The Two Component 5150 Mod (Details/Demos Inside)

[faisalbaig]

Good to know. Once i have my 5150 sorted out, i'll try this R101 mod!! Sounds promising!

 

[JakeAC5253]

Good to know. Once i have my 5150 sorted out, i'll try this R101 mod!! Sounds promising!

Yeah sorry to hear about that. If you do get your 5150 fixed, post back and let me know if you like it.

 

[chumbucket]

How come you didn't try the Cameron mods?

 

[JakeAC5253]

How come you didn't try the Cameron mods?

I did. I had the 10pF cap soldered to pins 6 and 7 of V5 for a long long time, sounded good to me. I also tried the R9 mod values that Cameron suggested on my own amp, but the suggested values I found to be far too low for my own tastes. I found that it lowers the gain and brings out the high mids. Great if this is what you want from the amp, didn't work for me. I liked a hard resistor value of 470k (equivalent to putting a 1M resistor in parallel with the 1M stock resistor for those who did the mod this way. When I found the R101 component, I wanted to have the fully stock amp available by switch in order to best tweak the mod. As a result of this, the 10pF cap was subsequently removed so that I could have fully stock/modded amp switchable.

As of now the only thing I desire from the amp is perhaps a bit more clean headroom from the power section. I have read that swapping the CF tube from a 12ax7 to some other tube type can have a great effect on this. Haven't tried it yet though.

 

[Anonymous]

Hey bro did u piggyback or replace the valve on r101 with a 470k resistor??? And on the r9 mod I used a 470k thinking about trying something higher.. Like a 1meg.. But I didn't like the anything lower.. Took away from amp.. I'm thinking about removing the r9 mod all together, I like the gain/fizziness of the amp!! That's why I bought it.. If u have a pic of the r101 mod or know of any other mods for the 5150 please let me know!! Thanks Thanks

 

[faisalbaig]

680k in R9 here, sounds awesome and still sounds like a 5150!

 

[JakeAC5253]

Hey bro did u piggyback or replace the valve on r101 with a 470k resistor??? And on the r9 mod I used a 470k thinking about trying something higher.. Like a 1meg.. But I didn't like the anything lower.. Took away from amp.. I'm thinking about removing the r9 mod all together, I like the gain/fizziness of the amp!! That's why I bought it.. If u have a pic of the r101 mod or know of any other mods for the 5150 please let me know!! Thanks Thanks

I used resistor replacement for both components. 1M is the stock value for R9, so if you are using the parallel resistors (piggyback) method, then 1M works fine, but it doesn't make much sense for replacement. Just making sure you aren't going to replace equal value resistors.

If you want other mod ideas, the main Cameron mod, 10pF cap on pins 6-7 of the middle tube, works well. That mod is known in industry as a Miller cap, and it's used to increase the miller capacitance of that stage, just darkens the output a small amount. Because of this mod simply summing with the tube's already existing miller capacitance, some engineers on other forums have stated that it is about equal to the difference from tube to tube due to minor manufacturing differences. Still a good mod though.

A spin off this mod that wouldn't be tube dependent, would be to put a high voltage cap in parallel with the 220k bias resistor on that stage (R96). The cap can be between 47pF and 220pF for varying degrees of effect. I would use caps with a voltage rating of at least 1kv (1000v). This will just smooth the high end and make the preamp output more linear. Compensate for the effect using the presence control and you should get a more balanced sound overall.

Any new changes? ...I know you can't leave well enough alone

lol

Actually, I haven't had much time to play lately, but since tweaking the mod once (470k - R9, 220k - R101) I haven't had the need to really alter anything else. It's a good sound, but I am glad to have the stock amp at my disposal as well. With the R101 mod, the amp sounds better at lower volumes as well, so that's a little perk for us home players.

 

[Anonymous]

i have the 10pf silver mica on 7 and 8.. should i try 6 and 7???? what is the difference?? psychodave told me but i deleted the message so i forgot.. could i do 6&7 and 7&8 at the same time??? which one do you like the most?? i might try 6&7 here and see which one i like better.. i want the hissing/noise to be very little but still have a good amount of gain.. i like the fizziness that is why i used a 470k at R9 i might try a 670k or might take it out all together...once it was gone i think i actually like it better.. what would happen if i put a cap on 6&7 and 7&8 on both of them..



sorry but on the r9 mod im sort of puzzled, so do i jsut piggyback or replace it??? sorry if this is a dumb question but i jsut want to make sure before messing with amp.. and what do you mean by make the pre amp output more linear??? but thanks for the help

