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Old 22nd May 2007, 06:47 PM   #1
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Default Help with hybrid mosfet valve amp

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.

Click the image to open in full size.
Un-modded CVT2030

Click the image to open in full size.

Click the image to open in full size.

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!
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Old 22nd May 2007, 06:54 PM   #2
EC8010 is offline EC8010  United Kingdom
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Do a search and you will find that the AMC amplifier has come up before...
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 14th January 2010, 02:09 PM   #3
Ivey is offline Ivey  United States
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Default 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

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Old 14th January 2010, 02:45 PM   #4
Ivey is offline Ivey  United States
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Default 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

Attached Files
File Type: doc front end.doc (37.5 KB, 227 views)
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Old 14th January 2010, 02:45 PM   #5
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Originally Posted by Ivey View Post
Because, believe me, my brain is no better that yours.

It didn't cross your mind to start a new thread?
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Old 14th January 2010, 02:54 PM   #6
Ivey is offline Ivey  United States
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Default Yes

But they recommended that I use an existing one.

Can this be moved, if you feel it would be better served as a new subject?

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Old 14th January 2010, 03:02 PM   #7
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Originally Posted by analog_sa View Post
It didn't cross your mind to start a new thread?
Why do you always sound insulting in your posts?
Heck, I think it is a wonderful idea for us to follow and explore.
I think; therefore will NOT be Politically Correct.
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Old 14th January 2010, 03:16 PM   #8
SY is offline SY  United States
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I agree- better here. The topic already exists.

Have you seen the Pass F4 unity gain power amp? Seems like the perfect place to start a hybrid.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 14th January 2010, 04:54 PM   #9
Ivey is offline Ivey  United States
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Default 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

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Old 14th January 2010, 05:17 PM   #10
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Originally Posted by samvel65 View Post
The Prologue The AMC's mod is kind of pricey and I haven't bothered, until now.

Thanks for your help, everybody!
I dont understand the pricey comments on this thread.
There is a 300watt hybrid amp on ebay for about £35.
Murton-Pike Systems PCBCAD51 pcb design software.
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