Now I'm learning on this next step so bear with me. I think I'd like to replace all the smaller transistors on this toneboard given that I have it out (again it took almost an hour to safely remove it) plus I'm looking to learn about transistor replacement. To keep original sound there are three smaller transistors on this unit. Any suggestions for good, modern, perhaps better performing replacements?
1) 2SA564
2) 2SC644
3) 2SC828
I was thinking of using this website which finds direct replacements:
Alltransistors.com
When choosing replacements is it best to find exact matching or improve and exceed while you're at it (like the voltages on cap replacement)
.
For example, it appears these 2222A transistors I have spares of exceed the values or the 2SC644, does that mean I can use it?
For transistors in the audio signal path, a generic 2222A would not be the best choice.
It is OK to look for a replacement transistor that "meets of exceeds all specs", but is also not the best way to go. For many reasons. To learn more, here is a start:
Transistor Replacement Guide.
Better would be to search AK here to see if anyone has done similar (asked about this and gotten replies, potentially a discussion). Like
https://www.audiokarma.org/forums/index.php?threads/hk-930-tech-advice.757415/
The best thing to do, however, is:
- For a given transistor in a specific circuit, like "TR101 on the tone board in a HK 930"
- Post here or in a new thread
- Tell us where the transistor is going to be used (i.e. "TR101 on the tone board in a HK 930")
- Post an image of the schematic (so those of us who don't have the service manual you're using can easily follow along and help)
- Tell us which transistor you want to replace
- Ask for help with that specific transistor being used in that particular spot of a specific circuit
That tells us
the application of the transistor. That knowledge helps to guide us to which parameters are important, which are not, and, sometimes, which of several replacements is best
for that application.
I don't see any 2sc564 on the tone board; only 2sc644 and 2sc828:
All of those are in the audio signal path, so you'll want to look for
low noise small signal transistor replacement. Getting the specs of the original devices from alltransistors.com is a great first step.
2SC644
NPN
Power Dissipation (Pc): 0.15 W
Collector-Base Voltage |Vcb|: 25 V
Collector-Emitter Voltage |Vce|: 25 V
Emitter-Base Voltage |Veb|: 5 V
Collector Current |Ic max|: 0.05 A
Transition Frequency (ft): 75 MHz
Collector Capacitance (Cc): 10 pF
Forward Current Transfer Ratio (hFE), MIN: 350
Noise Figure, dB: not stated
Package: TO-92
Pinout: ECB
For low noise, since the above 2sc644 is low current 50mA and low voltage 25V, I'd start with looking at the KSC1845F.
KSC1845F
NPN
Collector Power Dissipation (Pc): 0.5 W
(better than 2sc644)
Collector-Base Voltage |Vcb|: 120 V
(better than 2sc644)
Collector-Emitter Voltage |Vce|: 120 V
(better than 2sc644)
Emitter-Base Voltage |Veb|: 5 V
(same as 2sc644)
Collector Current |Ic max|: 0.05 A
(same as 2sc644)
Transition Frequency (ft): 50 MHz
(lower than the 2sc644, but we're doing audio that only goes to 20KHz, so this is fine)
Collector Capacitance (Cc): 1.6 pF
(better than 2sc644)
Forward Current Transfer Ratio (hFE), MIN: 300
(not quite as good as expected from 2sc644, but plenty fine)
Noise Figure, dB: not stated but amongst the best
Package: TO-92
(same as 2sc644)
Pinout: ECB
(same as 2sc644)
All its (important to us and our application in this circuit) specs meet or exceed, it does very well as a small (audio) signal amplifier (which is what the application of the 2sc644s on the HK 930 tone board are doing), and it is ECB pinout.
2SC828
NPN
Power Dissipation (Pc): 0.25 W
Collector-Base Voltage |Vcb|: 30 V
Collector-Emitter Voltage |Vce|: 30 V
Emitter-Base Voltage |Veb|: 5 V
Collector Current |Ic max|: 0.05 A
Transition Frequency (ft): 110 MHz
Forward Current Transfer Ratio (hFE), MIN: 65
Noise Figure, dB: not stated
Package: TO-92
Pinout: ECB
Same thing here for the 2sc828: low current, low voltage, best to have low noise... so, again, the KSC1845F would be amongst the best choices.
All this said, it would also be helpful to read the first page of
Noisy transistors to replace on sight as it may help you in your quest for what to replace and what to replace those with.
