replacement transistor for BDY24

I can't find this BDY24 transistor anywhere other that buying a whole bunch for $1000. They are the power transistors in the drive amps for my lathe. I had a couple that were given to me but they got used a couple of weeks ago. Now I'm out and that makes me very nervous.

Here is a link to the data sheet. Any suggestions for a substitution?
http://www.datasheetarchive.com/261.html

Here's a more direct link to a BDY24 datasheet:
http://www.halfin.com/comset/catalogue/bdy23-24-25-180t2-181t2-182t2.pdf

and it looks like this dealer has a small quantity available from stock:
http://www.partsvault.com/part_search/?part_number=bdy24

Considering that you certainly don't want to put your expensive cutterhead at risk needlessly, it'd be best to exhaust all reasonable options for obtaining the original type transistor, in my opinion.

Considering that you certainly don't want to put your expensive cutterhead at risk needlessly, it'd be best to exhaust all reasonable options for obtaining the original type transistor, in my opinion.

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Absolutely. This was a desperate move. I've had very bad luck with cross references in the past. I have a stash of every transistor in the VG66 save that one. No drive amp=no work. No work=no money.

Thanks for locating that part. I've looked for the past couple of weeks. Go figure.

I just took a second look at the site. USD $450 minimum order. A little rich for my blood. I think 20 would laste me a lifetime.

My bible, 'Franzis Tabellen' (29.000 transistors) lists the USA equivalent as; 2N3448

As others have noted I wouldn't fuck too much around. A lathe is big biz as you know :wink:

That said, the BDY24 is a standard TO-3 power transistor and many could take it's place. I'd look for a sub with similar specs that is NOT faster or have higher gain. FTmin should be 10MHz & hfe shuld be 15/180. Lots of subs there...

I have found a solution. Now I need to know if I should be nervous. On my schematic a 2N3055 was written as a sub. Certainly easy enough to find. I took another look at the modules and saw that there were 2N3055's in two of the drive amps already. Since I have been using them for a few years I guess they work. Judging from sismofyt's post it looks okay. Is it okay?
http://www.ee.latrobe.edu.au/internal/workshop/store/pdf/MJ2955.pdf

How much power in this amplifier? A pair of 3055 is not really safe for more than 75, maybe 100 Watts in a loudspeaker.

Also: the original 3055 was a Mesa process with low frequency response and wide safe area. About 20-30 years ago they all switched to a planar process with more speed but lower second-breakdown. How old is your note, and the 3055 in the working amp? Before 1975-1985?

The BDY24 is specified 10MHz gain-bandwidth, and the 3055 (even planar) is not. The 3055 will cover the top of the audio band, but is considered slow by modern standards. I don't know if the amp is designed for fast transistors, or not, or if it would matter.

[quote author="PRR"]How much power in this amplifier? A pair of 3055 is not really safe for more than 75, maybe 100 Watts in a loudspeaker. [/quote]

It doesn't really say in any of the literature alhtough I've been told 100 watts is about right.

How old is your note, and the 3055 in the working amp? Before 1975-1985?

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I don't really know. They have been there since I got the rack. It's a note by a previous tech. There is no substution suggestion from Neumann.

The BDY24 is specified 10MHz gain-bandwidth, and the 3055 (even planar) is not. The 3055 will cover the top of the audio band, but is considered slow by modern standards. I don't know if the amp is designed for fast transistors, or not, or if it would matter.

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Since I can't locate the BDY24 for less than an arm and a leg I'll keep looking for a better replacement. The SX74 cutterhead can only take about 5 watts of continuous power but can take a lot of peak power. The extra power is needed for acceleration of the stylus.

A little info on the different generations of 2N3055 can be found in this thread.
http://www.groupdiy.com/index.php?topic=1833

As for the best replacement for your application: Motorola makes a whole family of very good TO3 power NPNs. I think it would be worth your while to call Moto and talk to an applications engineer. Be prepared to supply a datasheet for the BDY24.

By the way, did you check out this place yet? It looks like they have 146 pieces in stock:
http://www.magnatec-uk.co.uk/semlst.shtml

If the whole "VAT" thing is killer, perhaps one of our UK friends would be willing to act as a go-between.

Solving this problem is going to involve an investment of either money or time, or both. It might be "cheaper" in absolute terms to buy a few expensive transistors and have the peace of mind of knowing they'll work in your circuit.

Solving this problem is going to involve an investment of either money or time, or both. It might be "cheaper" in absolute terms to buy a few expensive transistors and have the peace of mind of knowing they'll work in your circuit.

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There are tons of these types of distributors. They all have a minimum per line item fee. If I wanted to spend $250 I'd say I needed 500pcs. I already know the 2N3055 works because it has been working. I'm willing to do some experiments to see whether other options sound better. I think I will learn more from this approach and have a more reliable source for parts.

What are the markings on the 2N3055s that are already installed and working in your other amps? As has been mentioned already, not all 2N3055s are the same. But luckily, they're all cheap :wink:

A transistor with a higher gain-bandwidth may quite possibly sound better, but you have to be careful of stability issues. Do you have a scope and other test equipment at hand? Although the ears are the final arbiter, the test gear will (at least ideally) send up the red flag before the cutterhead can be wrecked.

I have a scope and I can borrow other things like an HP distortion meter,impedance meter, LC bridge as needed. I'm not out to hot rod it, just find a suitable replacement.

I don't think the drive amps are the weak link although, Neumann would disagree. In the next generation amplifier rack they went to 600 watts per channel. The extra power gets you better low level transient response. Since everything is cut relatively hot I can't see this making much of a difference. In the next couple of months I'll have one of these systems to play with so I'll see.