I'm starting to build up the ips boards I got from Terry and have come to the first of what may be many questions. For Q 10/13 it seems that 2sa1381 is E rank and the 2sa3503 is D rank. This is what the suppliers have available. Would this cause a problem? I see that there is an overlap of hFE between the two ranks. Can someone educate me on how to test this and see if I can get a bit of a match for these parts.
Thanks, Evan
I see that new even inexpensive multimeters have hfe test. Are these OK to use?
Thanks, Evan
I see that new even inexpensive multimeters have hfe test. Are these OK to use?
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Hi Evan, I've got from Mouser exactly the same ranks - ksa1381e and ksa3503d. Practical measurement with multimeter shows hfe around 150 for "E" and around 100 for "D" ones. This is fine - having rather high OLG, this design allows this kind of tolerance.
Using DMM with hfe test is fine for the purpose. Measurement is based on a simple principle there - it sets some calibrated base current and shows you collector current equivalent.
Cheers,
Valery
Using DMM with hfe test is fine for the purpose. Measurement is based on a simple principle there - it sets some calibrated base current and shows you collector current equivalent.
Cheers,
Valery
Thanks for the advice. I hope to have your set working after this weekend. I really look forward to giving a listen.
Thanks,
Evan
Thanks,
Evan
Great! Looking forward to your results!
If you will have more questions - you are welcome, as usual 😉
If you will have more questions - you are welcome, as usual 😉
Is it safe to run Tubesomo at 63 volts? I'm cleaned out of 100 volt caps. Nothing to filter a 50 0 50 transformer for testing.
Hi Jeff, it is safe, but it is on the edge - there are zeners at the rails for input section, they are exactly 63V, so they will be somewhat "starving" for current... resulting in a bit lower rails for the tube. It will still work, but probably with a bit higher measured distortion (although, you'll not hear it, most likely).
Cheers,
Valery
Cheers,
Valery
Thanks. I've got these built but haven't fired them up yet. I never thought to check my cap selection when ordering the transformer.😕
I'm finally back to starting up Tubesomo. I'm getting voltage on the input with the input(not the direct one) shorted. One tube is -9VDC, the other tube is -.3VDC. These were two brand new matched triode tubes. Can a tube produce voltage on the input normally or do I have two duds?
Hi Jeff,
No, the tube is a high-impedance device (somewhat similar to jfet), so in normal operation you should have literally zero voltage at the input.
Something is wrong.
Will there be any issues if I fire the input stage up with no tube? Both boards are behaving exactly the same. -.5V offset with one tube, -25V with the other.
It will be no trouble, but they will not work properly - global NFB will not work, you will have DC offset at the output - the circuit will be out of balance.
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Input stays at 0 volts with no tube installed. That's the best DC offset I've seen on the output too. The servo seems to be working.
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Everything is considerably lower than your schematic. I'm dropping 10 volts through R2 and R3. Are they overloaded?
