5150 mods... revealed w/ pictures

[glpg80]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

then shoot me a PM explaining what is incorrect? there is no reason to shoot me down if you are not going to correct me and explain why? i have no intentions to give wrongful information. if my theory is so far off, explain why it is so far off.

i enjoy talking electronics. if it is nothing but a hastle for you then by all means i dont mean to step all over your toes. the ignore button works all day every day on the forum. however i hope to hear from you because you have plenty of knowledge to share and i am all ears. if it is worded in a way that is wrong i apologize, however i can guarantee you the basic theory is taken care of. this is not a battle of the wits, not what this is at all. if you dont like talking electronics then fine - but dont go insulting me over it.

 

[jmgman69]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

Yeah.......but how does it sound playing BACK IN BLACK?

Thats the REAL question.........

Shit man,I thought you passed out already

 

[Mailman1971]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

Yeah.......but how does it sound playing BACK IN BLACK?

Thats the REAL question.........

Shit man,I thought you passed out already

I am here................ready for ANYTHING!!

 

[jmgman69]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

Yeah.......but how does it sound playing BACK IN BLACK?

Thats the REAL question.........

Shit man,I thought you passed out already

I am here................ready for ANYTHING!!

 

[Mailman1971]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

Yeah.......but how does it sound playing BACK IN BLACK?

Thats the REAL question.........

Shit man,I thought you passed out already

I am here................ready for ANYTHING!!

A man is only as good as his WORD correct?



I back up everything I SPEW!

 

[cliffc8488]

Okay, here goes....

the amount of voltage fed back determines the amount of gain reduction and the amount of distortion reduction, as well as the effective output impedance. this is the purpose of negative feedback - stability (and added tonal shaping by cutting frequencies where global NF is concerned) what is being done here is closely linked to negative feedback, but is actually more along the terms of frequency response shaping. with NF - The more voltage fed back, the less distortion, the lower the effective output impedance, the higher the dampening.

The lowpass response is entirely due to negative feedback. The negative feedback only happens at higher frequencies which reduces the gain at those frequencies (via A/(1 + AB)). In the case of a triode the output impedance actually increases because it is a current source with series-shunt feedback. This is basic feedback theory. You're spouting a bunch of generalizations about feedback without even understanding the basics of how it works.

same thing i mentioned, only in a much simpler explanation. appreciate the clarification Cliff! the plate voltage however is not what is out of phase, the original AC signal imposed onto the tube is what alters the DC bias of the tube internally creating a mirrored output at a higher voltage. current flows from ground to hot, not the opposite way. therefore it is the AC wave that is out of phase.

The plate voltage IS out of phase. A common-cathode triode stage causes a signal inversion. The DC bias is just that, bias. The whole point of bias is that it is a constant value. If the bias were altered by the AC signal then it wouldn't be bias or DC, now would it? Again, basic theory here. Current flows (in "hole propagation convention") from a node with a higher potential to a node with a lower potential. "Ground" is irrelevant and "hot" is meaningless in this context.

once again - DC current does not flow through a capacitor. AC current will be sent back onto the grid in an out-of-phase fashion which is where the dark term comes into play. because the DC bias is not altered or changed its a frequency response alteration. the capacitance does increase the internal grid capacitance because it is in parallel with the triode at this point - doubling the capacitance depending on the tube.

Of course DC current doesn't flow through a capacitor. I never said it did. A capacitor is a reactive element whose impedance decreases with frequency. No idea what "the dark term" is.

why would it not decrease the capacitance since the AC voltage signal is traveling to ground (or trying) and the capacitor is effectively in series with the bypassed cathode capacitor at that point? explain this for me if you could. i do agree - bypassing it would do no good unless the cathode is bypassed because your AC signal is going to to be imposed on the cathode anyway. how negative the grid is biased by the cathode resistor by making the cathode more positive than the grid dictates how much headroom you have before grid current flows and the tube's internal plate coating wears off. hence why analog valves have to be carefully biased in comparison to SS equivalents - tubes dont like the abuse too much .

A capacitor from grid to cathode will increase the effective grid-to-cathode capacitance simply because it is connected from grid to cathode. I can't explain it any simpler than that. I think you're not understanding the basic concept of tube triodes. Cathode stripping has nothing to do with grid conduction, which, to my knowledge, is not destructive at the limited currents available, although sounds bad. Tubes can withstand a heck of a lot more abuse than SS devices. Apparently you've never popped a MOSFET gate (just by handling it).

If you understand the basics then answer this simple question: In an amplifier stage with an open-loop gain of 100, how much negative feedback (beta) is required to lower the gain by 6 dB?

Bonus question: in a 12AX7 triode stage with a 1K cathode resistor, what is the approx. capacitor value required to give a zero frequency of 100 Hz?

Bonus question #2: How do you catch a unique rabbit? How do you catch a tame one?

 

[Gainfreak]

Okay, here goes....

Bonus question #2: How do you catch a unique rabbit? How do you catch a tame one?

Don't know #1 LMAO But 2 is an Oldie but goodie LMAO


How do you catch a unique rabbit? Unique Up On It.

