Replacing power supply resistors with chokes

[johnsonad]

The chokes were installed today.  It took about an hour or so and was very easy.  Attached are a few pics of the amps afterward.  There is zero 50 Hz hum (I'm on 50 Hz power if you're wondering) with 100 dB sensitive speakers when I stick my ear to the woofer. 

There are changes to the sonics but it’s hard to put my finger on exactly what it is.  It seems that the noise floor is a little lower and that there is more detail.  On two of my favorite recordings with tracks I know well there are details that the Paramounts have never been able to reproduce before where other amps could (SS and PP).  On one track there was a small change for the worse.  I find that I want to turn the preamp up some and this may account for part of that.  There does seem to be less sparkle for loss of a better way of putting it or lingering air around notes.  In short a little less magic but this may change as the chokes settle.   I’m going to leave them in for now and get used to the changes.  Hopefully I’ll be better able to explain the changes with time. 

The amps biased up the same and I didn’t notice a difference in B+ at A2. 

[Paully]

That is exactly how I installed mine, but I thought there was an immediate improvement in the high end, very small but noticeable.  Well, I have made so many changes since we installed them a day or two ago no way to check now!  Good luck, hope they improve.  Any hum?

[johnsonad]

A little 120 Hz hum with my ear to the woofer but no more than what I remember before.  I haven't adjusted the hum pots for these tubes if that gives you an idea of how low it is.

(edited to save on posts)
Day two with the chokes.  I'm listening at higher volumes and for longer periods without fatigue.  There seems to be a little less room information if that makes sense in the music.  The instruments are clear and focused but the room is less emphasized.  Not sure if this is a decay issue but it’s noticeable in my system. 

[Grainger49]

Response to David Bilss' post on the previous page:

An educated guess here... If you are designing from scratch you can find a more inductive choke (higher Henries) at your rated current, 20mA, for a given price.  Design around the needed current capability or higher and the needed DC resistance for similar voltage drop.  More inductance rejects more noise.  

[debk]

I have listened to my Eros with the choke now for about 10 hours.  I like the way it sounds more and more. I still feel there is a definite improvement in the high end.  Still have not reconnected the supertweeters, and don't feel like I need them as I did before the modification.


Debra

[Paully]

I put my two in my Paramounts, wishing I had order three now!  Guess I will have to pay to ship one more.

[Paully]

As noted we put the chokes on top of the chassis for the Paramounts.  The one picture I have seen on this thread for the Eros has them below.  Is there anything to be gained theoretically by putting the choke on top of the chassis for the Eros so it is next to the power transformer like the Paramounts or is it better to go ahead and mount it below next to the power supply board?  Happy to go ahead and try it but since I would have to drill an extra hole it would be nice to know which way has the most promise.

[Doc B.]

The empirical way to figure this out is to do what PJ does - clip the leads of a 1mH RF choke to the input of a scope. You now have a neat little "60Hz magnetic field detector" that will couple with the power trans radiated field. Move it around the places where you want to put the new part and see what kind of field strength you pick up.

[Paully]

Ok, that is a great idea.  Next question (if there weren't another things would get boring) has anyone put a grid choke on the Paramounts?  Just doing some reading and was curious as I know nothing about grid chokes, yet.

Never mind, found my answer:
http://db.audioasylum.com/mhtml/m.html?forum=bottlehead&n=123218&highlight=Grid+Chokes&search_url=%2Fcgi%2Fsearch.mpl%3F

Also from the old forum:
http://db.audioasylum.com/mhtml/m.html?forum=bottlehead&n=138238&highlight=Paramount+Grid+Choke&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fsearchtext%3Ddussun%26topic%3D%26author%3D%26date1%3D%26date2%3D%26slowmessage%3D%26sort%3Ddate%26forum%3DALL

So as far as that is concerned, don't think I am even going to mess with grid chokes.

[johnsonad]

Paully, no grid choke when direct coupled (per Paul).

Regards,

Aaron

[Grainger49]

The empirical way to figure this out is to do what PJ does - clip the leads of a 1mH RF choke to the input of a scope. You now have a neat little "60Hz magnetic field detector" that will couple with the power trans radiated field. Move it around the places where you want to put the new part and see what kind of field strength you pick up.

This is worthy of a new topic folder, Tech Tips.  I'm all for the empirical method.

[Paully]

Paully, no grid choke when direct coupled (per Paul).

Cool beans, thanks!

[xcortes]

I finished installing MQ CP-08 chokes (cortesy of keto) in my six Paramounts. These are 12H / 246ohm / 75mA. The 75 mA are a bit on the low side but we all know Mike rates his iron conservatively.

The effect is subtle but noticeable. There's a little bit more of everything good in these already fantasic amps.

Can't wait to do the mod in my Eros, FP3 and Sex amps.

The Paramounts are the 2A3 version with lots of upgrades.