Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on September 10, 2018, 05:40:41 pm

Title: Fender 5C3 master volume control?
Post by: Diverted on September 10, 2018, 05:40:41 pm

Hi all,

Just finished building an oddball Fender 5C3 clone for a friend. It's a cool amp, early tweed with octal 6SC7 pre and phase inverter.

http://schematicheaven.net/fenderamps/deluxe_5c3_schem.pdf

One of the things he wants is low volume overdrive, but this one doesn't start breaking up till around 6 or 7 - too loud for what he wants. So I was thinking a master volume control. Only thing is this is an odd phase inverter and I am unsure of how to tie one in. Any suggestions?

Thanks!

Ted

Title: Re: Fender 5C3 master volume control?
Post by: sluckey on September 10, 2018, 05:50:51 pm

I'd leave it be. Maybe suggest a speaker attenuator.

Title: Re: Fender 5C3 master volume control?
Post by: SILVERGUN on September 10, 2018, 06:02:52 pm

You could have him try it without the bypass cap on the 6V6 cathodes.
If he likes that, just put it on a switch.

Like sluckey suggested, a simple attenuator would be easy to implement.

Title: Re: Fender 5C3 master volume control?
Post by: PRR on September 10, 2018, 06:49:35 pm

Cathode bypass cap on a push-pull power stage does VERY little. (In effect, one cathode bypasses the other so there is little effect from a cap until LOUD.)

Minimalistic amps like this, it is hard to have the gain-up loss-down gain-up signal torture we use on more complex amps.

Yes, speaker pad is the obvious thing to try. There's no harm in slamming the 6V6es (they may even live longer) then throwing-away 13 of the 14 Watts they make.

Title: Re: Fender 5C3 master volume control?
Post by: Diverted on September 11, 2018, 11:50:36 am

Thanks for the suggestion on the attenuator. Thinking about this, a la Rob Robinette's site:

https://robrobinette.com/Generic_Tube_Amp_Mods.htm#10%_Power_Switch

This one uses 25W 16 and 12 ohm resistors to burn up most of the signal to heat. Question:

I have a 15 ohm 25w finned resistor so no problem there.
However the other resistor, called for as 12ohms/25w, I do not have. I DO have a 10 ohm, 20w finned resistor. Is this cutting it too close or should I be good with 20W?

Thanks!

Title: Re: Fender 5C3 master volume control?
Post by: sluckey on September 11, 2018, 12:25:12 pm

The 5C3 is only 10 to 14 watts. I think you are fine. Be sure to mount the resistors to the chassis to help dissipate heat.

Title: Re: Fender 5C3 master volume control?
Post by: Diverted on September 11, 2018, 12:29:15 pm

Thanks :)
It's such a tight, tight chassis (re-using an old junker chassis that's pretty small) that I can only mount the resistors behind the face plate, near knobs switches etc. It should give my friend nice warm fingers as he fiddles with the knobs :)

Title: Re: Fender 5C3 master volume control?
Post by: shooter on September 11, 2018, 12:55:23 pm

Quote

near knobs switches etc.

bringing the output back to the input might cause some un-intended coupling issues  :dontknow:

Title: Re: Fender 5C3 master volume control?
Post by: labb on September 11, 2018, 01:11:15 pm

Why try to force the amp to be something it is not. Keep what you have and build him something like this. http://www.ax84.com/4-4-0.html