6BR7 @ The National Valve Museum
8d8's are good if you give them a can over the top.
they are like the ef86 just a bit better.......there was some ef86's that had silvered grids
but they cost i mean COST
8d8's are good if you give them a can over the top.
they are like the ef86 just a bit better.......there was some ef86's that had silvered grids
but they cost i mean COST
Yes, it's a very versatile tube that SY and I both use in the front ends of our respective phono stages in fact. The internal equivalent noise resistance is about 68 ohms or so, and this equates to about 1.1nVrtHz - pretty hard to beat. The grid stopper resistor, and the internal resistance of most cartridges will be significantly noisier. Absolute overkill. The amazing thing about this tube is it also manages stellar linearity at obscenely large voltage swings as well making it as close to a Swiss Army knife in the tube world as there is. I really should learn to keep my mouth shut..
Hint: you should be running it at 15 - 20mA at relatively low voltages. (100 - 150V or so)
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Hmm, makes me wonder if I have missed an opportunity..
There is no hard and fast rule...
Thanks,
A pair of D3a and 4 6BR7 ordered. I'll be looking for another pair of D3a.
I intend to try them in MM/MC phono pre.
Also, would those tubes benefit from using them in Mu-Follower topology?
I'm not a fan of the mu-follower topology at all, and the rp of the D3A is low enough (~2K) that loading it with a CCS and then using it to drive a passive EQ a la Lipshitz with an initial R of 20 - 30K should give you just about all of the available gain.
FWIW I know the fellow who designed the 416 phono stage cited very well, and the very high mu would be of advantage with very low output mc type cartridges, but he experienced some significant problems sourcing tubes and finding ones that behaved well over time.
It is a hard tube to work with, sockets are largely a homebrew proposition, and they are prone to VHF oscillation if not handled carefully - as are all high transconductance types.
I get what you are saying and by looking at the D3a data sheet, you are right, of course.
Also, I respect your opinion, based on your experience.
However, out of curiosity, why are you not in favor of mu-follower topology?
Don't like the sound... A personal preference.. In the case of 12AX7A/5751 the increased linearity and gain seemed to come at the expense of both bandwidth and slewing performance - to me it sounded "slow." Measurements confirmed that there definitely was a tradeoff, and part of the problem could be traced to the miller capacitance in the 12AX7A. (The resulting higher gain, higher load impedance, and higher miller capacitance resulted in measurably less bandwidth) In the case of higher transconductance triodes the rp is low enough and the linearity in many cases good enough that the classic mu follower may measurably degrade the performance over a CCS (or gyrator) driving a reasonable load impedance.
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Ahhh, but how's a lad to learn without turning a couple $50 pre tubes into plasma globes
I learned that way just fine
Cheers!
Thanks, it does make sense (and I acquired the habit not to argue with experience
).Does it hold true also for ECC82, ECC83 and the rest of the dual triodes?
Yes, it is so.. Passive components are all generally noisier than the tube, as is the mandatory grid stopper resistor.
A 1K grid stopper will raise the input noise to 4nVrtHz so the smallest resistor that conclusively does the job is best in most instances. I generally use 221 - 1K in these applications.
Lossy ferrite beads right at the grid pin might allow you to avoid a grid stopper, but you will have to select very carefully based on sound and whether or not it prevents vhf oscillations. A plate stopper might be a good idea if you choose this route.
It's a shocking discovery for me, from this thread (and data sheets), that passive parts are noisier than SOME tubes.
For MC input I intend to play with low value grid stopper resistor, perhaps about 100 Ohm, combined with ferrite beads. The phono cartridge I use asks for 100 Ohm shunt resistor.
For MM input, the noisiest passive part seems to be the 47K input shunt resistor, so, I assume the grid stopper wouldn't add much noise.
What do you mean by plate stopper, ferrite beads?
Between D3a, 6688, 7788, EF86 and E184F/6EJ7, which are better choice for front end and 2nd stage?
What are recommended choice for CF?
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I wonder about 6BR7 with Ai 1.5 – 2.3 M as pentode and probably 10 K as triode.
I use 6N2P (6Н2П) in condenser mics. Before that I breadboarded with 6S62N (6С62Н) nuvistor; no difference, probably beacuse 2 centimeter diaphragm condenser microphone provides high enough output voltage. 6N2P is much cheaper than 6S62N.
Speaking of phono corrector, I am still searching for good reliable supply of 6J52P (6Ж52П) tubes. As soon as I bought I will put them on my on-line store page.
Speaking of phono corrector, I am still searching for good reliable supply of 6J52P (6Ж52П) tubes. As soon as I bought I will put them on my on-line store page.
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