Unknown choke current capacity?

[Dingleberry]

Hi.

I have a scratch build starting, 6G7-a normal channel preamp into EL34 power amp - sort of hybrid. I have a choke I got from "amp" that I bought from flea market. It was probably someones attempt to build a tube amp in the sixties... It most obviously had a 6L6 power amp or at least it had a OT from old Geloso model which had 6L6 power amp. It didn't have any tubes in it when I bought it but two octal sockets for power tubes (and of course two for pre amp tubes and one for rectifier)

I just wondered could I use that choke for my next project decribed above.
No markings on the choke. Size of the laminations are 70mm x 70mm x 20mm. (or 2,76" x 2,76" x 0,79" for you fellows overseas)

DCR of the choke is about 130 ohms.

To me it looks hefty enough for handling screen grid and pre amp tube current, but it feels a bit risky to throw in a choke you really don't know nothing about but the dc resistance. Is there any (simple) practice to measure the exact current capacity of an unknown choke anyway?
Measuring the wire size and core size and DCR will probably lead you somewhere in the ballpark and rest is hoping it will handle the current you are about to pull trough it.

There is a pic of the choke attached. There is also a 50W marshall OT in the pic just to get a visual reference of the size.

What more harm it can cause but burning of the choke that was practically free.
What do you guys think?

-T

[Structo]

The bandmaster probably uses the 022699 which is a 4H, 90ma choke.

Or the 022707 which is 4H, 50ma @ 167 ohms.

http://www.tubesandmore.com/products/choke

[martin manning]

Judging from the dimensions of the core I think it will be fine. You might want to measure the inductance so you know what you're working with there.

[Dingleberry]

Thank's for the replies.
The power amp will rather lean towards to traditional Marshall type than Bandmaster. It will be using EL34's as I already wrote in my first post.
The Marshall chokes what I came around were around 115 ohms.
I don't have a inductance meter, but I might have a access to one.
It would be really handy to know the inductance too.

-T

[passfan]

Typically a choke loaded power supply will feed the output plates before the choke. Wouldn't choke current demand be rather small? I think you'd be fine with the bulk of the current being pulled before the choke.

[Structo]

It will be using EL34's as I already wrote in my first post.
The Marshall chokes what I came around were around 115 ohms.
I don't have a inductance meter, but I might have a access to one.
It would be really handy to know the inductance too.

-T

Then just run a Marshall 50 watt choke.

[Dingleberry]

It will be using EL34's as I already wrote in my first post.
The Marshall chokes what I came around were around 115 ohms.
I don't have a inductance meter, but I might have a access to one.
It would be really handy to know the inductance too.

-T

Then just run a Marshall 50 watt choke.

That would be lame ;D
My goal with couple following projects is to use parts that have been sitting on the shelf for too long. I've promised myself to do that before I buy anything "new". I have some spare time and recycled iron for few projects now so this autumn will be "clean my workshop" season.
And yeah the plates will be fed before the choke so it will probably be very fine, screens and pre amp tubes won't draw much current anyway. I'll let you guys know how it turns out when the amp is ready for firing up.
Thank's.
-T

[tubeswell]

I'll second was Martin said. The choke looks plenty big enough for screens and pre-amp in almost any amp. I'm guessing its DC-current rated between 90 to 120mA. Besides, what's it gonna do? Take out the choke? No big monetary loss if it was a free choke. Try it and see how it holds up.

[barbapapa]

Hello TAG,

Can you please help me identify some specs on this choke:

[img:768:1024]http://users.volja.net/smarnagora/choke.jpg[/img]

The writing on the label says "Drossel" (German for choke) and "Na/Ne" (no clue about this bit).
It weighs 2646g (close to 6 lbs), the leads diameter seems to be 0.8 mm (around 20 AWG), the stacks are 85x85x47 mm (around 3x3x2"), the DC resistance of the winding measures 6,3 ohm.

I saw it at a flea market and just bought it based on it being cheap and big. Now I'm wondering what it could be used for. I'm a newb with no experience with chokes. I made an EL34 variant of the AX84 Hi Octane 10 years ago with CRC PS filtering, now I'm looking to reuse that amp's big OT for a simple single ended amp with a 6L6 or EL34 at around 300V on the plate and one or two preamp tubes. Could this choke be used to filter such an amp's power supply and handle that current?

I can measure the inductance by this advice from Martin https://tubeamparchive.com/viewtopic.ph ... 781#238781
but I don't know about checking current and voltage limits. Do the weight and wire gauge suggest it should work?

[Tillydog]

Hi,

I suspect that might be a ballast choke for a discharge lamp (something like this:

http://www.bltdirect.com/philips-bsn-15 ... wgod6isAbw

The "Na / Ne" might mean that it is suitable for both sodium (Na) and neon (Ne) lamps, but that is a guess.

Can you see if there is an air gap (a layer of paper) in the core anywhere? If the core laminations are completely interleaved with no gap, then I'd be pretty sure it is a lamp ballast which isn't designed to take substantial DC current. It may or may not work in an amp - I don't think you could do much harm by trying it. (Looking at the wire diameter it will obviously take the current, it may just not have much inductance with a DC current through it.)

[barbapapa]

Thank you very much for the information Tillydog, you're right, no air gap in the core. So I guess that means prone to core saturation then. I don't know how that works for discharge lamps but I guess it's of no use for a guitar amp. Unless I install a sodium pilot lamp.

[Tillydog]

.. I guess it's of no use for a guitar amp. Unless I install a sodium pilot lamp.

It may well be of some use - it's a decent hunk of metal, and if the current is low enough....

[Jana]

What if --

Take the laminations out and reassemble it with an air gap? I suspect the E I laminations are currently alternated. But if it was reassembled with all the E's in a stack and all the I's in the other stack with an air gap between them, might it work?

[barbapapa]

Indeed a decent hunk of metal, but I estimated the inductance as per the advice I linked to in my first post (if that method applies also to ungapped inductors) and it's only around 0.7H. It seems consistent with this article http://powerelectronics.com/content/why-have-air-gap

I'm thinking it would be too much weight for that little filtering effect so I'll have to look for a smaller and more effective choke. Thanks for saving me the trouble of trying it in the circuit.

Curiously, I cannot find the EI pattern on any side of the stack, it's uniform on all sides, quite unlike my PT for instance. The laminations seem like square O's with an extension from one side into the center, sort of E's with continuous link from first to last tip. I have no idea how this was assembled...

[Tillydog]

Ah well, time for the old floatation test, then...