5150 Mod Thread

[TheWinterSnow]

Um, no. It's the maximum power it can deliver to the correct load.

So let me think out loud here...if 60mA is traveling through a 6L6 with a plate voltage of 500v, that is 30W that is being dissipated across that tube. If the biasing point was set to 60mA for all the tubes, with 4 6L6GC, the dissipation is 120W. Simple Power Law, P=V*I. Now also from my understanding is that, active components do not theoretically dissipate any heat, however they do in small amounts particularly inductors, which is what a speaker is. The dissipation of the speaker is going to equal I=Vrms/R where R=DC Resistance and P=Vrms*I. At idle, the Power Dissipation of the speaker should be damn near zero (accounting for noise) and increase as the signal is being sent to the speaker. As the input signal increases on the power tubes, two of the tubes will begin to conduct harder, meaning current through those tubes are increasing, but the total current through all 4 tubes should stay close to the idle current when the other two tubes are cutoff, that is in a class B amplifier and Class AB should see a max dissipation of ~1.5 times idle depending on how hot they are biased. The speakers however since they are getting an AC signal, should being to see a larger dissipation, but still less than the total power tube dissipation and at saturation Tube Dissipation=(1.5)Speaker Dissipation, so an amp with 4 6L6s in class AB at saturation would dissipate 180w at the tubes and 120w at the load, which would bring the total power to 300w, exactly the 300 that I assumed/heard earlier.

Ok I am done with tech talk, we need to get back on track with the mods themselves.

I suppose it's possible that the power amp will clip itself despite a clean signal being fed to it if the presence and resonance were both on 10. I didn't measure that. Do people play with those settings?

I play with the Resonance on 10 and the Presence on 7


EDIT: WOOHOO!!! Post #100

 

[Omega_Void]

...The speakers ... see a larger dissipation, but still less than the total power tube dissipation and at saturation Tube Dissipation=(1.5)Speaker Dissipation, so an amp with 4 6L6s in class AB at saturation would dissipate 180w at the tubes and 120w at the load, which would bring the total power to 300w, exactly the 300 that I assumed/heard earlier.

This is wrong. Look at it this way:

Output impedance of the amp is equal to speaker impedance, to allow maximum transfer of power. Therefore in class A dissipation in the power valves is equal to speaker dissipation.

The whole point of class AB is that it is more efficient, and allows the power consumed in the power tubes to be less than delivered to the load.

 

[Omega_Void]

In fact let's take this elsewhere...

 

[mburton21]

Hey guys, real noob question. I'm doing the 5150 mod myself and have one question:

http://brentwisdom.com/?p=167

When it mentions clipping the 15k resistor, that is literally saying just snipping it at each end and remove it?
I had no doubts about it until my friend said that it wasn't that simple. He can be quite retarded though haha.

Thanks in advance.

 

[Omega_Void]

When it mentions clipping the 15k resistor, that is literally saying just snipping it at each end and remove it?

Yes. Exactly that.

 

[mburton21]

Awesome, thanks.

 

[endofall]

Hey guys! I am going to try out the mid sweep mod on the 5150 II, and I was trying to locate where I would install this, I know on the 5150 you guys said it would be R22, but I am a little unsure what it would be on the 5150 II
https://dl.dropbox.com/u/7832758/peavey_5150-II.pdf

Any help would be great. Thanks!

 

[Omega_Void]

Hey guys! I am going to try out the mid sweep mod on the 5150 II, and I was trying to locate where I would install this, I know on the 5150 you guys said it would be R22, but I am a little unsure what it would be on the 5150 II

On the schematic you linked to it's R151.

Resistance value is 33k.

The 5-band colour code for that value is:
orange-orange-black-red-(?)

If it has four bands will be:
orange-orange-orange-(?)

This should help to verify you've got the correct one. The last band colour (?) does not refer to the value, so ignore it.

I guess the schematic I found was for a different model. I didn't look too closely, sorry.

 

[TheWinterSnow]

Hey guys! I am going to try out the mid sweep mod on the 5150 II, and I was trying to locate where I would install this, I know on the 5150 you guys said it would be R22, but I am a little unsure what it would be on the 5150 II
https://dl.dropbox.com/u/7832758/peavey_5150-II.pdf

Any help would be great. Thanks!

R28, the 47K resistor

On the schematic you linked to it's R151.

Resistance value is 33k.

Thats the Rhythm/Crunch channel tone stack.

I guess the schematic I found was for a different model. I didn't look too closely, sorry.

It was the 5150 combo.

 

[Omega_Void]

Thats the Rhythm/Crunch channel tone stack.

Oh, yeah! On the lead channel it's R28 in the 5150II schematic.

47k resistor is:
5-band code= yellow-violet-black-red-(?)
4-band code= yellow-violet-orange-(?)

Thanks for the catch.

 

[mburton21]

Goddammit, now my friend is telling me my wire is inappropriate for the job, 18 gauge hookup wire. Should I just ignore the shit out of this guy or what?

 

[Omega_Void]

Goddammit, now my friend is telling me my wire is inappropriate for the job, 18 gauge hookup wire. Should I just ignore the shit out of this guy or what?

In what way inappropriate?

Insulation voltage too low? That's possible, you need to be sure of that.

Is he saying 18-gauge isn't heavy enough? I doubt the bias supply draws more than 16 amps of current, somehow.

Should I just ignore the shit out of this guy or what?

You should at least insist that he frames his objection in terms of a specific attribute of your wire.

Is that it smells funny, maybe?

 

[mburton21]

This is some tough ass wire, it's pretty unlikely the insulation voltage is too low.

What's odd is that he has a steady flow of customers and seems to fumble through it all. I think he wants me to get him to do it and is therefore feeding me bullshit

 

[Omega_Void]

What's odd is that he has a steady flow of customers and seems to fumble through it all. I think he wants me to get him to do it and is therefore feeding me bullshit

That seems a plausible analysis... :Smug:

Re: insulation voltage. The bias circuit is low voltage anyway. Onlt if the wire is able to come into contact with parts of the high-voltage circuitry would it be a problem.

In my book (and IEC safety standards) "is able to come into contact with" includes situations where the wire has come loose at the ends and is flapping around.

For myself, I won't put wire into any enclosure unless the insulation voltage is known to be higher than any voltage found inside the unit. But it's your call.

Your friend sounds to be full of shit, though.

 

[mburton21]

HOLY SHIT!

I just did the mod and I'm running at 36mv. and this thing sounds sooooooo fucking good!

A+++++

Thanks for the help OV!

 

[TheWinterSnow]

little bump for the noobies

HOLY SHIT!

I just did the mod and I'm running at 36mv. and this thing sounds sooooooo fucking good!

A+++++

Thanks for the help OV!

running mine at 42mA, and its smokin'. Still could do more to reduce the fizz though.

 

[155]

A couple. Pics of the mid mod would be awesome

 

[TheWinterSnow]

A couple. Pics of the mid mod would be awesome

its simple, you are locating a 47k resistor by the mid pot, clipping it out and soldering a pot and resistor in its place. Drill a hole in the chassis where you want the pot, secure it in there and get ready to rock!

 

[155]

hmm seems simple enough, but how does it look? im an idiot when it comes to understanding the terminology, but a picture is worth a 1000 words.

 

[TheWinterSnow]

hmm seems simple enough, but how does it look? im an idiot when it comes to understanding the terminology, but a picture is worth a 1000 words.

can't say I've seen any pictures of the insides post mod, but heres an outside pic from Jerry @ FJA mods: