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

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?)



This getting very interesting. Yes, all 4 valves have the same sticker with
the same values, but I have seen diffent values (33, not 31) on the labels
on the eBay pic. I have another identical amp coming in a couple of days
(hopefully) and it will be interesting to see what the values are on that
one.

It almost looks like they measure every valve and match them - is this
likely or is it ********???


Very likly, I think the numbers on the valves are just that, for
matching. They set up the valve tester at that anode, g1, and g2
voltages, plug in the valve, and write down what current flows through
it. Then when they send a amp out, they pick 4 valves with the same
number. Thats why you will have seen pictures with different numbers on,
they have matched another set about another current.

Doesn't help you to know what the design current is though. I would try
and find out from the makers. Without knowing what the B+ is you can't
know what dissapation the valves are running at, and even if the valves
would work fine at a higher current, you don't know what the power
supply can give. If it is running at 34ma, thats as Andy said quite low,
but remember the anode dissapation is not directly related to the output
power, it depends on when the move from A to B happens. if the valve is
dissapating 13w (for example) thats power thats not being passed to the
speakers, what you are interested in (in terms of output) is the power
the valve "dissapates" in the load, the output transformer primary, and
so to the speakers

--
Nick

"Nick Gorham" wrote


It almost looks like they measure every valve and match them - is this
likely or is it ********???


Very likly, I think the numbers on the valves are just that, for matching.
They set up the valve tester at that anode, g1, and g2 voltages, plug in
the valve, and write down what current flows through it. Then when they
send a amp out, they pick 4 valves with the same number. Thats why you
will have seen pictures with different numbers on, they have matched
another set about another current.


Yep, much as I suspected.


Doesn't help you to know what the design current is though. I would try
and find out from the makers.


I'm going to see if I can get the circuit from the designer.


Without knowing what the B+ is you can't know what dissapation the valves
are running at, and even if the valves would work fine at a higher
current, you don't know what the power supply can give. If it is running
at 34ma, thats as Andy said quite low, but remember the anode dissapation
is not directly related to the output power, it depends on when the move
from A to B happens. if the valve is dissapating 13w (for example) thats
power thats not being passed to the speakers, what you are interested in
(in terms of output) is the power the valve "dissapates" in the load, the
output transformer primary, and so to the speakers


OK. (There'll be more questions.... ;-)

"Keith G" wrote in message
...

"Nick Gorham" wrote


It almost looks like they measure every valve and match them - is this
likely or is it ********???


Very likly, I think the numbers on the valves are just that, for
matching. They set up the valve tester at that anode, g1, and g2
voltages, plug in the valve, and write down what current flows through
it. Then when they send a amp out, they pick 4 valves with the same
number. Thats why you will have seen pictures with different numbers on,
they have matched another set about another current.


Yep, much as I suspected.


Doesn't help you to know what the design current is though. I would try
and find out from the makers.


I'm going to see if I can get the circuit from the designer.


I'll agree with that as well. My matched quads of KT88's & 6550C's came with
similar test labels & identical numbers. It's easy with a tester to do a of
quick 'n dirty static test, & the've always been within okay limits. You
know yourself if you get an untested batch lot then they can vary quite a
bit sample to sample but I've always found the Svetlana output valves with
not too much unit variation (or have I been lucky?). Anyone else found
this? But if you want true accuracy then dynamic matching is the only
answer.

"Keith G" wrote in message
...

"Wally" wrote in message
...
The snip!

This getting very interesting. Yes, all 4 valves have the same sticker
with the same values, but I have seen diffent values (33, not 31) on the
labels on the eBay pic. I have another identical amp coming in a couple of
days (hopefully) and it will be interesting to see what the values are on
that one.

It almost looks like they measure every valve and match them - is this
likely or is it ********???


No ********, with computerised testers it's a very quick operation.(Valves
using solid state for their own advantage - ironic eh?) If you want the
best out of your amp and to know it's nicely balanced in regard to gm etc
then matched valves are the only way to go. With your amount of valve
equipment growing it might be worth picking up a valve characteristic
meter/tester on ebay and doing your own testing/checking.

