Crosley amp help

6/9/2009 8:10:44 PMIan

http://img149.imageshack.us/img149/8477/4555.th.gif

I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
There is audio on the grid.
does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/9/2009 8:11:43 PMIan

:
:
:
:
:I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:There is audio on the grid.
:does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/9/2009 9:10:09 PMLewis L

::
::
::
::
::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
::There is audio on the grid.
::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

That grid resistor looks awfully high to me.Why doncha try 470 K? I think the electrons are building up on the grid faster than 10 Meg can drain them to gtound,
Lewis

6/9/2009 9:39:20 PMIan

Changing the resistor did not do anything. I put signal at the plate of that tube and the the speaker played it but it was not amplified at all.

Here's the entire schematic

6/9/2009 9:40:11 PMIan

:
:Changing the resistor did not do anything. I put signal at the plate of that tube and the the speaker played it but it was not amplified at all.
:
:Here's the entire schematic
:

6/9/2009 10:18:28 PMIan

O.k I think I might have got it. the is no reistance from plates to ground. i just looked at the radio schmatic and saw a 4000 and 4700 ohm resistor from screem sub b+ to ground. I have two large resistors of these values (a few watts apiece), should i put these in from sub b+ to ground as the radio has it?

6/11/2009 4:36:37 PMRadiodoc

Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.

Radiodoc
*******************

::
::
::
::
::
::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
::There is audio on the grid.
::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/11/2009 4:51:23 PMIan

I just changed it back, what about the other resistors? The 4000 ohm and 4700 ohm the 4700 ohm is parallel to a .05mfd cap. These have drifted up to 6200 and 7000 ohms.
If that is good I'll go plug it in.
Thanks

:Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
:
:Radiodoc
:*******************
:
:
:
:::
:::
:::
:::
:::
:::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:::There is audio on the grid.
:::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/11/2009 5:35:32 PMRadiodoc

If the resistors are out of tolerence, I would replace them. Generally resistors with no tolerance color band are 20 percent, a silver band 10 percent. The handdrawn diagram you have in this thread shows a .022 mf capacitor hooked to B+ when it should be to the plate of the second triode tube. If it is hooked like your diagram the signal from the plate cannot get to the output tube(s).

Radiodoc
********************

:I just changed it back, what about the other resistors? The 4000 ohm and 4700 ohm the 4700 ohm is parallel to a .05mfd cap. These have drifted up to 6200 and 7000 ohms.
:If that is good I'll go plug it in.
:Thanks
:
::Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
::
::Radiodoc
::*******************
::
::
::
::::
::::
::::
::::
::::
::::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
::::There is audio on the grid.
::::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/11/2009 6:39:13 PMIan

I will try it with the original resistors first.How many watts should the resistors be, they're are quite large, and the schematic does not give wattages, only 4000 & 4700 ohms, parts 19, 20
I have a 4000 ohm 10 watts and a 4300 5w
and a large 20 w 4.7k

:If the resistors are out of tolerence, I would replace them. Generally resistors with no tolerance color band are 20 percent, a silver band 10 percent. The handdrawn diagram you have in this thread shows a .022 mf capacitor hooked to B+ when it should be to the plate of the second triode tube. If it is hooked like your diagram the signal from the plate cannot get to the output tube(s).
:
:Radiodoc
:********************
:
:
::I just changed it back, what about the other resistors? The 4000 ohm and 4700 ohm the 4700 ohm is parallel to a .05mfd cap. These have drifted up to 6200 and 7000 ohms.
::If that is good I'll go plug it in.
::Thanks
::
:::Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
:::
:::Radiodoc
:::*******************
:::
:::
:::
:::::
:::::
:::::
:::::
:::::
:::::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:::::There is audio on the grid.
:::::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/12/2009 9:22:20 AMRadiodoc

Ian,

The two resistors form a voltage divider to supply a lesser voltage to the tube(s) screen circuit. You can get an idea of the wattage of the resistors by measuring the voltage drop across the 4700 Ohm resistor (radio powered up). Use Ohms Law to figure the current thru the resistor: I=E/R (I current, E voltage drop across resistor, R resistance of the resistor). Once you have the current, use Ohms Law to figure the wattage of the resistor: W=I*E. The same current flows thru the 4000 Ohm resistor. You can use Ohms Law to figure its wattage. A safety factor would be to double the figured wattage.

