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grid choke comparisons

76.191.225.76
Posted on July 7, 2011 at 10:45:33
GSH
 I'm looking to hear anyone's comparisons/evaluations of the various available grid chokes. For my experiments I'd consider using them in two places: DHT power tube grid, and (DHT or IHDT) driver which is driven by a TVC (AVC).

Also considering the center tap of a Silk type to provide a step-up, knowing this will double the effective output impedance of the source, but if low enough already (mu out CCS) then I see no issue. Who has tried this with good results? compared to? Was a perceivable loss of highs detected in step up mode directly compared to the "normal" use of the same choke? If not Silk, then what compares or excedes? thanks in advance.

 

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RE: grid choke comparisons, posted on July 7, 2011 at 16:39:07
Stuben
Audiophile

Posts: 669
Location: Guber Ohio
Joined: December 30, 2005

This is the only experience I have with grid chokes..

Lundahl LL1670 540 H .8 mA

I have loaded the grids of 5842s and 6H30P...great results.

90 bucks a pop...

Stuben

 

RE: grid choke comparisons, posted on July 7, 2011 at 17:04:34
GSH
 What's the output impedance of what is driving them?

 

RE: grid choke comparisons, posted on July 7, 2011 at 18:37:37
TubeBuilder
 Anyone try these?

 

those are a bargain, posted on July 7, 2011 at 20:41:15
GSH
 but don't have a tap for step up. I believe they have highish DCR for a grid choke, but still way less than a grid resistor. I've heard they were an improvement over an Electra-print PSA-2n used as grid choke, which it wasn't designed specifically for.


Magnaquest BCP-16 GC HN gives no specs other than adjectives.
Silk's best model seems to have pleased many
Lundahl doesn't show one on their site, but apparently makes one or more.

To me, a good pair or several would be a good investment, as they can move
from project to project, easier than output transformers. In some cases they could provide "better" loading for higher than ideal source impedances.

I was really looking for builder's direct experiences with comparing brands if there were any. Also the step up feature seems more valuable than is discussed much here. Example: I, like many with efficient speakers, find than a common triode of mu 16-20 driving a common DHT of mu 3-4, is all the gain you need. With a 1:2 tapped choke, you can now use a type 10 DHT (mu 8) driving the same output valve, same gain, and perhaps lower distortion....?

 

RE: those are a bargain, posted on July 7, 2011 at 21:21:03
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 GSH

Magnequest BCP-16 GC HN
Over 3,000 Henries
3,850 DCR
No Center Tap
$125

Lundahl LL1670
540 Henries
5,300 DCR
Center Tap
$92

*** Beware step-up feature multipies the
driving impedance by a factor of 4 !!!
So a 2K driver becomes an 8K driver.
No free lunch - Sorry.

### Also the center tap has 1/4th the
impedance than the whole winding.
So it is 4 times harder to drive than
the grid choke used normally.

DanL



 

Yes, I've tried these and others ..., posted on July 7, 2011 at 21:36:38
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 They work fine but t's extremely difficult to compare grid chokes unless the specs are exactly the same.

You may already know this but for the sake of additional information for this thread ...

The tuning is way more important but often ignored and I'm convinced that the reported audible benefits of grid chokes emanate mainly from the LF boost they provide. There are three critical parts to this equation, the coupling cap value, grid choke value and damping resistor value. The driving impedance is also a factor but unless it's very high it can be ignored as it will have minimal impact.

Here's an example, sorry about the BW but you get my drift. Here, we are just varying the values of the coupling cap and damping resistor. The Grid Choke value will also affect resonant frequency.




Naz

 

RE: Yes, I've tried these and others ..., posted on July 7, 2011 at 22:56:15
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Naz

I have to disagree with you here.
In my amp (6P5 driving a 6L6gc/KT66)
when I went to a MQ HN grid choke
from a 100K grid leak resistor, and
everything openned up and got clearer.
And I am only using it above 200Hz.
A 1uFd Mundorf Silver/Oil is the coupling cap.
The micro-dynamics the biggest winner.
What was nice became finely detailed.
Low level notes had a more natural decay
but had a cleaner ending to the notes.
This made staging hugely improved.
The sound sounded more relaxed and
less stressed at the same time.
Like the amp wasn't working so hard.
That's my take on it anyway.

