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In Reply to: RE: 6AH4 tube for DIY Preamp posted by Freo-1 on March 31, 2014 at 17:40:08
The 6H30 and 6DJ8 are good when you need more gain.
Other tubes will offer lower output impedance.
It's apples and oranges, but I agree that your approach is a good one for a line stage.
Follow Ups:
I agree with your point about gain. Since the subject is a line stage, gain is not much of an issue.
I personally have developed a dislike for most frame grid tubes in general, and 6DJ8/6922/6H30 tubes specifically. I think they are too prone to microphonics, noise, overpriced, and can sound steely/strident. I think there are a lot of better alternatives out there for DIY applications than the frame grid tubes. To me, the main purpose of DIY is to use tubes that are high quality and reasonable cost, which rules out most current production tubes. Why pay a lot of money for a current 6L6 when a 1625 is MUCH better made, still available, and MUCH cheaper? The same logic applies to small signal tubes as well.
I remember reading in Stereophile years back a running debate about the suitability of the 6DJ8 for (commercial) audio applications. I believe David Manley was against it's use, and I agree with that assessment.
Having said all that, I do have an old Wavelength Audio Cosine DAC I kept that uses a single 6GM8. It's still very musical for CD playback.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
In the last six months, I have bought plenty of Amperex 6DJ8's for less than $5 each... suitable tubes are still around.
They do sound like crap if you don't have stoppers on the grids and plates though.
For an RIAA preamp, I would take them over a 12AX7 any day, though I do think there are other options worth investigating.
Might I ask what size grid stoppers do you find necessary? Mandatory? I've been running a 6kn8/6dj8, DAC/line stage for a few years without any grid stoppers... thanks CB. JH
For plate stoppers, I find that 50-100 Ohms works fine (carbon film or carbon comp).
For grid stoppers, I tend to go between 200 and 1K on a 6DJ8. (Sometimes higher on other tubes)
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