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-   -   use of 6dj8 as driver on a direct coupled 2a3 se amp (http://www.diyaudio.com/forums/tubes-valves/41275-use-6dj8-driver-direct-coupled-2a3-se-amp.html)

camotecue 21st September 2004 04:10 AM

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?

Sch3mat1c 21st September 2004 05:56 AM

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

fdegrove 21st September 2004 02:16 PM

Hi,

Here's an example:

BLACK ART 2A3 SE

Cheers,;)

Bigun 11th January 2016 04:25 AM

Quote:

Originally Posted by Sch3mat1c (http://www.diyaudio.com/forums/showthread.php?p=477882#post477882)
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!

Merlinb 11th January 2016 01:28 PM

Quote:

Originally Posted by Bigun (http://www.diyaudio.com/forums/showthread.php?p=4577714#post4577714)
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

thehoj 11th January 2016 02:09 PM

There's also the 6922, which is the same as the 6dj8, but with a higher average anode voltage rating.. 220V.

MrCurwen 11th January 2016 02:33 PM

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.

rongon 12th January 2016 04:50 AM

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?
--

Sch3mat1c 15th January 2016 06:34 AM

Quote:

Originally Posted by Bigun (http://www.diyaudio.com/forums/showthread.php?p=4577714#post4577714)
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!

Tim

tomchr 15th January 2016 06:42 AM

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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