View Full Version : JJ 6L6 or JJ 7591
10-04-2010, 01:06 PM
Which one of these would produce more watts in an amp and give more headroom
10-04-2010, 01:53 PM
"watts" and "headroom" do not, alone, come from the tube.
"Power" lives in the power transformer & a proper application of the available VA therein.
You've not provided anywhere near enough info to answer this question.
Old Tele man
10-04-2010, 05:14 PM
...check the operating characteristics for them, and you'll find that the 6L6 is a 30W tube while the 7591 is only a 19W tube...among OTHER differences (slight and major):
JJ 6L6GC: Pp = 30W, Ps = 5W, If = 900mA, S(gm) = 6mA/V, rp = 22.5K, µ1 = 7.99
JJ 7591: Pp = 19W, Ps = 3.3W, If = 800mA, S(gm) = 10mA/V, rp = 29K, µ1 = 16.8
...just from the 'numbers' the 6L6 is capable of more power, but needs more drive-signal to achieve that output power (due to lower S(gm)).
...conversely, the 7591 can achieve more power from a lower output PI circuit like a split-load (ala' Deluxe amp) circuit.
...so, the real question is: just what do you want?
10-04-2010, 05:29 PM
Glad you mentioned that.Im going to have a 5e3 built.By a good tech who has built for me before. He said he can build it anywhere between 12 and almost 30 watts depending on output transformer and values etc. I have the option of loading it with 6v6 '7591 or 6l6 . I will need the latter to get the higher watts. I want the ones that will basically produce the most output in that circuit ps I want the amp roughly around 25 to 30 watts , I would like to be able to do that with 7591 and avoid the 6l6 . (7591 just sound cool)
Old Tele man
10-04-2010, 06:27 PM
...since a normal 5E3 (2x6V6) can push about 17-22W, getting 30W from a pair of 7591's might be "marginal" because of the power supply (ps) capacity.
...there has to be 'enough' plate voltage available for the output voltage swing to traverse along the plate load line...if not enough ps voltage available, the plate swing will "clip" and output power will be limited.
...here's 'how to' guesstimate how much plate voltage swing (dVp) you can get: if the ps voltage is 450V and the idle current is quite low (ie" cold, as in almost Class-B), then simply subtract about 50V for the diodeline voltage, ie: dVp = (450V-50V) = 400V plate swing-per-tube.
...will this be a cathode-biased amp? If so, then, whatever cathode bias is used will ALSO have to be subtracted.
10-04-2010, 06:47 PM
Amp designations like 5E3 are taken so loosely these days that he's probably talking about a heftier power supply and transformers. Why not just call it something else like "cathode biased, split load PI, x watt amp" instead of 5E3 which is something entirely different than a 30 watt amp?
10-04-2010, 07:26 PM
He said he can build it anywhere between 12 and almost 30 watts depending on output transformer and values...
That's what he said, huh? :bonk
Go find another tech.
Old Tele man
10-04-2010, 07:36 PM
...believe it or not, but 30W *is* possible at only Vp = Vs = 350V and rp = 6.6K, but 9.0K and 450/400V needed with cathode-biasing:
...and 6.6K OT is what 6V6 typically use.
Our new amp the TP-40, the bigger one is designed around the 7591
So far people are digging it. The tube has a tonal characteristic all to itself...
Very linear with supply voltage variations. Among other things.
The really cool part about it is given the power supply capabilities (Voltage current)
It doesn't take anything to drive a pair of them.
For the most part, our front end on the 20 watt EL84 based amplifier and the 40 watt 7591 based amp are the same.
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