| Author |
Message |
Joe
Guest
|
 Posted:
Wed Dec 01, 2004 6:09 am Post subject:
Output Transformer - push pull or SE ??? |
|
|
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
|
|
| Back to top |
|
 |
Jon Yaeger
Guest
|
| Posted:
Wed Dec 01, 2004 6:09 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
in article dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com, Joe at
joe@emailserver.net wrote on 11/30/04 8:23 PM:
| Quote: | Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
|
Joe,
Single ended transformers are designed differently from push-pull types and
except in special cases (e.g. parafeed configurations) they aren't
interchangeable at all.
Unless you want to use a different push-pull circuit, I'd bite the bullet
and get the recommended SE transformer. You can sell the other on eBay or
use it for another project . . .
Jon |
|
| Back to top |
|
|
Joe
Guest
|
| Posted:
Wed Dec 01, 2004 6:09 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Thanks a lot Jon. I had a feeling that was the case.
On Tue, 30 Nov 2004 20:46:35 -0500, Jon Yaeger <jono_1@bellsouth.net>
wrote:
| Quote: | in article dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com, Joe at
joe@emailserver.net wrote on 11/30/04 8:23 PM:
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
Joe,
Single ended transformers are designed differently from push-pull types and
except in special cases (e.g. parafeed configurations) they aren't
interchangeable at all.
Unless you want to use a different push-pull circuit, I'd bite the bullet
and get the recommended SE transformer. You can sell the other on eBay or
use it for another project . . .
Jon |
|
|
| Back to top |
|
|
Rod Keys
Guest
|
| Posted:
Wed Dec 01, 2004 6:09 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Wellllll .. just wait a minute.
Actually you just have to use the transformer at lower power ....
The hidden issue here is "core saturation". Don't run away Joe, it's not
that complicated! If direct current goes through a transformer's primary
winding it puts magnetism in the transformer's iron core. The problem is
that the core is limited as far as how much magnetism it can "hold". If
it's loaded up with magnetism from DC there's no more left to pass the AC
signal. The answer to this problem is; a) a physically bigger core or, b)
another winding with the DC flowing the other way to offsetting the DC in
the first winding.
In a push-pull transformer the primary winding is split so that half the DC
goes one way and half goes the other way and they counter balance each
other. This minimizes "core situation".
A push-pull transformer will work just fine single ended as long as the
power level, especially the DC component in the primary, is so low that you
don't saturate the core. In other words, your eight watt transformer can't
put out eight watts single ended, but I wouldn't be the least surprised if
it worked just fine single ended at two or three watts.
When a core saturates the first thing to go is the bass (because bass eats
up tons of "core"). In a hi-fi amp this is a killer. In a guitar amp it's
less of a killer .. guitars amps usually emphasize treble, not bass. And
guitars only go so low anyway, (The lowest grunt you can get out of your
git-fiddle is about 100 cps and guitar's don't even do that very often).
Finally, you're going to bump into some impedance mis-match issues. But it
won't be deadly. Transformers actually work on a ratio. If you hook an 8
ohm secondary to a 4 ohm speaker you'll just cut the impedance of the
primary impedance (approximately) in half. Your Hammond transformer is
probably rated at higher impedance that the 2k called for in the circuit,
but use a 4 or 3.2 ohm speaker and things should be fine.
If this is your first project watch out for shock hazzards. Don't dink
around with stuff till you're SURE the electrolytics are discharged
(unplugged isn't enough) and remember, AC/DC circuits (usually using tubes
starting with 50 like 50L6 OR 50C5) are bad news for guitars.
Rod
"Joe" <joe@emailserver.net> wrote in message
news:2v9qq0t1dqoqcqhjc0pkprmrfkfd7f1e7l@4ax.com...
| Quote: | Thanks a lot Jon. I had a feeling that was the case.
On Tue, 30 Nov 2004 20:46:35 -0500, Jon Yaeger <jono_1@bellsouth.net
wrote:
in article dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com, Joe at
joe@emailserver.net wrote on 11/30/04 8:23 PM:
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
Joe,
Single ended transformers are designed differently from push-pull types
and
except in special cases (e.g. parafeed configurations) they aren't
interchangeable at all.
Unless you want to use a different push-pull circuit, I'd bite the bullet
and get the recommended SE transformer. You can sell the other on eBay or
use it for another project . . .
