• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Help with hybrid mosfet valve amp

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The Prologue
I own the AMC CVT2030 hybrid mosfet valve amplifier. This older version has a silly design flaw—the tubes are soldered in. AMC used to mod it for around $175 by installing sockets, new tubes, etc. I just got off the phone with them—they outsource all AMC business to retrodaze audio now (I think he's the guy I bought from). I've also read that some people do the mod themselves, but it's beyond my soldering and electrical skills. Interestingly, Deltronics, a local (Chicago) hi-fi repair shop looked at the photo (below) and said that there isn't enough room to install sockets—I'm know they're wrong, especially after looking at the photo of the mod :). The AMC's mod is kind of pricey and I haven't bothered, until now.

An externally hosted image should be here but it was not working when we last tested it.

Un-modded CVT2030

An externally hosted image should be here but it was not working when we last tested it.

Modded

An externally hosted image should be here but it was not working when we last tested it.

Close-up

The Problem
If you look at the image, the two pairs of tubes (Sovteks) are soldered to a couple PCBs. I keep having a problem with the one on the right. First it was the fuse, then a connection fried, now, after playing fine for a year or so, the tubes won't light up. I checked fuses and connections for continuity—the extent of my knowledge :( I suspect the tubes need to be replaced, since it's been about 4 years of use (light use).


The Questions
1. Can both tubes go out at the same time? If not, then it's something else, I guess.
2. Is it worth to spend $175 to $300 to socket the unit, bias the tubes, and do some minor upgrades? The amp cost me around $450

Even though I don't know how to tinker with them (yet), I still love tubes :) I just got myself a pair of ASL Wave-8's, modded slightly. Seems a little underpowered, but with a surprising bass. Just wanted to share.

Thanks for your help, everybody!
 
Let Engineer Our Own Hybrid/Moscode Power Amps

Hello to all:

I am an Electronic Engineer, and like most, I am self taught. Even thou I have papers from U of Penn, I left the classroom with a bunch of numbers, ideas, and little common sense. I was armed with math, theory, and I was very dangerous!

Just ask my bosses.

You learn in the field. You make mistakes in the field. Sometimes, if you are wrong. It could cost someone their life. Sad, but true.

But in the common man's realm of operation. As consumers, when we buy what others state is good to excellent piece of audio gear, and it ends up being a disappointment. The item ends up sitting it's life time (and yours) out in the attic, garage, or the basement. Unless something happens to change the out come.

In theory, we could be talking hundreds to thousands of dollars, pounds, or euros.

A good Hybrid Mosfet Power Amp or Moscode, cost a great deal of potatoes, pasta, bread, sausage, beer, wine...., well, you get the idea.

So lets engineer our own. It is easy!!!!!!!!!!!!!!!!!!!!!!

All you need is brains, and we all got a good set of those.

If we look at many of the hybrids out there, we can figure the thing out in no time. Because when it all comes down to it, it is just a bunch of carbon. Just like you and I.

This is what we can do.

We can build the best hybrid to date together. Not just me. But who ever is interested. Because, believe me, my brain is no better that yours. Maybe your brain is better than mine, after all the things I put mine through.

We can take the circuits from the best units available out there, tweak them, mold them, test and put them all together to get a great unit.

So lets get started. I'll begin, and you guys can jump in, where ever you like.

See the next post.


Take Care


Ivey.
 
Our front end to our new hybrid.

Engineer is like most things.

If it ain't broke..., don't fix it.

We should try to build a hybrid with low power first, about 20 to 30watts. Tweak it, still it sounds so good; we want and demand More.

I am posting two circuits that I feel will do us some justice. CabL1 and L2
are reminders to let you guys know, do not forget to use coax for your signal runs. Especially if you will chassis mount your tubes or valves. Twisted for heaters.

You can post something too.

Then we need to design, find, or steal, a SS regulator for our front end.
But here is the catch. There is a part limit to the design. Only 11 pieces. And no IC's, or OpAmps's. You have to use all your skills. To do this one.

Remember also, engineering is like yard sale hunting. If it works use it.

