Adding Another Gain Stage to a 5F1

[alexs973]

I've recently built a custom Fender 5F1 from scratch and I'm in the process of making some minor modifications to it. Some of them standard ones like switching out both 12AX7 cathode caps, adding a bright switch, and a variable NFB section with a presence pot. Also since my amp is going to a 1x12 instead of the original 1X8, it's sounds a lot more "bassy". The bright cap will help, but I also want to add a 3 band tone stack for added tonal changes.

Anyway, that's not really the question I wanted to ask. The schematic for all those changes is complete, but before I order the parts, I think it would be cool to add another gain stage. So I have a couple of questions:

-Has anyone done this to a 5F1?
- What tube(s) did you put in? I'm think a 12AX7, but wouldn't be opposed to a 12AY7.
- Did you use both sides of the dual triode?
- What other changes would I have to do to support this addition?
- Would I have to substitute the 10k and 22k resistors in the power section for higher wattage ratings?
- What about the filter caps? The capacitance should be OK, but maybe a higher rating on that too?
- I think my 5Y3GT rectifier should be able to handle it.
- Where should I put this? Before the tone stack or after? I'm thinking in between the 12AX7 1-A and 1-B but I'm open to suggestions
- I'm not sure what the dc plate voltage the 12AY7 takes but since I'm thinking of using a 12AX7, I could just theoretically pick off the dc needed in the same what that is being done with the 12AX7 already installed, right?
- Could I just copy the "basic" triode circuit already in the amp, or should I modify it slightly? I'm thinking I would have to modify a gird resistor somewhere so the amplification isn't too much.

P.S. If anyone want to see the previously mentioned schematic let me know and I'll add it in here.
Thanks,
Alex

[Ostinato Rubato]

Moding amps is soooo 2000



We just buy the right amp these days.

[alexs973]

Buying the right amp isn’t as fun as making the right amp though ; )

[Zozobra]

Post a schematic of what you're doing
It can be fun to simulate things with LTSpice to understand what things do too. I learned a hell of a lot about higher gain topologies that way.

[Ry Manchu]

Wouldn't cascading the Gain Channel into the Bright Channel be a whole lot easier?

[alexs973]

The 5F1 doesn’t have a bright channel. It just has a normal channel with two input jacks (high and low)

[alexs973]

I'll post the schematic in a little bit. I'm playing around with a second channel gain stage, so I need to fix it up before I post it. I'm a little concerned about if my transformer/power section caps and resisters can handle the extra wattage being drawn

[Zozobra]

Honestly, sticking an extra tube on is almost certainly fine in terms of the PT. Measure the heater supply voltage and if the heaters are within 10% you're fine. The resistor draw is easy enough to calculate:
http://www.valvewizard.co.uk/smoothing.html