Peavey EVH 5150 Choke mod

S

srv3089

New member
I am sure this has been asked before but I could not find the answer so....I just wanted to know that when doing the choke mod on the 5150 is it absolutely mandatory to change the screen resistors or can you use the stock ones that are in there? What is the reason for changing these resistors anyways?....Thanks to all for the help and info.
 
Do a google search on peavey 5150 screen grid resistor and you'll see over and over again the stock resistors have a tendency to fail. If yours are ok then they don't have to be replaced but be aware that they might go south on you and that always happens at the worst possible time.
 
I understand they fail but I see people changing the value of the resistor when doing the Choke mod and just wanted to know if is it because you have to change them to a different value for the choke to work properly or if it is just because of a just in case type of thing and the stock resistors are perfectly fine with to use with the choke..Thanks.
 
Generally speaking, yes you can try the choke without changing the screen resistors. But if they are known to be shitty and fail for no reason then change them. They are supposed to fail during a bad tube failure.
 
OK Thanks....One more question how do the Henry values affect the amp...is it tone, response, attack or what is it?....I am looking at a choke and I know that the value that is used for a 5150 is a 10H but I found a 7H lying around my parts box and just want to make sure this is OK to use...Thanks.
 
If it was pulled from another amp it should be fine. You could check the current rating. Replacements for a Fender Twin are rated at 90ma FWIW. Not too sure about what different Henry values will do, probably just make the power supply sag feel a little different.
 
Thanks to all for the help and info but have decided to put this off for a later project....power board is riveted in and don't trust myself to drill it out without causing damage will have some one add the choke for me later on down the road.but still if anyone can tell me How the Henry value will affect the amp greatly appreciated....Thanks :)
 
Hi guys, first post here. Been biding my time until I figured I could make a worthwhile contribution, so here goes:
To answer the original question, yes I would HIGHLY recommend you replace the screen grid resistors when adding a choke to these amps. The original screen resistors are 100ohm, and should be replaced with 470ohm. This is because the resistor that is removed and replaced by the choke is a large 10watt, 470ohm dropping resistor, and it feeds all 4 tube's screens in series with the 100ohm on each tube socket. The DC resistance of the choke will probably be around 100ohms give or take. 6L6's like to see minimum 470ohms on the screens or you can run into problems, so if you don't up the screen resistors, you'll be in the neighbourhood of 200ohms for the screens and that's too low. This is doubly important if you don't know the DC resistance of the choke when your using a found one from the scrap parts bin.

I've done a choke mod on both my 5150/6505's, and it's not that big a deal. My block letter had the rivets, and yeah, just drill'em out. My 6505 had screws, so no problem. I put a 3 henry in the block letter and a 10 henry in the 6505. The 3 henry is a little saggier, and the 10 is nice and tight. The 3 henry is kinda cool, but the 10 henry is probably better for all the stuff most guys use these amps for. Any higher than 10 would be REALLY stiff. So lower henry's = saggier, higher henry's = stiffer.

Also, HIGHLY recommend you have your tech move the position in the circuit of the standby switch. Stock, it's after the large 470ohm dropping resistor, but the standby should allways come be before a choke in an amp circuit. You just have to move 1 and cut 1 wire if I remember correctly, and your tech should be on it no problem.

Hope that helps!
 
fusedbrain":3mrs5ern said:
Hi guys, first post here. Been biding my time until I figured I could make a worthwhile contribution, so here goes:
To answer the original question, yes I would HIGHLY recommend you replace the screen grid resistors when adding a choke to these amps. The original screen resistors are 100ohm, and should be replaced with 470ohm. This is because the resistor that is removed and replaced by the choke is a large 10watt, 470ohm dropping resistor, and it feeds all 4 tube's screens in series with the 100ohm on each tube socket. The DC resistance of the choke will probably be around 100ohms give or take. 6L6's like to see minimum 470ohms on the screens or you can run into problems, so if you don't up the screen resistors, you'll be in the neighbourhood of 200ohms for the screens and that's too low. This is doubly important if you don't know the DC resistance of the choke when your using a found one from the scrap parts bin.

I've done a choke mod on both my 5150/6505's, and it's not that big a deal. My block letter had the rivets, and yeah, just drill'em out. My 6505 had screws, so no problem. I put a 3 henry in the block letter and a 10 henry in the 6505. The 3 henry is a little saggier, and the 10 is nice and tight. The 3 henry is kinda cool, but the 10 henry is probably better for all the stuff most guys use these amps for. Any higher than 10 would be REALLY stiff. So lower henry's = saggier, higher henry's = stiffer.

Also, HIGHLY recommend you have your tech move the position in the circuit of the standby switch. Stock, it's after the large 470ohm dropping resistor, but the standby should allways come be before a choke in an amp circuit. You just have to move 1 and cut 1 wire if I remember correctly, and your tech should be on it no problem.

Hope that helps!
Click to expand...

Thanks for that...That tells me that this choke will work as it is a 7H 100 Ohm 150mA.... But I am still gonna leave this for a project down the road because like I said I just don't trust my self to drill that out without causing damage....Is there any choke that would be just a straight drop in with out changing the screen grid resistors?...I know I had a Marshall JCM2000 DSL 100 and added a choke to that with no modifications other than the choke itself.....Just hoping there would be this kind of option for the 5150....Thanks. :)
 
fusedbrain":kmj8x026 said:
Hi guys, first post here. Been biding my time until I figured I could make a worthwhile contribution, so here goes:
To answer the original question, yes I would HIGHLY recommend you replace the screen grid resistors when adding a choke to these amps. The original screen resistors are 100ohm, and should be replaced with 470ohm. This is because the resistor that is removed and replaced by the choke is a large 10watt, 470ohm dropping resistor, and it feeds all 4 tube's screens in series with the 100ohm on each tube socket. The DC resistance of the choke will probably be around 100ohms give or take. 6L6's like to see minimum 470ohms on the screens or you can run into problems, so if you don't up the screen resistors, you'll be in the neighbourhood of 200ohms for the screens and that's too low. This is doubly important if you don't know the DC resistance of the choke when your using a found one from the scrap parts bin.

