Peavey Mace Mods

[skynyrd]

Anyone have any good mods to help the old mace vt amp?

[R.G.]

Anyone have any good mods to help the old mace vt amp?

It makes a great planter if you take that chassis-thingie with all those electronic particles out of it.

If you don't know where you're going, any road will get you there. (Lewis Carroll)

[Enzo]

Are you expecting different response from when you posted in March?

[iwantmypie]

i've posted on here a couple of times regarding the mace.

i can verify that the bias mod Enzo posted in your other thread works well and should be well advised.

I only run my Mace with 4 tubes, essentially making it a Deuce. I haven't played with 6 tubes in a while but running it this way with a "warmer" bias helped tame the beast a little, if that's what you are looking for.

Another mod I performed was to replace the power supply resistor with a choke. From what I remember reading, chokes help filter out unwanted ripple after the rectifier, thus improving clarity. The original power supply resistor in mine fried and turned my amp into a smoke machine so I needed to replace it anyway and it was an easy mod. From what I remember, I used a Fender style choke, don't remember the size.

Last mod I performed was replacing the screen grid resistors, which I also fried one of (due to a bad tube). The Peavey has 100ohm resistors in this place. I ended up changing all of them with 470ohm resistors, which are a more common value in 6L6 based amps. If you do this mod however, you will need to do the bias mod as this will affect the plate voltage, thus affecting the bias.

My Mace has been working great and I haven't had any problems for a while now. I do however want to install new filter caps as well as most of the old electro caps in the amp. They are old and tired and should be replaced.

Cheers!

[skynyrd]

Thanks IWMP, I had pulled the 2 outer tubes and didn`t really care for how it sounded, maybe going ahead and doing the bias mod will help some? The only real issues I have with mine is the EQ of the amp, some others have been very helpful on here with posting some mods to help brighten it up, as soon as I get by this electronics store before it closesI will be picking up all the parts so I can get her done. This is a awesome amp and a complete monster but to get the sound where I want it I am going to have to make some changes. From everything I have read the 6 JJ`s I am using more than likely are part of the darkness issue and will be switching over to some tung sols or grooves when funds are available. Enzo and several others have been very helpful, and their help as well as yours are very much appreciated ! ! I have only a minor understanding of electronics and doing the simple cap and resistor changes is the extent of my abilities, I have a schematic for the amp but being able to understand what I am reading is another thing,,lol. I am starting to pick up some various books to learn more about circuitry ( sp? ) And I know I ask way to many questions,,lol, and don`t mean to get on anyones nerves here or any other forum, these forums are a major help to beginner modders like myself and all help and insight is greatly appreciated.

[iwantmypie]

just a heads up too, be careful in there and make sure those filter caps are drained before touching the circuit. looks like you have the same exact Mace VT that I do so you'll be glad to know there are bleed resistors on those caps. if i plan on working on the amp after just playing with it, i turn it off, unplug it, and flip the standby switch "up". this will help drain the caps faster. if possible, make sure you have a multimeter to be certain those caps are empty.

[skynyrd]

Thanks for the heads up, any electronics I mess with I usually unplug it then turn it back on and let it sit for 20 min`s or so just to be safe.

[Doctordog]

Hello Skynyrd,

I used to have a Mace, but got rid of it long ago, there are a few things that I would try with it to try to tame it.

I know that some "authorities" do not recommend this, but you might try using 6v6's instead of 6L6's. It would cut the power in about half. I can't remember, does the Mace have any bias adjustment? If so you should of course rebias.

What kind of sound are you looking for? I know that most if not all Peavey amps are pcb builds so unless you are very good with electronics, they are difficult to do mods on.

JB

[Enzo]

Hi JB, welcome to the forum.

I don't know if I am an authority, but I sure don't recommend 6V6s in this amp. The B+ is 500v with 6L6s installed, it would run even higher with 6V6s. The stock bias is not adjustable, though it would not be hard to make it so.

But dropping power by half only gets you 3db less loud. And if power reduction is the goal, it would be simpler to just tank a pair of 6L6s from the sockets.

[Doctordog]

Hello Enzo,

You may be right, I'm just starting to get a handle on all this, I've read that the JJ 6V6's can handle 500V on the plates, but some others can't.

BTW, could you explain why that the B+ would be higher with 6V6's in? Obviously they wouldn't pull as much current, but it is my understanding that a rectified tap off of the transformer is going to deliver the same voltage regardless, unless the supply voltage changes. Again, you may be right, my knowledge is limited.

Things that I have read have stated that the 6v6's originally were built to handle very high voltages (flyback circuits in TV's, pulses up to 1200V) and that when the newer, more powerful tubes came into production, the older, less expensive tubes, (read: less profitable) became derated in the literature even though it was the same tube construction. That is not to say that many tubes made today may not be to the original specs of course.

And, without being able to adjust the bias, it is a moot point anyway as the 6V6 bias is much lower than a 6L6.

JB

[Enzo]

None of these supplies are regulated. The reduced current draw of the smaller tubes would be less of a load on the B+, and so the voltage would rise. The rectified voltage from the transformer will rise. The transformer AC itself will rise. If nothing else, the transformer winding has resistance, and that resistance can be considered in series with the voltage. Curent through resistance causes a voltage drop.


This is easily demonstrated. Measure B+ with tubes, then remove the tubes and measure again.

Transformers are generally given voltage ratings at their rated current. SO a 24VAC transformer rated for 10 amps will produce 24v when 10A are drawn. But it will likley be higher at smaller currents. Or check out a 12v wall wart when it is not loaded - probably closer to 16v.


Like anything else, part specs have a context, and context matters. One of my favorite transistors is the MJ15024. It is rated at 250v and 16A. But not at the same time. 16A is OK up to about 15v, or at 200v it is good for about a quarter amp.

