Bias adjustment II - 'The Reckoning'
 

Apologies for the delay for this 'joint reply' - interrupted by a little
post-prandial 'digestif' by way of a spot of Delius and VW (Larka Sending
and Symphony No. 6 - still playing! :-)

*Massive thanks* to *all* who responded and were, between you, just about
right on the money, from what I can see of it!! (Fekkin' valvies - too damn
sad/skint to be out on the ****/tiles/razzle on a Saturday Night!! :-)

(I dunno!!)

OK. First up, the valves read as follows (Test voltage, amp on / Resistance,
amp off - the DVM wuz under me bed!!)

V1 = 0.317 V / 10.2 ohms (10R2 ??)

V2 = 0.303 V / 10.0

V3 = 0.322 V / 10.2

V4 = 0.318 V / 10.5

(I'll check tomorrow, but I thought the voltage readings were all "+" ???)

Next, the valve labels are all as follows:

http://www.apah69.dsl.pipex.com/keit.../valvebase.jpg

Now, call me a bluff old cove, but this looks to me a bit like we want
is -37 VDC on the grid (am I right?) - ie. the 'test' voltage?? If so the
valves are all(consistently) 'underbiased?

What do each of these figures mean? (I understand about the valves being
'matched' but I thought was mA / V or summat??)

Many thanks, once again.

Bias adjustment II - 'The Reckoning'
 

I presume the test point is the cathode of the output valve, which has a 10 ohm
resistor. If the voltage is .32 then the current across it should be 32mA.
That's not very much - I wonder what the B+ could be - over 400v if you want
any power I imagine. Andy

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

Bias adjustment II - 'The Reckoning'
 

"Andy Evans" wrote in message
...
I presume the test point is the cathode of the output valve, which has a 10
ohm
resistor. If the voltage is .32 then the current across it should be 32mA.
That's not very much - I wonder what the B+ could be - over 400v if you
want
any power I imagine. Andy


OK, what about the label?

Ua: 430V

Vg2: 440V

Vg1: -36V


What are these telling us exactly?

(Apologies for my Ignore Ants.... ;-)

Bias adjustment II - 'The Reckoning'
 

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.

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

Bias adjustment II - 'The Reckoning'
 

"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'....???)

Bias adjustment II - 'The Reckoning'
 

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.

Bias adjustment II - 'The Reckoning'
 

"Keith G" wrote in message
...
Apologies for the delay for this 'joint reply' - interrupted by a little
post-prandial 'digestif' by way of a spot of Delius and VW (Larka Sending
and Symphony No. 6 - still playing! :-)

*Massive thanks* to *all* who responded and were, between you, just about
right on the money, from what I can see of it!! (Fekkin' valvies - too
damn sad/skint to be out on the ****/tiles/razzle on a Saturday Night!!
:-)

(I dunno!!)

OK. First up, the valves read as follows (Test voltage, amp on /
Resistance, amp off - the DVM wuz under me bed!!)

V1 = 0.317 V / 10.2 ohms (10R2 ??)

V2 = 0.303 V / 10.0

V3 = 0.322 V / 10.2

V4 = 0.318 V / 10.5

(I'll check tomorrow, but I thought the voltage readings were all "+"
???)

Next, the valve labels are all as follows:

http://www.apah69.dsl.pipex.com/keit.../valvebase.jpg

Now, call me a bluff old cove, but this looks to me a bit like we want
is -37 VDC on the grid (am I right?) - ie. the 'test' voltage?? If so the
valves are all(consistently) 'underbiased?

What do each of these figures mean? (I understand about the valves being
'matched' but I thought was mA / V or summat??)

Many thanks, once again.





Hi Keith,

I'm just wondering if they supply the amplifier with brand new but tested
valves i.e. not burnt in for say 10 hours to allow anode current to
stabilise. If this is the case they may supply the amplifier underbiased
with instructions (if you had them!!) to run it for a while then increase
the bias point to the correct anode current when all the output tube anode
currents are stable (i.e. the bias reading at test points are finally static
and settled down) Just a thought - I'd still get back to the supplier.

Cheers

Mike

Bias adjustment II - 'The Reckoning'
 

Keith G wrote:

V1 = 0.317 V / 10.2 ohms (10R2 ??)
V2 = 0.303 V / 10.0
V3 = 0.322 V / 10.2
V4 = 0.318 V / 10.5

If you adjust the tweakers so that the voltages measure as follows...

V1 = 0.3162V
V2 = 0.31V
V3 = 0.3162V
V4 = 0.3255V

....that should give each valve an Ia of 31mA. I'm assuming that the 31mA on
the valve label indicates what the anode current should be for all valves.
(Do they all have the sticker, and do they all have the same value for Ia?)


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

Bias adjustment II - 'The Reckoning'
 

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

Bias adjustment II - 'The Reckoning'
 

"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!!! )

;-)