Moderator: VelvetGeorge. Metropoulos Forum The place for vintage amp discussion. Skip to content. Quick links. The customer wasn't happy with the tone of the amp which was quite thin and buzzy, and it lacked punch. This amp is fixed bias and its four 6L6's were idling at an ice cold 12 ma.
A very popular mod for the is to add an adjustable bias circuit which I did on this amp. The mod is pretty simple - replace the 15k resistor in the last stage of the bias filter with a 10k pot in series with a 4.
I used a 10 turn pot which allows quite fine adjustments. I rebiased the tubes to 32 ma. What a difference! The fizz was gone and it had a lot more warmth and punch. The owner was extremely happy with the modification. Amp Biasing Tip: There are no resistors in the cathodes of the power tubes of the to measure the cathode current. The usual solution for this is to use a bias probe, which basically inserts the resistor temporarily. There is another way to measure bias current - measure the resistance of the output transformer secondary windings and measure the voltage drop across the windings with the amp powered up.
Don't assume both halves of a push pull transformer have the same resistance because they generally don't due to the way the transformer is wound. In this amp there are two tubes per side so don't forget to divide by two. Measuring the drop across the transformer secondary only measures the plate current. When you measure with a bias probe you are actually measuring the tube's plate current PLUS it's screen current, so you should account for that.
Screen currents vary by tube and voltage but if you assume 5ma you'll be in the ball park, so set the plate current a few ma lower than with the bias probe method. CAUTION - this is a dangerous method of measuring bias current because your voltmeter is attached to the highest voltages in the amp. Here is an even better example. I was suprised to find this amp had very few hours on it and still had all of the original tubes all 5 12AX7 and all 4 6L6GC!
I am quite certain that the amp had never been removed from the chassis. The pots were all very scratchy and it was so covered in dust it didn't appear to be black. Quite honestly I was disappointed in the sound. I decided to install the adjustable bias mod. Before the mod the high voltage read I decided to remove the chassis from the box and went further removing the main circuit board to thourally clean all the pots.
I did a variation on the mod, using 2 3. I was able to find the exact same type of resistor as used on the PCB which looks physically identical to the others. This allowed a very clean and professional installation with 2 points to solder in the pot.
When I finished I put down some hot glue to hold it securely, which oddly enough, looks like the exact same type of glue used all over the PCB.
I carefully laid out everything so it honestly looks like it came this way from the factory.
I mean you wouldn't know it was done if you didn't know this amp. After the mod I dialed in the bias to Re: mods It's like speaking Chinese to me So when are we going to start mass producing our own "new" amp with this?
Could make some money after some good marketing. If you delete this thread before many others get wind, anyway. Cameron won't mind. I am also wondering if your amp had a bias mod done on it to make the 6L6 tubes run a little hotter. I dont like how cold the 's are cold biased with those 6L6 tubes. This is the main mod!!! R9: piggyback a resistor on top of the 1 meg resistor. I used a k based on feel.
You can try out 68k, k, k, k, 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. I'm going to study this, that thing sounded phenomenal C cut one leg for less bottom end on the rhythm channel C 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.
Peavey 5150 II adjustable bias mod?
Have fun getting a killer sound Thanks Mark!! Dave thanks man,I really loved that clip you posted!!!! I told Mark it "Cameron-ized" the amp. It makes the amp slightly tighter as well.Modded Peavey 6505+ Playthrough: (plus 5150 vs 5150ii switch)
R9 tightens up the amp a lot depending on how low you go with a resistor. Too high and the amp is still flubby. Try testing a 68k, k and a k resistor. Get a feel for what it changes. FWIW, I did do a bias mod. No one gonna take me up on my offer? I'm a good business partner.When one of the tubes was failing I checked what the original tube configuration of a should be, mine consisted of two KT88's and two 6L6GC's.
Turned out my was fitted with an integrated quads mod and a hot bias mod. Even though the mods were properly done I wanted the amp to get its original personality and character back again so I removed the mods and popped four new JJ's 6L6GC's in again.
This mod allows you to use two different types of tubes in the power amp stage of ain my case two KT88's on both sides and two 6L6GC's in the middle. The guy I bought the amp from provided me with an extra set of these tubes, could this probably be because this setup wears out your tubes faster and the previous owner knew about this?
I also highly doubt if my ears could ever discern between a normal and an integrated quads setup at the levels I'm using my with lead post gain around 4. After opening up my first thing that struck me was the build quality and the quality of the used components. It all looks very tidy and sturdy, this thing is built like a tank.
First I pulled out the worn out tubes and unscrewed the tube sockets. Then I took out the power board. As you can see this mod is pretty invasive, several traces were cut, an 1 Ohm resistor was added and a bias measurement construction with four 10 Ohm resistors was added.