Looking at a 1959 tube book:
The old 6V6 was designed as a beam powr tube, but also spec'd for vertical deflection duty in TV sets. As a vertical sweep tube the specs show triode connection. There is a 1200v "absolute maximum" peak rating for that with the added note that duty cycle must not exceed 15% of one scanning cycle. That was 30 frames or 60 sweep scans per second. But the tube plate voltage rating was still only 315v. The specs for regular old audio look a lot more familiar.

SO yes, the tube has a 1200v rating, but only under certain special circumstances involving brief pulses, not continuous audio work.

[Doctordog]

Hello,

Thanks for the clarification for the B+ changing. Do you know what the difference in resistance would amount to voltage drop wise between a 6L6 and 6V6? As I said, this is still somewhat fuzzy concepts for me, and I have read a lot, but it seems everything that I read can have different meanings depending upon the context. But, that is my shortcoming I guess. I understand about the 6V6 and the 1200V@15% duty cycle. I wasn't trying to suggest (even though it may have seemed that way) that you could use that high of voltage on them.
The things that I have found interesting in my readings are that even the "experts" have many different views on many things regarding tube amplification. Some in direct contradiction to each other. Some with the warning "NO! don't do that... you can blow up your (whatever)" Other's with "Yes, you can do this, it won't hurt anything, the others are just passing along tribal knowledge. I do this all the time, it works because..."

Regardless, it has kind of left me with carrying around a salt shaker whenever I read things, unless I have experienced those things myself, I won't take them for gospel.
I appreciate your civil reply, I really wasn't trying to argue, just wanted to understand the science a little better.

JB

[Enzo]

When it comes to a "can I do this" question, you will usually get a variety of answers. To some people, if they get away with it, it must be OK. Well, even a drunk driver usually makes it home. That doesn't make it a good idea, some folks are just lucky. Some people extrapolate to make rules that are not really based upon anything. And some people are naturally cautious with specs. It takes all kinds.

Tube specs are a good example. SOme folks see 315v maximum in a 6V6 manual page and decide that 316v would therefore blow the tube apart and anyone using 6V6 over 315v is going to blow up the house. Other folks know that Leo Fender used 6V6s at 400v for decades with no particular problems. WHo is right? One has to be aware of what the specs in the tube manual are for. When RCA designs a tube, they intend for engineers to incorporate it into their designs and buy a lot of RCA tubes for the resulting products. The tube manual specs are what RCA promises a reliable level of performance and reliability from. That 6V6 will sit in a radio or TV set at those voltages for a LONG reliable life. Dad doesn't want to put a new 6V6 into his TV twice a year. So design that table radio with 300v B+ not 500v B+. It might or might not work at 500v, but RCA won't assure you that it will.

But in guitar amps we thoroughly accept we will have to change tubes regularly, and we are not trying to make little table radios. The difference is like car tires. Mom and dad want tires that last well and work reliably on the car driving around town. Someone racing the same car in stock car racecs will have a different view of tires and expect them to wear out as long as they get good traction around the track.

Bias is another one. To some folks bias is almost a religion, they have chanted bias-bias-bias so long they think it is critical. Well meaning people write in wanting to modify some little basic amp because they are aboput to put a new tube in it and they had heard you MUST ALWAYS adjust the bias any time you replace a tube. They believe this with all their heart and pass it along as gospel at any opportunity. Well, you won;t go wrong always setting the bias, but it is hardly that important. There is too hot and your tubes melt, and there is too cold and the crossover distortion eats you for breakfast. But in between is a wide fertile valley of perfectly acceptable bias settings. SO if it sounds OK and the tubes are not getting red hot, then it is close enough. And so back and forth that goes.


I have no idea what the voltage shift would be. You can estimate the reduced current needs of the 6V6, but I have no idea the winding resistance in the transformer. Difference might be a lot or a little. Can't use Ohm's Law with just one variable known.

[skynyrd]

Well I got her done, did alot of looking at the mods given and reading various articles and talked with a local guy who does work for some of the big names, like Nugent, Charlie Daniels, Dokken, he pretty much just pulled some mods out of his pocket and said here this is all ya need. Will post a short video of how he sounds now, UN FREAKIN REAL ! ! I would have never thought this amp could sound like this, some may not like it but for me? I have always wanted a cross between Skynyrds sound, ZZ Tops sound and Blackfoots sound, this baby covers em all now, she can get as rude as you like or whine with the best of em. I tried the diode clipping in the normal channel and now it has a bad squeal, even switched it back and still does it, so once funds are available will take it to the local guy and have it fixed, just using the effects channel and pretty much is all I need. Once I post the video if anyone has a Mace VT or a Duece VT and wants the mods let know, is actually pretty simple mods.

[iwantmypie]

Well I got her done, did alot of looking at the mods given and reading various articles and talked with a local guy who does work for some of the big names, like Nugent, Charlie Daniels, Dokken, he pretty much just pulled some mods out of his pocket and said here this is all ya need. Will post a short video of how he sounds now, UN FREAKIN REAL ! ! I would have never thought this amp could sound like this, some may not like it but for me? I have always wanted a cross between Skynyrds sound, ZZ Tops sound and Blackfoots sound, this baby covers em all now, she can get as rude as you like or whine with the best of em. I tried the diode clipping in the normal channel and now it has a bad squeal, even switched it back and still does it, so once funds are available will take it to the local guy and have it fixed, just using the effects channel and pretty much is all I need. Once I post the video if anyone has a Mace VT or a Duece VT and wants the mods let know, is actually pretty simple mods.

any videos available yet? i'd be interesting in hearing these mods.