D3A

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Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

D3A

Post by Maturin »

Are D3A's actually still available? Anybody know?

All these great D3A circuits and circuit ideas - but where to get the tube?

Some one recently pointed out to me the wisdom of using EF86's for small signal pentode work: "they're still in production"...Amen!!!
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »


I think they are still available in Europe. The last ones I bought were in stock in Washington state or Oregon. They are still listed at vacuumtubes.net

Remember D3a = 7721.

Good Luck.

D3a is a very nice sounding tube!
Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

Post by Maturin »

Ah, most excellent!!! Thanks!!
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Try www.ebay.de , D3a are easy to find there.
Brgds
Lars
Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

Post by Maturin »

very cool, thanks, Lars

Question for everyone: for small signal work, including REALLY small signal work (mm or even mc cartridges, playback heads, etc - but not RF stuff), what is the advantage of a D3A over the EF86?

The steilheit of the D3A is 35 mA/V, whereas for the EF86 it is but 1.8 mA/V, so I get that the potential gM of the D3A is almost 20 x the EF86, but that also means the D3A is more like a mosfet than an EF86 LOL...whereas the EF86 is more like a triode sans Miller effect (yes, it's still a pentode for the hair-splitters)...so, if we're going to go to a D3A, why not just cut to the chase and use a small mosfet?

While the D3A has more gain, it also is more susceptible to oscillation, noise, microphonics, clipping and odd harmonics...no?

OH! I think I just figured it out...more or less....my comments re just using a mosfet still hold, I think, but the essential difference between the D3A and the EF86 is CURRENT...20+ mA Ia vs 3 mA Ia. So, if you want a lot of gain AND a lot of current up front, in order to drive the capacitance of a big triode, the D3A gives you that. Hmmmmmm........
izzy wizzy
Posts: 64
Joined: Sun Jun 26, 2005 8:38 pm
Location: Folkestone, UK

Post by izzy wizzy »

D3a and E810F are good to drive lowish Z EQ networks which IMHO sound better than high Z networks. They are lowish noise too and sound good. I don't find them microphonic or noisy and are relatively easy to tame wrt oscillation.

cheers,

Stephen
Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

Post by Maturin »

Thanks, Stephen. When you say lowish impedance EQ networks, I am not sure of the application, since the only EQ network I ever work with is RIAA for phono preamps. Is that what you mean, or something else?
izzy wizzy
Posts: 64
Joined: Sun Jun 26, 2005 8:38 pm
Location: Folkestone, UK

Post by izzy wizzy »

I mean an RIAA EQ network with a series resistance of about 15-20k vs higher Z networks with a series R inthe region of 50-100k. I prefer the sound of the lower Z network. If I could go lower, I would.

cheers,

Stephen
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Note that an EQ network can be done without series resistance as shown in the other thread Maturin participated in the other day. Daves is with a D3a.
Brgds
Lars
izzy wizzy
Posts: 64
Joined: Sun Jun 26, 2005 8:38 pm
Location: Folkestone, UK

Post by izzy wizzy »

I must try that too one day. I like the idea of no series resistance however I had read that there might be an issue with HF overload though whether that is an issue IRL is another thing.

cheers,

Stephen
bigfunhorns
Posts: 10
Joined: Thu Aug 23, 2012 3:33 am
Location: New Zealand

D3A

Post by bigfunhorns »

Hi,
A D3A has a mu of 70 and was designed to give good
performance as a pentode or high mu triode.
I use D3As in a SET amp as an input/driver tube and yes they are available.
Another similar pentode which can be used as a high mu (50)
triode is the 7221 or E180F.
I use Mullard NOS E180Fs in my LCR phono stage as input tubes.
Kevin.
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