Fender Tweed deluxe 5e3 feedback loop

[intoxicado]

Hi, this is my first post (sorry for my bad english).

I finished recently my 5e3. It works fine, but I want to do 2 modification (reduce gain and improve frequency response). First I removed the bypass capacitor on the cathode of the second preamp triode to reduce the amplification factor. But I have a problem with the feedback loop resistor. I don't know where it would be added.

I soldered 56k resistor between the secondary of the output transformer and the 1k5 resistor connected to the cathode of second preamp tube but the amp doesn't sounds good! Is it ok?

Could somebody give me a modified schematic of 5e3 with feedback loop added?

Thanks!

[Jazz P Bass]

You could try to copy this Princeton 6G2 feedback circuit.

[intoxicado]

I tried it, but when I connect the resistor, the amp scream.

[MWJB]

Did the amp just not sound how you wanted, or did it howl at you? If it howled, swap over the 6V6 plate wires.

The NFB resistor goes between pin 3 of V2 and the hot speaker terminal - just where you had it. You've effectively made 2 changes at once, a gain drop by removing the bypass cap, plus adding a NFB loop. Try the amp with the loop and the bypass cap back in (the cap defeats the loop to some degree, but still makes a difference), try the amp with the bypass cap out and the NFB loop out...any of these sound any better?

To properly install the NFB loop copy the tolex princeton/champ loop - add a 47ohm resistor between the cathode resistor (& it's bypass cap) to ground, run a new NFB resistor (2.7K) from the junction of the 1.5K & 47ohm resistors to the OT secondary.

You still might not like the sound of it.

[intoxicado]

1)YES it howled so, would I need to swap the plate wires and reinstall bypass cap?
2) Is it ok install 56k resistor to do NFB?

[MWJB]

1) you only need to swap 6V6 plate wires, bypass cap is irrelevant to the howl.

2) Yes, OK to install the 56K...as long as you like the resulting sound.

[intoxicado]

ok I will try it tonight.

Thanks w

[intoxicado]

Ok, it works but you're right, I don't like the sound :s

I want a sound like tolex twin 5f8-a

I looked at tolex champ schematic (5F1) but I didn't see a 47 ohm resistor to ground. Is it ok?

Thanks

[Chuck H]

You can't cross schems with such different amps and expect consistent results. The 5f8a Twin, 5f1 Champ, 6g2 and 5e3 couldn't be any more dissimilar. The circuits have different requirements, therefore the part values (or even their existance) are also very different. You sould have built what you wanted.

Why not rebuild your 5e3 as a low power 5f8a? That would probably give you more satisfying results. It would pretty much require stripping out the board, punching an extra tube socket and rewiring the whole thing. OR... You could just put it back stock, enjoy your 5e3 and build a 5f8a when you get the chance.

jm2c

Chuck

[MWJB]

"I looked at tolex champ schematic (5F1) but I didn't see a 47 ohm resistor to ground. Is it ok?" 5F1 is a tweed champ, not the tolex BF/SF Champ, see AA764, 12AX7 pin 8.

+1 on what Chuck says...5F8A & 5E3 are not really comparable tonewise. There are lots of ways to improve headroom on a 5E3, but these will take you away from classic 5E3 tone, sounds like you really want a different amp.