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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
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.
In short, you want as low anode voltage as possible at the input. 100V is the practical minimum in my experience.
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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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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Actually, it is quite common: for RF transistors. Sadly, they don't tell you when it is this kind of rating!
Tim
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Joined 2009
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… and a cathode bypass cap on the second stage.
You can always run a split rail supply, with the first tube run from negative voltage with plate set up at to bias the next stage at some -ve voltage and voila, no caps (at all). Just say'n theres a better way.
L.H/S
This is very bad design thinking. You want the INPUT tube to be operating as vividly and as optimally as possible. In a tube "I" like to use, half a 12AX7, the tube comes to life OVER 150 VDC Ea, and it sounds better up to about 195 VDC Ea. I usually shoot for 175 VDC or better, at about 0.6 mA to 0.07 mA., and I do ALL I can to optimize the stage, paying special attention to every implementation parameter in the execution. One must do this for quality.
I simply combine two Mills MRA-12s, precisely matched to each other Ohmically, in parallel, to become the 24 Watt Rk of the 2A3, which is typically run between 42 and 44 mA., 250 VDC P-K, JJ 2A3-40 is the best overall choice Finals tube today.
Jeff Medwin
Yes, it does. But, the amp will sound more "alive" and more " lively", without being pushed at high SPLs all the time, if you use a mu of 100 Driver tube !!!
It takes CAREFUL implementation, of such a high mu tube. Email me and we will discuss what is needed,
Didn't you have a pair of JJ 2A3-40s??? Hear them yet. I had mine for about 8 years, and JUST plugged them into on of my DC SET amps..... last week, THE TUBES PERFORMANCE BLEW ME AWAY IN " MY " CIRCUIT, DID NOT EXPECT WHAT I HEARD !! LOVELY. WOW.
Jeff
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