 50 for my son. I'm ready to fire it up but I thought I'd post a pic of the finished wiring. I again purchased a Hoffman kit with his hot switch mod. I'll be using my light bulb limiter sometime tomorrow and see if it smokes or not. Tubes should be delivered sometime this week. I've only built that AB763 before this so I'm still a newb. Thanks in advance for your help.

Title: Re: New Hoffman Plexi build
Post by: shooter on August 11, 2025, 07:15:46 pm

nice build


my only 2cents, I typically ohm the power rail before any power, should "see" charging caps reaching many thousands of ohms to infinity, if you get something <50Kohms, I would suspect a problem.
1st power up I leave the PA tubes out and verify there is bias voltage at the pin-side of the PA sockets, it's stable and adjustable, then i'm confident enough to test with PA tubes.

Title: Re: New Hoffman Plexi build
Post by: Richs1979 on August 11, 2025, 07:20:44 pm

Thanks.... I'll set for max negative voltage b4 I install any tubes. I'm just a little nervous when lighting up anything for the 1st time. If anyone notices something out of the ordinary in my photos please inform me. Thanks.

Title: Re: New Hoffman Plexi build
Post by: uki on August 11, 2025, 10:13:08 pm

Here a good walk through before first power up

http://paulrubyamps.com/info.html

Title: Re: New Hoffman Plexi build
Post by: Richs1979 on August 12, 2025, 02:59:59 pm

Still waiting for tubes. I'll post my progress once I have them in.  :thumbsup: