Am I losing my mind?

Yes, I have seen that, but was a long time ago. I have owned an electronic assembly service for over 12 years. Once upon a time we built something with a discrete commonly available transistor. Suddenly the product would not work. The problem was traced to a certain transistor and after a lot of head scratching, we discovered the newly delivered transistor had a letter suffix after the regular id number.

The suffix meant the ecb configuration was actually a ebc for the same transistor. Never seen it since and suspect it was a manufacturing error that was being covered up and being sold to unsuspecting distributors.

Paul

I came across a similar problem years ago when spending hours trying to repair a C-Audio power amp. Turned out the BC184 and the BC184L have different pinouts. AAARRGGGHH!

Gareth.

I've come across that with BC184 or perhaps 212 and wrong suffix for the pinning

. 5 a I

Well thanks for the info guys. Almost thought it was time to retire. Yeah and live on Social Security. Not a chance. Lenny

Lenny,

Check on the back to see if the amp was made in South Korea. If so, Bogen used Korean versions of Japanese transistors which can have different pin outs. The beta and the bandwidth of the transistors, especially the outputs, are critical in these amps. Check for spurious oscillation and or notch distortion after the repair. If you see these anomalies on the scope, use an older transistor type for the outputs or order the parts direct from Bogen. I think 2N3055s works well as the output transistors. Chuck

I have two of these amps. The other one is about as bad as this one is. Transistors went down like dominoes. I replaced all defective small transistors in this amp and the outputs using 2N3055's as well. Except for a momentary slight "thump" when first turning it on I still can't seem to get a peep out of this thing. The output center point is unbalanced too. With 55V on the top collector and 35V measured in the center. Perhaps as you said the transistors may be that critical and I would really have to use originals as there are no adjustment pots in the thing. If that is actually what is happening here I probably will just shit can both of these units. I was going to fix one because I have a job coming up where I could have used it. And I would have liked to sell the customer something I had, and don't need at a discount rather than go out a buy a new one for them. I'm starting to think though that saving this customer some money is hardly worth it. This unit was made in Korea and by the way Bogen no longer supports it nor do they have any parts for it. If as you said the transistors are that critical and I've had to replace almost all of them how would I ever get this thing to work without originals? Lenny

Lenny-

I assume the output has two transistors stacked, with output taken from the point between them. I would expect this type of amplifier would have this DC voltage set by resistors rather than having to carefully match transistors. If the associated resistors are within specs, look for a leaky coupling capacitor that upsets the DC bias.

Fred

The power amp section is direct coupled. It is a close copy of the original RCA Quasi-Complimentry 70 W amp for a '60s databook that used

40407 through 40411 transistors.

--
You can't have a sense of humor, if you have no sense.

Lenny,

These amps have capacitor coupled output so there will be dc at half the power supply voltage at the output of the amplifier. Bogen will email you the schematic for free. I usually used parts from Bogen since I worked at a warranty station, but when parts weren't available in time, we had to use subs. If notch distortion was a problem, we changed the bias diode chain or changed a resistor value. If you stick with the original output number, oscillation shouldn't be a problem. I have worked on over a thousand of these amps and never had one I couldn't repair so you shouldn't have to toss them. I'm on vacation until after Memorial Day, but I might have a schematic at home. If I do, I can help you get these amps repaired. Chuck

Need to be cautious here, I think.

I've heard that parts sold under the "2N3055" label may vary a lot in their gain and fT - they may be a lot faster and/or "hotter" than the spec sheet "minimum" values suggest.

What I've been told, is that the "2N3055" part number has been used by some manufacturer as a sort of "dumping ground" for transistors from quite a number of different fabrication processes, that didn't test out well enough to meet the specs of their intended purpose.

If you end up with a part labeled "2N3055" actually built around a fast process, it might have an fT quite a bit higher than the usual

2.5 MHz, and might not be suitable for an amp which has "critical" requirements for beta and bandwidth.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
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It's no surprise a company would sell low-spec devices with a different part number. What is surprising in this case is that the devices don't use the same fabrication process, and aren't part of a numerical series (2N3053,

2N3054, 2N3055).

art

't use the

Hey I just thought that we all need a little excitement now and then. I don't really appreciate it though when I'm trying to make a living. Lenny