[bigwig]

Hello,
I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
Thanks Matt.

[Patrick Turner]

bigwig wrote:

Hello,
I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e).

I didn't know you could buy Chinese C-cores. Cores made with low grade
GOSS material would be OK as oposed to best grade GOSS strip.
Then there is plain GOSS E&I laminations of GOSS M6 which is fine.

Have you read my pages on OPT design and theory?

http://www.turneraudio.com.au/output-trans-theory.html

Following pages give examples which will have better bandwidth than
anything from Hammond.

But I have used 1650P 6k6:4,8,&16 for replacements in Jolida 502 amps
with no troubles except that critically damping the amps with gain
shelving networks was neccessary. The Chinese OPT were slightly more
difficult to damp properly with GNFB applied because the Chinese OPT did
not have such wide BW. Jolida omitted to include any damping, and they'd
oscillate with some load types.


Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.

Not really, but you should have 4 output tubes for 3k8 load a-a for best
fidelity.

Using your 6 ohms speakers connected to the 4 ohm connection selection
may give slightly poorer BW because if increased leakage inductance
because maybe not all the secondary windings are used. However, careful
critical damping shelving networks should allow 15dB of NFB
and BW of 7 Ha to 50kHz, -3dB and unconditional stability with UL
connection.

With 6 ohms connected to the 4 ohm outlet, the RL a-a rises to 5.6k a-a,
and OK for a pair of KT88, or even EL34, with Ea = 400V, and Ia per tube
= 60mA per output tube for fair class AB1 operation.

Patrick Turner.


Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
Thanks Matt.

[[email protected]]

On Oct 4, 5:14 pm, bigwig wrote:
Hello,
I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
Thanks Matt.


Who cares about the appearance???? They can be painted and the end
bells swapped out if someone did.

Hammond output transformers are the old 50s utility grade, good for
juke boxes, PA and instrument amps. They are not the high grade that
Peerless 20-20 and UTC LS were.

[bigwig]

On 5 Oct, 21:25, wrote:
On Oct 4, 5:14 pm, bigwig wrote:

Hello,
* I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
* Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
* Thanks Matt.

*Who cares about the appearance???? They can be painted and the end
bells swapped out if someone did.

*Hammond output transformers are the old 50s utility grade, good for
juke boxes, PA and instrument amps. They are not the high grade that
Peerless 20-20 and UTC LS were.

Sorry about taking so long to reply. It took 48 hours for me to be
able to see my post!. The cores are not that bad. They were advertised
as good for 100W, so I planned on using four output tubes as you
rightly guesed Patrick. I should have stated that instead of just
giving the impedence.
I have read your pages on OPT design and after working through it
all, it works out the available window would only allow 0.2mm wire on
the primary. This is a bit small for the DC current in the windings. I
had my misgivings about the cores when they arrived but figured hey I
will work it all out and see what can be done.
I know C-Cores can be a bit smaller but I am worried about
saturation at low frequency, so I tried to keep the turns per volt
up. After being unable to find a suitable compromise I did a little
experiment (If you would like figures I can repeat it). I wound 500
turns on and a 10 turn secondary. I dont own a Variac so I used a
large multi tapped tranny to power the primary with a 1R load on the
secondary, scope across this and the input. I am not sure if this is
the best way to test a core but it was what I thought would work at
the time. It turned out the cores were only capable of 40 odd VA at
50Hz. Pretty bad advertising, infact very misleading!!. I have noticed
that the original seller dissapeared from ebay. Then another seller
(the same one?) started selling them and also soon dissapeared.
Anyway back to the point and I am sure you have heard this many
times, despite your excellent encouragement for people to wind their
own. I now have all the components, power transformers etc. to build
my amps and just want to get it done. The Hammonds seem good value,
except for some reports of poor finish. After all the messing about I
have had with these perfectly good but wrongly specced cores, would I
be right to get the Hammonds and then use these cores for something
smaller(QQV 06-40A class A triode PP) ?
Thanks for taking an interest. Matt.

[Patrick Turner]

bigwig wrote:

On 5 Oct, 21:25, wrote:
On Oct 4, 5:14 pm, bigwig wrote:

Hello,
I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
Thanks Matt.

Who cares about the appearance???? They can be painted and the end
bells swapped out if someone did.

Hammond output transformers are the old 50s utility grade, good for
juke boxes, PA and instrument amps. They are not the high grade that
Peerless 20-20 and UTC LS were.



Matt, it isn't clear to whom you are replying, but I assume it is to me
and I quote the reply I made to your original post...


bigwig wrote:

Hello,
I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e).


I said.....

I didn't know you could buy Chinese C-cores. Cores made with low grade
GOSS material would be OK as oposed to best grade GOSS strip.
Then there is plain GOSS E&I laminations of GOSS M6 which is fine.

Have you read my pages on OPT design and theory?

http://www.turneraudio.com.au/output-trans-theory.html

Following pages give examples which will have better bandwidth than
anything from Hammond.

But I have used 1650P 6k6:4,8,&16 for replacements in Jolida 502 amps
with no troubles except that critically damping the amps with gain
shelving networks was neccessary. The Chinese OPT were slightly more
difficult to damp properly with GNFB applied because the Chinese OPT did
not have such wide BW. Jolida omitted to include any damping, and they'd
oscillate with some load types.


Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.

Not really, but you should have 4 output tubes for 3k8 load a-a for best
fidelity.

Using your 6 ohms speakers connected to the 4 ohm connection selection
may give slightly poorer BW because if increased leakage inductance
because maybe not all the secondary windings are used. However, careful
critical damping shelving networks should allow 15dB of NFB
and BW of 7 Ha to 50kHz, -3dB and unconditional stability with UL
connection.

With 6 ohms connected to the 4 ohm outlet, the RL a-a rises to 5.6k a-a,
and OK for a pair of KT88, or even EL34, with Ea = 400V, and Ia per tube
= 60mA per output tube for fair class AB1 operation.

Patrick Turner.


Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
Thanks Matt.

Here is your latest full reply with my comments placed within your text
so other readers will be able to follow the thread....


Sorry about taking so long to reply. It took 48 hours for me to be
able to see my post!. The cores are not that bad. They were advertised
as good for 100W, so I planned on using four output tubes as you
rightly guesed Patrick. I should have stated that instead of just
giving the impedence.

The 1650R is 5k:4,8,16 and good for 100W. So this allows many options.
Let us assume you have speakers to match the secondary outlets, ie,
either 4, 8 or 16 ohms, and you want to connect the right load to the
right outlet, so that the load will be 5k and UL for the tubes. For best
hi-fi, and when using 4 output tubes, each pair will see 10k, and with
Ea = +420V maybe you get about 60W AB1.

Load line analysis will confirm what you can get, and the amount of
class PO before the amp moves into class AB action.


I have read your pages on OPT design and after working through it
all, it works out the available window would only allow 0.2mm wire on
the primary. This is a bit small for the DC current in the windings. I
had my misgivings about the cores when they arrived but figured hey I
will work it all out and see what can be done.
I know C-Cores can be a bit smaller but I am worried about
saturation at low frequency, so I tried to keep the turns per volt
up.

C-cores are subject to the same rules about core saturation as I have
indicated in the formulas at my website. So the Afe of the central core
leg within the windings needs to be the same size as with M6 GOSS E&I
laminations. So C-cores only give a very slight reduction in weight.

After being unable to find a suitable compromise I did a little
experiment (If you would like figures I can repeat it). I wound 500
turns on and a 10 turn secondary. I dont own a Variac so I used a
large multi tapped tranny to power the primary with a 1R load on the
secondary, scope across this and the input. I am not sure if this is
the best way to test a core but it was what I thought would work at
the time. It turned out the cores were only capable of 40 odd VA at
50Hz. Pretty bad advertising, infact very misleading!!.


But you have not explained your full description of how you tested and
at what frequency.

What was the applied voltage across the 500turns?, core area? and so
what was the B in tesla at what you perceived to be core saturation?
Many people can become quite confused during such tests

I assume you used a mains tranny and 60Hz though. The taps on your
tranny will be low impedance and at the onset of saturation the 60Hz
mains voltage wave should remain the same as looking at the supply at
the wall socket. The wave at the wall socket will have flats top and
bottom and contain maybe 5% odd order distortion because of the
multitude of other people connected to your street powerline and their
use of gear with rectifiers such as PC supplies etc.

But across your 1 ohms R, when the distortion in the current wave
reaches 3% in excess of the distortion seen in the input voltage wave
then the core is beginning to saturate. At 10% rise in applied voltage,
distortion will leap maybe 10%, so the core sat has become more severe.



I have noticed
that the original seller dissapeared from ebay. Then another seller
(the same one?) started selling them and also soon dissapeared.
Anyway back to the point and I am sure you have heard this many
times, despite your excellent encouragement for people to wind their
own. I now have all the components, power transformers etc. to build
my amps and just want to get it done. The Hammonds seem good value,
except for some reports of poor finish.

The potted Hammonds look a lot better. You pay extra for the better
finish.

After all the messing about I
have had with these perfectly good but wrongly specced cores, would I
be right to get the Hammonds and then use these cores for something
smaller(QQV 06-40A class A triode PP) ?
Thanks for taking an interest. Matt.

Just what is the window size and double C-core centre leg Afe size for
the C-cores you say are underspec? C-cores are described by 'strip
width' and 'build up' of the wound strip, say 18mm x 55mm perhaps. With
double C-core the Afe of the central core becomes 36mm x 55mm, ok?


I have not seen the triode data for QQV O6-40A

But this tube has Pda max of 40W, although I'd never run them at 40W for
class A.

They say they are like an 807 and so 20W triode PO is probably possible
with RL about 6ka-a.

Patrick Turner.

[bigwig]

On 8 Oct, 10:18, Patrick Turner wrote:
bigwig wrote:

On 5 Oct, 21:25, wrote:
On Oct 4, 5:14 pm, bigwig wrote:

Hello,
* I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
* Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
* Thanks Matt.

*Who cares about the appearance???? They can be painted and the end
bells swapped out if someone did.

*Hammond output transformers are the old 50s utility grade, good for
juke boxes, PA and instrument amps. They are not the high grade that
Peerless 20-20 and UTC LS were.

Matt, it isn't clear to whom you are replying, but I assume it is to me
and I quote the reply I made to your original post...

bigwig wrote:

Hello,
* I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e).

I said.....

I didn't know you could buy Chinese C-cores. Cores made with low grade
GOSS material would be OK as oposed to best grade GOSS strip.
Then there is plain GOSS E&I laminations of GOSS M6 which is fine.

Have you read my pages on OPT design and theory?

http://www.turneraudio.com.au/output-trans-theory.html

Following pages give examples which will have better bandwidth than
anything from Hammond.

But I have used 1650P 6k6:4,8,&16 for replacements in Jolida 502 amps
with no troubles except that critically damping the amps with gain
shelving networks was neccessary. The Chinese OPT were slightly more
difficult to damp properly with GNFB applied because the Chinese OPT did
not have such wide BW. Jolida omitted to include any damping, and they'd
oscillate with some load types.

Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.

Not really, but you should have 4 output tubes for 3k8 load a-a for best
fidelity.

Using your 6 ohms speakers connected to the 4 ohm connection selection
may give slightly poorer BW because if increased leakage inductance
because maybe not all the secondary windings are used. However, careful
critical damping shelving networks should allow 15dB of NFB
and BW of 7 Ha to 50kHz, -3dB and unconditional stability with UL
connection.

With 6 ohms connected to the 4 ohm outlet, the RL a-a rises to 5.6k a-a,
and OK for a pair of KT88, or even EL34, with Ea = 400V, and Ia per tube
= 60mA per output tube for fair class AB1 operation.

Patrick Turner.

* Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
* Thanks Matt.

Here is your latest full reply with my comments placed within your text
so other readers will be able to follow the thread....



Sorry about taking so long to reply. It took 48 hours for me to be
able to see my post!. The cores are not that bad. They were advertised
as good for 100W, so I planned on using four output tubes as you
rightly guesed Patrick. I should have stated that instead of just
giving the impedence.

The 1650R is 5k:4,8,16 and good for 100W. So this allows many options.
Let us assume you have speakers to match the secondary outlets, ie,
either 4, 8 or 16 ohms, and you want to connect the right load to the
right outlet, so that the load will be 5k and UL for the tubes. For best
hi-fi, and when using 4 output tubes, each pair will see 10k, and with
Ea = +420V maybe you get about 60W AB1.

Load line analysis will confirm what you can get, and the amount of
class PO before the amp moves into class AB action.

* I have read your pages on OPT design and after working through it
all, it works out the available window would only allow 0.2mm wire on
the primary. This is a bit small for the DC current in the windings. I
had my misgivings about the cores when they arrived but figured hey I
will work it all out and see what can be done.
* I know C-Cores can be a bit smaller but I am worried about
saturation at low frequency, so I tried to keep the turns per volt
up. *

C-cores are subject to the same rules about core saturation as I have
indicated in the formulas at my website. So the Afe of the central core
leg within the windings needs to be the same size as with M6 GOSS E&I
laminations. So C-cores only give a very slight reduction in weight.

After being unable to find a suitable compromise I did a little
experiment (If you would like figures I can repeat it). I wound 500
turns on and *a 10 turn secondary. I dont own a Variac so I used a
large multi tapped tranny to power the primary with a 1R load on the
secondary, scope across this and the input. I am not sure if this is
the best way to test a core but it was what I thought would work at
the time. It turned out the cores were only capable of 40 odd VA at
50Hz. Pretty bad advertising, infact very misleading!!.

But you have not explained your full description of how you tested and
at what frequency.

What was the applied voltage across the 500turns?, core area? and so
what was the B in tesla at what you perceived to be core saturation?
Many people can become quite confused during such tests

I assume you used a mains tranny and 60Hz though. The taps on your
tranny will be low impedance and at the onset of saturation the 60Hz
mains voltage wave should remain the same as looking at the supply at
the wall socket. The wave at the wall socket will have flats top and
bottom and contain maybe 5% odd order distortion because of the
multitude of other people connected to your street powerline and their
use of gear with rectifiers such as PC supplies etc.

But across your 1 ohms R, when the distortion in the current wave
reaches 3% in excess of the distortion seen in the input voltage wave
then the core is beginning to saturate. At 10% rise in applied voltage,
distortion will leap maybe 10%, so the core sat has become more severe.

I have noticed
that the original seller dissapeared from ebay. Then another seller
(the same one?) started selling them and also soon dissapeared.
* Anyway back to the point and I am sure you have heard this many
times, despite your excellent encouragement for people to wind their
own. I now have all the components, power transformers etc. to build
my amps and just want to get it done. The Hammonds seem good value,
except for some reports of poor finish.

The potted Hammonds look a lot better. You pay extra for the better
finish.

After all the messing about I
have had with these perfectly good but wrongly specced cores, would I
be right to get the Hammonds and then use these cores for something
smaller(QQV 06-40A class A triode PP) ?
* Thanks for taking an interest. Matt.

Just what is the window size and double C-core centre leg Afe size for
the C-cores you say are underspec? C-cores are described by 'strip
width' and 'build up' of the wound strip, say 18mm x 55mm perhaps. With
double C-core the Afe of the central core becomes 36mm x 55mm, ok?

I have not seen the triode data for QQV O6-40A

But this tube has Pda max of 40W, although I'd never run them at 40W for
class A.

They say they are like an 807 and so 20W triode PO is probably possible
with RL about 6ka-a.

Patrick Turner.- Hide quoted text -

- Show quoted text -

Hello Patrick,
I tested at 50Hz. If you give me a couple of days I will re-run the
test. I had the scope on the 500t primary winding of my test set-up
and acroos the 1 Ohm load resistor. The primary did not show any
serious distortion (unless I go mad and really load it down). I dont
suffer much from a distorted mains waveform because the 11KV
transformer is at the bottom of my garden. My loop impedence is of the
order of 0.08 Ohm measured on a Fluke loop impedence meter.
I will get the cores and the boobin I wound with the test coils out
of the attic tomorrow when I can get in there. My daughter is asleep
under the hatch. I think I would be in the dog house if I go up there
now. I did have all the workings and dimensions etc in a notebook but
I think I kept it together with the cores.
Just looked at the data for the QQV 06-40 the two sections have a
common cathode and G2, so I guess this means a screen supply for AB1
pure tetrode. or paralleling both sections and connecting as triodes
for triode class A, meaning using two tubes for PP. I think I will
play with these at another time. They have twin anode connections on
top which isnt that clever with kids. Plus like you say it wouldnt be
wise to run them at full dissipation as the datasheet says they need
some form of heatsink on the anode pins (even more tempting for kids).
Matt.

[bigwig]

On 8 Oct, 16:47, bigwig wrote:
On 8 Oct, 10:18, Patrick Turner wrote:

bigwig wrote:

On 5 Oct, 21:25, wrote:
On Oct 4, 5:14 pm, bigwig wrote:

Hello,
* I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e). Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.
* Also I just got a pair of East German QQV06-40As for 99p/50c!.. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
* Thanks Matt.

*Who cares about the appearance???? They can be painted and the end
bells swapped out if someone did.

*Hammond output transformers are the old 50s utility grade, good for
juke boxes, PA and instrument amps. They are not the high grade that
Peerless 20-20 and UTC LS were.

Matt, it isn't clear to whom you are replying, but I assume it is to me
and I quote the reply I made to your original post...

bigwig wrote:

Hello,
* I have read the archives regarding Hammond transformers. I just want
to know what people think of their latest fair?. I see some people say
the finnish is poor. I know the endbells have stupid knockouts, but is
it still worth buying them?. I plan to use a pair of 1650Rs in my
5B255M amps as I have given up on winding my own due to the rubbish C-
Cores I bought(dont buy Chinese ****e).

I said.....

I didn't know you could buy Chinese C-cores. Cores made with low grade
GOSS material would be OK as oposed to best grade GOSS strip.
Then there is plain GOSS E&I laminations of GOSS M6 which is fine.

Have you read my pages on OPT design and theory?

http://www.turneraudio.com.au/output-trans-theory.html

Following pages give examples which will have better bandwidth than
anything from Hammond.

But I have used 1650P 6k6:4,8,&16 for replacements in Jolida 502 amps
with no troubles except that critically damping the amps with gain
shelving networks was neccessary. The Chinese OPT were slightly more
difficult to damp properly with GNFB applied because the Chinese OPT did
not have such wide BW. Jolida omitted to include any damping, and they'd
oscillate with some load types.

Im planning on using my
nominaly 6 Ohm speakers on the 8 Ohm tap to get 3.75K A to A, close
enough. Does anyone see a problem eg. reduced bandwidth?.

Not really, but you should have 4 output tubes for 3k8 load a-a for best
fidelity.

Using your 6 ohms speakers connected to the 4 ohm connection selection
may give slightly poorer BW because if increased leakage inductance
because maybe not all the secondary windings are used. However, careful
critical damping shelving networks should allow 15dB of NFB
and BW of 7 Ha to 50kHz, -3dB and unconditional stability with UL
connection.

With 6 ohms connected to the 4 ohm outlet, the RL a-a rises to 5.6k a-a,
and OK for a pair of KT88, or even EL34, with Ea = 400V, and Ia per tube
= 60mA per output tube for fair class AB1 operation.

Patrick Turner.

* Also I just got a pair of East German QQV06-40As for 99p/50c!. Does
anyone know what factory these were made in? because they seem to be
of excellent quality, perhaps better than the Mullard originals.
* Thanks Matt.

Here is your latest full reply with my comments placed within your text
so other readers will be able to follow the thread....

Sorry about taking so long to reply. It took 48 hours for me to be
able to see my post!. The cores are not that bad. They were advertised
as good for 100W, so I planned on using four output tubes as you
rightly guesed Patrick. I should have stated that instead of just
giving the impedence.

The 1650R is 5k:4,8,16 and good for 100W. So this allows many options.
Let us assume you have speakers to match the secondary outlets, ie,
either 4, 8 or 16 ohms, and you want to connect the right load to the
right outlet, so that the load will be 5k and UL for the tubes. For best
hi-fi, and when using 4 output tubes, each pair will see 10k, and with
Ea = +420V maybe you get about 60W AB1.

Load line analysis will confirm what you can get, and the amount of
class PO before the amp moves into class AB action.

* I have read your pages on OPT design and after working through it
all, it works out the available window would only allow 0.2mm wire on
the primary. This is a bit small for the DC current in the windings. I
had my misgivings about the cores when they arrived but figured hey I
will work it all out and see what can be done.
* I know C-Cores can be a bit smaller but I am worried about
saturation at low frequency, so I tried to keep the turns per volt
up. *

C-cores are subject to the same rules about core saturation as I have
indicated in the formulas at my website. So the Afe of the central core
leg within the windings needs to be the same size as with M6 GOSS E&I
laminations. So C-cores only give a very slight reduction in weight.

After being unable to find a suitable compromise I did a little
experiment (If you would like figures I can repeat it). I wound 500
turns on and *a 10 turn secondary. I dont own a Variac so I used a
large multi tapped tranny to power the primary with a 1R load on the
secondary, scope across this and the input. I am not sure if this is
the best way to test a core but it was what I thought would work at
the time. It turned out the cores were only capable of 40 odd VA at
50Hz. Pretty bad advertising, infact very misleading!!.