How do you catch a tame one..........Tame Way,

 

[Motorpud]

Okay, here goes....

Bonus question #2: How do you catch a unique rabbit? How do you catch a tame one?

Don't know #1 LMAO But 2 is an Oldie but goodie LMAO


How do you catch a unique rabbit? Unique Up On It.

How do you catch a tame one..........Tame Way,

 

[glpg80]

Okay, here goes....

Bonus question #2: How do you catch a unique rabbit? How do you catch a tame one?

Don't know #1 LMAO But 2 is an Oldie but goodie LMAO


How do you catch a unique rabbit? Unique Up On It.

How do you catch a tame one..........Tame Way,

jesus that's hilarious

 

[droptrd]

Ive had the 10pf mod done to my 5150 for a little bit now and I really like it. Got rid of the fizz and made the mids more present and colorful. I can still turn up the presence and treble for more highs and sizzle but the peach fuzz is all gone.

Today I did the R9 mod. Started with the 68K and worked my way up. 68K sucked the ballz and life out of the amp. I ended up at 150K. Its tight but doesnt suck out too much gain. Seems the lower you go the tighter it gets but it also loses gain as well. I might go a little higher but IDK. Gonna play it like this for a while. Once I get that settled Im gonna do the C15 and C26 mods.

So far these mods are offering great improvements to the amp without changing the core tone.

 

[vultures]

I did not like it

 

[droptrd]

Decided to try the bias mod. Correct me if im wrong - Looks like R68 (currently 15K) replace it with a 10K trim pot with a 5K resistor. Right? Is a 1/4 watt rating OK for the pot and resistor? Or does it need to be 1/2 watt or 1 watt?

 

[droptrd]

I tried R9 all the way up to 350K. I liked it better around 300K. But in the end I took the mod out completely. I made the mistake of A/Bing it with my Tverb. The 5150 sounded like an AM radio by comparison. I also took out the 10pf mod too, for 2 seconds and then put it back in. That ones the keeper for me. Still want to do the bias mod though.

Ran the 5150 and the Tverb together today also.........Warning, may evaporate small children and animals Finally found a good use for the Tverbs scoopy Red/Modern gain ch Paired great with mid heavy peavey

 

[diagrammatiks]

Hey so I'm thinking about picking up a 5150 to play around with and mod.

My question is...do the mods make the amp sound more like a slo or more like something else entirely?

 

[diagrammatiks]

Hey so I'm thinking about picking up a 5150 to play around with and mod.

My question is...do the mods make the amp sound more like a slo or more like something else entirely?

The mods make the 5150 sound like a tighter 5150 with less buzz/fizz.



To me the 5150 is simlar to the SLO, but with a shit ton more gain.

Hmm I was gonna do the mods drop some onetics in there and have a slo and an el34 slo/5150. Hmm gas is getting me again.

 

[endofall]

Rock God


Joined: Sun, Oct 08, 2006 9:06am
Posts: 8131 I spoke to Mark Cameron tonight and he said it was okay to reveal the mods he gave me for the 5150.... so here is what has been done to my amp:

V5B(middle preamp tube add 10pf silver mica cap to pins 7 and 8. This is the main mod!!!
R9: piggyback a resistor on top of the 1 meg resistor. I used a 120k based on feel. You can try out 68k, 100k, 120k, 150k, etc. This tightened up the map a lot!
C26: cut one leg for less bottom end on the rhythm channel
C15: bypass cap for better "feel"

I tried tinkering with R15 and using Marshall vlaues, but it took too much away from the original sound. The 39k is the SLO value as well.

There you have it. Have fun getting a killer 5150 sound

Thanks Mark!!

Could someone tell me how to do this to the 5150 II?
Thanks

 

[JeffGT]

Have a question about the C26 mod...does it only affect the clean channel and not the lead? Also, where is C26???? I can't tell from the picture.
thanks!

 

[JeffGT]

I've got it torn apart now ready to dig in.

Dave,thanks a bunch for the help, very much appreciated!!

 

[JeffGT]

uggg, one more question if I may. I can't get to the leads of C15....is it ok to chip away a little of the orange casing at the base to get to them without screwing up the cap? How does bypassing it change the feel...more dynamic or something?

Dave, thanks again...I owe you a beer or 3

 

[JeffGT]

well, I got the adjustable bias installed first (I hadn't done that yet either) and did the 10pf across pins 7 & 8 of the 3rd pre tube. One problem I had was when I went to bias the amp (with a new Weber bias riite i just picked up for this specifically), the power tubes were pretty mismatched. At about 500 plate voltage, when I set the first tube to an idle current of 36, the others were lower, a couple in the mid 20's, so I need some new output tubes.

I haven't done any of the other mods yet. From what I recall of the amp, the high end is definitely better. It's still pretty hissy tho, maybe something I can't get away from. Would the 120k resistor on the other pre tube have any effect on the noise issue?

I'll probably clip the cap on one end to lose some bass on the clean channel. I think it's better to but probably still to bassy when I get the lead set where I like. I'm not much on modern chugga chugga detuned type stuff...more older hard/progressive rock I guess, but still want good low end on the lead side. Doesn't have to be super tight tho.

Thanks again Dave!