 

[JakeAC5253]

i have the 10pf silver mica on 7 and 8.. should i try 6 and 7???? what is the difference?? psychodave told me but i deleted the message so i forgot.. could i do 6&7 and 7&8 at the same time??? which one do you like the most?? i might try 6&7 here and see which one i like better.. i want the hissing/noise to be very little but still have a good amount of gain.. i like the fizziness that is why i used a 470k at R9 i might try a 670k or might take it out all together...once it was gone i think i actually like it better.. what would happen if i put a cap on 6&7 and 7&8 on both of them..



sorry but on the r9 mod im sort of puzzled, so do i jsut piggyback or replace it??? sorry if this is a dumb question but i jsut want to make sure before messing with amp.. and what do you mean by make the pre amp output more linear??? but thanks for the help

Not a stupid question, but it is difficult to answer. You could do either really. If it helps, the formula for calculating the impedance of two parallel resistors is (R1 * R2) / (R1 + R2) with all resistors converted to the same prefix.

For the example of the stock 1M resistor with an additional 1M resistor wired in parallel to it, the math works out like this...

1M * 1M = 1M
--------------
1M + 1M = 2M
=
.5M (500k)

500k is the effective single resistor impedance that the circuit sees. In other words, two 1M resistors in parallel and a single 500k resistor are electrically the same. Plug in any other resistor size into the equation for R2 and see how it works out. You could use resistors in parallel and the equation above to narrow down a value that you like and then later replace it with a single resistor of that value. Doing this will cut down on board wear.

The 10pF cap from pins 6 to 7 should just have more effect. If all you want to do is change the voicing without changing the amount of gain, then don't worry about the 10pF cap mod, it's not affecting the amount of gain. The R9 and R101 mods affect the amp's gain staging, and have a discrete effect on the amount of gain. When modified in the correct proportions though, they balance out, much like I did with my own amp. To alter the amp's voicing without affecting the gain, i.e. to soften the fizz/high end a bit, then the Cameron 10pF mod, or the R96 cap mod I mentioned above, will do this just fine. By linearize, I just mean to bring the high end into proportion with the mids and lows of the tone.

 

[Anonymous]

i have the 10pf silver mica on 7 and 8.. should i try 6 and 7???? what is the difference?? psychodave told me but i deleted the message so i forgot.. could i do 6&7 and 7&8 at the same time??? which one do you like the most?? i might try 6&7 here and see which one i like better.. i want the hissing/noise to be very little but still have a good amount of gain.. i like the fizziness that is why i used a 470k at R9 i might try a 670k or might take it out all together...once it was gone i think i actually like it better.. what would happen if i put a cap on 6&7 and 7&8 on both of them..



sorry but on the r9 mod im sort of puzzled, so do i jsut piggyback or replace it??? sorry if this is a dumb question but i jsut want to make sure before messing with amp.. and what do you mean by make the pre amp output more linear??? but thanks for the help

Not a stupid question, but it is difficult to answer. You could do either really. If it helps, the formula for calculating the impedance of two parallel resistors is (R1 * R2) / (R1 + R2) with all resistors converted to the same prefix.

For the example of the stock 1M resistor with an additional 1M resistor wired in parallel to it, the math works out like this...

1M * 1M = 1M
--------------
1M + 1M = 2M
=
.5M (500k)

500k is the effective single resistor impedance that the circuit sees. In other words, two 1M resistors in parallel and a single 500k resistor are electrically the same. Plug in any other resistor size into the equation for R2 and see how it works out. You could use resistors in parallel and the equation above to narrow down a value that you like and then later replace it with a single resistor of that value. Doing this will cut down on board wear.

The 10pF cap from pins 6 to 7 should just have more effect. If all you want to do is change the voicing without changing the amount of gain, then don't worry about the 10pF cap mod, it's not affecting the amount of gain. The R9 and R101 mods affect the amp's gain staging, and have a discrete effect on the amount of gain. When modified in the correct proportions though, they balance out, much like I did with my own amp. To alter the amp's voicing without affecting the gain, i.e. to soften the fizz/high end a bit, then the Cameron 10pF mod, or the R96 cap mod I mentioned above, will do this just fine. By linearize, I just mean to bring the high end into proportion with the mids and lows of the tone.

okay starting to make sense.. going to try the r101 mod 2morrow and see what happens.. then going to remove the r9 mod, to see if i like it.. but the 10pf cap mod is a must i think.. thanks bro, and if you come up with anything else lmk...