Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: B-Rex on January 17, 2025, 02:23:27 pm

Title: Robinette JCM 800 Adjusted to an old chassis Help
Post by: B-Rex on January 17, 2025, 02:23:27 pm

Hello! I’ve been moving things around quite a bit trying to make the Robinette JCM 800 20-25W design work with an old chassis and cabinet I have. Hopefully someone can have a look and see if I have missed something or the placement and flow of things is likely to cause noise and hum. I also have wondered if anyone can share the combination that tames the treble on these, I’ve seen a lot of different paths and would appreciate some first hand thoughts on the solution. Hopefully the images will be clear enough to get the idea. Thanks!

Title: Re: Robinette JCM 800 Adjusted to an old chassis Help
Post by: Rontone on January 17, 2025, 03:30:21 pm

Rob recommends starting at the 2nd treble peaker cap that is on the board, but I was lazy! Didn't want to start redoing the solder joints in that area so I just got the cutters out and snipped the first 'treble peaker' cap, the 470p from the low input jack to the preamp volume pot, I left the bright cap on the volume pot alone and it works nicely for me now, I get a better range on the treble pot

Title: Re: Robinette JCM 800 Adjusted to an old chassis Help
Post by: mresistor on January 17, 2025, 07:39:31 pm

oops my post was for the micro  sorry   

Title: Re: Robinette JCM 800 Adjusted to an old chassis Help
Post by: B-Rex on January 18, 2025, 03:36:48 pm

Thanks for having a look!