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Thanks for clarifications George and Michael. The servo (opto servo) I'm talking about needs both OP27 and 4N25 installed and the jumper next to the 4N25 shortened (do not shorten the other jumper). The trimmer must be set high enough. The opto servo is only capable of lowering the offset set by the trimmer.

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Just like Carbon we built. Same box, same PS. Relay=120s. Separated filament transformer.      

Another Grounded Grid lives.  Have been listening to it for about a week. Powered by the same GRHV/GRLV PSU I use to power my KGSSHV, Carbon and Blue Hawaii. 400VDC rails and 20mA plate current.

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16 hours ago, JoaMat said:

Thanks for clarifications George and Michael. The servo (opto servo) I'm talking about needs both OP27 and 4N25 installed and the jumper next to the 4N25 shortened (do not shorten the other jumper). The trimmer must be set high enough. The opto servo is only capable of lowering the offset set by the trimmer.

Kevin mentioned in his post some time ago that the opto servo only works in one direction and it needs the cold-start offset to be +15VDC or higher to function IIRC.

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  • 3 weeks later...

I think joehpj may have more. That's where I got mine. 

Mine's up and running and doing long listening tests, finally enjoyable. Details to finish, along with getting the left channel opt servo to work. Sounds glorious. 

Thanks to Kevin and Spritzer. These electrostatic amps that Kevin designs and Birgir fine tunes are just an incredible learning resource. They are damn near fool proof and bullet proof. And drive my SR-009'with TOTL SQ. 

Also, kudos to all the experienced members here on Head-Case for the elevated discussion. 

Now back to my listening. Nanci Griffith is singing to me in my living room. 

 

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Thanks! I owe everything to Kevin, joehpj, and The Head-Case community. 

I bought cases, transformers and bits & pieces from Head-Case member joehpj. 

Finished the PS around a month ago. Posted some details and internal photos here: 

I'll post some more photos of the intervals of the Amplifier case after I get home tonight. It's still a little messy, but WTF. 

Edited by Laowei
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Here's a few of the Amplifer Case interior. 

Signal input is not final. Assembled with a TDK 4CP-2500 volume control from s recent GB. The ALPS RK50 is waiting for me have a machine shop make me an adapter plate (already designed).

Wire from the PCBs to the STAX jack is not final (too short). Longer solid silver/gold teflon wire on order.

Also, to do: devise a permanent Star/Chassis Ground connection. A better solution is needed, 

The photo of with the top plate installed is from an earlier trial fitting. Shown with Svetlana Winged C EL-34 (2000 vintage). Even on a short listen, they sounded like "Meh...." Now up and running with a matched quad of JJ 6CA7s. Highly preferred, this amp sings now. Thanks for the tip Whitigir! 

Also to note, in the umbilical with the heater wires tightly twisted and all the other wires scramble wound, there is zero, zip, nada, NO hum. Deathly quiet. 

 

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I have also been listening to my Grounded Grid with a matched quad of the beam tetrode EH 6CA7 and like its sound a lot.  

JJ and EH seem to be the only manufactures of current production beam tetrode 6CA7. Most other current production tubes labeled 6CA7 are really EL34 pentode. 

Edited by mwl168
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16 hours ago, joehpj said:

Nice build! Quite interested about how will RK50 affects the sound. Never heard one before.

Thanks Joe! You are a BIG factor in how nice this amp turned out. 

Earlier in my KGST, I loosely swapped in the RK50 to the Alpha pot I originally bought from Spritzer. A noticable improvement. Never the less, that Alpha is a really nice sounding pot for the inexpensive price. 

Also in the KGST, tried a 50K Dale RN60 in series with the input, with the RK50 as a variable shunt volume attenuator. That configuration did not sound as pristine as the conventionally wired RK50. 

The TDK 4CP-2500 currently in the GG sounds really good. Its in a new fresh circuit so everything sounds good compared to the KGST. Lol..  

No comparisons yet, it will be a while. Things have to settle in and I have to get more familiar with the character of the amp before I start to fine tune the sound to my preferences.  Will report back. 

Edited by Laowei
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1 hour ago, mwl168 said:

I have also been listening to my Grounded Grid with a matched quad of the beam tetrode EH 6CA7 and like its sound a lot.  

JJ and EH seem to be the only manufactures of current production beam tetrode 6CA7. Most other current production tubes labeled 6CA7 are really EL34 pentode. 

 
I have been listening my GG with EL34 Tung sol and Mullard (current production) but I feel that the sound is like an "U" : Strong basses, middles are low and the trebles are good but nothing special. I'm a little disappointed with the sound. 
 
I'm waiting an EH 6CA7 quad too and I hope to get lucky. 

 

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1 hour ago, eggil said:

Thanks Laowei for the pictures. 

Between the Carbon and the GG, any preference in sound?

Never heard a Carbon, so no opinion.

Got crossed up on the casework of the one I was building. Have the stuffed Carbon PCBs so one day I could swap out with the ones in my GG. Would use the same PS. One day.... But by that time Keven will have designed at least 8 more stellar electrostatic amps to build. :D 

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12 hours ago, eggil said:

Thanks Laowei for the pictures. 

Between the Carbon and the GG, any preference in sound?

 

Generally speaking, Carbon has the speed and the balances or neutrality more than GG.  The GG has better fluidity and musicality.  On top of that, the GG is more tubes like and the Carbon is all....Solid State.  Your personal preferences will be the decisive factors.  

I love those J&J :D

Edited by Whitigir
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I like the powerful amps with "flat" sound, like Dynalo/hi or Beta22, so the Carbon is the one that best suits my tastes between the GG/KGST/SRX-P. For this reason, Carbon has become my reference amplifier for Stat.

Anyway, I'm not being fair because I haven´t found a quad of valves for the GG that sound good to me. Maybe when I try the 6CA7 I will be more comfortable with the GG.

Excuse the long answer for such a short question :sadcat:

 

Edited by jose
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1 hour ago, jose said:

I like the powerful amps with "flat" sound, like Dynalo/hi or Beta22, so the Carbon is the one that best suits my tastes between the GG/KGST/SRX-P. For this reason, Carbon has become my reference amplifier for Stat.

Nice to have the SRX-P included in the group.  Of course, you can roll different 12AT7 and 6SN7GTB in that too, which may change the flavor a bit.  I like the Sylvania GTAs myself.

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3 hours ago, jose said:

I like the powerful amps with "flat" sound, like Dynalo/hi or Beta22, so the Carbon is the one that best suits my tastes between the GG/KGST/SRX-P. For this reason, Carbon has become my reference amplifier for Stat.

Anyway, I'm not being fair because I haven´t found a quad of valves for the GG that sound good to me. Maybe when I try the 6CA7 I will be more comfortable with the GG.

Excuse the long answer for such a short question :sadcat:

 

Thanks for the detailed answer. Really helps in understanding your perspective. 

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