5150 mods... revealed w/ pictures

[glip22]

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!
(Please note that JerryP gave me some other ideas, but I didnt use them and I wont reveal )

What does the 10pf change about the sound on it? And the R9, does it tighten up the higher you go? I'm very interested, been looking for ways to tighten up my 5150's sound.

Thanks a lot for posting! I feel giddy thinking about changing up the amp.

The 10pf will help with parasitic oscillations by shunting some of the higher frequencies. This is probably why it helps with the amps's fizz. Its called a cathode bypass cap. I just istalled a 47pf across the plates of my PI in a JMP. Also installed a .1uf poly 600v on the last pre filter cap aross hot to ground. If I can do these mods on any amp I have had it's always been good.

 

[droptrd]

Free mods rule

 

[JakeAC5253]

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!
(Please note that JerryP gave me some other ideas, but I didnt use them and I wont reveal )

What does the 10pf change about the sound on it? And the R9, does it tighten up the higher you go? I'm very interested, been looking for ways to tighten up my 5150's sound.

Thanks a lot for posting! I feel giddy thinking about changing up the amp.

The 10pf will halp with parasitic oscillations by shunting some of the higher frequencies. This is probably why it helps with the amps's fizz. Its called a cathode bypass cap.

Similar to a Collector to Base cap in a stompbox gain stage?

 

[LP Freak]

 

[glpg80]

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!
(Please note that JerryP gave me some other ideas, but I didnt use them and I wont reveal )

What does the 10pf change about the sound on it? And the R9, does it tighten up the higher you go? I'm very interested, been looking for ways to tighten up my 5150's sound.

Thanks a lot for posting! I feel giddy thinking about changing up the amp.

The 10pf will halp with parasitic oscillations by shunting some of the higher frequencies. This is probably why it helps with the amps's fizz. Its called a cathode bypass cap.

Similar to a Collector to Base cap in a stompbox gain stage?

yes.

however, it is not called a cathode bypass capacitor. a cathode bypass capacitor acts as a shunt capacitor for AC around the cathode resistor increasing the output gain of a transistor at a -3dB Fstop frequency determined by the value of that capacitor. this is not the same purpose of this mod. the purpose of the 10pF capacitor is to shunt grid AC around the amplification stage and to the cathode resistor. this 10pF is also in parallel with the internal plate-to-grid capacitance called the miller capacitance which changes tube to tube, brand to brand, type to type. it is also a negative feedback loop at the same time feeding current into the grid in a controlled manner - somewhat simillar to how krank revolutions work.

 

[Digital Jams]

Oh man very cool post, that looks like 30 minutes worth of work.

 

[gbsmusic]

It's like speaking Chinese to me....but looks good on paper?

 

[glip22]

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!
(Please note that JerryP gave me some other ideas, but I didnt use them and I wont reveal )

What does the 10pf change about the sound on it? And the R9, does it tighten up the higher you go? I'm very interested, been looking for ways to tighten up my 5150's sound.

Thanks a lot for posting! I feel giddy thinking about changing up the amp.

The 10pf will halp with parasitic oscillations by shunting some of the higher frequencies. This is probably why it helps with the amps's fizz. Its called a cathode bypass cap.

Similar to a Collector to Base cap in a stompbox gain stage?

yes.

however, it is not called a cathode bypass capacitor. a cathode bypass capacitor acts as a shunt capacitor for AC around the cathode resistor increasing the output gain of a transistor at a -3dB Fstop frequency determined by the value of that capacitor. this is not the same purpose of this mod. the purpose of the 10pF capacitor is to shunt grid AC around the amplification stage and to the cathode resistor. this 10pF is also in parallel with the internal plate-to-grid capacitance called the miller capacitance which changes tube to tube, brand to brand, type to type. it is also a negative feedback loop at the same time feeding current into the grid in a controlled manner - somewhat simillar to how krank revolutions work.

Yes, I see it is added to one triode's grid and cathode. The shunt usually goes across the plates or plate to cathode.

 

[sled]

So has anyone tried it yet?



I am still in awe how versatile the amp is now

I'm reluctant to do much to my 5150. I use it for recording and it really records very well. that said I'm going to do two things...

I have bypassed C15, a mod I've wanted to do for some time.

I thought I had a 10pf Silvered Mica but I had to order some. If they're here by Wednesday I'll do that Wednesday.

I may play with R9 sometime later but not right now.

Maybe my definition of loose is different than most others but I can dial my 5150 very tight and loose. I'm definitely not wanting it approaching SLO territory.