I took that all out and restored the board to its original condition. This mod allows you to bias the power tubes hotter than the factory default. But from what I understood the power tubes being biased colder is one of the characteristics that help define the sound of a Also if the amp is biased this way it's easier to replace the power tubes as the amp doesn't have to be biased again for the new tubes which isn't even possible in a stock MkI as it has a fixed bias.
No blown fuses, blue smoke or weird sounds so this restoration was a success. Had a rehearsal with McClane that very same night and the revised stood up way better against the Mesa Boogie Dual Rectifier of the other guitarist, the blend of those two now felt like it should, just awesome. Peavey biassen Dutch.Discussion in ' Amps and Cabs ' started by paulgrasbyMar 7, Log in or Sign up.
The Gear Page. Output transformer upgrades??? Mar 7, 1. Messages: Ive been thinking about upgrading the output transformer on my combo for a very long time, but never have coz i dont know anyone who has done it. Ive been looking at Mercury Magnetics in particular OT and choke upgrade.
Id love to hear some feedback. Has anyone here done this mod to theiror any other high gain amp for that matter?? How did it change the amp and was it worth it?? Mar 7, 2. Messages: 1, That amp can drown out drummers as it is.
Its a lot of money to spend. I don't even know if it would sound better. Keep some good tubes in that amp and it should do exactly what its supposed to. Mar 7, 3. I read some review online where a guy bought a Mercury Magnetics OT for his Peavey Windsor, just assuming that it must sound better than the Chinese made OT, and he said it didn't sound better.
He ended up reinstalling the original factory OT. Bill BraskyMar 7, Mar 7, 4. Thats a bit of a concern! Maybe I should just have a play around with some different preamp tubes Mar 7, 5. You may notice more of a voicing change for the better upgrading to a choke rather than trying to use golden ears to identify possibly only subtle changes from swapping transformers. I know adding the choke mod to a Yamaha T50 I used to have made a huge difference in that amp, with a much more alive low end.
Mar 7, 6. Maybe if you found a dirt cheap with a blown OT it might be worth trying this experiment. I can't see replacing a perfectly working OT. Peavey and the designer, James Brown, aren't total idiots re:amp design. I'm sure they tried to make an OT that would sound good with that design.Discussion in ' Amps and Cabs ' started by FaldoeJul 30, Log in or Sign up. The Gear Page. Jul 30, 1. Messages: 1, I'm thinking of getting a but I want to know which version is better, or may suite me better.
I like good clean channels - my current amp is a non-master volume Ampeg v4 but it doesn't have a gain channel or effects loop. I'm not dogging the amp. I've had it for years and it is a beast, but I may want something different. I play clean but also love heavy high gain distortion. I've been using pedals for years with the v4 but I feel I can't find the right pedal that really gives a tube amp channel feel.
The v4 takes pedals well and can produce good results but I always feel its not enough. I read the II has a better clean channel but compromised gain availability in terms of distortion, is this true?
What else is there to look out for between the two, or say earlier versions of the ? What mods are there out there, what would you suggest? FaldoeJul 30, Jul 30, 2. Messages: 5, At least the first version didn't have a useable clean sound IMO.
A friend of mine who is a great player has a III and it sounds really good on 80's crunch stuff, but clean is just "meh". B MoneyJul 30, Jul 30, 3. Messages: 3, Clean is just OK on amps. Maybe a Wampler or Bogner pedal will be the fix for high gain on the Ampeg V4.
Jul 30, 4. Messages: 2, ReginaldBisquetJul 30, Jul 30, 5. The III has the best clean channel out of all of them. Jul 30, 6. Jul 30, 7. I've heard the III has an excellent clean channel. Some of the clips I've heard have been pretty damn good.
SchafrocksJul 30, Jul 30, 8. It's very Hifi and compressed. The original is a fun sounding amp the crunch channel sounds cool when you turn down the guitars volume, It's sorf of a hairy clean.Forgot your password?
By derpackswasyesAugust 31, in Amps. I want to get my peavey bias modded. I am wondering if after everything is done if I hand my tech the amp, the money, and this link:.
I'm sorry if my question seems dumb but I don't know much about this stuff I thought if I got this modification done that the "bias trim pot" would be poking up out of the inside so I could just remove the back cage of the amp and use a flat head screw driver to bias it after obviously using a bias probe and volt meter connected but then I saw this picture and got confused:. If you want it accessible from the outside, tell your tech to make it accessible from the outside.
Sorry, it's very like me to over think things The reason I ask is because the guy I'm going to have do it is good with electronics but I'm not sure if he's familiar with working on guitar amps In case he forgets that I specified for him to make the adjustment pot accessible from the outside. Many amps have the trimpot mounted to the board inside of the chassis. If you want it on the outside, then you need to specify that. That PDF shows it to be on the inside, not chassis mounted, so you definitely wanna specify that.