But you have not explained your full description of how you tested and
at what frequency.

What was the applied voltage across the 500turns?, core area? and so
what was the B in tesla at what you perceived to be core saturation?
Many people can become quite confused during such tests

I assume you used a mains tranny and 60Hz though. The taps on your
tranny will be low impedance and at the onset of saturation the 60Hz
mains voltage wave should remain the same as looking at the supply at
the wall socket. The wave at the wall socket will have flats top and
bottom and contain maybe 5% odd order distortion because of the
multitude of other people connected to your street powerline and their
use of gear with rectifiers such as PC supplies etc.

But across your 1 ohms R, when the distortion in the current wave
reaches 3% in excess of the distortion seen in the input voltage wave
then the core is beginning to saturate. At 10% rise in applied voltage,
distortion will leap maybe 10%, so the core sat has become more severe.

I have noticed
that the original seller dissapeared from ebay. Then another seller
(the same one?) started selling them and also soon dissapeared.
* Anyway back to the point and I am sure you have heard this many
times, despite your excellent encouragement for people to wind their
own. I now have all the components, power transformers etc. to build
my amps and just want to get it done. The Hammonds seem good value,
except for some reports of poor finish.

The potted Hammonds look a lot better. You pay extra for the better
finish.

After all the messing about I
have had with these perfectly good but wrongly specced cores, would I
be right to get the Hammonds and then use these cores for something
smaller(QQV 06-40A class A triode PP) ?
* Thanks for taking an interest. Matt.

Just what is the window size and double C-core centre leg Afe size for
the C-cores you say are underspec? C-cores are described by 'strip
width' and 'build up' of the wound strip, say 18mm x 55mm perhaps. With
double C-core the Afe of the central core becomes 36mm x 55mm, ok?

I have not seen the triode data for QQV O6-40A

But this tube has Pda max of 40W, although I'd never run them at 40W for
class A.

They say they are like an 807 and so 20W triode PO is probably possible
with RL about 6ka-a.

Patrick Turner.- Hide quoted text -

- Show quoted text -

Hello Patrick,
* I tested at 50Hz. If you give me a couple of days I will re-run the
test. I had the scope on the 500t primary winding of my test set-up
and acroos the 1 Ohm load resistor. The primary did not show any
serious distortion (unless I go mad and really load it down). I dont
suffer much from a distorted mains waveform because the 11KV
transformer is at the bottom of my garden. My loop impedence is of the
order of 0.08 Ohm measured on a Fluke loop impedence meter.
* I will get the cores and the boobin I wound with the test coils out
of the attic tomorrow when I can get in there. My daughter is asleep
under the hatch. I think I would be in the dog house if I go up there
now. I did have all the workings and dimensions etc in a notebook but
I think I kept it together with the cores.
* Just looked at the data for the QQV 06-40 the two sections have a
common cathode and G2, so I guess this means a screen supply for AB1
pure tetrode. or paralleling both sections and connecting as triodes
for triode class A, meaning using two tubes for PP. I think I will
play with these at another time. They have twin anode connections on
top which isnt that clever with kids. Plus like you say it wouldnt be
wise to run them at full dissipation as the datasheet says they need
some form of heatsink on the anode pins (even more tempting for kids).
* * Matt.

Hello,
I still have not had a chance to do a re-test. I have been on the go
with family things and will be going back to college on Monday,
Tuesday and Wednesday. Im doing my 17th edition wiring regs. A piece
of paper saying I can do what I already know (I have 16th). You know
the way it is these days with all the health and safety and threats of
litigation. Oh well, its another feather in my cap and I have an
interveiw for a better job off the back of it. Will do it Thursday
afternoon, so I will post that evening.
The cores are quite good and I am going to search out where they
originaly came from in China. They should be cheaper direct from the
manufacturer. They had larger ones up to what they qute as 400W. This
seems a strange way to rate any transformer component. Also they
randomly quote 400Hz so I guess they are intendended for aerospace.
The material is M6 (Z11) .26mm. The dimensions of one leg of a core
are 16.25mm by 32.2mm. Too small for 100W unless double cores are used
and even then (from what you say that the center leg should be the
same as E I core material) marginal.
Matt.