Hi, I'm interested in building a simple tube stereo headphone amp, I
found a circuit but have a few questions.

Link to circuit (Site is in Japanese, but schematic is perfectly
readable) http://www.geocities.jp/dads_projects/radio/12K5.html

First, the schematic calls for a 117 volt/12.6 volt transformer
across what I think is the output, I can only find a 115 volt/12.6
volt 2.5 amp transformer. Will this work? Another question is about
the numbering of tube pins on the 12AU7A, there's two sets of
numbers. Which ones am I supposed to read? Last question is
regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks
for your help.

Thanks in advance.

Dave

On Mar 9, 10:56 pm, "Dave.H" <the19...@googlemail.com> wrote:
> Hi, I'm interested in building a simple tube stereo headphone amp, I
> found a circuit but have a few questions.
>
> Link to circuit (Site is in Japanese, but schematic is perfectly
> readable)http://www.geocities.jp/dads_projects/radio/12K5.html
>
> First, the schematic calls for a 117 volt/12.6 volt transformer
> across what I think is the output, I can only find a 115 volt/12.6
> volt 2.5 amp transformer. Will this work? Another question is about
> the numbering of tube pins on the 12AU7A, there's two sets of
> numbers. Which ones am I supposed to read? Last question is
> regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks
> for your help.
>
> Thanks in advance.
>
> Dave

Forgot one thing, all the ground connections, are they going to signal
ground, or B-?

On Mar 9, 10:58 pm, "Dave.H" <the19...@googlemail.com> wrote:
> On Mar 9, 10:56 pm, "Dave.H" <the19...@googlemail.com> wrote:
>
>
>
> > Hi, I'm interested in building a simple tube stereo headphone amp, I
> > found a circuit but have a few questions.
>
> > Link to circuit (Site is in Japanese, but schematic is perfectly
> > readable)http://www.geocities.jp/dads_projects/radio/12K5.html
>
> > First, the schematic calls for a 117 volt/12.6 volt transformer
> > across what I think is the output, I can only find a 115 volt/12.6
> > volt 2.5 amp transformer. Will this work? Another question is about
> > the numbering of tube pins on the 12AU7A, there's two sets of
> > numbers. Which ones am I supposed to read? Last question is
> > regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks
> > for your help.
>
> > Thanks in advance.
>
> > Dave
>
> Forgot one thing, all the ground connections, are they going to signal
> ground, or B-?

Specs for the transfomrer is as follows:
* Primary 115 VAC, 60 Hz.
* Center tapped secondary.
* Enclosed, 4 hole chassis mount.
* Minimum 6" long leads.
* Dual bobbin design - no electrostatic shield required.
* Class B insulation (130 degrees, C)
* Hi-Pot test of 2,000 V RMS.
* UL listed (# E50394) & CSA certified (# LR3902).


Specifications
Rating: 12.6 VCT, 2.5 A
Mounting Centers: 1.5" x 1.56", vertical

Or another transformer I found

TRANSFORMER, POWER, 125 V, 15 mA

Primary: 117 volt, 50/60 Hz
Secondary: 125 V, 15 mA
Filament winding: 12.6 volt, 0.3 amp
Mounting centers: 2", U-bracket

"Dave.H" <the1930s@googlemail.com> wrote in message
news:c9619a87-2c7e-4c02-8538-38dbb5b2b5b2@d4g2000prg.googlegroups.com...
> On Mar 9, 10:58 pm, "Dave.H" <the19...@googlemail.com> wrote:
>> On Mar 9, 10:56 pm, "Dave.H" <the19...@googlemail.com> wrote:
>>
>>
>>
>> > Hi, I'm interested in building a simple tube stereo headphone amp, I
>> > found a circuit but have a few questions.
>>
>> > Link to circuit (Site is in Japanese, but schematic is perfectly
>> > readable)http://www.geocities.jp/dads_projects/radio/12K5.html
>>
>> > First, the schematic calls for a 117 volt/12.6 volt transformer
>> > across what I think is the output, I can only find a 115 volt/12.6
>> > volt 2.5 amp transformer. Will this work? Another question is about
>> > the numbering of tube pins on the 12AU7A, there's two sets of
>> > numbers. Which ones am I supposed to read? Last question is
>> > regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks
>> > for your help.
>>
>> > Thanks in advance.
>>
>> > Dave
>>
>> Forgot one thing, all the ground connections, are they going to signal
>> ground, or B-?
>
> Specs for the transfomrer is as follows:
> * Primary 115 VAC, 60 Hz.
> * Center tapped secondary.
> * Enclosed, 4 hole chassis mount.
> * Minimum 6" long leads.
> * Dual bobbin design - no electrostatic shield required.
> * Class B insulation (130 degrees, C)
> * Hi-Pot test of 2,000 V RMS.
> * UL listed (# E50394) & CSA certified (# LR3902).
>
>
> Specifications
> Rating: 12.6 VCT, 2.5 A
> Mounting Centers: 1.5" x 1.56", vertical
>
> Or another transformer I found
>
> TRANSFORMER, POWER, 125 V, 15 mA
>
> Primary: 117 volt, 50/60 Hz
> Secondary: 125 V, 15 mA
> Filament winding: 12.6 volt, 0.3 amp
> Mounting centers: 2", U-bracket
>Specs denote 'CT' for Secondary of Transformer, meaning the secondary must
>have a centre tapped winding. Otherwise the item you have found would
>probably work.

