Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dpm309 on September 23, 2015, 05:20:29 pm

Title: Choke Identification
Post by: dpm309 on September 23, 2015, 05:20:29 pm

Found what looks like a choke in my junk bin. It reads: 343CF-245 and 839009 (See picture). Googled the  number and came up with nothing. It reads about 3.5 ohms across the leads. Is there anyway to determine what the value of this choke is? I think it might of come out of an old Yamaha SS Bass amp. Any other tests or measurements I can take to help ID it?
Thanks,
Dan

Title: Re: Choke Identification
Post by: pompeiisneaks on September 24, 2015, 05:34:27 pm

Here is a site that explains three different ways to test the inductance:

http://daycounter.com/Articles/How-To-Measure-Inductance.phtml (http://daycounter.com/Articles/How-To-Measure-Inductance.phtml)

But they require a variable voltage system where you adjust input voltage until output hits a specific point.  If you don't have that, seems pretty difficult to figure it out.

Title: Re: Choke Identification
Post by: PRR on September 24, 2015, 07:20:28 pm

As a *rough* guide: the 60-120Hz impedance will be 5X to 20X the DC resistance.

So a 3 Ohm DC lump is a few dozen Ohms of filtering.

That's about no-good for any tube circuit.

The common Fender choke is rated for 1K Ohm impedance at ripple frequency (is probably 100r resistance).

It is *barely* possible it is a filter for a transistor power amp. These will run near equivalent 50 Ohms of DC, so 3 Ohms in series is a "tolerable" loss. However transistor amps *usually* can reject ripple without the help of a choke. (But Yamaha design is sometimes "unique".)

It *could* be a speaker crossover but 3 added Ohms is a lot in a 8 Ohm circuit.