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

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

Chris Albertson wrote:
> On Thu, May 21, 2009 at 5:00 PM, Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx> 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? I think the highest I had was about 5K.
>> At 5000 volts on the plates ...
> 
> OK off by "just one decimal point".  My point still is that tube amps
> have to deal with a huge impedance mis-match and they handle it with a
> transformer.    Then you ask "what transformers can handle a load that
> is well under 1 ohm.  So I thought about arc welders.
> 

Point-contact welders may also be an option.


> While on the subject, I'm wanting to build a tube amp.  But my goal is
> not to re-create an old design.  Mostly for entertainment and
> education I want to design and build the transformers too.  Anyone
> have any leads or links to places to buy the parts?  I know you can
> buy frames and the metal plates used to stack a transformer core but
> where?.  I'd start by building something small and easy, like a low
> power 12V power supply but the goal is to learn the art of high power
> transformer building
> 

Hammond makes tube-stage transformers, even quite large ones. But those 
cost a pretty penny and I couldn't bring myself to chop up some of those 
beauties to stack the cores. Paralleling, yes. You might want to ask in 
a hardcore audio-freak group.

As for tubes I found that HV-driver tubes for color TVs were the best 
deal. But this was decades ago, today you'd have to take a look at which 
current production tubes are available and at what cost. Sovtek, 
Svetlana and so on.

The biggest tube amp I ever built was with two of these and you almost 
had to call the utility before turning it on:

http://www.pll.gr/qb5-1750.pdf

-- 
Regards, Joerg

http://www.analogconsultants.com/



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