transistors

[The Dude]

Were is all the electronic guys. I have a HK 830 or maybe its a 730 I can't quit remember right now at the moment . But I had a tech tell me that three out of four were bad on one channel. So I started searching and didn't really find anything other from electronic companys over in China mainly that carried them. Then here recently I have stumbled upon a few on ebay. Some being old stock from the states for around 20.00 each shipped, then some that are refurbished from Japan for 10.00 dollars shipped.

What would you trust I have herd of people getting counter fits how could I avoid this.

Thanks

Nick

[Guest " "]

be careful and make sure you understand what you are buying on ebay. Most solid state amps, if they use transistors, use two types at the same time. PNP and NPN transistors. One is a push, and the other a pull. When replacing output stage and driver stage transistors, you need to use matched sets. If you have an amp that has 16 output transistors, 8 per channel, 4 NPN and 4 PNP, and if three of these are bad, you will most likely need to replace 6 transistors because you may be involving 3 matched sets. So whats the stuff your buying on ebay. could be transistors that did not match other transisters and were casts offs. Could be transisters that if you buy 4 NPN and 4 PNP of, might match together. But it is highly unlikely that a transistor you buy today is going to match by happenstance a transister that was installed in your amp 10 years ago.

[The Dude]

Tubes and transistors, there's just no getting away from the need to match. So your saying that between channels you need to be matched not just with

In the 4 for one channel. The ones that were refurbished were available in two pairs as 2 pnp and 2 npn I was going to replace the 4 on the one channel but you might be saying I should replace all 8. I wonder if the seller has data on them if they can be matched or not.

[DrWho]

You should be able to find new transistors in the $1 range or less...

If it's just the output stage that needs fixing, then there should be a lot of comparable options. Although it'd be best to get an engineer involved. Also, do you know why the output stage is damaged? That may be a sign of other things that may need repair.

[Guest " "]

So your saying that between channels you need to be matched not just with In the 4 for one channel. The ones that were refurbished were available in two pairs as 2 pnp and 2 npn I was going to replace the 4 on the one channel but you might be saying I should replace all 8. I wonder if the seller has data on them if they can be matched or not.

I would not worry so much between a repaired left channel and a normal right channel and vs versa. The issue is more about how PP amps work in general regardless if they are tube or transistor based. It's important to understand that in a 4 transistor per channel senerio, it is likely that 2 or PNP and 2 or NPN. There is usually either 1 Bias adjust for both PNP circuts and 1 Bias adjust for both NPN circuts on the power supply board, OR, two Bias adjust pots on each channel driver board, one for the PNP side and the other for the NPN side. In either case, there are no individual bias adjust. AND, even if there was, just becuase the transistors bias the same, does not mean they are going to have the same amplification factor.