Cheers,

Mike

In message , Mike Gilmour
writes

"Keith G" wrote in message
...

"Wally" wrote in message
...
The snip!

This getting very interesting. Yes, all 4 valves have the same sticker
with the same values, but I have seen diffent values (33, not 31) on the
labels on the eBay pic. I have another identical amp coming in a couple of
days (hopefully) and it will be interesting to see what the values are on
that one.

It almost looks like they measure every valve and match them - is this
likely or is it ********???


No ********, with computerised testers it's a very quick operation.(Valves
using solid state for their own advantage - ironic eh?) If you want the
best out of your amp and to know it's nicely balanced in regard to gm etc
then matched valves are the only way to go. With your amount of valve
equipment growing it might be worth picking up a valve characteristic
meter/tester on ebay and doing your own testing/checking.

Cheers,

Mike



Matching valves is easier said than done. OK, it's a simple matter to
match for a particular anode current, at a particular anode voltage, for
a given grid voltage, and this is all that is normally possible by
measuring the cathode current.

But this is only measuring one parameter at one setting. Valves vary so
much from one to another (compared with SS) that to find the best match
over the operating range that the two (in a P-P amp) have to cover is
non-trivial without a full curve tracer.
--
Chris Morriss

"Chris Morriss" wrote in message
...
In message , Mike Gilmour
writes

"Keith G" wrote in message
...

"Wally" wrote in message
...
The snip!

This getting very interesting. Yes, all 4 valves have the same sticker
with the same values, but I have seen diffent values (33, not 31) on the
labels on the eBay pic. I have another identical amp coming in a couple
of
days (hopefully) and it will be interesting to see what the values are
on
that one.

It almost looks like they measure every valve and match them - is this
likely or is it ********???


No ********, with computerised testers it's a very quick operation.(Valves
using solid state for their own advantage - ironic eh?) If you want the
best out of your amp and to know it's nicely balanced in regard to gm etc
then matched valves are the only way to go. With your amount of valve
equipment growing it might be worth picking up a valve characteristic
meter/tester on ebay and doing your own testing/checking.

Cheers,

Mike



Matching valves is easier said than done. OK, it's a simple matter to
match for a particular anode current, at a particular anode voltage, for a
given grid voltage, and this is all that is normally possible by measuring
the cathode current.

But this is only measuring one parameter at one setting. Valves vary so
much from one to another (compared with SS) that to find the best match
over the operating range that the two (in a P-P amp) have to cover is
non-trivial without a full curve tracer.
--
Chris Morriss

I understood that a number of the major valve suppliers have computerised
characteristic testers that plot and map various parameters rapidly. I know
a manual plot is very time consuming (got the T shirt ;-) but it's a very
different ball game with their equipment.

Mike

"Mike Gilmour" wrote


No ********, with computerised testers it's a very quick operation.(Valves
using solid state for their own advantage - ironic eh?) If you want the
best out of your amp and to know it's nicely balanced in regard to gm etc
then matched valves are the only way to go. With your amount of valve
equipment growing it might be worth picking up a valve characteristic
meter/tester on ebay and doing your own testing/checking.


Yes, I've been thinking of getting summat simple and learning how to use it.

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!!

Thanks to all, once again.

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

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

"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

"Mike Gilmour" wrote in message
...

"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
Another thought, if the cathode resistor is 10 ohms then the output valves
are under running by about half (I guess...not gospel) so you should be able
to get an idea by the envelope temperature of the valves i.e. are they
running less hot than you'd nornally expect?

I know VTL amp output valves generally run cool cos de man sez keeps dem
electrons under restraint :-) i.e. instead of 60 or 70mA they run at 45mA
or so and a lot cooler and last longer - he says they sound better...I don't
agree but hey it's a free world (but they sure last looooooonger)

Cool,

Mike