Hi --

I started a project 9 years ago to build my first pair of tube
monoblock amplifiers --- the Shishido Loftin-White 2a3. A link to the
schematic is:

http://www.diyzone.net/diy/tube/loftin-white2a3.htm

A friend of a friend offered to modify the schematic to use 6sl7's and
a few other favorite parts the he thought would be more compatible. In
the mean time i shopped for a pair of Tango U808s, a pair of Raytheon
5r4wgb's, a pair of Sylvania 6sl7wgt's, a pair of Sylvania 2a3's, a
pair of Magnetek F-1x 2.6v CT filament transformers, and a pair of
Magnetek c-7X choke (10h i think).

Well my friend of a friend left town suddenly (a much longer story than
this one.... ;- ); and my box of parts moved to the basement until a
few weeks ago. I ended up purchasing a Sun SV-2a3 kit and almost put it
together by myself.....

Now, i would like to finish the project but need some help adapting the
schematic from a 12ax7 to a 6sl7. Plus, i have a more questions about
how to wire the power transformer (hmmmm....which one to buy), the
chassis ground in relation ship to signal ground, paper/oil cap values
(want to use them throughout if it makes sense), etc.

I have searched for info on the internet and there are circuits that
are almost what i am looking for. I have even tried to "translate" the
article "A Direct Coupled Single Triode Amplier" (by Ciro Marzio and
Cristiano Jelasi) in Sound Practices (Spring 1994). Interesting reading
and clearly aimed a more experienced DIY hobbiest. I am more of a
virgin with my almost tragic attempt to build my Sun SV-2a3 kit.

I live in near the SF airport and would love to find someone (local or
who i could talk on the phone/email with) who would be willing to give
me a hand with the schematic and my questions. I am even willing to pay
but have no references that i feel comfortable trusting.

For me, local would be better, because i would be interested in getting
assistance in power up the amplifiers for the first time.

Thanks for all who have read this far. And thanx for any assistance you
can provide.

sincerely
Steve

Reply

Hi,

I believe you just need to pull out the 2A3 for the first power up. Test all
the voltages are good. Then, put the 2A3 back and fire it up for voltage
checks.


Johnny

"kar2n"
groups.com...
Hi --

I started a project 9 years ago to build my first pair of tube
monoblock amplifiers --- the Shishido Loftin-White 2a3. A link to the
schematic is:

http://www.diyzone.net/diy/tube/loftin-white2a3.htm

A friend of a friend offered to modify the schematic to use 6sl7's and
a few other favorite parts the he thought would be more compatible. In
the mean time i shopped for a pair of Tango U808s, a pair of Raytheon
5r4wgb's, a pair of Sylvania 6sl7wgt's, a pair of Sylvania 2a3's, a
pair of Magnetek F-1x 2.6v CT filament transformers, and a pair of
Magnetek c-7X choke (10h i think).

Well my friend of a friend left town suddenly (a much longer story than
this one.... ;- ); and my box of parts moved to the basement until a
few weeks ago. I ended up purchasing a Sun SV-2a3 kit and almost put it
together by myself.....

Now, i would like to finish the project but need some help adapting the
schematic from a 12ax7 to a 6sl7. Plus, i have a more questions about
how to wire the power transformer (hmmmm....which one to buy), the
chassis ground in relation ship to signal ground, paper/oil cap values
(want to use them throughout if it makes sense), etc.

I have searched for info on the internet and there are circuits that
are almost what i am looking for. I have even tried to "translate" the
article "A Direct Coupled Single Triode Amplier" (by Ciro Marzio and
Cristiano Jelasi) in Sound Practices (Spring 1994). Interesting reading
and clearly aimed a more experienced DIY hobbiest. I am more of a
virgin with my almost tragic attempt to build my Sun SV-2a3 kit.

