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eBay 200w class a amp  

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lightwriter62
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27/07/2019 2:41 pm  

Hi all, I’m new here, I’ve seen videos of 123toid building amps, I saw this class a,  200wpc amp board on eBay, I have no idea how to make something like this work, or if I would want to, but I know I would never be able to afford one, even in the used market. Can anyone clue me in as to what I’m looking at?

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Thanks, Kent 


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Speaker Builder
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27/07/2019 4:52 pm  
Posted by: @lightwriter62

Can anyone clue me in as to what I’m looking at?

Its and old technology audio power amplifier... In fact it appears to be 4 of them placed together for the photo. Being Class A it's going to be wildly inefficient and would likely consume 600 watts or more to produce 200 and, being that inefficient it's likely to run very hot. (as in burn your fingers, hot)

You surmised that you may not want to make it work ... I would suggest you got that part right.

 


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lightwriter62
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27/07/2019 6:26 pm  

@douglas-blake

Hi Doug, I tried to post the eBay link, but it got removed, it’s class a, so yes, it will be hot, needs a case with huge cooling fins for sure, it calls for two 1000w transformers with 24-26v taps,  a 200w class a amp even used would be five figures, this is $500, I was just wondering if I could find the parts, would it be worth the trouble? Kent 


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Speaker Builder
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27/07/2019 6:33 pm  

@lightwriter62

I can't answer that for you... if you really really want a class A amp, it might be. 

Now for me, nope, this doesn't interest me any more than tubes.

Just lately I've been playing with a lot of Class D stuff... Like Class A, D doesn't suffer from gross non-linearity or crossover notches, but it is many times more efficient and runs nice and cool. This permits both lower complexity and smaller sizes both of which I find very attractive.

(As a new member you probably need to post a few more messages before the links are allowed.)

 


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TVOR-Ceasar
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27/07/2019 7:00 pm  

I agree that it's 4 of the same board arranged in a pleasing symmetrical order.

The board is labeled Musical Fidelity A1000, which can be found here: Ebay and is listed as a 30w + 30w amp. Old school for sure, using MJ15011 and MJ15012 complementary TO3 case transistors. If you like Class A and don't mind heat, then go for it. They even show the Schematic, albeit pretty much unreadable for component values.

-Charlie


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Speaker Builder
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27/07/2019 8:20 pm  

@tvor-ceasar

Good luck finding replacements for those transistors...

I don't know if that's the right schematic or not. It looks more like an AB amp to me. But I would have to check the bias points to be sure.


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123Toid
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28/07/2019 6:38 pm  

@lightwriter62

You need, I think, 5 posts before links are allowed, although I may have changed it to 2.  But feel free to introduce yourself and comment on a few more and then you can post the link.  

I don't really mess around with class A amplifiers, but just keep in mind the other costs.  Such as your toroidal transformer, case, binding posts, etc.  I can't say for sure if it is a good deal or not.  Just count your costs to see if you think it adds up to being a decent deal. I might even suggest checking out Facebook marketplace for used call A amplifiers.  I find them at decent prices fairly often.  One word of caution.  Depending on their age, you may have to replace some components.


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lightwriter62
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29/07/2019 12:01 pm  

@123toid

Mr. Toid, thanks for chiming in, I can see that I’m in way over my head here, I’m going to need a lot more knowledge before attempting anything like this, I only have a rudimentary understanding of tube amps, but SS might as well be in Chinese. An EE degree would come in handy, I’m sure.  I see too many if’s with a project like this, I had a feeling that this was the case, I’d like to thank you and the other guys for clueing me in.

Thanks again, Kent


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shrub0
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29/08/2019 2:36 pm  

I've never built a class A but I believe the heatsink would also be costly.


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