DanL



 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 00:21:30
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 Dan, I can't comment on what I haven't tried, (grid choke on amp 200Hz up) but in normal applications the response matches what I hear, ie some VLF boost is the clear winner. Interestingly, with grid chokes I get much the same result as you, including subjectively better highs however on this point I've also observed that boosting VLF in other ways (without grid chokes) can produce the same HF effects. In all cases the peak must be kept well below 50Hz.

I only arrived at my conclusion for grid chokes sounding better after attempting to disprove the idea. By completely dampening the peak caused by the resonance the sound was never appreciably different to a simple resistor on its own.

I'd be interested in some more detail on the way your system is configured and even Simming your amp, along with your method of filtering the lows. I'm always looking for possible technical reasons for what I hear and no doubt you do the same.

In any case, it appears that we generally agree about the sonic benefits of grid chokes.

Naz

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 00:35:02
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002

Naz

My Audax speakers have a
natural ~200Hz roll-off.
The 4" & 5.25" are in parallel
with no crossover at all and
the Dynadio tweeter has just a
GE Mtr Run with a VitQ bypass.
My amp has 50Hz roll-off due to the
sizing of the cathode bypass cap.
Each woofer has it's own Rhythmic
Mosfet Plate Amplifier with a
2nd order Linkowitz-Riley slope.

DanL



 

RE: those are a bargain, posted on July 8, 2011 at 03:38:26
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000
 GSH wrote:

"Magnaquest BCP-16 GC HN gives no specs other than adjectives."

Please see our products page at www.magnequest.us for prices, specs,
and core material options.

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 04:43:02
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 Thanks for the info Dan. The natural roll-off in your amp is -3db at 50Hz, which is not steep. As crazy as it seems I'll almost bet that the grid chokes are still providing some VLF bass boost and this can be anything from very little to almost 20db which would overcome the natural roll-off at some point.

Are the grid chokes damped and if so with what resistor value? Can you tell also me the value of coupling cap and grid choke? Just a hunch but this info may be a pointer.

Naz

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 06:50:17
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002

Naz

But my midranges only go down to ~200Hz.
These are my midranges in parallel -
http://www.audax.fr/archives/hm100z0b.jpg
http://www.audax.fr/archives/hm130z0b.jpg
Aerogel (Carbon Fiber/Kevlar/Silicone Gel)
Light dampened cones for speed without resonances.
They are in an open baffle as you can see.
I do have a hinged board to defract outwards.
1uFd Mundorf Silver/Oil coupling cap
Magnequest BCP-16 HI NICKEL
3,000+Henries 3,850 DCR
No Dampening Used

DanL



 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 07:24:58
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 >>But my midranges only go down to ~200Hz

Yeah Dan, but because you said that you aren't using a crossover my thought was that the sound is still being slightly affected by the LF peak created by the grid choke. As it happens the values you are using are resonant at only 3Hz so although you have almost a 20db peak, even I would have to say my hunch looks to be busted in this case.

Nevertheless, it would be interesting to hear the effect of total dampening, which requires a resistor of about 47K. I'm willing to bet that the sonic benefits will be lost in which case it would beg the question, is it due to the absent peak (which at least is real and measurable) or some other phenomena?

Naz

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 07:30:02
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Naz

I think, and the general consensus is,
that the low DC resistance to the grid
locks the bias better providing improved
clarity and resolution from the tube.

DanL



 

RE: those are a bargain, posted on July 8, 2011 at 07:32:36
GSH
 Yes, agreed regarding the "no free lunch". But when using the mu out of a CCS (Pimm self-biased board) even with the 5K Rp of a type 10 tube, the
source will be very low, like 100 ohms, which "should" still have no troubles driving a quadrupled load. Or am I missing something?