I live in near the SF airport and would love to find someone (local or
who i could talk on the phone/email with) who would be willing to give
me a hand with the schematic and my questions. I am even willing to pay
but have no references that i feel comfortable trusting.

For me, local would be better, because i would be interested in getting
assistance in power up the amplifiers for the first time.

Thanks for all who have read this far. And thanx for any assistance you
can provide.

sincerely
Steve

Reply

Thanx Johnny.

You power up tip is helpful.

And you other suggestion of...

The design is pretty straight forward. I would recommend to add a Standby
Switch and a 150mA Quick Blow Fuse for the B+. This would allow the tubes
heated up before applying the B+. Otherwise, the 2A3 probably will take
excessive current during power up. The B+ fuse will protect the 2A3 in case
there's anything happened to 12AX7 like loose connections etc.
Johnny.

Now....(sorry for being greedy)....what i really want to do is swap out
the 12ax7 for 6sl7 and change the 5ar4 for a 5r4....I am trying to use
the parts that i have...if possible......

thanx again....

Hi the

The only 'practical' advice I can give to you comes from direct application
of the Triad F-1X 2.5 VCT
3 Ampere filament transformer to feed the 2A3 filaments.

If you connect this transformer directly to the the filaments
on a 2A3, the voltage settles a bit on the high side, meaning the
filaments will glow like a toaster.

I placed in parallel with the 2A3 filament a 5 Ohm, 5 Watt load resistor
to settle the voltage down to 2.5 Volts while consuming the extra 0.5 amps
of current that the F1-X provides.

This may or may not be a factor for you depending on your primary line
voltage.
But where I live the mains voltage is typically 120-123 VAC / 60 Hz and the
older Triad
Transfomers were wound with 115-117 VAC primaries. They experience a little
boost from the extra volts.

I can't recall now that I did read about 2A3 filaments before. These types
of filaments
don't seem to take kindly to being fed more than 2.5 Volts. If the 2A3's are
connected to more or less than 2.5 Volts, the current draw will decrease or
increase
over a range. More than 2.7 volts and one can risk shortening the life of
the tube.

Old radio receivers that used the 2A3 tube from the 30's, will often have a
rheostat control
that allowed the user to vary the filament voltage to the 2A3's over a
specified controlled range.

This control allowed the user to vary the receiver sensitivity or gain
(can't recall, but
I do have the book at home) a bit.

In short, feeding 2A3's with the proper voltage and curent helps them last
longer.

Good luck,
Rich

"kar2n" wrote in message
ups.com...
Hi --

I started a project 9 years ago to build my first pair of tube
monoblock amplifiers --- the Shishido Loftin-White 2a3. A link to the
schematic is:

http://www.diyzone.net/diy/tube/loftin-white2a3.htm

A friend of a friend offered to modify the schematic to use 6sl7's and
a few other favorite parts the he thought would be more compatible. In
the mean time i shopped for a pair of Tango U808s, a pair of Raytheon
5r4wgb's, a pair of Sylvania 6sl7wgt's, a pair of Sylvania 2a3's, a
pair of Magnetek F-1x 2.6v CT filament transformers, and a pair of
Magnetek c-7X choke (10h i think).

Well my friend of a friend left town suddenly (a much longer story than
this one.... ;- ); and my box of parts moved to the basement until a
few weeks ago. I ended up purchasing a Sun SV-2a3 kit and almost put it
together by myself.....

Now, i would like to finish the project but need some help adapting the
schematic from a 12ax7 to a 6sl7. Plus, i have a more questions about
how to wire the power transformer (hmmmm....which one to buy), the
chassis ground in relation ship to signal ground, paper/oil cap values
(want to use them throughout if it makes sense), etc.

I have searched for info on the internet and there are circuits that
are almost what i am looking for. I have even tried to "translate" the
article "A Direct Coupled Single Triode Amplier" (by Ciro Marzio and
Cristiano Jelasi) in Sound Practices (Spring 1994). Interesting reading
and clearly aimed a more experienced DIY hobbiest. I am more of a
virgin with my almost tragic attempt to build my Sun SV-2a3 kit.

