# BasinStreetDesign

50
67 yo electronic design engineer, effectively retired. Historically sometimes employed, sometimes self-employed. Have always had a home lab. Just can't let it go.

## Achievements

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• BasinStreetDesign commented on randofo's instructable Basic Electronics7 months ago

Given power, P, and resistance, R, the maximum current a resistor can stand is I = SQRT( P / R ). So for the first resistor the maximum current it can stand is I = SQRT( 0.125 W / 100 Ohm ) = 0.035 Amp. For the second resistor the max current is I = SQRT( .5 W / 330 Ohm) = 0.0389 Amp. Since they are in series and both will experience the same current and since neither one can exceed its maximum current then the current through them both must be limited to the lower of the two values and that is 0.035 Amp.

• Nicely written!However the operating point of any transistor should be chosen appropriately for the transistor involved if you intend to build it. Your circuit may simulate without smoke but it will not do so in real life! I notice that the resistor values on your board are not those you calculated. Always calculate the power dissipation of all components. I assume you have looked at the datasheet for the bc547. It is a low to medium level BJT amplifier. It will definitely not tolerate a collector current of 1/2 Amp without burning up! Since its hfe peaks at about 30 mA collector current that is the operating point I would shoot for and keep in mind that even then the bc547 will dissipate .03 x 7V = 210 mW and warm up quite a bit.Keep up the good work!

• Not quite THAT old, but thanks anyway. No, I haven't made any changes to it and it still works well for me. If anything, the only thing I might change is to make a better way to capture the screen shot. If you try to make one, then just a couple of things to keep in mind:1 - Try to use the same type op-amp for the anode current amp., a LMC6082. If you cant get that type then use a similar precision, low-noise, single supply op-amp with very low offset voltage (LT 1 mV max) that will run from 15V.2 - depending on how many different kinds of tube you want to test, dont worry so much about having many filament voltages available. I just used what I had.3 - The bias output amp is a LF412 instead of a LM741 because the LF412 is a FET-input type so the R/2R network is not loaded down by...

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Not quite THAT old, but thanks anyway. No, I haven't made any changes to it and it still works well for me. If anything, the only thing I might change is to make a better way to capture the screen shot. If you try to make one, then just a couple of things to keep in mind:1 - Try to use the same type op-amp for the anode current amp., a LMC6082. If you cant get that type then use a similar precision, low-noise, single supply op-amp with very low offset voltage (LT 1 mV max) that will run from 15V.2 - depending on how many different kinds of tube you want to test, dont worry so much about having many filament voltages available. I just used what I had.3 - The bias output amp is a LF412 instead of a LM741 because the LF412 is a FET-input type so the R/2R network is not loaded down by op-amp input bias current. A LM741 there would give different results. If you do use a LF412 as I did the be sure to tie off the unused amp the way I did to the R/2R network so that it follows along at the same voltage as the other one in its package.4 - Diodes on the schematic marked D2N4148 are just 2N4148 and transistors marked Q2N3904 are just 2N3904, etc. The initial D or Q is from my database and are not part of the actual part number.If you have any other questions then message me. I'll be happy to answer anything.Good luck!

• For parallel resistors, it would be better to say that the final resistance will be less than any one of the resistors in parallel. Also, using a Dremel like that will raise the final value not lower it.

• 1 year ago

Excellent instructable! This is essentially the way we do them!I can offer an optimization. Cut the ends off the ears before they go into the microwave then you wont need to do that when they are hot.

• Excellent work. Kudos especially for repairing that machine on essentially zero budget. I never would have thought of hand-building a replacement cartridge from found materials.

• BasinStreetDesign commented on 5girls's instructable Cinnamony Sticky Monkey Bread2 years ago

Oh-oh - You've pasted the ingredients list in twice.

Oh-oh - You've pasted the ingredients list in twice.