Pete Millett's DIY Audio pages
For technical books, tube data, vintage data, transformer data, and McIntosh data, go to: www.tubebooks.org
Last update: 5/16/2024 - Added a cascode CCS board
5/10/2024 - Finally posted some info on my 520B (Emission Labs) Push-Pull DHT Amps
5/9/2024 - Added "Gossamer" RAF VT-62 SE Amp
4/9/2024 - Updated the design of the sound card interface
3/17/24 - Added an A2 driver board and (Yet another) HV power supply using the MEC electronic choke
PLEASE READ - Commercial usage of information on this site:
I consider all the information that I post here to be in the public domain. So, you can use it however you want, for commercial or non-commercial use.
That said, I would appreciate it if you at least let me know if you are going to use any of the circuits or especially PCB Gerber files to make commercial products, or to sell bare PCB's.
There are some cases where products are being sold not only with my permission, but active involvement. The "Millett Hybrid" effort and others at HeadFi are examples (and excellent models of how the DIY community should work, in my opinion). There are other cases where I have asked vendors to sell PCB's as a service to hobbyists. And there are other cases where companies are manufacturing and selling PCB's, chassis, etc. without contacting me at all.
In ALL of these cases, I make no profit from any of the sales. Zero, zip, nada. I have a normal "day job" that pays the bills, this is strictly a hobby with me. So please do not expect me to provide the level of technical support that you might expect when buying a product. I try and help, but it sometimes takes me days - even weeks if I'm traveling for work - to respond.
Thanks for your indulgence in reading this!
All that said... I do sell things, including projects I no longer need, PC boards for my designs, and occasionally parts and tubes. I do this through eBay - I maintain an eBay store "pmillett". You can click here to see what I may be selling at the moment.
"Gossamer" - RAF VT-62 (4304CB, etc.) SE class A2 amp
This is a depository for various audio designs and projects - mostly tube - that I've put in the public domain, as well as additional info to support magazine articles that I've written, and an ever-growing amount of technical data archives relating to vintage and tube audio. I'm constantly adding and updating things, so come back every once in a while and see what's new. Remember: you may have to hit the "refresh " button to see the updated versions of pages!
Follow the links below for detailed info.... Most pictures are hyper-linked to full-size pictures, so you can zoom in if you click on them.
If you have questions please feel free to e-mail me at:
Please, if you send me e-mail, make sure that there is a logical "subject", or your mail will get dumped along with all the junk mail (spam) that I get - it's up to about 100 junk e-mails per day now. If I don't respond within a few days, try again, just in case I missed your message. I try and return everybody's mail within a week, though I travel quite a lot for work and find I get very behind at times. Please be patient...
Standard disclaimer: This info is provided with no guarantees as to accuracy, usefulness, etc. There's no guarantee that if you try and build anything like this stuff that you won't electrocute yourself, the kids, or your cat, or burn your house down... especially if you don't know what you're doing. Be careful!
Many files on this site, especially scanned documentation, are in Adobe Acrobat (PDF) format. I recommend that if you don't already have it you download the latest version of Adobe reader. Some files have compressed images that may not work correctly with older versions of Acrobat reader.
Scanned vintage books, manuals, catalogs, papers...
Please go to www.tubebooks.org for this material.
Audio projects and experiments:
Power amps
New 5/10/2024 - Push-pull 50W 520B triode amps
New 5/9/2024 - "Gossamer", a single ended class A2 amp using the RAF VT-62 tube
4D32 single-ended ultralinear power amp
The "NuclassD" 50W class-D hybrid amp using the nutube
A hybrid (SS driver) class A2 DHT amp
A 50 watt monoblock version of the "Engineer's Amp"
A PL177 single-ended amplifier
"La Luxuriante" stereo R120 SE amp
"Fatboy", a low-distortion zero-feedback push-pull 300B amp
A compactron triple-triode driver for push-pull amps
"Mr. Potatohead" 815 amp - 50W from 2 tubes in class AB2
The "807" Push-Pull amp using driver boards below
Push-pull driver PCB, a (nearly) universal driver for push-pull amps
"Jonokuchi", a single-ended tube headphone / speaker amp
Class-A2 1636 amp using a power opamp driver
The "Engineer's Amplifier", an affordable, high-performance push-pull TV pentode amp
The "Unnecessarily Complex 300B Amplifier" (from audioXpress 2009)
The 307A tube, and a push-pull 307A amplifier
"The Mighty Midget" (from audioXpress 5/08)
Low-voltage Hybrid amplifier with adjustable damping
"A Single-Ended E-Linear Amp" (from audioXpress 4/05)
Push-pull 6B4G class-A amplifier
Push-pull KT88/6L6/EL34/2A3/300B amp with "universal" driver / power supply PCB
813 single-ended triode amp with microprocessor-controlled power supply
2-8 watt push-pull amp using 7044 computer triodes
EL802 push-pull single-stage "spud" amp experiment
EL34 active-loaded (SRPP) parafeed amp experiment
Preamps / Line Stages
A Nutube Balanced Amp - a true differential amp for line stage or headphone amp use
A buffer PCB using the Korg Nutube 6P1 low-voltage DHT
"el escorpion", a simple line stage in a cigar box that runs off of 12VDC
A solid-state LR phono preamp (no caps in the EQ) from ETF.13
A high-end Tube Microphone Preamp
"A Low-mu preamp" (from AudioXpress 2/04)
Headphone Amps
Sangaku DIY nutube headphone amp / preamp
The NuHybrid headphone amp, a hybrid headphone amp using the Korg Nutube
The DIY "Butte" solid-state headphone amp
"Jonokuchi", a single-ended tube headphone / speaker amp
The "Starving Student" hybrid headphone amplifier
Wheatfield Audio HA-1 tube headphone amp
Low-voltage tube hybrid headphone amp - the original "Millett Hybrid" amp (from AudioXpress 11/02)
Wheatfield Audio HA-4 headphone amp (solid-state, with crossfeed and EQ!)
SRPP ECC99 tube headphone amplifier (drives AKG K1000's!)
Test equipment
A breakout board for banana cables
A "Sound Card Interface / AC RMS Voltmeter" you can build
Tube-regulated high-voltage bench power supply
Software for the HP 8903 audio analyzer - Make professional plots from this affordable audio test system!
Other stuff
New 5/9/2024 - Low voltage filament / heater supply using Vicor modules (used in Gossamer)
New 3/17/2024 - (Yet another) HV power supply using the Tentlabs MEC (multiple outputs)
New 3/17/2024 - A2 driver PCB
A B+ power supply with delay using the MEC electronic choke
A vibration mount for the Korg nutube to help eliminate microphonics
General-purpose 2-channel 15/25VA low-voltage DC power supply for audio projects
DC Power supply board used with the NuclassD or class AB power amps (look down the page)
Opamp power supply (used with the LR Phono, look down the page)
Voltage selector PCB for transformers like the Hammond 300-series with multi-voltage primaries
A power supply PCB for B+ supplies using the Tentlabs MEC Mini Electronic Choke
A linear "USB adapter", a 5W power supply
A power (AC) sequencing board for big amplifiers
A 10W B+ flyback supply (switching power supply) that runs off of low-voltage DC (5-20V)
Muting relay PCB to eliminate the "thumps"
A two-channel shunt-regulated adjustable bias supply
High-voltage regulator ("Maida" regulator) that fits Landfall Systems heatsink
Tube amp power supply PCB with bias supply
An isolated current sensor board to measure plate current using a PanelPilot meter
MOSFET follower buffer for class-A2 grid drive
A simple regulated DC power supply / filament supply
High-Frequency filament converter for DHT's
Speaker projects:
MLTQWP speaker using the Jordan JX-92S driver
Bert Doppenberg's TQWP project
Downloadable drawings for "An Affordable Full-Range Speaker Project", AudioXpress 6/03 (uses Fostex FE-164)
Glass Audio and AudioXpress articles:
audioXpress has been gracious enough to allow me to reproduce here some of the articles that I've written for Glass Audio and AudioXpress magazines in their entirety:
"A Low-Mu triode Preamp" (1.3MB PDF file) from AudioXpress 02/04
"Build A Low-Voltage Tube Hybrid Headphone/Line Amp" (612kB PDF file) from AudioXpress 11/02 - the original "Millett Hybrid".
"Power Transformers For Audio Equipment" (1.3MB PDF file) from AudioXpress 6/01
"All About Wire" (476kB PDF file) from AudioXpress 8/01
"The Power Line Interface" (1.3MB PDF file) from Glass Audio 6/00
Miscellaneous technical information:
"LR Phono Preamps" presentation from ETF.13 (PDF or PPT)
Where to get stuff - an assorted list of some of my suppliers
Tektronix power transformer information - Info I've collected on classic tube-type Tektronix power transformers
ResCalc, a cool utility program you can download that calculates combinations of standard resistors to get a particular value.
Parts shopping in Asia (sorry, getting a bit out of date)
"The Sound of Distortion" presentation from ETF.04
High-Gm driver pentode test data
Ixys current regulator as a CCS plate load
Other non-audio stuff:
A picture collection of interesting old QSL cards that I received in the early 1970's.
Who I am:
A lifetime electronics geek, I got a ham radio license at the age of 8 and a first-class commercial radio license at 14. I'm just old enough that I actually build and used tube some stuff when it was still in production. I've been an electrical engineer for nearly thirty years, doing mostly computer and consumer electronics design work. I owned and operated Wheatfield Audio, which made tube headphone amps (but no money!) for a few years. I also have written articles for AudioXpress magazine (formerly Glass Audio) on occasion.
I do some commercial audio design work outside of my "day job". Some of my work includes the Apex Hi-Fi product line, which is sold by TTVJ (Todd the Vinyl Junkie).
I'm currently living near Fort Collins, Colorado, and work for a Silicon Valley semiconductor company.
These are the Wheatfield Audio HA-1 and HA-2 tube headphone amps, which I designed a long time ago:
I've put some info from the old Wheatfield Audio web site here that might be useful, especially if you own an HA-1 or HA-2.