Jon |
|
|
| Back to top |
|
|
Jon Yaeger
Guest
|
| Posted:
Wed Dec 01, 2004 6:09 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
in article keKdnWgZDZ2mpTDcRVn-pg@comcast.com, Rod Keys at rkeys@comcast.net
wrote on 11/30/04 10:19 PM:
| Quote: | Wellllll .. just wait a minute.
Actually you just have to use the transformer at lower power ....
The hidden issue here is "core saturation". Don't run away Joe, it's not
that complicated! If direct current goes through a transformer's primary
winding it puts magnetism in the transformer's iron core. The problem is
that the core is limited as far as how much magnetism it can "hold". If
it's loaded up with magnetism from DC there's no more left to pass the AC
signal. The answer to this problem is; a) a physically bigger core or, b)
another winding with the DC flowing the other way to offsetting the DC in
the first winding.
In a push-pull transformer the primary winding is split so that half the DC
goes one way and half goes the other way and they counter balance each
other. This minimizes "core situation".
A push-pull transformer will work just fine single ended as long as the
power level, especially the DC component in the primary, is so low that you
don't saturate the core. In other words, your eight watt transformer can't
put out eight watts single ended, but I wouldn't be the least surprised if
it worked just fine single ended at two or three watts.
When a core saturates the first thing to go is the bass (because bass eats
up tons of "core"). In a hi-fi amp this is a killer. In a guitar amp it's
less of a killer .. guitars amps usually emphasize treble, not bass. And
guitars only go so low anyway, (The lowest grunt you can get out of your
git-fiddle is about 100 cps and guitar's don't even do that very often).
Finally, you're going to bump into some impedance mis-match issues. But it
won't be deadly. Transformers actually work on a ratio. If you hook an 8
ohm secondary to a 4 ohm speaker you'll just cut the impedance of the
primary impedance (approximately) in half. Your Hammond transformer is
probably rated at higher impedance that the 2k called for in the circuit,
but use a 4 or 3.2 ohm speaker and things should be fine.
If this is your first project watch out for shock hazzards. Don't dink
around with stuff till you're SURE the electrolytics are discharged
(unplugged isn't enough) and remember, AC/DC circuits (usually using tubes
starting with 50 like 50L6 OR 50C5) are bad news for guitars.
Rod
"Joe" <joe@emailserver.net> wrote in message
news:2v9qq0t1dqoqcqhjc0pkprmrfkfd7f1e7l@4ax.com...
Thanks a lot Jon. I had a feeling that was the case.
On Tue, 30 Nov 2004 20:46:35 -0500, Jon Yaeger <jono_1@bellsouth.net
wrote:
in article dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com, Joe at
joe@emailserver.net wrote on 11/30/04 8:23 PM:
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
Joe,
Single ended transformers are designed differently from push-pull types
and
except in special cases (e.g. parafeed configurations) they aren't
interchangeable at all.
Unless you want to use a different push-pull circuit, I'd bite the bullet
and get the recommended SE transformer. You can sell the other on eBay or
use it for another project . . .
Jon
|
Rod,
Technically, you're right . . . but I took into account the experience of
the builder and the fact that after all, it's a guitar amplifier . . . I
could be wrong, but I don't think he's be happy with 2 watts and the
technical considerations are (normally) far beyond the scope of a first-time
KIT builder.
Jon |
|
| Back to top |
|
|
Fabio Berutti
Guest
|
| Posted:
Wed Dec 01, 2004 12:11 pm Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Let's be practical: the right one costs 13.95$ @ Triode Electronics
(http://store.yahoo.com/triodeel/tfchxfwi48oh.html), and maybe it can be
found at a flea mart or gutted from a broken Fender Champ @ a price even
lower... is it worth the pain? The RIGHT tranny is responsible for most of
the harmonic content (hence for the sound) of a guitar amp. Considering that
it costs 10 euros, ie. 2 pints of beer (at our local fool prices), I'd just
buy it.
Ciao
Fabio
"Jon Yaeger" <jono_1@bellsouth.net> ha scritto nel messaggio
news:BDD2AF1F.EE70%jono_1@bellsouth.net...
| Quote: | in article keKdnWgZDZ2mpTDcRVn-pg@comcast.com, Rod Keys at
rkeys@comcast.net
wrote on 11/30/04 10:19 PM:
Wellllll .. just wait a minute.
Actually you just have to use the transformer at lower power ....
The hidden issue here is "core saturation". Don't run away Joe, it's not
that complicated! If direct current goes through a transformer's primary
winding it puts magnetism in the transformer's iron core. The problem is
that the core is limited as far as how much magnetism it can "hold". If
it's loaded up with magnetism from DC there's no more left to pass the AC
signal. The answer to this problem is; a) a physically bigger core or,
b)
another winding with the DC flowing the other way to offsetting the DC in
the first winding.
In a push-pull transformer the primary winding is split so that half the
DC
goes one way and half goes the other way and they counter balance each
other. This minimizes "core situation".
A push-pull transformer will work just fine single ended as long as the
power level, especially the DC component in the primary, is so low that
you
don't saturate the core. In other words, your eight watt transformer
can't
put out eight watts single ended, but I wouldn't be the least surprised
if
it worked just fine single ended at two or three watts.
When a core saturates the first thing to go is the bass (because bass
eats
up tons of "core"). In a hi-fi amp this is a killer. In a guitar amp
it's
less of a killer .. guitars amps usually emphasize treble, not bass. And
guitars only go so low anyway, (The lowest grunt you can get out of your
git-fiddle is about 100 cps and guitar's don't even do that very often).
Finally, you're going to bump into some impedance mis-match issues. But
it
won't be deadly. Transformers actually work on a ratio. If you hook an
8
ohm secondary to a 4 ohm speaker you'll just cut the impedance of the
primary impedance (approximately) in half. Your Hammond transformer is
probably rated at higher impedance that the 2k called for in the circuit,
but use a 4 or 3.2 ohm speaker and things should be fine.
If this is your first project watch out for shock hazzards. Don't dink
around with stuff till you're SURE the electrolytics are discharged
(unplugged isn't enough) and remember, AC/DC circuits (usually using
tubes
starting with 50 like 50L6 OR 50C5) are bad news for guitars.
Rod
"Joe" <joe@emailserver.net> wrote in message
news:2v9qq0t1dqoqcqhjc0pkprmrfkfd7f1e7l@4ax.com...
Thanks a lot Jon. I had a feeling that was the case.
On Tue, 30 Nov 2004 20:46:35 -0500, Jon Yaeger <jono_1@bellsouth.net
wrote:
in article dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com, Joe at
joe@emailserver.net wrote on 11/30/04 8:23 PM:
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
Joe,
Single ended transformers are designed differently from push-pull types
and
except in special cases (e.g. parafeed configurations) they aren't
interchangeable at all.
Unless you want to use a different push-pull circuit, I'd bite the
bullet
and get the recommended SE transformer. You can sell the other on eBay
or
use it for another project . . .
Jon
Rod,
Technically, you're right . . . but I took into account the experience of
the builder and the fact that after all, it's a guitar amplifier . . . I
could be wrong, but I don't think he's be happy with 2 watts and the
technical considerations are (normally) far beyond the scope of a
first-time
KIT builder.
Jon
|
|
|
| Back to top |
|
|
Ian Iveson
Guest
|
| Posted:
Wed Dec 01, 2004 12:11 pm Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
"Fabio Berutti" <fabio.berutti@aliceposta.it> wrote
| Quote: | it costs 10 euros, ie. 2 pints of beer (at our local fool prices)
|
10 euros would get me 6 pints at my local pub, or 8 during happy
hour. Shame I don't drink.
That's why there are few valves in Bradford. They cost too many
pints.
cheers, Ian |
|
| Back to top |
|
|
Engineer
Guest
|
| Posted:
Thu Dec 02, 2004 12:12 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
"Joe" <joe@emailserver.net> wrote in message
news:dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com...
| Quote: | Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls
for
a 3 Watt output transformer with a 2K primary and an 8 Ohm
secondary.
|
(snip)
Try a scrapped "wallwart" transformer of 120 VAC (primary) to 7.6 VAC
(secondary) at 1 amp or so, i.e. 15.8:1. You could "unwind" a 12 VAC
one (see below.) This should get you by until you can find the proper
transformer (or you might even like it!). Let's recognize that this
in not "Hi-Fi", it's a tiny practice guitar amp! Don't worry about
the DC magnetic saturation, either.
I've used the above approach in tube radio restoration (a 6K6 plate,
at about 8000, ohms to 4 ohms but I had to unwind the secondary to 2.7
VAC.)
Caution and disclaimer: don't do anything until you understand the
dangers of vacuum tube operating voltages!
