Liverpool: It's alive...HELP!!

[hans-jörg]

Oh, I would say it is too much gain without NFB

Hans-Jörg

[JoeCon]

OK

8 ohm tap to 100K to tail and 4k7 from tail to ground.
Turn up master volume and I get a low frequency WOOOOOO...hmmm.

Anyone?? Bueller?

[JoeCon]

Nevermind...

I changed R7 to 33K and now it sounds better, still no NFB. A little hard to control, but aren't they all!! Amps I mean.
It's a lot more aggressive than my Rocket or Rockster and I'm beginning to think that's how it is. It's a "learn how to play it" experience.
With The Vol at 1/2 and master at 3/4 this is one loud Twin Tube amp.
It doesn't have the versatility of the Rocket type amps but for a Lead Guitar amp...quite nice.
All in all...I Like It!!

[cbass]

OK

8 ohm tap to 100K to tail and 4k7 from tail to ground.
Turn up master volume and I get a low frequency WOOOOOO...hmmm.

Anyone?? Bueller?

Sounds like you need to swap the ot primaries

[JoeCon]

Cbass
But only when I tried the NFB. So is that it, need to swap OT primaries? But why only when the feedback is connected?

[cbass]

Cbass
But only when I tried the NFB. So is that it, need to swap OT primaries? But why only when the feedback is connected?

Yes . I'm probably not the guy to explain why. But basically you are applying positive feedback instead of negative feedback

[matt h]

(deleted)

[JoeCon]

Matt

Here in Manch-Vegas we don't need no Negative Feedback...

[cbass]

Isn't feedback an ac signal? so it really wouldn't have positive or negative but in phase or out of phase. Just thinkin out loud sorry

[martin manning]

Yes the signal is AC, but if you swap the polarity the signal is inverted, which is like shifting phase 180 degrees.

[Blackburn]

Without NF, that thing is even brighter. I'm surprised you prefer this. Speakers? And maybe the room in which you play? These variables can really affect the percussive nature of amplifiers, and the LP in particular, because of how much high end there is. I dropped the feedback resistor down because I wanted to cut some high end/gain and without NF at all...

But hey, if you dig, you dig.

[JoeCon]

Blackburn
I have a cut control that takes this brightness down a good bit. Also not so bright with HBs, but the Tele needs it way down.
I guess I'm digging the rawness of this amp, but at some point I'll have to swap the OT primaries and try the NF. So you dropped the 100k to a lower value? How low?
Thanks...

[Blackburn]

Interesting that you have a cut control in there. My LP has a 6SL7 for v2, a choke and a tube rectifier, which is a 5AR4. I tweaked the feedback resistor down to 33k. I've made the amp MUCH more to my liking with these changes, which are new. My B+ is a good deal lower, resulting in lower plate voltage. It's more like a Rocket now, but I like this setup more, honestly. Cleans are very nice early on, and it still has some great gain, but not crazy like the stock circuit. I'll probably do a thread on it since I'm digging it much more now. Hope you get it to where you're digging it. I've learned to work with the brightness and am not as averse to it anymore.

[geetarpicker]

The feedback loop will tame the amp down. The feedback loop would be my top priority to add based upon your description of your amps performance. It's not about the presence control, that's just a separate addition to the feedback circuit. Actually the feedback loop reduces gain overall, but the presence control actually reduces the loop signal specifically in the high end making the amp more gainy up top. It all may sound backwards. In other words when the presence control is turned up your are actually reducing the feedback in just the high end. In your case it's like you have the presence control wide open, along with all the other frequencies running wild just the same compared to stock. In regards to the feedback resistor 100k is stock, but 47k and 27k are also popular in some amps. My Superbass Marshall 100 uses a 27k feedback resistor, but the circuit is a little bit different overall.

[JoeCon]

Glen

Thanks for the info. So a smaller resistor will cut it more with 100K being stock. Got ya!

So switch the OT primaries, connect the NF loop to the tail/cap and try again...
So the presence control has that cap to reduce the high end and I don't really need it with my cut control so just NF to start with.

Get the iron hot!!