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Old 21st August 2012, 09:48 PM   #11
tomchr is offline tomchr  United States
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Quote:
Originally Posted by Vincent77 View Post
What's wrong with the D3a? It can swing more than 200Vpp...
There's nothing *wrong* with the d3A. In fact, it's a very nice tube. But I found I got better performance (lower THD) with the ECC99. I just wasn't able to find a good operating point on the d3A - one that would allow both for low THD and provide the needed swing. The d3A is also fairly pricey... I would prefer to use a tube that's in current production or abundantly available.

Quote:
Originally Posted by wrenchone View Post
6N6P for driver?
That's much more interesting than the 6H30 mentioned earlier. At least much more reasonably priced. I may take a look at that.

~Tom
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Old 22nd August 2012, 05:43 AM   #12
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I built my SET amp for a JJ ecc99 driver tube, but I ended up preferring Sylvania 12BH7A. I think the JJ ecc99 is a close copy of a 12BH7, no parts value changes were required or even ideal for the swap... I got 3 of them right now, all are good tubes and cost under $15 each.

Congrats on your 300b amp, looks great!

Last edited by Davec113; 22nd August 2012 at 05:45 AM.
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Old 22nd August 2012, 04:00 PM   #13
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I've been doing some nosing around on the net, and opinions vary as to whether the ECC99 or the 6N6P is the better driver tube. If I recall, someone did a "shootout" comparison between the ECC99 and various other tubes in Audio Amateur when the ECC99 first came out. The 6N6P may have been one of the contenders, maybe not. I'd have to go back and look at the article again to get the particulars. I was only mildly interested at the time, as I wasn't actively building tube stuff back then. Times have changed...
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Old 22nd August 2012, 04:26 PM   #14
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Hello,

I have directly compared these tubes in the same headphone amplifier, as the voltage amplifier, coupled by a teflon cap to a SS buffer.

The 12BH7 (various brands) is one of my favorite tubes, one of the few "magical sounding" ones.
The D3a also sounds fantastic, definitely better than the ECC99 to my ears.
I tried a gold pin, factory selected ECC99; it's a good tube, but lacks a little something...
I also tried different 6N6P tubes. I don't like them, I'll never use them in any amp.

Oh, and 12BH7 and ECC99 are quite different - lower plate resistance / higher transconductance and 3x maximum current for the ECC99. But they can be sometimes substituted, indeed.
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Old 22nd August 2012, 06:02 PM   #15
tomchr is offline tomchr  United States
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For those using the d3A; what operating point are you running at?

I seem to recall running at 12 mA, Vgk = 1.75 V without great success. It was decent, but the THD was a bit high. It looks like operating points around 20 mA, Vgk = 1.25 V would be better.

~Tom
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Old 22nd August 2012, 08:38 PM   #16
euro21 is offline euro21  Hungary
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Hi Tom!

My 300B SET:

Siemens E280F/D3a (the last is most dynamic, but the 280F is most refining), 10mA anode current, green LED bias, cascode (DN2540) anode CCS, V-Cap TFTF 100nF coupling, "powerdrive" (TubelabSE) by FET, 300B 70mA, 5K:8 OPT, 400V B+.

Over 6W A2 mode (160Vpp Ug), clipping at 10W.

Driver schematic, and spectrum at 200Vpp:
Attached Images
File Type: jpg E280F, CCS, 70V RMS_Right.jpg (142.6 KB, 1474 views)
File Type: jpg D3a driver.jpg (63.2 KB, 1431 views)
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Old 22nd August 2012, 08:39 PM   #17
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by tomchr View Post
For those using the d3A; what operating point are you running at?

I seem to recall running at 12 mA, Vgk = 1.75 V without great success. It was decent, but the THD was a bit high. It looks like operating points around 20 mA, Vgk = 1.25 V would be better.

~Tom
I'm running at 20mA triode connected and approximately 1.6V grid bias.. Seems to work pretty well with the LL1635.. They've run for nearly a year without problems.
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Old 23rd August 2012, 01:18 PM   #18
palmas is offline palmas  Portugal
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Quote:
Originally Posted by wrenchone View Post
6N6P for driver?
That was my best choice to drive a 300B. Wonderfull!

Of course the 300B is just driving a GM70, but there is never lack of swing or power.
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Old 15th October 2012, 01:18 AM   #19
tomchr is offline tomchr  United States
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Default Universal 300B Driver?

Folks,

I've read through your suggestions, which so far include: 6H30, 12BH7A, d3A, and 6N6P.

I'm landing on attached circuit. It is capable of using 6N6P, ECC99, 12BH7A, and with some wired-in sockets, d3A in triode configuration. Switching between 6N6P and ECC99/12BH7A is accomplished by moving two wire jumpers. These could be connected to a switch if one wanted to roll tubes.

I haven't been able to dig up an actual data sheet for the 6H30, but Triode Electronics have posted some plate curve measurements. It looks like a nice tube. And judging from the $35/EA cost, it looks like others like it too. But without a data sheet and with measured characteristics that will requiring operating points that stress my circuit thermally, I think I'll pass.

So far, I have listened to the ECC99, d3A, and 6N6P. I really like the latter. To my ears and on my system, the d3A sounds slightly muddy in the highs. There's a pronounced lisp on hard consonants. But it also resolves a lot of detail on metallic instruments (cymbals and the like). In the end, I find the lisp hard to listen to. The ECC99 looses the lisp, but also some of the detail. It's quite pleasant to listen to in my view. The transient response with the ECC99 is quite nice. But the 6N6P takes the cake. It's a good middle ground between the ECC99 and the d3A. I find it really pleasing to my ears.

The THD (1 kHz) comes in as follows:
d3A: 0.32 % @ 1 W; 1 % @ 8.5 W
ECC99: 0.18 % @ 1 W; 1 % @ 8.9 W
6N6P: 0.16 % @ 1 W; 1 % @ 9.7 W

These were the bias conditions:
d3A: Vgk = 2 V; Ia = 10 mA
ECC99: Vgk = 6 V; Ia = 10 mA
6N6P: Vgk = 6.2 V; Ia = 15 mA

I have a pair of Electro-Harmonix 12BH7A on the way and will have a look at those later in the week. My intent is to use Vgk = 11 V (two 5.6 V zeners in series) for biasing. I'll run them at 10~12 mA.

Note that both the ECC99 and the 12BH7A are in current production.

~Tom
Attached Images
File Type: png 6N6P_ECC99_12BH7A-300Bdriver.png (60.9 KB, 1273 views)
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Last edited by tomchr; 15th October 2012 at 01:28 AM.
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Old 15th October 2012, 01:58 AM   #20
rongon is offline rongon  United States
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Best info I know of for 6N6P and 6N30P (6H30).
--

I'm interested to hear what you think of the EH version 12BH7A.
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