I'm planning out a build of Pete Millet's NuHybrid HA. I've ordered the PCB and truly appreciate the comprehensive build instructions.
The BOM from Mouser has a few components that are out of stock that I dont trust myself to find replacements:
Cheers
The BOM from Mouser has a few components that are out of stock that I dont trust myself to find replacements:
- Mean Well Wall Mount AC Adapters 25W 24V 1.04A Level VI USA plug (GST25U24-P1J)
- TI Linear Voltage Regulators 3.3 V 500mA Fix Pos Voltage Regulator (UA78M33CKCS)
TE Connectivity Low Signal Relays - PCB 24VDC Non-latching Single coil P2 (V23079A1005B301)In stock in 01/24- Kemmet Common Mode Chokes / Filters 0.5amp 3.4mH (SU9V-R05034)
- onsemi MOSFET FET 60V 5.0 OHM TO92 (2N7000)
- STMicroelectronics ESD Suppressors / TVS Diodes SM6T Transil series (P6KE33A)
- Kobiconn RCA Phono Connectors PHONO DUAL RED/WHITE (161-4218-E)
Cheers
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For the wall AC adapter, this looks similar (identical besides price and "region" spec, that I can see). The spec sheet says its for medical vs. industrial.:
Mean Well Wall Mount AC Adapters 25W 24V 1.04A Medical USA plug
Mfr. Part #
GSM25U24-P1J
Mouser Part #
709-GSM25U24-P1
Mean Well Wall Mount AC Adapters 25W 24V 1.04A Medical USA plug
Mfr. Part #
GSM25U24-P1J
Mouser Part #
709-GSM25U24-P1
I dont see a quick replacement for TI Linear Voltage Regulators 3.3 V 500mA Fix Pos Voltage Regulator (UA78M33CKCS); putting that aside a bit.
onsemi MOSFET FET 60V 5.0 OHM TO92 (2N7000)'s alternate on the XLS BOM is in stock -- https://www.mouser.com/ProductDetail/Microchip-Technology/2N7000-G?qs=yU2N9dt%2BrfnyR/OhNomgZw==
Phono connectors have an in-stock alternate on the XLS BOM -- https://www.mouser.com/ProductDetail/CUI-Devices/RCJ-2123?qs=WyjlAZoYn50RZapIrjfyUQ== as well as several "optionals" in the doc.
The Digikey alternate part # for STMicroelectronics ESD Suppressors / TVS Diodes SM6T Transil series (P6KE33A) lists a direct substitute at https://www.digikey.com/en/products/detail/littelfuse-inc/P6KE33A/285943, also listed at https://www.mouser.com/ProductDetail/Littelfuse/P6KE33A?qs=sGAEpiMZZMu2MsBvHNoAnJMUr%2BBs2TVC on Mouser.
I may need assistance verifying if this is identical.
I may need assistance verifying if this is identical.
Medical grade are better as the leakage currents have to be very low, ie less problems with hum
Using a 7805 would simply mean that the bias could be adjusted from -5 to 0 instead of -3.3 to 0. LM78033 are also hard to find because linear regulators are a poor choice for low voltages, unless you are talking about a voltage reference like TL431, which might be a better choice.
At first I noticed that the regulator needed to sink the tube cathode currents when such regulators have no sink capability, but when I did the math, I realized that the tube current is only about 2x 10/475k, ie 42uA which will only drop 0.02Volts across the bias pots, so the regulator is just powering the pots up to 3.3VDC (6.6mA).
I assume you understand that this project is deliberately low fidelity. There are a lot of these audio devices with a tube stuck in the middle in order to generate the tube sound, i.e., distortion. I would use a TL431 or a 3.3V Zener instead of the 78M33, but then, I have no sympathy for the whole project.
At first I noticed that the regulator needed to sink the tube cathode currents when such regulators have no sink capability, but when I did the math, I realized that the tube current is only about 2x 10/475k, ie 42uA which will only drop 0.02Volts across the bias pots, so the regulator is just powering the pots up to 3.3VDC (6.6mA).
I assume you understand that this project is deliberately low fidelity. There are a lot of these audio devices with a tube stuck in the middle in order to generate the tube sound, i.e., distortion. I would use a TL431 or a 3.3V Zener instead of the 78M33, but then, I have no sympathy for the whole project.
I appreciate the feedback. As for being low fidelity -- no need to worry, I am in this for the DIY fun of the hobby.
BTW, if you use a SWPS, be sure the AC input is grounded to earth ground. Otherwise, the input filter puts half the AC line voltage on the DC output, a huge source of hum noise.
It occurred to me that I would not use a 3.3V supply and pots. I would use DC servos from the outputs back to the tube cathodes, ie DC feedback that centers the tube current automatically.
It occurred to me that I would not use a 3.3V supply and pots. I would use DC servos from the outputs back to the tube cathodes, ie DC feedback that centers the tube current automatically.