This will mean drilling a hole in the chassis somewhere. Okay, will I need to buy any extra parts for this or the tech will just modify how he does the procedure? I dont think you need to buy anything extra, just make sure you have a pot that can be chassis mounted BTW, it wont really matter in my opinion if it is mounted outside or not, because you will most likely have to take the chassis out of the headshell to bias anyways, because those bias probes are so tall, and wont fit in the headshell while attached to the tubes.
Have the tech add some externally accessible test points while he's in there. They sell bias probes that are curved 90 degrees just so I don't have to deal with the hassle of getting the amp out of the headbox when I bias.
Here's another question I've heard that when you do the bias mod it makes the louder volumes have better tone and when you have the amp turned down sound a bit worse depending on how hot you bias it after well Not that I have too much to add to this other than do it! I've had a tech tell me that amps that rely on preamp gain Rectos, 's, Tube power amps in my case do not need biasing, but nothing could be further from the truth IMO.
Every amp that I've owned that had power tubes biased to the correct range always sounded warmer and just over all better tone. The ones that didn't felt stiff and sounded sterile. I just thought I would chime in here. I've bias modded 1 of my 3 's. I gigged with the bias modded amp for years.
I have to say that IMO it's not worth it. It will sound very slightly thicker, but the resulting loss of low end tightness isn't worth it at all. It also becomes somewhat congested in the midrange. Of course you can set it back to a colder setting if you don't like the sound of it with a hotter bias, but I wouldn't even go through the trouble. I've got clips of EMG 9 vs 18 shoot out and they're almost identical ya and I've also got clips of different miliamp ratings for the tubes on the and there is a bit of a difference I guess I need to first get an overdrive boost and see if I'm happy with that.
Of course, it's all about the application - an OD that will make the Rhythm channel sound amazing will really thin the crap out of the Lead channel, and an OD that will be perfect on the Lead channel won't make the Rhythm channel tight enough IMO, of course. I think you're missing the point of the bias mod, at least what I'd consider to be the point anyway. It's not so that you can just bias it warmer, it's so that you can bias it.
There's a misconception that the amp, due to not having a bias pot, is "self biasing" somehow.Forum Rules. Remember Me? Last Jump to page: Results 1 to 10 of Sign in to disable this ad. Earlier this month I got my inheritance early, my mom had an earlys Peavey Rage 8" practice amp, which oddly enough she used as a PA for puppet shows Since I am due to get a new guitar for Christmas yes, the So-CalI thought if I was gonna use this thing, I was gonna need to hot-rod it.
So I popped that bad boy open, called Peavey and got the schematic. On top of that, there is the standard diode arrangement on the lead channel.
I started to wonder why the Peavey's infamous Saturation control sounds like such poo, given its not very unique selection of components. Certainly, the complete crap speaker the RAGE suffers with is part of the problem, but looking at the lead channel opamp gain, it seems that it ain't real long before the opamp is driven into disgusting clipping. I ain't no wizard of opamp gain calculations, but I think the gain maxed at something like Needless to say, the lead channel had to go.
I've designed a replacement with a 12AX7 stage, the design largely stolen from a Fender Champ. Of course that necessitated a revised power supply. The clean channel I'm leaving largely intact, except for a few component changes: OPA for theand few capacitor upgrades.
The goal of the hybrid design is to get a clean channel as squeaky clean as it can get, and a tube that can be moderately overdriven.
The other thing the amp needed was reverb. I scored a spring reverb unit from the manufacturer, which sells custom reverbs on eBay. Cool, as I could spec exactly what I wanted--a short delay reverb, perfect for my surf-style guitar The circuit board has a bunch of empty holes and lonely traces, a brief review indicates that it was designed for a reverb.
That's the plan, along with a new Eminence 8" speaker. Here's my schematic:. Now the fun stuff: it has to look the part too, matched up with the So-Cal The Peavey cheap black vinyl had to go, along with the cheesy pointy logo and aluminum strips.
I chose burgundy carpet and a turquoise-silver grill cloth. Tomorrow the speaker and grille cloth go on, but here's where I am right now:. Stay tuned for more updates! This weekend I'm starting work on the circuit boards, I'll post pictures as I go, and hopefully I'll finish by Christmas, then I'll post a clip with the new axe.
Originally Posted by Jamal Bucket. What's a so-cal? I must be really out of the loop. That amp project is looking fun I've been dying to build one of thoose ax84 amps forever.
The whole kit is like bucks. But the total cost would probally be well over or so. Your project is looking good though. You'll have to post mp3's when you finish. Where are you in N.