Cheers,
Roger |
|
| Back to top |
|
|
robert casey
Guest
|
| Posted:
Thu Dec 02, 2004 12:13 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Joe wrote:
| Quote: | Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
|
An issue is that SE transformers have a gap in the
laminations to reduce the effects of the quiescent
DC current thru the primary. P-P transformers don't
have this gap, as the pair of DC currents cancel out.
But nothing will blow up, but you'll get distortion
before you get to 8 watts. As power = current squared*R,
1/2 the current would get you 1/4 the power. In a
guitar amp, the distortion you may get might be interesting
anyway. Give it a try. But be prepared to be able to
easily change the transformer if it sounds bad. |
|
| Back to top |
|
|
mick
Guest
|
| Posted:
Thu Dec 02, 2004 12:13 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
On Wed, 01 Dec 2004 11:14:54 +0000, Ian Iveson wrote:
| Quote: |
That's why there are few valves in Bradford. They cost too many pints.
|
I can't get over all these people that seem to find trannies & things at
car boot sales. Certainly none turn up around here! They are all full of
non-amplifier-related junk.... :-(
--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk |
|
| Back to top |
|
|
Lou deGonzague
Guest
|
| Posted:
Thu Dec 02, 2004 6:05 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Joe, send me an email, I think I have just what you need.
zenith@nycap.rr.com
"Joe" <joe@emailserver.net> wrote in message
news:dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com...
| Quote: | Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe |
|
|
| Back to top |
|
|
Jon Yaeger
Guest
|
| Posted:
Thu Dec 02, 2004 6:10 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
in article PbCdnUbQDrWtxjPcRVn-og@rogers.com, Engineer at nobody@nowhere.net
wrote on 12/1/04 7:00 PM:
| Quote: | "Joe" <joe@emailserver.net> wrote in message
news:dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com...
Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls
for
a 3 Watt output transformer with a 2K primary and an 8 Ohm
secondary.
(snip)
Try a scrapped "wallwart" transformer of 120 VAC (primary) to 7.6 VAC
(secondary) at 1 amp or so, i.e. 15.8:1. You could "unwind" a 12 VAC
one (see below.) This should get you by until you can find the proper
transformer (or you might even like it!). Let's recognize that this
in not "Hi-Fi", it's a tiny practice guitar amp! Don't worry about
the DC magnetic saturation, either.
I've used the above approach in tube radio restoration (a 6K6 plate,
at about 8000, ohms to 4 ohms but I had to unwind the secondary to 2.7
VAC.)
Caution and disclaimer: don't do anything until you understand the
dangers of vacuum tube operating voltages!
Cheers,
Roger
|
Don't confuse the possible with the practical. Remember, this poor guy is
building his 1st KIT . . . (After he gets some confidence, he may want to
rewind wall warts, but I doubt it. I wouldn't!)
;-)
J |
|
| Back to top |
|
|
Engineer
Guest
|
| Posted:
Fri Dec 03, 2004 6:19 am Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
"Jon Yaeger" <jono_1@bellsouth.net> wrote in message
news:BDD412EE.F09F%jono_1@bellsouth.net...
| Quote: | in article PbCdnUbQDrWtxjPcRVn-og@rogers.com, Engineer at
nobody@nowhere.net
wrote on 12/1/04 7:00 PM:
"Joe" <joe@emailserver.net> wrote in message
news:dg5qq0tj87ck13qld1oorgvp4tjmmf94kb@4ax.com...
Hi guys,
I'm building my first guitar amplifier (my first electronics
project
actually), a small two-tube single-ended amp. The schematic calls
for
a 3 Watt output transformer with a 2K primary and an 8 Ohm
secondary.
(snip)
Try a scrapped "wallwart" transformer of 120 VAC (primary) to 7.6
VAC
(secondary) at 1 amp or so, i.e. 15.8:1. You could "unwind" a 12
VAC
one (see below.) This should get you by until you can find the
proper
transformer (or you might even like it!). Let's recognize that
this
in not "Hi-Fi", it's a tiny practice guitar amp! Don't worry about
the DC magnetic saturation, either.
I've used the above approach in tube radio restoration (a 6K6
plate,
at about 8000, ohms to 4 ohms but I had to unwind the secondary to
2.7
VAC.)
Caution and disclaimer: don't do anything until you understand the
dangers of vacuum tube operating voltages!
