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Hi, im sorry foy my english.
i have finished a kit st-70 and i have problem with channel black.
see a picture
http://www.mirastelescopicas.com/dyn2.jpg

a bias set is very good. i have setup in 1V (2 bias).
a Channel red work very good!.
but i dont know why not work a channel black.
i have tried with change slots EL34 rightt and left and left and right
but a problem is the same. the 4 tubes work good.

Please if any can help me !
i have many pictures.

board capacitor:
http://www.mirastelescopicas.com/dyncap.jpg

pcb board:

http://www.mirastelescopicas.com/dyn3.jpg
http://www.mirastelescopicas.com/dyn1.jpg

mati1979 wrote:Hi, im sorry foy my english.
i have finished a kit st-70 and i have problem with channel black.
see a picture
http://www.mirastelescopicas.com/dyn2.jpg

a bias set is very good. i have setup in 1V (2 bias).
a Channel red work very good!.
but i dont know why not work a channel black.
i have tried with change slots EL34 rightt and left and left and right
but a problem is the same. the 4 tubes work good.

Please if any can help me !
i have many pictures.

board capacitor:
http://www.mirastelescopicas.com/dyncap.jpg

pcb board:

http://www.mirastelescopicas.com/dyn3.jpg
http://www.mirastelescopicas.com/dyn1.jpg

To eliminate one possible problem, make sure that the source: cdplayer, preamp, etc. is not at fault. Plug the left channel audio plug into the right jack and plug the right channel audio plug into the left jack.

With your voltameter, take measurements on all pins of all of the left-hand channel tubes. Write them down as you go. Compare them with the values given in the manual.

Make sure the left audio channel's input is not grounded. Look at the left channel audio jack.

Looks like there are two filament connections that nothing is connected to. I'll bet only half of the center tube is lit.

thank you "friends" !

this is my first tube kit and im I am a little scared

i have empty 2 eyelets in a board. (18 and 3)
i see in a manual board:

Eyelet #3 to Pin 5 of left power take off socket
Eyelet #18 to Pin 5 of right power take off socket

(i have checked a pre with my power SAE and work good a 2 channel )

wh?t is power take off socket ? (pin 5 in right and left) ?

mati1979 wrote:wh?t is power take off socket ? (pin 5 in right and left) ?

Your chassis does not have take off sockets. You can ignore those instructions.

Take the voltage measurements of the tubes in the bad channel.

kheper wrote:

mati1979 wrote:wh?t is power take off socket ? (pin 5 in right and left) ?

Take the voltage measurements of the tubes in the bad channel.

with a amp "on" ?

mati1979 wrote:

kheper wrote:

mati1979 wrote:wh?t is power take off socket ? (pin 5 in right and left) ?

Take the voltage measurements of the tubes in the bad channel.

with a amp "on" ?

Yes. That is the only way you will get any readings. Be very careful. The voltages are lethal.

kheper wrote:

mati1979 wrote:

kheper wrote:

mati1979 wrote:wh?t is power take off socket ? (pin 5 in right and left) ?

Take the voltage measurements of the tubes in the bad channel.

with a amp "on" ?

Yes. That is the only way you will get any readings. Be very careful. The voltages are lethal.

ok, with or whitout tubes ?

mati1979 wrote:

kheper wrote:Yes. That is the only way you will get any readings. Be very careful. The voltages are lethal.

ok, with or whitout tubes ?

You need tubes in the amp to take the voltage measurements on the pins of the tubes.

If you are not sure what you are doing, take the amp to a friend who does. The voltages are very dangerous.

im seeing a manual New st-70 board and i see many difference with a old board. (I worked looking at the older model board i think )

new st-70 board say:
Eyelet #4 & #5 to Pins 1 & 2 of the left power take-off socket (Note 1) (i have soldered eyelets 4 and 5 to pin 2 and 7)Eyelet #24 & #25 to Pins 1 & 2 of the left power take-off socket (Note 1) (i have soldered eyelets 24 and 25 to pin 4 and 5)Eyelet #15 & #16 to Pins 1 & 2 of the right power take-off socket (Note 1) (i have soldered 15 and 16 to pin 2 and 7)

old board say: Step 28: Connect two wires from pins 2 & 7 of the EL34’s with the green filament wires going to them
(right side looking from bottom of amp) run these wires to eyelets #4 and #5 on the driver board. Before
soldering to eyelets #4 and #5 also connect a second set of wire into the holes which we will connect to eyelets #24 and #25 on the driver board
Step 29: Connect two wires from pins 2 & 7 of the EL34’s with the brown filament wires going to them (Left side looking from bottom of amp) run these wires to eyelets #15 and #16 on the driver board.

in a new board manual i see a NOTE 1:

NOTE 1: These are the input tube filament connections. A stock ST-70 uses the front panel power take-off
sockets as a tie point for the input board tube filament wiring. Many amplifier modifications use these
socket holes for input jacks or other purposes. If the tube filament power is not present on these jacks or the
jacks themselves are not present, then the filament wiring can be run (as twisted pairs to reduce hum) from
the output tube filament connection (EL34: pins 2&7). The phase inverter position (V2) now has extra flexibility to use tubes with different pinouts, to use 12AU7, 12BH7, ECC99 solder a wire from J1 to J2 and make your filament connections to eyelets 24 & 25, to use 6CG7, 6922, 7308, or 6DJ8 do not jumper J1 and J2 and instead make your filament connections to J1 and J2 and ignore eyelets 24 and 25.

mati1979 wrote:NOTE 1: These are the input tube filament connections. A stock ST-70 uses the front panel power take-off
sockets as a tie point for the input board tube filament wiring. Many amplifier modifications use these
socket holes for input jacks or other purposes. If the tube filament power is not present on these jacks or the
jacks themselves are not present, then the filament wiring can be run (as twisted pairs to reduce hum) from
the output tube filament connection (EL34: pins 2&7). The phase inverter position (V2) now has extra flexibility to use tubes with different pinouts, to use 12AU7, 12BH7, ECC99 solder a wire from J1 to J2 and make your filament connections to eyelets 24 & 25, to use 6CG7, 6922, 7308, or 6DJ8 do not jumper J1 and J2 and instead make your filament connections to J1 and J2 and ignore eyelets 24 and 25.

i have a 4 EL34 , 1 GZ34 , 2 EF86 and in a center board Ecc82

.

recently, I went to put a 4 EL34 and now in channel Red I listen quietly and in a channell Black (with a problem) i listen very very quietly but i listen "a signal" in a channel black.

i see before 5` a blue light in gz34 (Short Circuit) and then disappears

mati1979 wrote:im seeing a manual New st-70 board and i see many difference with a old board. (I worked looking at the older model board i think )

Where did you get the new driverboard?

It looks like no filaments were getting voltage.