Re: gEDA-user: [OFF] high current amplifier

[John Doty <jpd@xxxxxxxxx>]

On May 21, 2009, at 6:00 PM, Joerg wrote:

> Chris Albertson wrote:
>
> [...]
>
>> I'm thinking about tube amps that had an output impedance of about 1M
>> ohm that used transformers to drive 8 ohm speakers.  About a 100,000
>> to 1 ratio.
>>
>
> 1M? What kind of tube was that?

Well, that's a typical plate resistance for a small signal pentode, but

Power pentodes have lower plate resistance.

For a large signal amplifier, the load generally isn't matched to the  
output resistance. Instead, it's roughly (peak output voltage)/(peak  
output current), which is different. If you match the output  
resistance, in most cases you'll clip at an output power well below  
the capacity of the amplifier.

And finally, the real issue here is the current required. 100 amps  
will melt the wire in any audio transformer I've ever seen.

Everybody seems to think Mark's soldering gun suggestion is a joke,  
but I don't know. I think I'd get one, pull the transformer, measure  
its characteristics, see if it might work (maybe a couple of them in  
series/parallel or something). They're light, cheap, and the closest  
thing to the requirement here I can think of. I'm sure they won't run  
at full power all day without overheating, but for a test set that  
might be OK.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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