Cheers,
Roger
Don't confuse the possible with the practical. Remember, this poor
guy is
building his 1st KIT . . . (After he gets some confidence, he may
want to
rewind wall warts, but I doubt it. I wouldn't!)
;-)
J
|
Good point, Jon, and I agree! As an avid reuser and recycler of old
electronic stuff this sort of thing is both a challenge and fun.
Cheers,
Roger |
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John Stewart
Guest
|
| Posted:
Fri Dec 03, 2004 12:07 pm Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
Joe wrote:
| Quote: | Hi guys,
I'm building my first guitar amplifier (my first electronics project
actually), a small two-tube single-ended amp. The schematic calls for
a 3 Watt output transformer with a 2K primary and an 8 Ohm secondary.
I have a nice 8 watt transformer (Hammond 125J), but the primary is
center-tapped and the description says it's for use with "push pull"
circuits. They have a separate set of "single ended" transformers
(125SE).
Here's some information from the Hammond site:
Hammond 125J Description:
Designed for general purpose or replacement use in push-pull tube
output circuits.
Hammond 125J Data:
Cat. No. Audio Watts Primary Secondary
Impedance Impedance
(Ohms) (Ohms)
---------- --------------- -------------- ---------------
125J 8 2.5K or 4K 6/8 or 3.2/4
Can such a transformer not be used in a SE circuit? I had thought I
could use one primary lead and the center tap to form a 2.5k primary,
and just ignore the other primary lead.
Am I way of the mark here? Should I use an actual "single ended"
transformer?
Thanks!
Joe
|
The Hammond 125 Series PP Output Transformers does work
"A OK" in a SE circuit. I've done that not once but many times
beginning more than 40 years ago.
If you like you can even use the center tap to form an ultralinear
mode connexion. Done that, too!!
If you want to take the time you can even read about how to do it
complete with comprehensive test results in two of my published
articles on SE amplifiers as follows-
AN AFFORDABLE SE TRIODE AMP-
Uses a 6EA7/6EM7 Double Triode into a 125E
Glass Audio Magazine Issue 4, 2000
MORE POWER FOR THE AFFORDABLE SE AMP-
Uses a 6LU8 in Triode or UltraLinear Connexion into a 125E
Glass Audio Projects Book
See www.audioXpress.com for these publications.
There are several other unpublished amps, both SE & PP
using the Hammond 125 Series.
The description you give of your proposed amp leads me to
believe that it is a "transformerless" design, that is, there is
no power transformer. If that is the case you should immediately
abandon that circuit because of safety concerns. Whatever
you do should include a power transformer to get you off
the power line to avoid grounding & electrical shock problems.
Good Luck (And be careful) with your project, John Stewart |
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Jon Yaeger
Guest
|
| Posted:
Sat Dec 04, 2004 6:15 pm Post subject:
Re: Output Transformer - push pull or SE ??? |
|
|
| Quote: |
The Hammond 125 Series PP Output Transformers does work
"A OK" in a SE circuit. I've done that not once but many times
beginning more than 40 years ago.
If you like you can even use the center tap to form an ultralinear
mode connexion. Done that, too!!
If you want to take the time you can even read about how to do it
complete with comprehensive test results in two of my published
articles on SE amplifiers as follows-
AN AFFORDABLE SE TRIODE AMP-
Uses a 6EA7/6EM7 Double Triode into a 125E
Glass Audio Magazine Issue 4, 2000
MORE POWER FOR THE AFFORDABLE SE AMP-
Uses a 6LU8 in Triode or UltraLinear Connexion into a 125E
Glass Audio Projects Book
See www.audioXpress.com for these publications.
There are several other unpublished amps, both SE & PP
using the Hammond 125 Series.
The description you give of your proposed amp leads me to
believe that it is a "transformerless" design, that is, there is
no power transformer. If that is the case you should immediately
abandon that circuit because of safety concerns. Whatever
you do should include a power transformer to get you off
the power line to avoid grounding & electrical shock problems.
Good Luck (And be careful) with your project, John Stewart
|
Thanks, John, I stand corrected relative to the advice that I offered this
poster.
Is it something about the construction of this particular PP transformer
that makes it particularly suitable for SE? In general, is it not true that
most PP transformers tend to saturate when used in SE mode?
No doubt you've tried other PP XFMRs in SE mode. What's been your
experience?
TIA,
Jon |
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