5150 R9 mod?

[Nate808]

I was searching the net for this mod and this forum had the goods but, Does anyone have a good pic to locate R9 (1m) on a first run 5150? It's supposed to be a 1meg to ground off of pin 2 on V2a . I tried to trace it off the tube but I can't find it? Could my '91 be different?

 

[RedPlated]

What is this mod supposed to do?

I just picked up an early original 5150 today. Pretty nice amp, but has some fizziness and lack of tight bottom end. I considered rolling preamp tubes, but decided to hit it with a Tubescreamer just to boost it. Wow. Thing sounds AMAZING now. Very tight and mean. Loving the amp...

 

[Nate808]

Do the 10pf cap trick on pins 6&7 of V3. It helps the fizz a lot!

 

[RedPlated]

Do the 10pf cap trick on pins 6&7 of V3. It helps the fizz a lot!

Right on, I'll check that out.

I can typically get a loose/ fizzy amp to tighten up on its own with the right selection of preamp tubes. I'm very interested to experiment with this one. It's got matched JJ 6L6's in it.

 

[Dopethrone]

Hope this helps!


you can measure this one in circuit also with a multimeter.

that pic there shows the mod.

the r9 1m resistor, as you're looking at the back of the board (with the lugs facing you and the tubes facing out) will be the 2nd tube from the right, and the first half of the v2 tube (also on the right side, as you see in the pic).

viewtopic.php?f=3&t=80183&hilit=5150
this thread goes into some good detail.
there are other mods and info i posted a while back when i modded the crap out of my 5150 posted under "yeti"

 

[Nate808]

Well that's what I was looking at? My amp must have been messed with as it does not have a 1m here?

 

[sg guy]

-all PEAVEY's suffer from the same thing,.... they come biased ice cold from the factory,... even with the trim pots maxxed there still not in range,... some of the HIGH GAIN PEAVEY's come with a EL34/6L6 selector switch,... If your running 6L6's, put the selector switch in the EL34 mode and adjust your bias, if you don't have the tube selector switch you'll need a bias mod-(change resistor value on the bias pots)-

-most find this to be the only mod needed-

 

[5150clone]

-all PEAVEY's suffer from the same thing,.... they come biased ice cold from the factory,... even with the trim pots maxxed there still not in range,... some of the HIGH GAIN PEAVEY's come with a EL34/6L6 selector switch,... If your running 6L6's, put the selector switch in the EL34 mode and adjust your bias, if you don't have the tube selector switch you'll need a bias mod-(change resistor value on the bias pots)-

-most find this to be the only mod needed-

If I'm not mistaken I think the cold bias is part of the design, I thought I read that somewhere

 

[Nate808]

Oh ya I did a bias pot years ago!

 

[Nate808]

Looking at that pic. It looks look that is on pin 3 (cathode) not pin 2 which R9 is on this schematic. Is this wrong ?

http://rudn2.nodevice.com/preview/big/352/352912-2.jpg

 

[Nate808]

Can anyone confirm this? I think the pic above is on pin 3 not 2. The mod is supposed to be on R9 (1meg) but this looks to parallel on the cathode not grid.

 

[Dopethrone]

-all PEAVEY's suffer from the same thing,.... they come biased ice cold from the factory,... even with the trim pots maxxed there still not in range,... some of the HIGH GAIN PEAVEY's come with a EL34/6L6 selector switch,... If your running 6L6's, put the selector switch in the EL34 mode and adjust your bias, if you don't have the tube selector switch you'll need a bias mod-(change resistor value on the bias pots)-

-most find this to be the only mod needed-

Excellent point. i like mine biased cold as the feel of it is more to my liking.
bias mod is an easy fix too.

the original 5150 block and script logo do need the bias mod added though, as it wasnt part of the OEM design.

 

[Dopethrone]

Can anyone confirm this? I think the pic above is on pin 3 not 2. The mod is supposed to be on R9 (1meg) but this looks to parallel on the cathode not grid.

It is on pin 3, you are correct. not sure why i posted that pic, lol.

look at the front of the board where it's populated.. follow pin 2. you can see the lugs from the back where the 1m resistor jumpers from v2a pin 2 to ground (up top).


make sure your amp is off and unplugged from the wall, you dont wanna get bit fucking around in there.

 

[Nate808]

I gotta re-check my amp. Those 2 resistors in my amp might have been changed because the schemo says they should be a divider with a 470k and a 1 meg. I tested them and that's not what I saw? I will open it up again tomorrow. I did end up ordering a Mercury choke to install. So I'm excited to get that and put it in.

 

[sg guy]

-I like my women & my amps hot!!-

 

[Dopethrone]

I gotta re-check my amp. Those 2 resistors in my amp might have been changed because the schemo says they should be a divider with a 470k and a 1 meg. I tested them and that's not what I saw? I will open it up again tomorrow. I did end up ordering a Mercury choke to install. So I'm excited to get that and put it in.

theres a certain way to rewire the power and standby switches after you put the choke in.

google "5150 choke standby" should come up on one of the ultimate metal boards IIRC.

if i can dig it up for you i will later on!

Best of luck!

 

[Nate808]

Ok ok, so after scratching my head on this I realized that the mod on R9 was on pin 7 not pin 2 as the schematic shows. Drove me crazy! Anyway I put a 200k pot on r9 and I did not like it. It seemed to have taken some mojo away. I couldn't find a sweet spot so I took it out.