Ed's grid chokes

Design and use of Chokes for PS, anode and filament use.
Post Reply
Ed Sawyer

Other chokes

Post by Ed Sawyer »

Dave wound me a couple pairs of interesting grid chokes, which I will do my best to report on here shortly. One is 80% nickel, the other is amorphous. Both will be tried as grid choke on a 37(in combo with 12GN7 as a mu-stage), and also likely as a grid choke on a 45, which is the output tube on the same amp. They are designed for no DC, but Dave mentioned they could probably handle a little bit if needed. Inductance varied, when the time comes I will start a new thread for it and maybe Dave can post the graphs.

Just another note, it's great to have a dedicated forum like this for discussion of these topics! Thanks Dave!

-Ed
dave slagle
Posts: 2038
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

hey ed,

looking forward to the listening comparisons... here is the info on the small current behavior of the two beasts.
Attachments
the "blip" just below the .25ma line is surely measurement error and not an actual behavior.  The LCR meter said it was around 1000hy's
the "blip" just below the .25ma line is surely measurement error and not an actual behavior. The LCR meter said it was around 1000hy's
ed amorph.gif (4.24 KiB) Viewed 12357 times
The meter said about 500hy's on these... don't quite know what to make of the curve shape.  the leveling out at 2-300hys isn;t saturation... i wish i ran it up to 10ma... oh well... next time.
The meter said about 500hy's on these... don't quite know what to make of the curve shape. the leveling out at 2-300hys isn;t saturation... i wish i ran it up to 10ma... oh well... next time.
ed nick.gif (4.5 KiB) Viewed 12357 times
dave slagle
Posts: 2038
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

hey ed,

any reports yet???

dave
Ed Sawyer

Update on these

Post by Ed Sawyer »

hi Dave -

sorry for being so slow to get back to you and everyone on these. I have them wired and ready to go, and just need to finish up a few other wiring tasks, then should be able to listen and compare. Will try them in another amp I am working on too (75TH->50 or 300B)

thanks
-Ed
slm25
Posts: 17
Joined: Thu Aug 04, 2005 12:05 pm
Location: Australia

Hey Ed Reports yet ??

Post by slm25 »

O.K. I know dave rushed you a few months ago but
have you had these guys running ??

Have been planning to try grid chokes and was kind of keen to hear how you went

Anything to report ???

Sorry for the hurry up

:D

Simon
Ed Sawyer

I have tried them, here's some data.

Post by Ed Sawyer »

Thanks for the patience and for winding these for me, Dave! You're the man. ;-)

I tried both sets of chokes in a couple different locations, in 2 different amps.

Overall thoughts: Both are great, easily besting the grid-leak resistor I had set up in one amp (which was there when I got it, it was a DIY amp built by hifiTom, Tom Scoville, that I have since modified... ). The differences are subtle between the amorph and the nickel, but they are noticable with comparitive listening. You can't go wrong with either, I think. Lately I have been partial to amorphous but nickel has a lot going for it too.

I ended up using the amorphous at the input grid choke on the 37 in the 37-12gn7-45 amp. It replaced a 1k gridstopper (which probably wasn't needed anyway? mu of 37 is only 9 I think, so not really a high-gain tube prone to oscillation I'd think) and a 220k grid-leak resistor. I liked the sound of it in this position a little better than the nickel grid choke, which I think goes contrary to some of the other experiences where folks like nickel earlier in the signal chain and amorphous later in the signal chain. Pretty much everything else in this amp is amorphous so maybe there was some sympathetic sonic connection there. The grid choke on the 45 I ended up using a mQ bcp-16nigc, mainly for the reason that I already had it in place, and had calculated the LC coupling from the previous stage based on its' value. (Yes, could likely have changed it to one of Dave's grid chokes, without any problems I'd think). In general I feel grid chokes have tons of advantages and no disadvantges vs. using a grid-leak resistor. I plan to use them in general in any LC-coupled project I build in the future.