I've done a choke mod on both my 5150/6505's, and it's not that big a deal. My block letter had the rivets, and yeah, just drill'em out. My 6505 had screws, so no problem. I put a 3 henry in the block letter and a 10 henry in the 6505. The 3 henry is a little saggier, and the 10 is nice and tight. The 3 henry is kinda cool, but the 10 henry is probably better for all the stuff most guys use these amps for. Any higher than 10 would be REALLY stiff. So lower henry's = saggier, higher henry's = stiffer.

Also, HIGHLY recommend you have your tech move the position in the circuit of the standby switch. Stock, it's after the large 470ohm dropping resistor, but the standby should allways come be before a choke in an amp circuit. You just have to move 1 and cut 1 wire if I remember correctly, and your tech should be on it no problem.

Hope that helps!
Click to expand...

That's a pretty good first post!!
:thumbsup:
 
I've done a few of these. As posted lift the power board and change the screen grid resistors to 470 ohm. Also the bias mod is a must. I would do that before adding a choke. I do mine nice and neat with a Bourns pot glued to the board. I lift the board and solder in the bias resistor and lead clean. I also relocate the standby switch. I use the stock plastic plugs and hide the new wiring inside so it looks clean. Getting the old pins out of the plastic is a bitch. I think it's two plugs you need to push through. Drill your choke in a good spot. When I was into it, I did one for free for a member on here. You can see where the two leads come through the connectors for standby relocation. Pics blow up.
 
glip22":3abfgtdi said:
I've done a few of these. As posted lift the power board and change the screen grid resistors to 470 ohm. Also the bias mod is a must. I would do that before adding a choke. I do mine nice and neat with a Bourns pot glued to the board. I lift the board and solder in the bias resistor and lead clean. I also relocate the standby switch. I use the stock plastic plugs and hide the new wiring inside so it looks clean. Getting the old pins out of the plastic is a bitch. I think it's two plugs you need to push through. Drill your choke in a good spot. When I was into it, I did one for free for a member on here. You can see where the two leads come through the connectors for standby relocation. Pics blow up.
Click to expand...

I appreciate the pics but like I said I don't want to take any chance on my drilling and causing damage to anything at all....I may try it later down the road if I have more confidence in my ability to do that part of it....but for now will just do the Bias mod....Just want to check though is it better to use a audio taper or linear taper pot?.....I am going to mount it so I can adjust the bias without cracking the amp apart..Thanks.
 
srv3089":k3gqtd9f said:
glip22":k3gqtd9f said:
I've done a few of these. As posted lift the power board and change the screen grid resistors to 470 ohm. Also the bias mod is a must. I would do that before adding a choke. I do mine nice and neat with a Bourns pot glued to the board. I lift the board and solder in the bias resistor and lead clean. I also relocate the standby switch. I use the stock plastic plugs and hide the new wiring inside so it looks clean. Getting the old pins out of the plastic is a bitch. I think it's two plugs you need to push through. Drill your choke in a good spot. When I was into it, I did one for free for a member on here. You can see where the two leads come through the connectors for standby relocation. Pics blow up.
Click to expand...

I appreciate the pics but like I said I don't want to take any chance on my drilling and causing damage to anything at all....I may try it later down the road if I have more confidence in my ability to do that part of it....but for now will just do the Bias mod....Just want to check though is it better to use a audio taper or linear taper pot?.....I am going to mount it so I can adjust the bias without cracking the amp apart..Thanks.
Click to expand...
I think most bias pots are linear.
 
Hey guys, re: the standby switch location - the switch does indeed need to be moved, but the explanation should have been that in the stock amp, the standby switch is directly before the 400 ohm resistor that the choke is replacing, which will leave one end of the choke not connected to anything when open which can be fatal for the choke. The correct location is to move the standby switch to before the main B+ supply to the plates. And the big 10 watt resistor that the choke replaces is 400 ohms, not 470.
Good article on this in Premiere Guitar here:
https://www.premierguitar.com/articles/c ... shooting-1
Sorry about that, I was posting from memory and I did the last one about a year ago. :doh:
 
I just finished modding a '92 block letter 5150 head doing the bias mod, choke mod with new 470r screen resistors and standby switch relocation. If anyone is interested I can post photos and instructions for the standby switch relocation. I still can't find any information about how to correctly relocate the standby switch but I figured it out.
 
Rolteus":15z70wbd said:
I just finished modding a '92 block letter 5150 head doing the bias mod, choke mod with new 470r screen resistors and standby switch relocation. If anyone is interested I can post photos and instructions for the standby switch relocation. I still can't find any information about how to correctly relocate the standby switch but I figured it out.
Click to expand...

Post it up if possible. Lots of people use it as a resource for info. :thumbsup:
 
@ psychoDave , Cameron had a block letter 5150 mod. What did that entail? Were there schematics for that floating around?
 
bhuard75":2m24yvvu said:
@ psychoDave , Cameron had a block letter 5150 mod. What did that entail? Were there schematics for that floating around?
Click to expand...

I think someone bumped that original thread. Sadly I didn’t save any pictures of the mod.
 
You must log in or register to reply here.
Back
Top