6H30 vs 5687 vs 12AU7 vs ? - diyAudio
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Old 20th June 2002, 11:54 AM   #1
bcherry is offline bcherry  Hong Kong
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Default 6H30 vs 5687 vs 12AU7 vs ?

The last few months I've tried various tube combinations in a tube regulated, choke filtered preamp circuit with the following results:
12AU7 into 12BH7 cathode follower: overall balanced and punchy sound but coloured not the last word in clarity and immediacy
5687: Great bass slam and dynamics across the spectrum but with a slight pervasive graininess
6H30: Not the bass authority of the 5687 but very sweet ESL57ish sound with rich harmonic textures

I'm wondering if that matches other user's experiences with these tubes, or if I just haven't hit the 'sweet spot' with operating points and more is available?

Comments on experiences with other tubes welcome.

Brian
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Old 21st June 2002, 10:01 AM   #2
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Default 6H30

Hello,

the sound of the 6H30 is very much depending on the current through the tube and the operating point. Try the tube with a plate voltage of approx. 100 V and at least 20 mA per system.
I Had best results with a plate loaded amp, 1K
plate resistor and 40ma from a 135 Volt supply voltage.

Reinhard
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Old 21st June 2002, 01:06 PM   #3
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Hi Brian,

My experiences are

6H30: Run it hot and low. Begins to come alive at 20mA. It has lots of plate dissipation, a huge peak current and an Rp of 1100-1300R according to Steve Bench. I like this tube a lot, but I need to experiment more. I have 10 pairs of nicely matched ones waiting to be used.
Been thinking about an MC cart stage with an MAT-04 in cascode with a 6H30 at about 30mA standing bias.

5687: never used one

12AU7: Blech. Don't like the 12__7 series at all. They sound all fat and tubey (in the worst way) to me.

Cheers
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Old 21st June 2002, 02:45 PM   #4
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Default Brett

Hello,

Do you think of a balanced or single ended MC Stage? Please let us know the results when you finished it.

To me the 12AT7 at lots of current is a fine sounding tube. Compare with you with the AU7.
AX 7 sometimes useful in phono or mic appl.

Reinhard
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Old 21st June 2002, 03:55 PM   #5
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Default 6H30 clarification

Ref the suggested value of 100V and 20mA min per system proposed by Reinhard:

Per system, is this per tube section, i.e total of 2W plate dissipation per tube half and total of 4W plate dissipation per tube?

Also, what would be a fairly optimal value? I have been leaning towards about 80V with 30mA. Any thoughts on this?



On another note:

The datasheets provide values of dissipation. They rarely if ever specify whether this is on a per tube basis or a per section basis. What can be said about that?


Petter
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Old 21st June 2002, 04:28 PM   #6
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Default petter

Hello tube gurus,

the 6H30 is 4 Watt per system but you can run the tube up to 6 Watt per system, beyond that the plates will glow.
BATīs Victor in his 50SE is running four systems in parallel for each phase at 65 mA (save side, 16mA per section at approx. 100 Volt plate voltage) to get a plate resistance of 200 Ohm and a tranconductance of 72 mA/V. Amplification factor is 15.

As I know AR is using the tube as cathode follower.

No, I donīt speak about football.

Regards from Germany
Reinhard
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Old 21st June 2002, 06:02 PM   #7
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Default Re: Brett

Quote:
Originally posted by reinhard
Do you think of a balanced or single ended MC Stage? Please let us know the results when you finished it.
Howdy,

I was just 'blue-skying' an idea that's been echoing in my skull a while. I would build it as a differential stage with a ccs loading the bottom. Can't even claim credit for it probably. I'm building an Allen Wright RTP, so guess where I got the idea? The 6H30 is a lot more linear than the 6DJ8, so I thought it might take a good topology another step further and with the MAT there should still be enough gain. Redesigning the RIAA is what's stalled me: lots of figgerring wiv numbers is hard 'cos I can only count to 21 when I'm nekkid Nearly.

The RTP is being built with two phono stages though.

Thanks for the info on the BAT pre's too. It's what I'd suspected, especially since that internal pic they published allowed me to trace some of it, and make an educated guess at the rest. Do they use a mosfet to load the tail of the diff pair?

I'm also pretty sure VK said on AA a while back that the 6H30 would take 7W for the envelope.

Cheers
Brett
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Old 22nd June 2002, 09:22 AM   #8
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Default brett

Hello,

havnīt tried the H30 for Allenīs RTP, But I think
with the MAT instead of J-fet the gain will be high enough.

Yes, BAT is using a Mos Fet as tail with an additional little Bipolar as reference in a "ring of two" arrangement. The negative supply is a stab. 15 Volts, I think.

Reinhard
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