Have A question. I have NOS of these A1304/C3296. The C3296-y have a hfe of 216, (all 15 of them). The A1304, they are green with a "T", they have an hfe of 160, six of them, and the rest have lower numbers. Using these in the Rubicon 1002, I was wondering if they will upset the bias as they are not equal?
I can get KSA940/KSC2073 from mouser which have the same specs.
Reason...Its been a few years (10+) and decided to get two of these going. The power supplies are good and I have NOS 2sa1302/c3281 that I'm going to install. The best matched sets. Front end boards are new from Lance, (X-Soundstream employer) so those are good.
When I set and measure bias, (1.5mV across the emitters of one pair a1302 and c3281), The other pairs measure lower and there is a difference between the pairs. One emitter resistor has 1mV and the other has 0.5mV across them.
Only thing I can think of is the hfe difference between a1304 and c3296.
Am I correct?
Scott
I can get KSA940/KSC2073 from mouser which have the same specs.
Reason...Its been a few years (10+) and decided to get two of these going. The power supplies are good and I have NOS 2sa1302/c3281 that I'm going to install. The best matched sets. Front end boards are new from Lance, (X-Soundstream employer) so those are good.
When I set and measure bias, (1.5mV across the emitters of one pair a1302 and c3281), The other pairs measure lower and there is a difference between the pairs. One emitter resistor has 1mV and the other has 0.5mV across them.
Only thing I can think of is the hfe difference between a1304 and c3296.
Am I correct?
Scott
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The difference bias isn't really an issue since the current passing through the transistors is minimal. There would likely be a difference between mismatched parallel transistors, however.
The reason to use matched transistors is due to performance at higher power. Transistors that are roughly matched (same date code) will have very similar properties through the range of operating temperatures (properties change across the operating range). Transistors from different production batches may not take the same load at higher power.
You can see if there is a significant difference between the transistors by driving the output to higher power (10v into a 4 ohm load) and measuring the voltage across the emitter resistors. This will tell you how the transistors are sharing the load. Measure when the transistors are relatively cold and as the amp comes up in temperature (test with all transistors clamped to the heatsink).
Also confirm that bias is relatively stable throughout the range of operating temperatures.
These tests will only be valid if the emitter resistors are all within tolerance.
To confirm what you believe about the hfe, you could measure the hfe and mark each transistor to see if the current through it (idle and at high power) follow the hfe for every transistor.
I don't understand this:
hfe difference between a1304 and c3296
Do you mean, between the NPN and the PNP?
Were you measuring the bias with no load?
The reason to use matched transistors is due to performance at higher power. Transistors that are roughly matched (same date code) will have very similar properties through the range of operating temperatures (properties change across the operating range). Transistors from different production batches may not take the same load at higher power.
You can see if there is a significant difference between the transistors by driving the output to higher power (10v into a 4 ohm load) and measuring the voltage across the emitter resistors. This will tell you how the transistors are sharing the load. Measure when the transistors are relatively cold and as the amp comes up in temperature (test with all transistors clamped to the heatsink).
Also confirm that bias is relatively stable throughout the range of operating temperatures.
These tests will only be valid if the emitter resistors are all within tolerance.
To confirm what you believe about the hfe, you could measure the hfe and mark each transistor to see if the current through it (idle and at high power) follow the hfe for every transistor.
I don't understand this:
hfe difference between a1304 and c3296
Do you mean, between the NPN and the PNP?
Were you measuring the bias with no load?
Yes, set bias with no load per the RUBICON 1002 FINAL TEST doc.
Set bias to 1.5mV. Verify DC Offset of 15mV or less.
And yes the hfe measure on the 2sa1304 is 160 and hfe on 2sc3296 is 216.
The 0.27 emitter resistors measure good.
I remember Lance telling me to look for current hogs by measuring across the emitter resistors..
I guess my main question should have been...Is it critical to have matched pairs?
I will test it as you said
It's only critical that you have all transistors carrying an equal load, especially at high power.
Some people have a load connected when setting the bias and that can cause errors due to slight DC offset.
Some people have a load connected when setting the bias and that can cause errors due to slight DC offset.
I would have never thought to test it how you explained...you have been so helpful to many of us over the years. Thank you for sharing your knowledge.
Scott
Scott
If I remember correctly, when i had this running a sub years ago, it would get pretty hot. More than I like. So I put it away and it's been sitting for about 10+ years.
Some amps don't hold the bias setting at higher temperatures. Confirm for your amp.
Some amps need fans to keep them cool enough for some people. Also bear in mind that the manufacturers have set the thermal protection to limit the amp from running too hot. I don't like extreme thermal cycling so I always use fans for amps that run really hot.
Some amps need fans to keep them cool enough for some people. Also bear in mind that the manufacturers have set the thermal protection to limit the amp from running too hot. I don't like extreme thermal cycling so I always use fans for amps that run really hot.
Hello all... I had NOS of 2sc3296/2sa1304 and finals, 2sc3281/2sa1302. All fairly matched and installed. I also replaced the 2k bias pots with multi-turn types. everything else was refreshed years ago. Idle current after bias setup is 1.7A. DC Offset is 4mV and -2.1mV. Bias is now 1.5 to 1.6mV across all emitter pairs.
Stays cool after playing it at moderate levels. This thing sounds VERY good. Wow, hate to sell it.
Stays cool after playing it at moderate levels. This thing sounds VERY good. Wow, hate to sell it.