 

[droptrd]

Ive only done the 10pf mod. Its noticable. Took some presence off the lead ch and made the mids more dimensional if that makes sense. Dont know how else to describe it.

I dont know if ill try the other mods as im not looking to "tighten" the amp up any more

but anyway, so far i really like the mod

 

[JakeAC5253]

I wonder what would happen if instead of putting a single 10pF cap on the one stage, if you put a ~5pF cap on all stages?

 

[Mailman1971]

Ive only done the 10pf mod. Its noticable. Took some presence off the lead ch and made the mids more dimensional if that makes sense. Dont know how else to describe it.

I dont know if ill try the other mods as im not looking to "tighten" the amp up any more

but anyway, so far i really like the mod

yeah, the 10pf cap changes the presence a little bit...but for the better IMO. For me, I wanted the amp tighter so I didn't have to use a pedal to keep it together when cranking the resonance. As it is now, I can crank the gain on the rhythm channel and not fart out. Slap a pedal in front and the amp slays. Stock, the 5150 is a cool amp, with these mods, it is a killer amp.

Damn Dave......have a 5150 on the way to FJA to mod.......
now I want to pick up a 2nd one to do these mods too......
Your amp sounds great!!

Dan

 

[madrigal77]

I don't know a thing about this, and there really isn't a good amp tech in my town. Do you think if I were to bring my 5150 into an electronic repair shop with the schematic and these instructions, that they would be able to do it?

 

[droptrd]

Yes its very easy

 

[madrigal77]

Yes its very easy

Ok cool. Then I can get this done for like 20 bucks. Win!!!

 

[madrigal77]

Yes its very easy

Ok cool. Then I can get this done for like 20 bucks. Win!!!

I think you should spend the $20 on an iron and do it yourself. The bottom of the preamp board is visible and V5 is wide open. I think I will take a few pictures to show how easy it is...

Trust me. Me with a soldering iron is NOT a good idea, lol. I once tried to install pickups by myself; didn't work out to well and I ended up frying a pot and having to bring it to a guitar tech anyway. I would probably end up lighting the whole board on fire somehow if I tried this, lol. I'd rather just spend 20 bucks and have someone that isn't so clumsy and knows what they are doing do it.

Also. I have to say, that silver mica mod sounds like it gives similar results as Jerry P's "clarity mod". I wonder if it's the same thing...

 

[madrigal77]

Ive only done the 10pf mod. Its noticable. Took some presence off the lead ch and made the mids more dimensional if that makes sense. Dont know how else to describe it.

I dont know if ill try the other mods as im not looking to "tighten" the amp up any more

but anyway, so far i really like the mod

yeah, the 10pf cap changes the presence a little bit...but for the better IMO. For me, I wanted the amp tighter so I didn't have to use a pedal to keep it together when cranking the resonance. As it is now, I can crank the gain on the rhythm channel and not fart out. Slap a pedal in front and the amp slays. Stock, the 5150 is a cool amp, with these mods, it is a killer amp.

Damn Dave......have a 5150 on the way to FJA to mod.......
now I want to pick up a 2nd one to do these mods too......
Your amp sounds great!!

Dan

These mods don't take away from the fact that Jerry has some killer mods for the 5150. You can't go wrong with an FJA modded 5150

Yeah, I would LOVE to have mine done by Jerry, but shipping alone from where I am in Canada would come to 250-300 bucks, so that kind of makes that idea a no go. So if I can find out what these mods are and have them done locally, that's awesome.

 

[Mailman1971]

Ive only done the 10pf mod. Its noticable. Took some presence off the lead ch and made the mids more dimensional if that makes sense. Dont know how else to describe it.

I dont know if ill try the other mods as im not looking to "tighten" the amp up any more

but anyway, so far i really like the mod

yeah, the 10pf cap changes the presence a little bit...but for the better IMO. For me, I wanted the amp tighter so I didn't have to use a pedal to keep it together when cranking the resonance. As it is now, I can crank the gain on the rhythm channel and not fart out. Slap a pedal in front and the amp slays. Stock, the 5150 is a cool amp, with these mods, it is a killer amp.

Damn Dave......have a 5150 on the way to FJA to mod.......
now I want to pick up a 2nd one to do these mods too......
Your amp sounds great!!

Dan

These mods don't take away from the fact that Jerry has some killer mods for the 5150. You can't go wrong with an FJA modded 5150

Your right Brother.....
but its a different flavor.........
and if I can do it ........

hell ya!!

 

[droptrd]

 

[Mailman1971]

I added pictures to show how easy it is....

Thanks Dave.....I have a 2nd 5150 lined up coming in........


gonna try your mods on it.......
Should be fine....