Peavey Ultra 60 bias mod

[chunkitup]

I have been contemplating making a probe. For now I didnt go under -45v and it sounds real good. Although the tubes get rather hot. I noticed on the schematic that there was a fan on this model but is not there anymore. I might start looking for a fan, if anyone knows where to get one. The tubes dont glow any brighter than any of my other amps that have the same JJ 6l6's. I wonder if you could explain how the ultra channel eq works. I can upload the schem if needed but Enzo I bet you got one. The top end was just nail biting so I changed the two 100pf on the edge channel to 470pf's and holy crap it sounds so much better. I also changed the 1meg grid resistor for the 2nd stage to 470k and it really tamed this beast down but still with over the top gain.

[Enzo]

It was designed as a gain monster. You can mod it to tame it, but don't be surprised if it fights back. Why you think they call it Ultra?

-45 is pretty hot for a Peavey, they usually spec at -55, so I don't doubt it runs hotter than usual.

There is a fan SUPPLY terminal on the schematic, but I don't recall fans on the Ultras. If there is one, I suspect it is on the 120 watt model, they used the same circuit board. These are the same 6L6s running at the same voltages and dissipations as every other 60 watt amp on the planet, and darn few have fans.

If you have to have a fan, look at the schematic, the fan terminal is just a tap off the +24v rail, so the fan needs to be a 24VDC model of a size to suit. Where you'd put it is another story.

Look up the schematic for the PV Triumph PAG60. You will note it is just about the same schematic as the Ultra. The power supply is the same, and the fan is from that. I suspect they just transferred the drawing and the fan came along. The Triumph PAG - the PAG stood for Parallel Axial Geometry or something like that - had the tubes sticking straight out the back horizontally, so they needed more help cooling. I don't think the fan came along for the ride when it became the Ultra. I could be wrong or course.

[Enzo]

I wonder if you could explain how the ultra channel eq works. I can upload the schem if needed

I have them all.

The clean channel EQ on these is the standard passive tone stack used all over. The Ultra channel EQ is an "active EQ" stage. Active EQ is more versatile, has more range, but can be touchier to dial in. Once you get it, it is real cool.

Active EQ involves a gain stage, in this case V3A. The output from the stage is from the plate, down through C24, and on down to relay K5B, where it exits the preamp. But after C24, it also taps through the three EQ pots. The wipers of the pots fedd through some RCs to set the freq bands and are then gathered together and fed back to the grid of the tube. The other end of the pots are tied together, and that point is where the signal from the gain channel post pots is injected. The pots then serve as controllable feedback elements for that stage. The RCs make them frequency specific.

[chunkitup]

Enzo, thank you so much. I have this amp sounding so good that my bro, lead guitarist in a band that was picked to play at the Harley Davidson 105th anniversary a few weeks ago has decided to use this head as his main amp. The only thing is I need to get the channel switching right. We cant find the footswitch which uses a 7 pin connector. The thing is he took off the reverb tank and only uses the clean and ultra channel. I want to put in a simple on off switch that goes between the clean and ultra channel. Can you help?

[Enzo]

You have several options.

Peavey may still have that footswitch - call PV parts.

Peavey, bless their hearts, will make up a footswitch for you for any obsolete model - call and ask price on that.

It is just a 7-pin DIN connector, get a plug and wire it to your own pedal. It is just simple relay control.

You can only get at the Crunch channel with a footswitch, so making one up or buying one would allow all three channels to be used.

[chunkitup]

I am ordering the 7pin DIN and I will do it myself with help. Why hand the ball off now!

[chunkitup]

Another EQ question

alright so I have this thing sounding real good. I am going through and replacing the coupling caps with nice 715p's and I replaced the edge caps with 470p mica and that got rid of alot of the piercing high end. My question is this:
What purpose does having C20(.0022) and C21(.001) in the Body of the eq? What is happening when you roll thru the pot? Why doesnt the Bottom have any caps? Yes I am still learning and all experience has been with Marshall tonestacks. I do understand how the feedback works but the RC/freq specific portion is boggling me.

[Enzo]

I never thought about it. My expertise is troubleshooting. I never parsed that circuit out. You might call Gene Ford at Peavey ( or gford@peavey.com) or one of the guys in service and ask about it. I don't recall whether DUncan or AIken cover active EQ on their wonderful web sites. Add amps dot com to either one and study the materials there anyway. Look up active EQ circuits in general.

Chapter 15 in the RDH has some coverage - look under boosting with feedback

RDH can be found online various places. I downloaded mine from here:
http://headfonz.rutgers.edu/RDH4/ If you are not aware of this book, it belongs on your "shelf."

I have no idea what the center bands of each segment are, and I would expect them to be interactive anyway


There is no cap specifically next to the bottom control, but there is a cap in the circuit, C24. This is an active EQ circuit. The "standard" Marshall or Fender TMB tone stack is a passive stack. Regardless of the knobs, they are cut only. Active EQ can boost and cut. Active EQ requires a gain element in the stage. (Otherwise, how could it boost anything?)

[alien620]

Hello!

I play on a PV Ultra Plus 120 and I'd like to know if it's the same modification on ultra 60 and ultra plus 120?
If yez, what component(s) must I modify?
It's the same architecture?

thanks!

[tedmich]

they are the same except the larger power tube board; do you have the schematics?

[alien620]

Yes I have the schematics.

Could I send it to you into a MP or Mail?

thanks!

[tedmich]

Yes I have the schematics.

Could I send it to you into a MP or Mail?

thanks!

I have an Ultra 60 212 and its schematics too, what mod are you thinking about?

Variable bias is doable, a "universally accepted as better tone mod" is unavailable IME!

The tone stack mods discussed above are a real taste issue and can potentially damage the delicate PCB (or you) if you are not a seasoned amp tech. What do you want out of your Ultra 120? One persons "awesome mod" is another's "trashed amp"; what exactly are you looking for?