Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on July 13, 2019, 12:41:30 pm

Title: Flubby bass/Fender 5D3
Post by: Diverted on July 13, 2019, 12:41:30 pm

Hi all,

A while ago I built a point to point 5D3 circuit (paraphrase PI) for a friend of mine. He absolutely loves it apart from hitting bass notes at high volume.. it tends to get flubby/farty. I’ve done a few things that helped a bit but did not eliminate it. Any suggestions?

So far I:

1. Replaced both output tubes coupling caps with .015s
2. Replaced preamp bypass cap with 1uf.

https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_5d3_schem.pdf

Thanks,

Ted

Title: Re: Flubby bass/Fender 5D3
Post by: sluckey on July 13, 2019, 12:55:07 pm

There are four .05µF coupling caps. Replace all four with .01µF caps.

There are three 25µF cathode bypass caps. Replace all three with smaller caps. I'd try 5µF or 1µF.

Title: Re: Flubby bass/Fender 5D3
Post by: Diverted on July 13, 2019, 02:42:56 pm

Thank you Sluckey👍
Will report back.

Title: Re: Flubby bass/Fender 5D3
Post by: ac427v on July 13, 2019, 08:28:21 pm

Cutting bass by changing caps might be the answer for your friend. But if he wants to keep bass frequencies only with less distortion,  you could try raising the headroom by increasing voltage. Using a 5AR4 or a 5V4 instead of a 5Y3 would increase voltage for the entire amp. Or changing one of the 10k dropping resistors in the power supply to something smaller--like 2k would increase voltage on the power tube screens and the preamp tube plates. The downside of increased headroom is that it increases headroom. That means less of the sweet distortion at middle volumes.