Take Care

Ivey
 

Attachments

  • front end.doc
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Yes, I have.

I seen it, yet I was hoping to save it for the next building faze. I have some ideas that I want to toss out there to the people.

One of the circuits that I posted is from the Moscodes. The other, is one that I kicked up, to drive a simple mosfet amp I found on the net.

We need to build things that sound good, but will not cause our families to much financial pain.

With a slow or sluggish economy, we must conserve.

Therefore, if we can build a 20-30 watt hybrid, for $80.00 dollars or less, using new parts. We can greatly reduce that cost, by using flea market parts.

And not only that, it is my intention to teach and to show the people on the forum, how to make an beautiful chassis using thatch wood construction and sheet metal; with materials that can be obtained from home depot.

How would you like a beautiful maple wood polish frame chassis, with red colored metal front, side, and top panels; with white lettering?

Well you can.

I could sit down and R & D all day long. But why should I. I learned my lessons well.

When I was in schooling all those years. I studied all the circuits that someone else had designed. When I got my first chance to design something, I was so happy. I called my father.

The next day the boss came to me, as I was bending over my drafting table full of templets, books, data, and ask "Hey kid, what are you doing"?
I am designing the circuit, I answer.

"NO, NO, NO, NO, he yelled". "Here use this"

He toss me a folder of other peoples designs, and order me to create something from them. No time and no money for R & D. Find something that works.

Another lesson; well learned.


Take Care


Ivey
 
Which eBay? Nigel

I saw car amps, TO3 mosfets claiming to be Toshiba's, and amps on bids, plus one "buy it now" for 122.00 pounds.

Is that module stereo or mono? If it is mono, that is $60.00 US. Two is $120.00 dollars plus post. Could be pricey.

Did you see where they are selling PCBCAD30 for 14.99 pounds.

check it out, buy one and let me know if it is worth the trouble. I will buy one too before it, becomes too pricey.

Take Care

Ivey
 
Poynton

Hi:

I looked at those leds you posted and they look truly nice, yet I have a tough time trying to see how they are getting 300w out of that module with mosfets that appear to be IRF240's.

40 watts yes, into 8 ohms, 80 into 4 ohms. But 300 watts. They must be doing that numbers games, 120 watts into 2 ohms or 240 watts into 1 ohm.

The amp may short out if you try to drive too low of a load. Dangerous, is it not.

But at approx $120.00 dollars, it is worth looking into. Oh, and that includes shipping.

The other amps look good too. But the cost is not always a factor Poynton.

I am trying to assist people who really do not have $120.00 dollars laying around. And even those that do, importing items into ones country, can at times, bring unwanted attention from the officials, that you may want to avoid.

I hope to assist the guy that digs around the trash pile and find old Televisions, and remove a few n-channel mosfets, to build his system.

Like Western Africa. England sends tons of electronic trash down there every year. So maybe one of those guys can stripe enough parts to build himself a system.

That what I am trying to do. To make it fun and interesting for them as well.

It is just like me.

When the US went digital, in television trammission. Thousands of TV's found their way into the dump. So I took advantage of it. I collected 30 TV's, removed all of the degaussing coil wire. Found two big power transformers with the same size core. And made output transformers out of them, using the all the copper wire salvaged from the TV's.

Took me two weeks, beer, and chips.

Saved about $200.00 dollars.

So yes, some can purchase those items, but on the other hand. Some can not.

What do we do, give me an answer. How do we try to help the few, knowing that the many, has less means.

Take Care

Ivey
 
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I looked at those leds you posted and they look truly nice, yet I have a tough time trying to see how they are getting 300w out of that module with mosfets that appear to be IRF240's.

They can't. The power claim in the "fine print" is actually 150W RMS (at what frequency? what distortion? In the US, the FTC would want to have a word with him...) into 4 ohms, rather than the eye-catching 300W in the headline. That's almost believable as long as you don't follow the other FTC regulations for power claims, i.e., preconditioning and continuous power test. Trade laws must be different in England regarding power claims.

I am a bit disappointed that the link was given without even a hint that the poster was the one selling it.
 
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