Radiodoc
*******************

:I will try it with the original resistors first.How many watts should the resistors be, they're are quite large, and the schematic does not give wattages, only 4000 & 4700 ohms, parts 19, 20
:I have a 4000 ohm 10 watts and a 4300 5w
:and a large 20 w 4.7k
:
::If the resistors are out of tolerence, I would replace them. Generally resistors with no tolerance color band are 20 percent, a silver band 10 percent. The handdrawn diagram you have in this thread shows a .022 mf capacitor hooked to B+ when it should be to the plate of the second triode tube. If it is hooked like your diagram the signal from the plate cannot get to the output tube(s).
::
::Radiodoc
::********************
::
::
:::I just changed it back, what about the other resistors? The 4000 ohm and 4700 ohm the 4700 ohm is parallel to a .05mfd cap. These have drifted up to 6200 and 7000 ohms.
:::If that is good I'll go plug it in.
:::Thanks
:::
::::Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
::::
::::Radiodoc
::::*******************
::::
::::
::::
::::::
::::::
::::::
::::::
::::::
::::::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
::::::There is audio on the grid.
::::::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/12/2009 9:28:12 AMRadiodoc

:Ian,
:
:The two resistors form a voltage divider to supply a lesser voltage to the tube(s) screen circuit. You can get an idea of the wattage of the resistors by measuring the voltage drop across the 4700 Ohm resistor (radio powered up). Use Ohms Law to figure the current thru the resistor: I=E/R (I current, E voltage drop across resistor, R resistance of the resistor). Once you have the current, use Ohms Law to figure the wattage of the resistor: W=I*E. The same current flows thru the 4000 Ohm resistor. You can use Ohms Law to figure its wattage. A safety factor would be to double the figured wattage.
:
:Radiodoc
:*******************
Ian,

I have to correct my self already. The current thru the 4000 Ohm resistor will be greater than that thru the 4700. It will have the current of the 4700 resistor plus the current drawn by the screen grids of the tubes. You can measure the voltage across the 4000 and use Ohms Law to figure its wattage.

Radiodoc
*********************

:
:
:
::I will try it with the original resistors first.How many watts should the resistors be, they're are quite large, and the schematic does not give wattages, only 4000 & 4700 ohms, parts 19, 20
::I have a 4000 ohm 10 watts and a 4300 5w
::and a large 20 w 4.7k
::
:::If the resistors are out of tolerence, I would replace them. Generally resistors with no tolerance color band are 20 percent, a silver band 10 percent. The handdrawn diagram you have in this thread shows a .022 mf capacitor hooked to B+ when it should be to the plate of the second triode tube. If it is hooked like your diagram the signal from the plate cannot get to the output tube(s).
:::
:::Radiodoc
:::********************
:::
:::
::::I just changed it back, what about the other resistors? The 4000 ohm and 4700 ohm the 4700 ohm is parallel to a .05mfd cap. These have drifted up to 6200 and 7000 ohms.
::::If that is good I'll go plug it in.
::::Thanks
::::
:::::Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
:::::
:::::Radiodoc
:::::*******************
:::::
:::::
:::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:::::::There is audio on the grid.
:::::::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/11/2009 5:20:33 PMRadiodoc

:Ground the bottom of the volume control and place a .047 mf cap in series with the wiper of the control to the grid and 10 meg resistor and the circuit should work.
:
:Radiodoc
:*******************
Actually, with a 10 meg resistor for the grid return resistor, probably a .0047 to .01 mf cap may be better. Whatever sounds best to you.

Radiodoc
******************

:
:
:
:::
:::
:::
:::
:::
:::I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:::There is audio on the grid.
:::does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)

6/11/2009 10:54:21 AM!-

:
:http://img149.imageshack.us/img149/8477/4555.th.gif
:
:
:I built an amp, this is the first stage, I get no audio on the plate. why? The amp is based off of the crosley 0c3p I was asking about a couple of days ago.
:There is audio on the grid.
:does the plate capacitor need to be bigger(i am using 2 mica caps in paralell to make 250 mmf)