The nickel grid choke, after trying in a few locations, ended up finding a home in an amp I just completed, a 75TH->300B/50 amp. The nickel grid choke ended up serving duty on the input of the 75TH tube. It works well there, and helps keep that amp sounding clean and precise. The outputs on it are James 6123, which perhaps aren't the most botique OPTs out there, but they are pretty good for the price, and I had them to start with. I may change them someday but for now they work pretty well. (I built the amp on the chassis of a previous effort by Tuck Thean, which I bought at auction on audiogoon. I proceeded to rip out everything except the output trannies and one power supply choke, and rebuilt it all from scratch, completely changing the design at the same time. More details on that later, but some basic info and pics are here: http://www.edsawyer.com/75TH-300B/ )

The nickel grid choke worked well on the 75TH, I liked the sound of it there better than the amorphous grid choke. The difference in inductance and DCR may have had some effect too. That amp uses some awesomely righteous amorphous plate chokes from Dave on the plate of the 75TH's. I think he may have posted the specs here somewhere, but depending on the gap the inductance ranges around 125H +/-, with current capability in the 20-40ma range IIRC. They are built on BIG cores, and really worked great in this amp. (makes me want to try some Intact 5K:8 amorphous outputs for the same amp.... )

This amp can handle the 300B or the 50 as output tubes. It has switchable filament supplies, and the biasing is close enough to work well for both tubes I think. I have the output set up to the 5k tap (I tried it originally on the 3.5k tap but 5k sounded better to me). Mostly I have used it with 300b's so far, but I am about to embark on trying 50s too, just to see what it will sound like. With bias resistor changes, it could likely also run stuff like 842, vt-52, et al. This was my first scratch-built DIY amp effort, and overall it came out well, I am happy with it. Many thanks to Dave for the great Iron, and also especially to the Dowdylama for his excellent and patient tutelage. I had many questions and he was great about helping me learn.

----

Overall the sound of the nickel grid chokes seemed very clean and clear, tending towards the drier side of neutral. The amorphous was just as clean and clear, perhaps on the warmer side of neutral (very subtly so though), but it also seemed to have more depth and 3dimensionality for whatever reason. There's a lot of variables in any design, but these were my experiences with these 2 sets of grid chokes. They mirror to some degree my experiences with these core materials in other magnetics also (output trannies, etc.)

Hope that helps,
-Ed
shinebox
Posts: 88
Joined: Fri Jan 28, 2005 9:44 am

Dave's 5k:8

Post by shinebox »

Allo Ed,
Nice writeup.

With respect to Dr Clips' 5k OPTs - I heard them a while ago in NYC, chez-il, A/B'd vs Pieter's 5k OPTs in a 2A3.

Pieter's were as impressive as you would expect, Dave's had the same stuff going on, but with a somewhat calmer presentation, less "obviously" present but maybe even more natural. Not completely night-and-day but basically, both rocked.

I'd imagine they'd be *perfect* partners for the more colourful compression drivers (or indeed, Lowthers, like wot Dave got).

I guess what I'm trying to say is grab a pair and take your amp up a few notches. If you don't agree with me, I will gladly relieve you of them :-)

Cheers
shines
Ed Sawyer

Good idea! now just to talk Dave into it... ;-)

Post by Ed Sawyer »

Hi Shine -

Good idea! I had imagined Dave's OPTs are top-shelf. He really is on the cutting edge of things magnetic I think.

Interestingly I have a pair of Pieter's 5k trannies in that 45 amp I had mentioned. Quite nice, of course. Would be fun to compare.

I wonder if it would be worth going even higher on the K scale, e.g. a 7k trannie on the 300B maybe...? Where is the point of dimininshing returns? 5k provides more than enough power output so seems like could trade a bit more of that for more linearity and lower distortion... hard to guess what would be best. 5k is a good place in any event Id' think (at least with 300b). I forget inductance offhand on the James trannies, I want to say in the 28-30h range on the 6123 @ 5k?

Now to just talk Dr. Dave into it... ;-)

-Ed
Guest

Post by Guest »

Allo,

Not sure where the turning point would be. I suspect it depends on how uncompressed the music you're listening to is... the 7k load may be fine and even more linear most of the time, but if a peak comes along, the amp may or may not struggle.

I guess that with 7k load, you'd have a more consistent cancellation of 2nd with the driver stage too.

Who the hell knows though? Only one way to find out and at least with the horns, 4W will go a long way :-)

cheers
shines
Post Reply