How to tell bpc-15 40 mA from 50mA version?

[Jim R.]

Is there an easy and reliable way to discern the difference between the two versions of the bpc-15 plate chokes? Without being able to read labels, that is...

-- Jim

[johnsonad]

I have a meter for measuring the Henrys of a piece of iron. It's no bridge meter but is close enough.  Does your meter have the function by chance?

[Jim R.]

No, meters only have capacitance. I do have a little woofertester module that can measure complex impedances but it is windows based and I don't have a windows machine at the moment.
Maybe I should just get around to installing win 7 on my mac.

-- Jim

[Paul Joppa]

The only difference is the thickness of the spacer in the gap. I'm not sure, but it's on the order of 8 vs. 10 mils. Nobody is going to see or feel the difference - the impregnant would distort the thickness outside the core even if you had access to it.

The problem with measuring inductance is that it's a moderate function of signal level, frequency, and DC bias - so you'd really need to measure both kinds of choke and compare to guess which was which. But I'm sure they are marked in ink on the outer wrap.

[Jim R.]

Paul,

I was kind of afraid of that. I'll see if my wife can see any markings.

Hey, aren't you supposed to be on a vacation? ;-)

-- Jim

[Jim R.]

Ok, I asked my wife to have a look and all she saw one each was a marking of "EL" (not an "I") and bpc-15 -- no to identify current or inductance on either side of the coil.. Are these one-off custom chokes and is there any other info about them?

Thanks,

Jim

[debk]

I just got a pair of them also the 40mA version.
They just say BCP-15 on them nothing else

Debra

[Jim R.]

Hi Deb,

Thanks much. These are not new though and are the ones that came in the SR-45s I bought from Doc and I wonder if the EL means something like extra laminiations or something. Since it is in the 45 amp it most likely is the 40 mA version

-- Jim

[Jim R.]

Hmmm, I also suppose the EL could stand for extra or enhanced inductance? So I wonder if this confirms the 50 henry rating or possibly something a bit more? I'm still thinking that Deb is right that this is the 40mA/50 Hy version.

-- Jim

[Grainger49]

You might contact Mike and see what he says.

[Paul Joppa]

This IS the Magnequest sub-forum, so hopefully Mike will show up.

I'm guessing EL is Mike's "Extra-Linear" winding technique. This, or a variant of it, goes into our custom chokes for the upgrades - I'm guessing that choke predates the BH-2 and BH-6 designations. It might have been an early prototype of the new technique which Doc B got hold of. For what it's worth, the original SR45 assumed an upgraded Paramour II as the starting point, which would have been the original BCP-15, 40 henries at 50mA.

It didn't occur to me until now, but since Mike stockpiles coils and stacks the laminations later, the coil might not say what gap was installed.

[Jim R.]

More interesting stuff. So maybe this is more or less equivalent to the bh 6, which would be fine with me. That would actually make things work out nicely for me.

-- Jim

[mqracing]

Pj gets the prize     The EL stands for "extra linear" which is a special winding geometry that we use to enchance performance of the plate chokes.  It is moreso labor intensive than a traditional winding geometry
so it usually costs more.

The BCP-15 was an original Freed design.  It was originally spec'd at 50 madc and 40 Henries.  We built many of these to the original specs.  These would tend to have only the BCP-15 marked on them. 

Later... realizing that most people who were purchasing these plate chokes were using them with the type 45 tube which runs moreso typically at 35 to 40 mils of plate current.  After careful analysis of the original design we were able to regap the unit and optimize it for use with the 45 tube at the ballpark 40 mils instead of 50 mils of plate current.  With the smaller airgap we picked up more L (50 henries).

Once we offered the second choice--- 40 mils at 50 henries or 50 mils at 40 henries--- I've tried to be consistent (bearing in mind the existence of human frailty) and mark the coils that were gapped for 40 mils.  Often times (but not always) this demarcation might be written on the back side of the coil.  The 50 mil coils may or may not have the marking--- if it's not marked--- again allowing for the occasional human error--- it is most likely gapped for 50 mils. 

MSL

[Jim R.]

Hi Mike,

Great -- this is all very useful and as I said in my last post, works out very nicely for my situation.

Thanks again,
Jim