here is my schematic
http://www3.telus.net/demos/6V6cathode.jpg
THanx
Bubba
::Hello, I have built an amp that's working with a 6V6GT cathode bias push pull output and wonder about the ultra linear grid taps that come on the Hammond output transformers. Should I use them? What are your thoughts what pins do they go on if I do use them? Do I need resistors. Values?
::
::here is my schematic
::
::http://www3.telus.net/demos/6V6cathode.jpg
Bubba
:::Hey Bubba: Screen grid taps (known as Williamson taps) connect to pin 4 of each corresponding 6V6. Be sure that you do not cross these up tube to tube. Typically, the plate xformer wires are blue for one side and brown for the other with the Williamson tap a color with a tracer stripe. The red wire is fed by the B+ line which should be disconnected from pin 4 of each tube prior to connecting the tap wire. I recommend a 33 ohm resistor in series with each tap wire going to pin 4.
:: Since your amp will have cathode bias I recommend another change that will MARKEDLY improve its performance. Assuming you now have a cathode bias resistor connected from pin 8 to ground for a bias of about -14 volts. REMOVE THE CATHODE BIAS RESISTOR(S). Connect both cathodes (pin 8) together and connect them to ground through a 5 watt 15 volt zener diode. This essentially clamps the bias which renders the cathode voltage rock stable and greatly improves the low frequency response of your amplifier. You will notice a tremendous difference. You might want to use a small piece of sheet metal to mount the zener on as a heat sink. Tom.
:Thanx for the Diode tip. But am I going to gain anything by using the taps as opposed to having the voltage feeding the grids from the power supply?
:Or am I splitting hairs. What changes would I notice. This is a guitar amp buy the way.. So with the cathode voltage fluctuating don't I gain self compression. WIth the Resistor as opposed to the diode?
:
:THanx
:
:Bubba
:
:
:::Hello, I have built an amp that's working with a 6V6GT cathode bias push pull output and wonder about the ultra linear grid taps that come on the Hammond output transformers. Should I use them? What are your thoughts what pins do they go on if I do use them? Do I need resistors. Values?
:::
:::here is my schematic
:::
:::http://www3.telus.net/demos/6V6cathode.jpg
2. The zener diode makes the bias ultra stable which is what we are all after in an amplifier. A cathode bias resistor varies its voltage drop (and therefore the bias) in direct proportion with tube current. This change is in phase with the incoming signal which causes "negative feedback" or degeneration which is a form of "compression" reducing the overall gain of the stage. Many guitar amps utilized fixed bias to get away from this characteristic of cathode bias. You might want to just try the resistor vs: the diode since it is an easy hookup.
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::::Hey Bubba: Screen grid taps (known as Williamson taps) connect to pin 4 of each corresponding 6V6. Be sure that you do not cross these up tube to tube. Typically, the plate xformer wires are blue for one side and brown for the other with the Williamson tap a color with a tracer stripe. The red wire is fed by the B+ line which should be disconnected from pin 4 of each tube prior to connecting the tap wire. I recommend a 33 ohm resistor in series with each tap wire going to pin 4.
::: Since your amp will have cathode bias I recommend another change that will MARKEDLY improve its performance. Assuming you now have a cathode bias resistor connected from pin 8 to ground for a bias of about -14 volts. REMOVE THE CATHODE BIAS RESISTOR(S). Connect both cathodes (pin 8) together and connect them to ground through a 5 watt 15 volt zener diode. This essentially clamps the bias which renders the cathode voltage rock stable and greatly improves the low frequency response of your amplifier. You will notice a tremendous difference. You might want to use a small piece of sheet metal to mount the zener on as a heat sink. Tom.
::Thanx for the Diode tip. But am I going to gain anything by using the taps as opposed to having the voltage feeding the grids from the power supply?
::Or am I splitting hairs. What changes would I notice. This is a guitar amp buy the way.. So with the cathode voltage fluctuating don't I gain self compression. WIth the Resistor as opposed to the diode?
::
::THanx
::
::Bubba
::
::
::::Hello, I have built an amp that's working with a 6V6GT cathode bias push pull output and wonder about the ultra linear grid taps that come on the Hammond output transformers. Should I use them? What are your thoughts what pins do they go on if I do use them? Do I need resistors. Values?
::::
::::here is my schematic
::::
::::http://www3.telus.net/demos/6V6cathode.jpg
B
::
::Thanx for the Diode tip. But am I going to gain anything by using the taps as opposed to having the voltage feeding the grids from the power supply?
::Or am I splitting hairs. What changes would I notice. This is a guitar amp buy the way.. So with the cathode voltage fluctuating don't I gain self compression. WIth the Resistor as opposed to the diode?
::THanx
::
::Bubba
::;Bubba:
:1. The screen grid taps will make the amp more linear with less distortion if that appeals to you. It is also a little more efficient since the screen current changes are conducted by the transformer and are therefore converted into audio. Using pp 6V6's you will be fortunate to get 10 to 12 honest rms watts according to the B+ voltage you are running.
:
:2. The zener diode makes the bias ultra stable which is what we are all after in an amplifier. A cathode bias resistor varies its voltage drop (and therefore the bias) in direct proportion with tube current. This change is in phase with the incoming signal which causes "negative feedback" or degeneration which is a form of "compression" reducing the overall gain of the stage. Many guitar amps utilized fixed bias to get away from this characteristic of cathode bias. You might want to just try the resistor vs: the diode since it is an easy hookup.
::
::
::
::
::
::
::
::
:::::Hey Bubba: Screen grid taps (known as Williamson taps) connect to pin 4 of each corresponding 6V6. Be sure that you do not cross these up tube to tube. Typically, the plate xformer wires are blue for one side and brown for the other with the Williamson tap a color with a tracer stripe. The red wire is fed by the B+ line which should be disconnected from pin 4 of each tube prior to connecting the tap wire. I recommend a 33 ohm resistor in series with each tap wire going to pin 4.
:::: Since your amp will have cathode bias I recommend another change that will MARKEDLY improve its performance. Assuming you now have a cathode bias resistor connected from pin 8 to ground for a bias of about -14 volts. REMOVE THE CATHODE BIAS RESISTOR(S). Connect both cathodes (pin 8) together and connect them to ground through a 5 watt 15 volt zener diode. This essentially clamps the bias which renders the cathode voltage rock stable and greatly improves the low frequency response of your amplifier. You will notice a tremendous difference. You might want to use a small piece of sheet metal to mount the zener on as a heat sink. Tom.
:::Thanx for the Diode tip. But am I going to gain anything by using the taps as opposed to having the voltage feeding the grids from the power supply?
:::Or am I splitting hairs. What changes would I notice. This is a guitar amp buy the way.. So with the cathode voltage fluctuating don't I gain self compression. WIth the Resistor as opposed to the diode?
:::
:::THanx
:::
:::Bubba
:::
:::
:::::Hello, I have built an amp that's working with a 6V6GT cathode bias push pull output and wonder about the ultra linear grid taps that come on the Hammond output transformers. Should I use them? What are your thoughts what pins do they go on if I do use them? Do I need resistors. Values?
:::::
:::::here is my schematic
:::::
:::::http://www3.telus.net/demos/6V6cathode.jpg