 

RE: grid choke comparisons, posted on July 8, 2011 at 07:36:13
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 Sorry for highjacking your thread further down. To contribute to your questions, whilst I'm sure the quality of the grid choke makes a difference IME the tuning is still the dominant factor.

As for putting a grid choke after a TVC, my take is that the TVC makes it redundant.

Also, I personally wouldn't step up unless I was desperate for every bit of gain and even then I'd consider other options first.

Naz

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 07:39:28
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 You know Dan, I was gonna mention that I didn't buy the general consensus. There are many ways of locking down the bias but I've never heard any of them sounding like a grid choke have you?

Naz

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 07:43:10
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Naz

Can you say direct coupling.

DanL



 

RE: those are a bargain, posted on July 8, 2011 at 07:45:50
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 GSH

Nope you are good.
Just wanted to establish the
limitations for the record.

DanL



 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 07:54:17
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 That's the point:-)

Dan FWIW, would you mind throwing in a 47K dampening resistor one day and letting me know what happens to the sound please? And if you really have nothing better to do could you the disconnect the grid choke but leave the resistor in for comparison please? I know it's a big ask but I sure would be interested.

I'll leave you in peace now, going on 1AM here.

Naz

 

RE: grid choke comparisons, posted on July 8, 2011 at 08:10:44
GSH
 A question might be: which is more distortionless, a tube with with twice the mu or using the tap on a grid choke? In many cases with tubes, lowering the mu also lowers the distortion. Does using the step up add any?

Agreed the TVC is also a "grid choke" for what it drives, but it's also in a position to need a load beyond itself, right?

 

RE: Yes, I've tried these and others ..., posted on July 8, 2011 at 08:27:14
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 2 points

What is the DCR of L1?

High DCR (listed as the 'series resistance' of the inductor in spice) in the choke will damp out the resonance allowing the use of small value coupling caps without creating the LF response peak.

"The driving impedance is also a factor but unless it's very high it can be ignored as it will have minimal impact. "

I don't know what is meant by "very high".

A low pass filter is the result of the drive impedance vs. the amount of capacitance that needs to be driven.

If we want good HF phase response to 20kc, the shunt capacitance (the capacitance of the grid choke in parallel with the Miller capacitance of the output tube) must be driven from a low enough impedance to achieve a -3db point no lower than 200kc.

Just right click on the L1 in the sim and add the total shunt capacitance as parallel capacitance.

Now you can sim what different source impedance will do to the HF. Be sure to run the sim clear out to 200kc.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: grid choke comparisons, posted on July 8, 2011 at 16:43:41
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 Distortion is a very long and discussion of it's own. As far as tubes go it depends on the tube and the circuit configuration. (Very) generally higher mu tubes do tend to have slightly higher distortion but, for example, I would put a 6C45P with a mu of circa 50 up against any tube with far lower mu. High gm is an important factor and this tube has it in spades and very low rp as well, it could also easily drive a step-up!

I'm not against step-up as long as they are driven properly and the load presented to a tube can be a major contributor to distortion. In fact I think this is often a bigger issue in the real world.

>> Agreed the TVC is also a "grid choke" for what it drives, but it's also in a position to need a load beyond itself, right? <<

I guess it depends on the real benefits of a grid choke and I'm not sure that the common wisdom is a given here. I seriously doubt adding a grid choke would be any better than a resistor in this instance. But, If you are anything like me you will just have to try it for yourself, if only to put it to bed:-)

Naz

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 03:25:10
TubeBuilder
 Actually this is why I haven't tryed them yet. My PC scope been out of commission for 2 years. They seem like there not good for amateurs.And I also thought they would have to be very good low capacitance chokes to be worth trying.BTW I thought it was getting the the valves grids so close to ground that makes the difference. This is why I like to use a lot of trans.

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 03:32:39
TubeBuilder
 As above trans. I have them everywhere.

