C3200 bias transistor

[mike49504]

Im working on a directed amp and the bias transistor is defective. The orginal is a C3200. Is there a good replacement ?? I have the following transistors on hand.

2N4400
MPS6571
MPS6521
MPS6533
KN2222
MPSA 56
2N3904
MPSA42
C3112
2SA1023
2n6517
B647
MPSA06

[amc32]

What is the model of the amp?

[Michel]

Dear mike49504,

You have some work ahead of you...
First, you have to eliminate the PNP transistors from your list since your defective is a 2SC3200, the C meaning NPN.
Your B647 is a 2SB647, the B meaning PNP.
The same goes for your 2SA1023, the A meaning PNP.
Do the search for the rest and when you have a list of only NPN transistors it will be much easier to give you a hand.

[Perry Babin]

The original transistor was rated for 120v but most amps don't require high voltage transistors for the bias transistor. The original was a high gain transistor which is often required. The MPS6521 should be a good sub but the pin configuration is wrong. You'll have to swap the base and emitter legs.

After doing this, you need to confirm that the bias holds at high temperatures. This means that you'll have to run the amp long enough to get it to thermal. The idle current when hot should be very nearly the same as the idle current when cold. If the current is significantly more when hot, you'll have to adjust the bias. If this is like most amps, it's class B so there is no bias adjustment and any changes will require replacing resistors. If it's a class AB (most have bias pots), you can reduce the bias current with the pot so that the 'hot' idle current is acceptable.

[mike49504]

I didnt want to flip legs around so i talked to digikey and they said this transistor is a good replacement Just wanted to know what your opinion is on this transistor if it makes a good sub or not?


Digi-Key - ZTX690B-ND (Manufacturer - ZTX690B)

[Perry Babin]

The pin configuration is still wrong.

It's odd that they recommended a 45v transistor to replace a 120v transistor. It will probably work but that's not generally the case.

You would still need to run the amp up to thermal to confirm that the bias hasn't drifted.

[mike49504]

Would a C3198 transistor work?

[Perry Babin]

If it's a 3198BL, it should work. If it's a 3198GR, it will probably work. Any other suffix would be questionable.

[mike49504]

I cant seen to find a C3198BL transistor. Im placing an order with future electronics later and wondering if anyone knows a good replacment Transistor for the C3200 I could order from Future.

Any help would greatly be appericated

[StevenOH]

Well, threads like this reappear periodically. And I mean, that people don't
know how to find the replacement for their part, but it is them, who decide, what info is relevant, and what not, to help them
The transistor case has more markings, than just part number...
Anyway, the equivalent replacement will be 2SC2240 with the same grade,
that C3200 has on its case (GR/BL).
This part is easy to find.
Additionally, never ask any distributor for replacement recommendation -
they don't know. And people must be very careful using all those replacement databases - some of the recommendations are incorrect, many
of the equivalents are not included.