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Has anyone used these as drivers for 2A3's or 300B's , how do they sound compared to 5687, 7119 types?
Follow Ups:
It seems rather a waste to use these tubes as simple common cathode voltage amplifiers. Their low Rp and relatively high filament power provide more advantage in other topologies. They also exhibit a much greater heater-cathode breakdown than is commonly known. This can have distinct benefits in high-level SRPP, where the upper half of the stage can utilize anode voltages of 450V or more without difficulty. However, for simpler tasks, other tubes are less demanding and more routine to utilize and tweak.
and I'd be curious as to what you'd use in their stead. The use being a push-pull driver stage, as low an output impedance is practicle, and good section-section balance. Other points to consider is the interchangeability, withsimilar types, all the way from a 6AS7 to a 6BL7 can work in the same circuit if there is enough filament power and dissipation rating in the tail load.
regards,
Douglas
Did I phrase it correctly? Seriously, it depends on the exact requirements. I agree with KevinC, however, that 6BL7/6BX7s are difficult to locate with good internal matching. I have twenty-five or so lying on the shelf, and only a couple are close enough for use as push-pull drivers.
though I've heard them to perform well. Used a s a voltage amp in a linestage. One in ten useable, due to section matching and god knows what other criteria he uses before OK-ing a valve...wouldn't mind getting one or two ov his rejects.Thanks for the suggestion though, if you would part with some ov your rejects, drop me a note....
regards,
Douglas
I have high regard for the 6BX7GT as a driver tube for P-P DHTs. I have liked the 6BL7GT much less. I use the tube driving the outputs through LL1671/PP tranformers. I think that they have a somewhat gutsier sound than 7119/5687/6900 (if that means anything to anyone but me).
Kevin Carter
K&K Audio
www.kandkaudio.com
can you use a LL1635/5ma?
So long as you take care to make sure that the bias current imbalance is less than 5mA. I have not had much luck finding many 6BX7GTs that have sections matched to 10%, so it is better to use two tube sockets for P-P and select the matches between tubes.
Kevin Carter
K&K Audio
www.kandkaudio.com
Hooking them up as common cathode, across 25k loads, I get plate voltages within a few volts of each other. That's a fraction of a mA difference out of 8 to 10 per section.
regards,
Douglas
maybe you did something bad in a previous life?
(kidding of course)
"maybe you did something bad in a previous life?"I suspect that I did, perhaps in several past lives. (not kidding, well really I don't know)
I am typically using the tube at more like 25-30mA per section, so perhaps that is my problem.
Kevin Carter
K&K Audio
www.kandkaudio.com
HEy-Hey!!!,
I have not tried them on DHT but the triode strapped KT90. I slightly prefer the 5687. I found the 6BL7 a bit fuzzier and the 6BX7 a bit too sharp sounding. And the 5687 was juuuuust right. Kidding there. None of them sounded bad, minor nuance stuff. I am currently running a pair of 12B4A in an octal adapter I built and haven't taken them out after the first few swaps. The split plate 12B4 also looks cool with the exposed cathode glowing orange.
By the plate curves, teh lower gain tubes will give a bit more swing, but it is a small thing. I point to 7N7 and other's work to look for a tube with lower odd harmonic distortion and 5687 is about a quarter of the others. I will make another adapter or maybe a hole filler to use them direct wired. part of the 12B4 attraction is the gain is almost perfect. may try 5998 there if I can find one or two.
Tried a half dozen 7119 and did not like the sound, hard to describe why, but it wasn't as nice as any of the alternatives. Grainy and bland is probably as good as I can do without a shared listen.
regards,
Douglas
I have experience with both of these types - and indeed some of the others mentioned.I have used 6BX7 to drive a pair of 813s which it did very well. 6BL7s I am using in my line stage which like most of my stuff is "temporary".
I do not like E182CC/7119 - it is the one valvbe that I would say sounds nasty - a sort of sharp edge; 6350 is better if you like a sharpish sound - it is much smoother. 6463 is good too and these types are cheap although they are nowhere near the 6SN7 class when it comes to distortion.
5687 will work properly only if a lot of current is run through it; a glance at the composite curves will show that those exciting figures put out by the makers apply to 40mA anode current!
Choice of driver ultimately depends on how much gain is required; if there are to be two stages, then my favourite choice at present would be either 6EW7 (or the 10, 15 or 19V variants) or 6DN7. For those who do not know these, they are "dissimilar" double triodes used as line osc./amp in old TV sets. Both 6EW7 and 6DN7 have a section that roughly approximates to half a 6SN7, the other half being a beefy triode with mu of around 6 and gm of about7 - Ra is therefore in the order of 800 ohms or so depending on the current you care to run.
I have tested these thoroughly and their distortion performance is excellent..
Recommended.
7N7
What current is optimal for the 6BX7 and the 6BL7?
This depends to a certain extent on a) the amount of HT you have available and b) how many volts you wish to swing.Having a higher anode resistance, 6BL7 should have a higher value of load resistor.
I would say aim for 20mA per section minimum for both types
7N7
5998a is the sledgehammer and the grid of the KT90 is the nut ! I've often wondered what this valve would sound like as a driver . The 7236 (computer grade 5998a) I have test very close between sections , as an output valve they are very good , but as a driver ?...FB
Send it over, I'll plug it in and report. I have ooodles ov heater corrent, the power trans used to run a pair of 6336A's and the socket is already based 8BD....
As to the sledgehammer and nut thing, I've done my share of work on Milwaukie's finest 2-cylinders so I know how to weild a big hammer. In defense fo the KT90, it is triode strapped so it is just a bit harder than a tetrode connected valve might be to drive.
regards,
Douglas
I just can't bring myself to do it though ! A 7236 is bigger than an S11E12 which is what I'm using for the output valve , would possibly work very well , even with only 400V HT . Being a power valve itself , the drive problems would be moved upstream a stage...FB
I used the 6BX7 as a driver in a PP 300B amp and it worked very well in that capacity.
I have not compared it directly to the 5687 or the 7119.
Have fun.
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