I live in near the SF airport and would love to find someone (local or
who i could talk on the phone/email with) who would be willing to give
me a hand with the schematic and my questions. I am even willing to pay
but have no references that i feel comfortable trusting.

For me, local would be better, because i would be interested in getting
assistance in power up the amplifiers for the first time.

Thanks for all who have read this far. And thanx for any assistance you
can provide.

sincerely
Steve

Reply

Rich ----

Thanx a bunch. Great tip. Found resources in SF @ the Randall Museum.
Will be going to meet up with some on Nov 11th.
regards

Rich Sherman wrote:
Hi the

The only 'practical' advice I can give to you comes from direct application
of the Triad F-1X 2.5 VCT
3 Ampere filament transformer to feed the 2A3 filaments.

If you connect this transformer directly to the the filaments
on a 2A3, the voltage settles a bit on the high side, meaning the
filaments will glow like a toaster.
snip

Old radio receivers that used the 2A3 tube from the 30's, will often have a
rheostat control
that allowed the user to vary the filament voltage to the 2A3's over a
specified controlled range.

This control allowed the user to vary the receiver sensitivity or gain
(can't recall, but
I do have the book at home) a bit.


No, they didn't.

Filament voltage control-by a series rheostat-was used in battery
radios of the 1920s. These had 6 volt filaments. 2.5 volt filaments
were used in early AC radios that had to use raw AC on small signal
tube filamentary cathodes. When the heater-cathode replaced the
filament, 6.3 vac became the standard voltage. 2.5 was the standard raw
AC filament voltage and rectifiers were double that so two windings
could be seriesed with a center tap because they thought the B voltage
should not be from either side. That went by the wayside but 5 volts
remained the standard rectifier heater voltage until the rectifier tube
was sensibly replaced by diodes.

The Loftin-White circuit is a pain in the ass and beginners should be
deterred from fooling with it.

In short, feeding 2A3's with the proper voltage and curent helps them last
longer.

Bret Ludwig wrote:

Rich Sherman wrote:
Hi the

The only 'practical' advice I can give to you comes from direct application
of the Triad F-1X 2.5 VCT
3 Ampere filament transformer to feed the 2A3 filaments.

If you connect this transformer directly to the the filaments
on a 2A3, the voltage settles a bit on the high side, meaning the
filaments will glow like a toaster.
snip

Old radio receivers that used the 2A3 tube from the 30's, will often have a
rheostat control
that allowed the user to vary the filament voltage to the 2A3's over a
specified controlled range.

This control allowed the user to vary the receiver sensitivity or gain
(can't recall, but
I do have the book at home) a bit.

No, they didn't.

Filament voltage control-by a series rheostat-was used in battery
radios of the 1920s. These had 6 volt filaments. 2.5 volt filaments
were used in early AC radios that had to use raw AC on small signal
tube filamentary cathodes. When the heater-cathode replaced the
filament, 6.3 vac became the standard voltage. 2.5 was the standard raw
AC filament voltage and rectifiers were double that so two windings
could be seriesed with a center tap because they thought the B voltage
should not be from either side. That went by the wayside but 5 volts
remained the standard rectifier heater voltage until the rectifier tube
was sensibly replaced by diodes.

The Loftin-White circuit is a pain in the ass and beginners should be
deterred from fooling with it.

I'd agree with that.
The reason for the direct coupling in the LW amp
was that caps made at the time of the LW invention were unreliable;
resistors were barely reliable, but moreso than caps,
and of course inductors were fine but costly and of limited BW.
So the LW could offer good BW.

But with the good caps made now that almost never fail,
there is no need for the LW.
I just cannot think of any advantages sonically or technically
with LW.

Patrick Turner.




In short, feeding 2A3's with the proper voltage and curent helps them last
longer.