"Dave.H" wrote:

> Hi, I'm interested in building a simple tube stereo headphone amp, I
> found a circuit but have a few questions.
>
> Link to circuit (Site is in Japanese, but schematic is perfectly
> readable) http://www.geocities.jp/dads_projects/radio/12K5.html
>
> First, the schematic calls for a 117 volt/12.6 volt transformer
> across what I think is the output, I can only find a 115 volt/12.6
> volt 2.5 amp transformer. Will this work?

Well, it's certainly a close enough match to the specified part for
sure, but using a MAINS transformer as the output transformer will
assure truly dismal audio quality.

Sorry to tell you but many (most) hobby projects of this ilk are truly
dreadfully designed and will assure at best mediocre results that
somewhat defeat their original purpose.

Graham

"Dave.H" wrote:

> Another question is about the numbering of tube pins on the 12AU7A,
> there's two sets of
> numbers. Which ones am I supposed to read?

Hello ! Ting ting ! Wakey wakey ! The 12AU7 / ECC82 is a DUAL triode.
One set of numbers refers to the first triode and the second to the err
... second triode.

Have you been using valves long ?


> Last question is regarding the 12AU7A itself, will I regular 12AU7
> work here?

Yes, a 12AU7 works very well in a socket designed for a 12AU7.

If you mean 12AX7 or 12AT7 then the answer is NO.

Graham

"Dave.H" wrote:

> Forgot one thing, all the ground connections, are they going to signal
> ground, or B-?

Read the thread on grounding and star points in rec.audio.tubes. It's very
recent.

Graham

On Mar 9, 7:56=A0am, "Dave.H" <the19...@googlemail.com> wrote:
> Hi, I'm interested in building a simple tube stereo headphone amp, I
> found a circuit but have a few questions.
>
> Link to circuit (Site is in Japanese, but schematic is perfectly
> readable)http://www.geocities.jp/dads_projects/radio/12K5.html
>
> =A0First, the schematic calls for a 117 volt/12.6 volt transformer
> across what I think is the output, I can only find a 115 volt/12.6
> volt 2.5 amp transformer. =A0Will this work?

Yes, it's the same thing. But you might be happier with the results
if you use real audio output transformers.

> Another question is about
> the numbering of tube pins on the 12AU7A, there's two sets of
> numbers. =A0Which ones am I supposed to read?

The two numbers refer to the first and second sections of the tube.
Use the first set of numbers for one channel and the second set for
the other channel.

> =A0Last question is
> regarding the 12AU7A itself, will I regular 12AU7 work here? =A0

Yes, no problem.

Mike

On Sun, 09 Mar 2008 04:56:46 -0700, Dave.H wrote:

> Hi, I'm interested in building a simple tube stereo headphone amp, I
> found a circuit but have a few questions.
>
> Link to circuit (Site is in Japanese, but schematic is perfectly
> readable) http://www.geocities.jp/dads_projects/radio/12K5.html
>
> First, the schematic calls for a 117 volt/12.6 volt transformer
> across what I think is the output, I can only find a 115 volt/12.6 volt
> 2.5 amp transformer. Will this work? Another question is about the
> numbering of tube pins on the 12AU7A, there's two sets of numbers.
> Which ones am I supposed to read? Last question is regarding the 12AU7A
> itself, will I regular 12AU7 work here? Thanks for your help.
>
> Thanks in advance.
>
> Dave

http://www.tubesandmore.com has audio transformers that'll work much
better than mains transformers. You can start with mains transformers,
but as Eeyore so diplomatically mentioned, your sound quality may suffer.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html