Is the 4-400A a good choice for something cheap to start with?
There seems to be a steady stream of cheap used ones on that internet
place.
Chris
w0ep
On Mon, 2006-10-23 at 22:01 -0400, Joe Subich, W4TV wrote:
> Clint,
>
> You have gotten good advice ... but a couple more thoughts
>
> Almost any amplifier is a good starting amp but be prepared to make
> some changes and learn from the experience.
>
> 1) The MLA-2500 is to be avoided - as others have said - because of
> the fragile and out of production 8875. Yes, it can be converted
> to other tubes but the small chassis is a significant handicap to
> a clean conversion.
>
> 2) home built amplifiers using ex-USSR tubes are probably not a good
> vehicle for learning. Replacing the ex-USSR tubes can be a problem
> as many are not being made and surplus sources are not reliable.
>
> 3) External anode tubes (8874/3CX400, 3CX800, 8877/3CX1500) are
> expensive and have fragile grids. The 3CX800 and 3CX1500 are
> great tubes in the hands of an experienced designer but are
> probably not a good place for the beginner to start.
>
> Recommendations:
>
> A solidly built single 3-500Z or pair of 3-500Z amplifier ...
> SB-1000, AL-80, SB-220, L4B, L7, AL-82, etc. You can learn
> much but be prepared to eliminate the "floating grids", add
> the proper glitch resistor, improve the cooling of any external
> power supply, fix the bias and metering circuits, and convert
> the T/R switching to low voltage and (possibly vacuum relays).
> Converting any of the 3-500Z amplifiers to one of GM3SEK's
> "triode board" controllers would be worthwhile from both a
> reliability and learning prospect.
>
> A clean amplifier with FOUR 572Bs is not to be avoided. With
> the proper voltage 4 x 572B will produce nearly the legal
> limit and the tube cost will not break the bank. Again, be
> prepared to fix many of the "floating grid," bias and T/R
> switching issues. I would avoid the two tube 572B amps if
> only because they are generally too small, undercooled have
> poor layout are difficult to service and cost as much or more
> than a single 3-500Z amplifier.
>
> 73,
>
> ... Joe, W4TV
>
>
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