| But I'm still on step 9... [message #31884] |
Mon, 22 May 2006 22:35  |
Forty2wo
Messages: 163
Registered: May 2009
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Master |
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I have an implementation of the D3a running now. I used a honking big anode choke in place of the CCS and am currently running the cathodes unbypassed .
While I was under the hood. I retaped the B+ to give me 380v on the plate of the 300b at 70ma. I had been meaning to try a lower current, at the suggestion of several who thought it might help get the sound I am looking for. In any case it was the easy way to get the D3a plate to a good starting point 160v on the plate at 8ma.
I ran a few rough test, I will post them a little later.
As to the sound. They are more dynamic, which I thought was the chief failing of the past reiterations of these amps. Although maybe a bit forward. Need to let things run a bit.
I had started a post, more of a story really, on these amps. How they started what they’ve been and what I have been looking for from them. If anyone is interested I will finish it. I am a two finger typist so these things take time…John
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| Re: But I'm still on step 9... [message #31885 is a reply to message #31884] |
Tue, 23 May 2006 07:13  |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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Hey, I`m interested - it`s a DRD amp, yes?
If you can find a pair, try E180F, too - it seems to me that D3a "sounds" a little more "raw/rough", although very similar like E180F. (In my application/system and with just a few tubes I tried:-)).
E186F is a low michrophony/noise version of E180F - didn`t try it yet.
Unbypassed cathode (although I use CCS+low imp. out) sounds to me somehow "flat, warm, soft, rolled off, undynamic"... And various caps bypasses have their own "sounds" - currently experimenting with this.
And one more thing just remembered - it`s a better to stay away from 0V bias "border"; according to the M. Jones, significant grid-current flows when Ugk < -1,1V - distortion on signal peaks. I tried various OPs, from -1,7V to -2,5V and "higher" bias sounds better to me, but it`s sometimes not easy - the new D3a tubes I get have Ua>260V when Ugk=-2,4V! Out of specs (about 217V with -2,4V/11mA OP), but it`s a common with those high-gm tubes, where fraction of the Ugk volts means tens of Ua volts change with constant Ia.
C3g is interesting, too - but "softer" then both E180F and D3a - good for some music, bad for the other... 
Anyway, those are my "listening tests results" for now, I`m glad to hear other experiences with these tubes...
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| Re: But I'm still on step 9... [message #31892 is a reply to message #31890] |
Tue, 30 May 2006 06:52 |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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Try a little "higher" OP, about 200V/-2,3V/8mA. Try to bypass the cathode with good cap, 100µF or more. I`d try rechargerable battery and/or diode bias (LED+1N4148 = 2,2...2,3V), or maybe LED+resistor?
I tried two LED-biased C3g - better, IMO, then any RC combination I tried.
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