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catssquirrel
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« Reply #15 on: June 23, 2009, 04:50:41 PM » |
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anyone use EF86's, either pentode or triode wired? I know they were used in Quad, Leak and Mullard circuits, only I have 6 Mullard EF86's, and thought they may be good as input or line stage. Failing that, a guitar and two mic circuits might be on the table.  |
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brian
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« Reply #16 on: June 23, 2009, 05:00:52 PM » |
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By today's standards EF86 in pentode mode is too hissy ("partition noise") for low-level circuits. In triode mode they are known for sweet sound and would be fine for the voltage amplifier 1st stage of a power amp.
I've never tried using them myself.
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« Last Edit: June 23, 2009, 05:05:28 PM by brian »
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catssquirrel
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« Reply #17 on: June 23, 2009, 05:31:33 PM » |
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partition noise would apply to a pentode connected as a pentode, right? but what if it was connected as a triode?
I have 6SH7's as input pentodes in my power amps, into 6SN7's (it might be 6SL7's come to think of it) feeding wide bodied 6L6GC into Partridge trans, and a brace of Mullard GZ34's in the power supply.
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« Last Edit: June 23, 2009, 05:44:15 PM by catssquirrel »
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brian
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« Reply #18 on: June 23, 2009, 05:41:27 PM » |
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partition noise would apply to a pentode connected as a pentode, right? but what if it was connected as a triode?
Then no partition noise. |
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catssquirrel
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« Reply #20 on: June 23, 2009, 10:03:26 PM » |
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thanks Carsten, that looks mighty interesting, especially the 'balanced' approach. |
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carawu
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« Reply #21 on: June 23, 2009, 11:11:11 PM » |
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thanks Carsten, that looks mighty interesting, especially the 'balanced' approach. I know you would like the link!  BTW: I´m tempted too, if I look into my drawer full of NOS TFK EF804(S) .... these are low noise variants built for german broadcast.  Carsten |
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Regards, Carsten
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brian
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« Reply #22 on: June 24, 2009, 08:24:53 AM » |
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Sehr interresant Carsten, hadn't seen that before. TFK EF804S eh?  |
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catssquirrel
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« Reply #23 on: June 24, 2009, 11:36:09 AM » |
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the problem is how to derive an unbalanced signal, transformer, I suppose?
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Jolyon
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« Reply #24 on: July 23, 2009, 11:20:36 PM » |
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Pentodes connected as pentodes exhibit partition noise and the noise goes down when they are connected as triodes but so does the gain. But partition noise is only audible if pentotes are used to provide a lot of voltage amplification to low level signals. They don't tend to cause a noise problem if they are used as the first stage of a valve power amp. However, I remember spending hours and hours on old Leak Varislope pre-amps eliminating switches, replacing resistors, etc. in a vain attempt to lower noise. No real success to report but the greatest improvement came from making a highly specified separate power supply for it as opposed to using the one from the power amp. Good, clean power is a must for low signal level circuitry.
I'll be making a valve phono-stage one day myself so I'll be interested in what you do !
J.
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roger15ohm
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« Reply #25 on: August 13, 2009, 03:49:03 PM » |
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catsquirrel and carawo
Regarding the modify circult for the EAR phono amp, as mention does it need a line stage? What that means? Don't need a pre amp?
thanks.
Wan
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rfgumby
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« Reply #26 on: August 13, 2009, 04:09:05 PM » |
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catsquirrel and carawo
Regarding the modify circult for the EAR phono amp, as mention does it need a line stage? What that means? Don't need a pre amp?
thanks.
Wan
I've modded a few 834's they have nice potential, but ultimately, also a few limits. Good sound though. I've also seen one modified with a volume control, although I don't remember where it was in the circuit, presumably ahead of the gain stage. That could then be used with no preamp Wan. |
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Scott
Like a leper messiah When the kids had killed the man I had to break up the band -David Bowie
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brian
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« Reply #27 on: August 13, 2009, 04:20:48 PM » |
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The volume control is simply a pot replacing the 220k resistor on the cathode follower output.
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rfgumby
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« Reply #28 on: August 13, 2009, 04:24:06 PM » |
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The volume control is simply a pot replacing the 220k resistor on the cathode follower output.
On the CF output? huh. I never would have guessed that. I've replaced more than a few of those 220K resistors- cool. Thanks for the clarification Brian. You da man. |
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Scott
Like a leper messiah When the kids had killed the man I had to break up the band -David Bowie
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brian
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« Reply #29 on: August 13, 2009, 04:29:01 PM » |
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Thanks for the clarification Brian. You da man.
I'm de Daddy  |
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