Bias adjustment II - 'The Reckoning'
 

"Wally" wrote in message
...
Keith G wrote:

... All I can say is that the EL34 amp
is most definitely louder into 84 dB speakers than the KT88 amp is
into 86/87 db speakers. In real terms the amp is *plenty* loud enough
where it is and the valves look *decidely* unruffled....???

Maybe you could compare each amp into one pair of speakers, and then into
the other pair.


I'll be making such comparisons in the next week or two. All I can say is
that the DM2As appear to 'soak up' the output from the KiT88 but respond
much 'earlier' to the EL34 amp and I would say it goes quite a bit louder.
No measurements have been taken - going by 'ear' here, which is not
reliable, as we know....

Bias adjustment II - 'The Reckoning'
 

"Nick Gorham" wrote in message
...
Wally wrote:
Nick Gorham wrote:


Not quite, Ht is 510, cathode is at 10v so at 67ma, it would be
500*.067=33.5 ...


Ah, yes, it's a 10V section and a 500V section, each with the same
current.
:-)



Also, the powers being quoted here 34W and 13W are the power being
dissapated by the valve at idle, not directly related to the power
output of the amp. To find that, you need to draw a set of composite
lines for the valves at the paticulat DC bias point, and then plot the
loadline of the reflected load the speaker presents via the output
transformer.


Could the volume difference be down to how each amp handles the speakers?



Yes, one amp could have a OPTX wound for 8R and the other 4R for example.
I think its also the case that the Kit88 is a pure class A design, whereas
the el34 may well shift into B quite early on, the low bias would
certainly make me think thats the case.


The KiT88 is tapped for 8R as you know, the EL34 amp is tapped for both 4
and 8R - the 8R tapping is the one in use. The DM2As are a good load, never
dropping below 7.9R in the 20-20K range, according to the accompanying
booklet.

Bias adjustment II - 'The Reckoning'
 

"Andy Evans" wrote in message
...
It's about time I got a bit more 'into' it!! The idea of getting these
cheap
Chinese amps is to do exactly that and so far it's getting to be very
interesting!!

The problem for tweaking these cheepo chinese amps is that
a) everything is on pcbs, I think, so a pain to fit larger componants in
the
same slots


Yep, I would say you ain't wrong there - pain but probably 'doable'...???


b) there may not me be much room inside the chassis for adding stuff, e.g.
chokes.


Yebbut, it would be easy to jack the chassis up on a nice wooden plinth to
create a bit of space if necessary - stain it and varnish it or paint it
black? (Plinth Of Darkness?? :-)

It would be tempting to leave one amp as is (I shall be doing that anyway)
and 'tweak' the other as far as it possible to check out this 'component
thing'. I'm a cleft stick on this myself - there's no doubt the Triode amp
sounds extra special with it's Black Gates, Sprague and Cerafines, but I
don't see how it should sound any different if 'ordinary' components of
equal spec. were used?? (If I had a thearey - I'd say it's mostly in the
trannies??)

Anyway, this presupposes the second amp is ever going to arrive - I've no
evidence that this at all likely atm...!!!