Removing my Negative Feedback Loop?

[reddinis]

The only tube amp I have right now is my Pignose G40V. I've never had trouble with it and I really like it (with 12AT7 in V1 and speaker change), but I know it's cheaply made and I have to be careful that it doesn't overheat. I guess I got lucky because I haven't had much problem with it (had it for 6 years).

Anyway, the question is, will removing the negative feedback loop make the amp run hotter, as in temperature?

Here is a link to the schematic - http://www.blueguitar.org/new/schem/...gnose_g40v.gif

I am going to replace the filter caps and improving the grounding and want to see what it sounds like without a negative feedback loop. I will probably also install a fan.

Any help will be sincerely appreciated. Thanks!

[MWJB]

If it runs hot, why not back off plate current at the power tubes? This where the heat is typically generated in an amp, PTs can run hot too.

Removing the NFB loop won't cause the amp to generate more heat, but it may lead to instability, try & see how you go. The amp's tone may just go brittle?

[reddinis]

Thanks, MWJB. Luckily, my amp has never run hot. But these amps are well known for frying transformers. The components (especially transformers) are super cheap and the cabinet/ chasis is very small with the tubes very close togehter.

I'm thinking preventative maintenance here, as this is the only tube amp I have right now to take out and jam with. It hasn't been out of the house much or played through for several hours. It has been left on all day, though, but so far I haven't had any overheating problems.

I want to play with the loop to hear the difference in sound.

This will show my level of in-expertise, but it just seemed to me that since a larger signal would be going into the power amp that it may run a little hotter? But from everything I've read and heard, it's never been mentioned, but I still wanted to ask.

Thanks for your help! Like I said, this is all I have right now and it may take a little while before I'm able to get something more reliable. (It's been reliable, but I know what I'm dealing with here.)

[Chuck H]

With the feedback loop removed there will be more signal into the power tubes and the amp may break up and distort sooner. It will also sound more aggressive and have more harmonics. This makes the amp seem louder. While the amp may in fact be a tad louder it's the effect that really makes it seem that way. But if the power tubes are saturating and cutting off (over driven) then there won't be any more wattage dissapated than with the loop in place. The tubes can only make so many watts for a given voltage and bias before they start to clip the top and bottom off the waveform creating a cieling for watts. In the process of making watts your amp also makes heat as a by product. If your not making more watts you won't make more heat either.

[reddinis]

Thanks, Chuck H.

[Jazz P Bass]

Mesa Boogie Nomad 45 has a switch to remove the FB resistor from circuit.

[jrfrond]

Just open up the resistor and try it. If you don't like it, put it back. You aren't going to hurt a thing.

[reddinis]

Thanks, guys. I took it out and like it a lot. I may put a pot/ switch in there so I can have it either way and adjust it.

Right now it's on the bench while I'm waiting for some parts. I've got some filter caps on the way. I did't get nice ones, I don't want to put too much into this thing. And Sprague Atoms won't fit, anyway, LOL.

I will probably have more questions aobut other things. Thanks for your help!