 

RE: those are a bargain, posted on July 9, 2011 at 04:08:36
TubeBuilder
 orright have ta try sum. btw if you have the proper input trans you dont need a step up gsh :)

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 05:17:13
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 Point 1) I assumed 2K for L1 which is more than reasonable for a decent 640H. Granted it would be somewhat higher for a 5000H but with higher inductance so too is the peak which tends to mitigate the decrease due to higher winding resistance.

Point 2) I always include some leakage capacitance in my Sims. Unfortunately this figure is guesswork as I've never seen it published. I agree with you that this must be taken into account for good HF but this is a separate argument. This discussion is about the LF response.

As for the driving impedance I purposely showed this as a separate series resistor of 1K to make it obvious. I could have omitted it and included this value in the AC voltage source.

To clarify my meaning of high driving impedance, it would need to be anywhere from 20K to almost 100K to completely dampen the peak depending on the values used and this, I consider extremely high. Up to a few K you'll still wind up with a peak of 15 - 20db without damping and in extreme cases up to 25db even if the series resistance of the grid choke is increased to 5K!

Naz

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 08:43:33
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 "Point 1) I assumed 2K for L1 which is more than reasonable for a decent 640H. Granted it would be somewhat higher for a 5000H but with higher inductance so too is the peak which tends to mitigate the decrease due to higher winding resistance."

The chokes in the ebay link have a DCR of 20k ohms and probably way too much winding capacitance.

I use these chokes on my 300B and the HF difference between driving them from a 3k source impedance and a sub 1k source impedance is clearly audible.

"This discussion is about the LF response."

You're right. The impact of source impedance on the LF response will be very small. I just didn't want the HF to be forgotten.

Tre'



Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 15:38:38
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 "I thought it was getting the the valves grids so close to ground that makes the difference. "

It is that and high load impedance as well.

It's like having your cake and eating it too.

Low (relatively) DCR to ground to keep the DC bias stable and high (very high) load impedance (for the driving stage) compared to a grid resistor.

But winding capacitance and LC tank circuit resonance must be accounted for.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Yes, I've tried these and others ..., posted on July 9, 2011 at 22:53:43
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 >>The chokes in the ebay link have a DCR of 20k ohms and probably way too much winding capacitance<<

I think you read it wrong, the chokes have 20,000 turns and I don't think each turn would be an ohm. From memory they were somewhere around 3-5K, which, granted may still be on the high side for a 640H but don't take this as gospel I'm really going on memory.

Agree that HF response is important and leakage capacitance becomes a greater factor with high value grid chokes like 5000H. I like to keep them low, around 300H or so.

Naz

 

RE: Yes, I've tried these and others ..., posted on July 10, 2011 at 02:24:01
TubeBuilder
 Thanks guys. I am getting my scope out before I try them.Indeed there somthing that needs carful testing.

 

I'm sorry, I wasn't clear..., posted on July 10, 2011 at 12:10:39
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 I own 2 pairs of the chokes offered in the ebay link.

They do measure 20k ohms. I just remeasured one of them with my ohm meter.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: I'm sorry, I wasn't clear..., posted on July 10, 2011 at 21:19:43
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 That's incredibly high DCR and couldn't possibly match up with 20000 turns specified by the seller (at least IMHO). No wonder you were pushing the point on leakage capacitance, it would have to be very high.

I was sure that I've tried these very chokes too but it was a long time ago and I ended up running with something else. I will have to find them and check DCR.

Naz

 

RE: I'm sorry, I wasn't clear..., posted on July 10, 2011 at 21:56:20
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 "I will have to find them and check DCR."

So, you don't trust me? :-)

They work just fine but do need to be driven from a low impedance.

That high DCR really does help controlling the LF hump.

