"Andy Evans" wrote in message
...
Ua: 430V this is the voltage on the anode of the output valves

Vg2: 440V this is the voltage on the screen grids (g2) -

Vg1: -36V this is the fixed bias on the grid, or g1 (grid one, the
control
grid, where the signal goes in)

32mA at 430v would only give you about 13 watts, which is pretty
conservative,
but OK I guess.


No, summat's not right here - this amp'll trounce my KiT88 which pushes out
32wpc. (Volume, not*quality* mind....;-)

It's running into a pair of Fluffy Bunny DM2As (84dB according to that nice
Mr P) and it stoke's 'em like a wild thing! (Runs out of puff at about the 2
o' clock mark, tho'....???)

No, summat's not right here

Well, according to Ohms law .32 volts across 10 ohms is 32mA. I'm assuming this
is the cathode....................... but I don't know the circuit. You'd
expect about double that, really.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

"Andy Evans" wrote in message
...
No, summat's not right here

Well, according to Ohms law .32 volts across 10 ohms is 32mA. I'm assuming
this
is the cathode....................... but I don't know the circuit. You'd
expect about double that, really.


OK. Thanks for that.

I gotta go do a movie now - Swim's getting the arse!! :-(

(I know, I know - slap that bitch's face!!! )

;-)

Keith G wrote:

No, summat's not right here - this amp'll trounce my KiT88 which
pushes out 32wpc. (Volume, not*quality* mind....;-)

It's running into a pair of Fluffy Bunny DM2As (84dB according to
that nice Mr P) and it stoke's 'em like a wild thing! (Runs out of
puff at about the 2 o' clock mark, tho'....???)

That sounds like a sensitive input, as if it's maxing out at a relatively
low volume setting due to the size of the signal it's being fed. After that,
it would just get progressively dirtier. (On mine, o/p from the DAC straight
into the power amp reaches max volume at about 1/3rd of the way up.)

My amp's anode current is about 60mA, and the HT is, I think, 450V (hence
the spec 27W absolute max: 0.06 * 450 = 27). Yours has about half the
current for a similar HT, so Andy's 13W sounds about right.

Does it go audibly louder than the KiT88 (both amps at max, use a preamp to
control volume)? What's the rated output of the KiT88? Could one amp find
the speakers easier to drive than the other?


--
Wally
www.artbywally.com
www.wally.myby.co.uk

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

No, summat's not right here - this amp'll trounce my KiT88 which
pushes out 32wpc. (Volume, not*quality* mind....;-)

It's running into a pair of Fluffy Bunny DM2As (84dB according to
that nice Mr P) and it stoke's 'em like a wild thing! (Runs out of
puff at about the 2 o' clock mark, tho'....???)

That sounds like a sensitive input, as if it's maxing out at a relatively
low volume setting due to the size of the signal it's being fed. After
that,
it would just get progressively dirtier. (On mine, o/p from the DAC
straight
into the power amp reaches max volume at about 1/3rd of the way up.)

My amp's anode current is about 60mA, and the HT is, I think, 450V (hence
the spec 27W absolute max: 0.06 * 450 = 27). Yours has about half the
current for a similar HT, so Andy's 13W sounds about right.


OK, it's crunch time. I'm going to have to get into this quite a bit deeper,
I can see...



Does it go audibly louder than the KiT88 (both amps at max, use a preamp
to
control volume)? What's the rated output of the KiT88? Could one amp find
the speakers easier to drive than the other?


I haven't had the chance to compare the amps directly, but I would say the
EL34 goes quite a bit louder than the Kit88 which is 'supposed' to be rated
at 32 wpc with the cathode resistor mod that I carried out on it....???

Keith G wrote:

I haven't had the chance to compare the amps directly, but I would
say the EL34 goes quite a bit louder than the Kit88 which is
'supposed' to be rated at 32 wpc with the cathode resistor mod that I
carried out on it....???

What value are the cathode resistors on the KiT88, what's the voltage across
them, and what's the anode voltage?


--
Wally
www.artbywally.com
www.wally.myby.co.uk

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

I haven't had the chance to compare the amps directly, but I would
say the EL34 goes quite a bit louder than the Kit88 which is
'supposed' to be rated at 32 wpc with the cathode resistor mod that I
carried out on it....???

What value are the cathode resistors on the KiT88, what's the voltage
across
them, and what's the anode voltage?


The original design of the KiT88 produced 36wpc with 150R cathode resistors.
It ate a couple of valves (common on this amp I found out) and I swapped
them for 220Rs on the advice of Nick Lucas at WAD. He said that would reduce
the output to 32wpc. Since then it has been fine. (They didn't carry this
kit for long as I gather it was a bit of a bugger - Nick G might know more
about this.) Having said that, it's a fine amp IMO.....

I'm sorry, but I can't lay hands on the paperwork to see what the voltages
measured when I built it and I'm not easily in a postion to measure them
atm.....

"Keith G" wrote


I'm sorry, but I can't lay hands on the paperwork to see what the voltages
measured when I built it and I'm not easily in a postion to measure them
atm.....


There's a .pdf of the circuit here if you are curious/interested:

http://www.apah69.dsl.pipex.com/keit...t88circuit.pdf

Keith G wrote:

What value are the cathode resistors on the KiT88, what's the voltage
across them, and what's the anode voltage?

The original design of the KiT88 produced 36wpc with 150R cathode
resistors.

According to the voltages specced on the diagram, it has 10V at the 150R,
giving 67mA for Ia (V/R=I). HT is 510V, so It should be producing 510 *
0.067 = 34W. I can't imagine that changng to 220R would drop the power
substantially - should still be much more than the 13W we reckon the EL34
jobbie is producing.


--
Wally
www.artbywally.com
www.wally.myby.co.uk

Wally wrote:
Keith G wrote:


What value are the cathode resistors on the KiT88, what's the voltage
across them, and what's the anode voltage?


The original design of the KiT88 produced 36wpc with 150R cathode
resistors.


According to the voltages specced on the diagram, it has 10V at the 150R,
giving 67mA for Ia (V/R=I). HT is 510V, so It should be producing 510 *
0.067 = 34W. I can't imagine that changng to 220R would drop the power
substantially - should still be much more than the 13W we reckon the EL34
jobbie is producing.



Not quite, Ht is 510, cathode is at 10v so at 67ma, it would be
500*.067=33.5 the spec for kt88's states the max anode dis is 40w, so
quite a way from that. The change of cathode resistor will make more of
a change than you are suggesting. increasing the value, will increase
the voltage on the cathode, and in that way slightly reduce the voltage
across the valve, BUT it will also reduce the current, so having more of
a effect of anode dis than you may be expecting.

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.

This is a good starting site for such composite load lines.

http://members.aol.com/sbench102/composit.html

Actually its a good starting site for many valve related things.

The fact that the El34 is running at 13w, just points that its a AB1
amp, not a A1 amp, no big deal, and only sensible for El34's IMHO given
the market I suspect they are trying to get into.

--
Nick