Loss of volume and gain after modification

[Mikante]

Hello,

As i said in a previous post, i have done some modification on my fender champ 600.
I have bypassed the eq and removed some resistor to make it sound more Tweed like.
Everything was fine before to make one more modification, i have put a switch on the feedback loop and replaced the stock resistor with a 2watt 22k. I had some problem putting back of the power transformer wires on their pins but that as been sorted out thanks to your support.
Now everything is back in place and i have re assembled the amp, just to discover that the volume is decreased a lot and i have no distortion at all, not even with the volume knob cranked all the way.
What happened?
I have followed this video to make the modifications.
I have checked all the connections and new components, everything is fine.
I have no clue at this point.

[R.G.]

There is not enough information there to make a good guess. If it were mine, I would reverse the process and remove one change at a time until it works again. If you reverse them all, you've killed something while debugging that "wrong primary pins" thing.

[sluckey]

Show us some pics of your handy work.

[Stevem]

In one of those new Champs there are only a total of four 2 watt resistors, and if you increased the value of any of them up to 22K then you have lowered needed voltages a lot, that such is now the root cause of your low volume and no gain condition!

Please look at a schematic like I did and post up for use the resistor numbers ( R number ) that you changed, the we can help you.

[Mikante]

Hello,
Alright, i guess i should have done that in the first place.
First I got rid of the eq by removing r18 r19 r20 r21 r22 and connected a 0.1uf 600v cap from the bottom of c1 to bottom of r21.
Replaced r3 r7 r14 r17 r25 r26 with jumper wires.
Replaced r12 with a 22k 2watt
Replaced r11 with a 10k 2watt
Replaced r23 with 1.5k 2watt
Removed c10
Tubes are new.

[Stevem]

I don’t know where you got those mod’s from but they should be titled “ a April fools joke “from what I see with the changes you made!!
I would put it all back to stock, but you can leave C10 out, or make it a 5 uf cap if you want the amp to stay cleaner as you crank it wide open.
That mod will give less output stage distortion and more preamp if your guitars output is hot enough.

[Mikante]

I got them from the video I have posted. Anyway, I didn't like the fixed eq. So I will leave that by passed.
Is 0.1uf ok for this?
The r7 is the feedback loop resistor, shouldn't I get more distortion without it?
I can put all the other resistors back to place together with the c10 and see what happen.
Right now the amp is giving out half of the volume and crystal clear sound even when pushed hard. The opposite of what i expected.

[Mikante]

Double

[JD0x0]

Sounds like you may have way too much NFB and it neutering the stage it's wired to. Check your wiring and all the component values, might have a decimal in the wrong place somewhere like a 2.2k in place of the 22k NFB resistor.

[Mikante]

I will check tomorrow, listening to the amp in the video after the mod it doesn't sound nearly as bed as mine. There must be something I did wrong.

[Stevem]

Your main problem is not the feedback!
It’s that with the changes to R11 and R12 you added 21k more resistance to the power supply which might be leaving you with only 1/2 of the voltage that the amp should run on!

[Mikante]

The mod should make it sound more like a tweed champ. But as I said in my first post, I m no expert. I will first check those two resistors and I will put the old ones back in.

[Firestorm]

Replaced r3 r7 r14 r17 r25 r26 with jumper wires.

If you really jumpered r7, you're pumping a huge amount of negative feedback onto the cathode of V2B.

[Mikante]

That is a pretty common mod on this amp, it is usually replaced with a switch so you can choose to have the negative feedback or not.
I thought this could add more grit and distortion.

[JD0x0]

Jumpering the NFB resistor will give you a TON of NFB. Lifting/disconnecting the NFB resistor is what will give you more grit as you're breaking the connection between the OT and the cathode of the preamp stage, completely, eliminating the NFB network. Jumpering the NFB resistor will eliminate all resistance between the OT and cathode of the preamp stage, giving the maximum amount of NFB possible.