Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Keyboy on July 09, 2022, 04:44:42 pm

Title: Gibson GA-5 build - good till 9.5
Post by: Keyboy on July 09, 2022, 04:44:42 pm

Howdy!
I am on the last couple steps of a GA-5 build. I stayed very close to one of the original schematics (hopefully attached). Testing the circuit went very well with one exception. The sound from volume level 1 all the way to 9 is amazing, but when I get past 9 - say to 9.5 - the amp sounds like it's having a clipping fit. The sound is different than typical desired distortion - it has the feeling like the circuit is overwhelmed. I could live with this, no problem, but wanted to check and see if this is typical or can be corrected relatively easily.

Title: Re: Gibson GA-5 build - good till 9.5
Post by: pdf64 on July 09, 2022, 04:59:33 pm

Oscillation comes to mind; I suppose scoping the output isn’t an option?
Photos of your build?
Video / sound clip demoing the issue?

Title: Re: Gibson GA-5 build - good till 9.5
Post by: shooter on July 09, 2022, 07:00:54 pm

Quote

different than typical desired distortion

which is?
A SE amp distorts uniquely from a PP amp
the one's i've worked on "got nasty" with too much guitar AND to much amp gain.  There are guitar players that play that nasty sound really well.


as pdf64 suggests, a scope is your eyes to the amps sound, your DVM is your stethoscope to ensure the amps gonna live

Title: Re: Gibson GA-5 build - good till 9.5
Post by: Keyboy on July 09, 2022, 07:32:19 pm

Thank you both - great suggestions. I will try and post an example of the clipping sound. It's odd how the volume and performance is ideal right up to the the very end of the pot travel.

Title: Re: Gibson GA-5 build - good till 9.5
Post by: PRR on July 09, 2022, 07:54:39 pm

Says right on the plan: "service by a reliable radio man".

> It's odd how the volume and performance is ideal right up to...

As Nigel didn't say "These go to 9.5!! That's not-much less than 11!"

Last time I built a Champ-like amp, I was surprised how easily it squealed, and how "minor" change of lead routing changed even killed the squeal.

It can squeal supersonic so you don't hear the squeal, but do hear the circuit "overwhelm".

Title: Re: Gibson GA-5 build - good till 9.5
Post by: ShoemanGB on July 10, 2022, 06:04:35 am

Quote from: PRR on July 09, 2022, 07:54:39 pm

It can squeal supersonic so you don't hear the squeal, but do hear the circuit "overwhelm".

Very fitting, given the time period these were made. Supersonic was a hot topic, along with who would claim the moon first :laugh: