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Grid choke on Se84 selected? (Read 8224 times)
Hotsauce
Ex Member



Re: Grid choke on Se84 selected?
Reply #15 - 04/19/06 at 01:23:18
 
A pair of the BCP-16 nickel chokes arrived yesterday, and I installed them in my SV83 monos.

I did only one first.  In fear that I might want to undo it, I only unsoldered one end of the resistor.  The choke is small, and easily fits in the mono chassis right by the input jack,  I JB welded it into the case.

The immediate impression is that its quite a bit louder.  The resistor it replaces was draining some signal off.  The choke is essentialy inert to AC(signal) at audio frequency, but easily passes DC to ground.  

Now, a day later I have both done and I'm very impressed.  Theres more air, more finger sound on strings, but suprisingly more bass too.

I did wait 2 months for these chokes to arrive, so order well in advance.

John C.

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Yoda
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Re: Grid choke on Se84 selected?
Reply #16 - 04/20/06 at 01:38:38
 
That seems like a really interesting upgrade.  I guess there's a way I could more permanently bridge my amps so that I'd only need one pair of chokes (vs a pair each)?

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crazy bill the eel killer
Ex Member



Re: Grid choke on Se84 selected?
Reply #17 - 04/20/06 at 02:03:57
 
Hello Yoda,
A grid choke presents an infinite impedance to AC, so there should be no reason I can see why you couldn't strap the grids of both sides of the 6922 and use one grid choke for each channel. However, since I'm new to this stuff, I may be wrong and would stand humbly corrected if so.

John C, Yoda, and others,
I had a long talk with Jack Elliano at Electra-Print yesterday, and Eddie today, and learned a few things about grid chokes.

First, because of the way they are wound , they  suffer from high capacitance, which is directly coupled to the grid of the tube and there is absolutely no way to do anything about it.; So if that high capacitance will raise issues, you're stuck with it(hopefully it won't raise issues, which appears to be the case for John C. and Bjorn judging by the sonic reports).

I don't know the capacitance values for the Magnequest units, but I do know that Lundahl uses a double C core which will keep the capacitance very low, but also doesn't give the crazy high inductance values of the Magnequest units.

So I guess it's a tradeoff. I will try and find out the capacitance of both units and report back. Right now I'm leaning towards the Lundahl units unless Jack can wind me comparable units with low capacitance. I'll let you all know.

Cheers,              Bill                 Cheesy ??? ???
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« Last Edit: 04/20/06 at 02:06:59 by Crazy Bill the Eel Killer »  
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Yoda
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Re: Grid choke on Se84 selected?
Reply #18 - 04/20/06 at 18:17:30
 
Thanks, Bill.  Let me know what you find out and what kind of sources  / pre-amps work well.  It would be particularly interesting to know how this might work when driven by a CSP...

If the above works out and you have Jack making two for you, I'd be interested in having two made for me.

Matt
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« Last Edit: 04/20/06 at 18:18:38 by Yoda »  
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Ludo
Ex Member



Re: Grid choke on Se84 selected?
Reply #19 - 04/20/06 at 21:10:13
 
I got a tip from a well known constructor. He looked at the schematics for the SE84SC and commented on the gridresistor on the 6922. He recommended to lower the 100k to 50k due to millereffect. Migth be something to concider for those of you still using resistor?

Cheers
Bjorn
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« Last Edit: 04/20/06 at 21:11:03 by Ludo »  
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Rap
Ex Member



Re: Grid choke on Se84 selected?
Reply #20 - 04/20/06 at 23:10:32
 
I thought Miller effect in an amp would depend on 3 things
a) input impedance
b) amount of gain in the tube
c) capitance of tube, grid to plate.

The input impedance of the sorce in question can play a big role in were the high frequency roll of would ocure ??? (ring a bell why amps like low imput impedance) ???

I think that running one stage of amplification over a tube with low internal capacitance and low amplification like in the Zen will moves Mr Miller comfortably out of the audible spectrum ???
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crazy bill the eel killer
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Re: Grid choke on Se84 selected?
Reply #21 - 04/21/06 at 02:25:33
 
Hello Ludo,

I'll be talking to Jack again in approx. one week, and I'll send Magnequest an e-mail requesting some numbers so we can compare.

FYI, I'm still vacillating between the grid choke and an input transformer. I'm not decided yet on which route to take. The final decision will rest on whether I decide to do balanced cabling. I'll figure it out soon.     ???  ???

In your case, when you implement the grid chokes (one for each channel should be fine), I would still keep both grid stopper resistors, one for each side of the 6922. Don't do a single resistor there.


Cheers,                        Bill                           Cheesy       Smiley

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Ludo
Ex Member



Re: Grid choke on Se84 selected?
Reply #22 - 04/21/06 at 06:16:34
 
Hi Bill

I'm not using any gridstopper on the 6922.  ;D

Bjorn
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Rap
Ex Member



Re: Grid choke on Se84 selected?
Reply #23 - 09/29/06 at 12:40:17
 
Just did the same upgrade on my monoīed selects. Works very nicely and the Lundahls fit perfectly inside the standard chassis.



I canīt see how this would be classed as a mod, as it doesnīt change the scematic or operational points of the amp. Itīs just a parts upgrade.

But this upgrade makes a wonderfull amp sound just a bit better. Smiley

Rap.
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« Last Edit: 09/29/06 at 14:05:58 by Rap »  
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chrisby
Ex Member



Re: Grid choke on Se84 selected?
Reply #24 - 10/02/06 at 15:48:56
 
[quote author=Rap  link=1115200444/15#23 date=1159530017]Just did the same upgrade on my monoīed selects. Works very nicely and the Lundahls fit perfectly inside the standard chassis.



I canīt see how this would be classed as a mod, as it doesnīt change the scematic or operational points of the amp. Itīs just a parts upgrade.

But this upgrade makes a wonderfull amp sound just a bit better. Smiley

Rap. [/quote]


Gee Rap, I dunno - if your upgrade consists of adding parts that didn't exist on the original schematic (or changes to any original part values), then I'd call that a mod not a "tweak".

For example, more than a few folks have modified power suppy filter stage of their  Zen amps to include chokes and or Solen etc poly film caps, or even upgrading cathode bypass cap.  Carefull twiddling of downstream component values would ensure that final operating voltages/bias currents remain unchanged, but few would have trouble hearing difference in sonic performance of the amp.
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« Last Edit: 10/04/06 at 17:46:15 by chrisby »  
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Rap
Ex Member



Re: Grid choke on Se84 selected?
Reply #25 - 10/02/06 at 16:41:20
 
Hmm then I guess using other tubes than stock qualifies as a mod ??? a gz32 has more impact on the voltage specs than the choke, which is just passing Dc curent to ground, but you say tomato and I say tomayto. Smiley

Hmmm maybe it is a mod, I dunnow.
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« Last Edit: 10/02/06 at 19:02:34 by Rap »  
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