*****es brew step 2 ... or grid bias ... how to?

Gluca · 2nd August 2005, 07:25 PM

I finished my first amps a couple of months ago, now they are happily running.

Time to move to step 2 and get something upgraded/experimented.

I would try to bias the grid leaving the cathode alone and it should be quite simple as my amps are transformers coupled all the way ... but ...

... how to do that when you have DHT?

I mean, I can easily give -x volt to the CT of the input splitter transformer and -y volt to IT's CT but, as there will be no resistors in the cathode path to ground, I am not pretty sure I can just connect one side of the heater/cathode to ground without center pot or hum balancing resistors.

I could not find any example?!?!? HELP!!

Just for reference by amps are:
-XLR in
-input trans for splitting duties
-6H30pi PP
-interstage LL1660
-2A3 PP
-OPT LL1623 5.6K:8

Gianluca

PS bitches brew ... that was the very first CD I played on the amps

PRR · 2nd August 2005, 09:20 PM

Grounding one end of the heater will work, but hum bad.

Center-tap the heater supply. If you don't have a 2.5VAC CT transformer, use two 10Ω resistors in series across it and take the center as your "common". (Yes, this adds 10Ω||10Ω= 5Ω of "cathode resistor", but this is negligible in 2A3.)

Gluca · 2nd August 2005, 09:22 PM

Oh thanks!

Gianluca

2nd August 2005, 07:25 PM	#1
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	*****es brew step 2 ... or grid bias ... how to? I finished my first amps a couple of months ago, now they are happily running. Time to move to step 2 and get something upgraded/experimented. I would try to bias the grid leaving the cathode alone and it should be quite simple as my amps are transformers coupled all the way ... but ... ... how to do that when you have DHT? I mean, I can easily give -x volt to the CT of the input splitter transformer and -y volt to IT's CT but, as there will be no resistors in the cathode path to ground, I am not pretty sure I can just connect one side of the heater/cathode to ground without center pot or hum balancing resistors. I could not find any example?!?!? HELP!! Just for reference by amps are: -XLR in -input trans for splitting duties -6H30pi PP -interstage LL1660 -2A3 PP -OPT LL1623 5.6K:8 Gianluca PS bitches brew ... that was the very first CD I played on the amps

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2nd August 2005, 09:20 PM	#2
PRR diyAudio Member Join Date: Jun 2003 Location: USA	Grounding one end of the heater will work, but hum bad. Center-tap the heater supply. If you don't have a 2.5VAC CT transformer, use two 10Ω resistors in series across it and take the center as your "common". (Yes, this adds 10Ω\|\|10Ω= 5Ω of "cathode resistor", but this is negligible in 2A3.)

2nd August 2005, 09:22 PM	#3
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	Oh thanks! Gianluca

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