BTW using my crude method they measure more like 870Hy.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: those are a bargain, posted on July 11, 2011 at 05:35:47
Al Noakes
 I don't consider the Valabs to be a bargain . Cheap for grid chokes but in terms of performance and sound : these are lacking . You get what you pay for and Mr Valab , 'Kevin' or whatever he calls himself has proven to me already he is slightly economical with the truth . Crack open his 'nickel' plate chokes and you'll find no nickel at all , just iron . Drive the Valabs with a low Z source for best performance . I eventually went for the Silk Supermalloys and found these to be far superior and allow a far greater spread of tube types to be used . The Valabs for example roll the highs off in some driver / output stage scenarios

In terms of stepups I don't think these split-bobbin grid chokes are suitable for this purpose . Each winding has it's own chamber so there won't be much in the way of coupling between the two going on unless I'm mistaken... IMO what you need is an autoformer rather than a split bobbin choke

Al

 

wait, posted on July 11, 2011 at 08:32:57
GSH
 The Silk Supermalloys you are using have 3 taps, right?

 

RE: wait, posted on July 11, 2011 at 12:24:26
Al Noakes
 No just a centre tap...

Al

 

DDDDDduh, posted on July 11, 2011 at 23:44:27
GSH
 OK, so have you tried coming into the not third of three, center tap? Accounting for the already mentioned above considerations? I wonder what those troublemakers at Silk had in mind here?

 

RE: those are a bargain, posted on July 12, 2011 at 07:15:23
PakProtector
Audiophile

Posts: 12413
Joined: May 14, 2002
 Split bobbin, CT chokes with one half in each bay will have ~10% leakage L between them( v. end to end L ). Rather suprising, in some apps this leakage seems to improve things, as when driven balanced v. the CT. When used as anything else I've seen plenty of issues...:)
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: DDDDDduh, posted on July 12, 2011 at 08:11:12
Tre'
Industry Professional

Posts: 18013
Location: So. Cal.
Joined: February 9, 2002
 Assuming that the Silk's were not intended to work as a step up autoformer.........

A grid choke for each output tube in a push pull amp, all in one package???

That's my guess.

Edit, Doug beat me to it. "when driven balanced "

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: I'm sorry, I wasn't clear..., posted on July 12, 2011 at 08:51:40
TubeBuilder
 ouch Iam out. Explains the discount. They used to be double that. I think! I think have something better anyway. I cant measure them. There vintage new on a core the same size as the average vintage el84 SE amp trans. The smaller ones. They have a dcr of 1200ohms and seem to have no gap at all. I suspect they have a lot of inductance. I guess I would have to get my scope going and build a inductance bridge to measure them. Don't bother correcting me if Iam wrong. Basic electronics is well out of the scope of this forum. I will do some study in the appropriate places.God know what military use they once originally had. Wouldn't think grid chokes where used.

 

RE: those are a bargain, posted on July 12, 2011 at 09:02:28
Al Noakes
 I've never even considered grid chokes for push pull :) I suppose the Silks have tons of inductance when used this way

Al

 

RE: DDDDDduh, posted on July 12, 2011 at 09:03:34
Al Noakes
 Windings have a start and a finish , anything in between is a tap

Al

 

RE: those are a bargain, posted on July 12, 2011 at 10:00:59
dave slagle
Manufacturer

Posts: 5447
Location: NYC
Joined: April 27, 2001
 I don't think the increased leakage is what improves things. I suspect it is the nature of the balanced and matched capacitances working against that leakage that keeps the responses of either half the same. When you work to improve the leakage numbers the capacitances between halves become unbalanced and the resonant peak of each half becomes different. (same thing happens with SE to PP splitters) When you sum together dissimilar frequency responses with peaks a few Khz apart you can get sum and difference nodes that fold back into the audio middle of the band.

dave

 

RE: those are a bargain, posted on July 12, 2011 at 15:46:00
PakProtector
Audiophile

Posts: 12413
Joined: May 14, 2002
 I don't think that unbalanced capacitances are the issue; those interleaved ones were symetrical...as were the ones with maximum leakage L.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: those are a bargain, posted on July 12, 2011 at 15:48:40
PakProtector
Audiophile

Posts: 12413
Joined: May 14, 2002
 That is one nice benefit to the CT grid choke; you get more L per turn on each side of the CT...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

I guess I confused taps with tabs, apologies (nt), posted on July 12, 2011 at 18:49:26
GSH
 .

 

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