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Old 21st September 2004, 03:10 AM   #1
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Default use of 6dj8 as driver on a direct coupled 2a3 se amp

can anyone please help me if i can use a 6dj8 driver in a direct coupled 2a3 se amp? i've noticed that the maximum plate voltage of the 6dj8 is only 130v. is this relevant? any schematics please that i can try?
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Old 21st September 2004, 04:56 AM   #2
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No, 130V means it can be used at 260V supply resistance coupled. Plate voltage ratings assume inductive supply (i.e., choke or transformer) which allow peak voltages up to 2*B+.

And yeah, it'll work great.

Tim
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Old 21st September 2004, 01:16 PM   #3
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Hi,

Here's an example:

BLACK ART 2A3 SE

Cheers,
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Old 11th January 2016, 03:25 AM   #4
Bigun is offline Bigun  Canada
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Originally Posted by Sch3mat1c View Post
No, 130V means it can be used at 260V supply resistance coupled. Plate voltage ratings assume inductive supply (i.e., choke or transformer) which allow peak voltages up to 2*B+.

And yeah, it'll work great.

Tim
So max plate voltage in the datasheets is only half the max allowed for a signal voltage on the plate. That sure ain't the case for transistors!
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Old 11th January 2016, 12:28 PM   #5
Merlinb is offline Merlinb  United Kingdom
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So max plate voltage in the datasheets is only half the max allowed for a signal voltage on the plate. That sure ain't the case for transistors!
The 130V rating is for the maximum average anode voltage. The datasheet also specifies 550V as the maximum peak / cold anode voltage.
http://www.shinjo.info/frank/sheets/030/e/ECC88.pdf
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Old 11th January 2016, 01:09 PM   #6
thehoj is offline thehoj  Canada
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There's also the 6922, which is the same as the 6dj8, but with a higher average anode voltage rating.. 220V.
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Old 11th January 2016, 01:33 PM   #7
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When I made DC coupled amps I always wanted to get the input stage plate voltage as low as possible, so that the output stage cathode doesn't have to be at such a high voltage. 100V at input stage anode means 120V or whatever the bias needed is, at the output stage cathode. If it's 150V at the input anode, then it's 170V at the output cathode, which means more heat to burn, and higher B+ needed for headroom.

In short, you want as low anode voltage as possible at the input. 100V is the practical minimum in my experience.
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Old 12th January 2016, 03:50 AM   #8
rongon is offline rongon  United States
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A 2A3 has a directly heated cathode, so its cathode and heater are always at the same potential. So DC coupling isn't quite as fraught with peril as when using indirectly-heated tubes. I'm not sure if that's what you were thinking of, though.

One good thing about a 6DJ8 is that it will work pretty well with plate to cathode voltage of only 100V or so.

Were you planning to stack the power supplies so that the B+ supply for the 2A3 sits on top of the B+ supply for the 6DJ8 (two separate power transformers), or were you going for a more Loftin-White type of thing, with a big stack of hot resistors?
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Old 15th January 2016, 05:34 AM   #9
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Quote:
Originally Posted by Bigun View Post
So max plate voltage in the datasheets is only half the max allowed for a signal voltage on the plate. That sure ain't the case for transistors!
Actually, it is quite common: for RF transistors. Sadly, they don't tell you when it is this kind of rating!

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Old 15th January 2016, 05:42 AM   #10
tomchr is offline tomchr  Canada
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I use the 6DJ8/ECC88/E88CC/6922 tube in my DG300B. CCS loaded grounded anode input with an cathode follower driving the 300B. Works very well. If it can drive a 300B it should drive a 2A3 without breaking a sweat.

Tom
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