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Old 21st August 2006, 06:28 AM   #1
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Default new driver for se 2A3

guys,

i want to try a new driver for my se 2a3 amp which was previously driven by a 6dj8 in a grounded cathode then cap coupled to the 2a3. i now happen to have 2 pcs. 6gk5 tubes that i want to try. can anyone please help me redesign my driver circuitry using these tubes. my b+ is 300v, i have a 5k opt, and i use sovtek 2a3 tubes.

i searched the forum and i see a similar design but with 3k opt. instead of 5k opt.

thanks in advance for any help.
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Old 22nd August 2006, 01:53 AM   #2
Sheldon is offline Sheldon  United States
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How about a schematic, or at least a description of the driver stage - plate voltage, plate resistor, cathode resistor, etc.?

Sheldon
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Old 22nd August 2006, 03:15 AM   #3
arnoldc is offline arnoldc  Philippines
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larry, you need to get something like 100V p-p to drive the 2A3 to full power. 5K, 3K, 2.5K will be ok, with higher OPT load less distortion and less power.

looking at the loadline, it seems good at 1V bias. So, I'd stick to the textbook operating point first of 1V bias, 135V plate voltage. Nice candidate for LED as we can run it at 11mA.

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Old 22nd August 2006, 04:59 AM   #4
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sheldon and arnoldc,

i dont know how to post a schematic. but yes i'm looking at the textbook 135 plate voltage, 13k5 plate resistor for the driver tube. i just want to implement a grounded cathode circuit. am i right that at -1v bias and 11 mA plate current, the cathode resistor should be 90 ohms? my other question is - is it ok not to bypass the driver cathode resistor?

btw, the 2A3 is cap coupled to this driver stage running at around 60mA..

arnoldc, can you show me how to introduce LED instead of the usual cathode resistor? i thought that you need more than 1v before you can use LED bias. please illuminate me on this. also, will this tube (6gk5) which will be run at 11mA be a good candidate for CCS.

thank you very much.

larry
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Old 22nd August 2006, 05:28 AM   #5
arnoldc is offline arnoldc  Philippines
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hi larry, what stuck in my head is around 10mA for the LED to become effective. I have a table of LEDs and I don't remember having one that can do 1V... maybe I'm wrong. Hope the LED guru (SY) can chime in.

Also, I'd consider one of Brian Beck's cathode CCS if you're going for a resistive plate load. Or diyAudio CCS on the anode if resistor on the cathode...

Couple of options for you How about choke load? He he

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Old 22nd August 2006, 05:49 AM   #6
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arnoldc,

maybe i try this the conventional way first (i mean just using resistors) to hear how this sounds and then tweak later. thanks
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Old 22nd August 2006, 06:38 AM   #7
rdf is offline rdf  Canada
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Quote:
Originally posted by arnoldc
I have a table of LEDs and I don't remember having one that can do 1V...
Hi arnoldc, look through the infrared LEDs. I'm pretty sure some in my kit were ~1.2 volts.
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Old 22nd August 2006, 06:56 AM   #8
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i also remember having found at a local electronic shop 1.5volt LEDs. can these be used for a -1V bias?
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Old 22nd August 2006, 07:53 AM   #9
arnoldc is offline arnoldc  Philippines
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Quote:
Originally posted by rdf


Hi arnoldc, look through the infrared LEDs. I'm pretty sure some in my kit were ~1.2 volts.
Oh! I avoided infrared, because they're not "cheap" he he.

But thanks for the lead!!

So larry, there you go!
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Old 22nd August 2006, 11:16 AM   #10
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Just to toss in my two bits....

I've driven tubes with similar drive requirements (80Vp-p) with a pair of trioded 6EJ7's in mu-follower configuration
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