View Single Post
  #5   Report Post  
at
 
Posts: n/a
Default


"Krzysiek Słychań" wrote in message
...
But consider surge on valve anodes and OPT when the amp is "underloaded"
(the load's impedance is higher than the amp's output one)... It's not

like
the transistor (whew!) amp. If you connect i.e. 16 Ohm speaker to 4 Ohm

amp
output, the amp's likely to be damaged.

--
Pozdrawiam,
Krzysiek Słychań


Wouldn't that quadruple the impedance of the OPT primary? A 5000 ohm OPT
primary would became 20kohm. That would make the output impedance of the amp
four times lower. So, where's the safe margin?

I've heard that for best speaker control, the output impedance should be
lower than 1ohm, or 10 times lower than the speaker impedance. If it was 10
times lower, with a 4 ohm speaker it should be 0.4ohms.
A single-ended class A amp with a 300B tube with Rp 700ohms and a OPT
primary 4000 and 4 ohm speaker the Zo would be 0.7ohms [7004000:4)].
That's lower that 1 ohm but not 10 times lower. To get 10 times lower Zo,
the OPT primary should be 7000ohms. That would give Zo of 0.4 ohms.

Or have I misunderstood something?

Are there some problems? What things should be taken into account when
deciding upon a OPT and it's primary impedance?


-at