Welcome to
I've Never Lost the Wonder.

This is a noncommercial site
operated by Max Robinson and
dedicated to passing on and preserving
knowledge of vacuum tube circuits and techniques.

Keep the electrons flowing and the tubes glowing.


Join the Fun with Tubes discussion group.
Now all of you who have been exchanging email
messages with me can communicate with each
other directly. To subscribe send an email to
See you on the list.

Activity Log
Improved Interface.

Finishing up the Equalizers Article. 7/22/21.
Protecting my Expensive Scope 5/1/21.
Tubeman is Back.
Adventures With a Network Analyzer. 9/16/2020.
Winding IF Coils.
Musings upon building a tube analyzer.
Spectrum Analyzer Impedance Buffer.
Modifying the HP334A RF Detector Circuit.
Low Distortion AM Detectors.
Filter Choke in the Negative Lead.
A New Radio with Old Tubes.
Daily Activities click here.

Fun With Tubes now has a sister site.

It's called Fun With Transistors.
If you would like to tinker with electronics
But you would rather not poke around among
High voltages, check it out.


Build Your Own Website with a KISS
In How To Do It.
Receive and Transmit on separate Antennas.
In Ham Radio Corner.
Hantek® Model 6022BE
2 Channel USB Oscilloscope

In Equipment Reviews.
Circuit Specialists® CSI4810A
Semiconductor Curve Tracer

In Equipment Reviews.
What more is there to say?
What is LT Spice
And why should I care?
Learning LT Spice
It's not as hard as you may think.
LT Spice for the Blind
Yes, it is Possible.
Preamp Design.
Pulled Out From Tone Controls and Expanded.
Practical Tone Controls.
Totally reworked using LT Spice Simulations.
Low Voltage Radio Tubes.
Don't want to poke around the high voltage?
Try this.
Vibrator Power Supplies.
Plate Voltage for Low and Medium power.
Revisiting the Newcomb D-10.
What. Again?
A Tough Nut, Cracked At last.

What do I need to have fun with tubes?
Click here for the answer.

The Basics of Electricity and Electronics.

DC Circuits: Series Circuits, Parallel Circuits, Ohms Law, and Scientific Notation.
AC Circuits: RC, RL, and RLC Networks, Filters.
Vacuum Diodes: Tubes with two elements.
Vacuum Triodes: Adding a grid to the diode.
Tubes with 2, 3, and 5 grids.
Amplitude Modulation (AM), Single Side-band (SSB), and Frequency Modulation (FM)
What is ground? One of the Most Misunderstood Concepts in Electricity.

Test Instruments.
How they work and how to use them.

Bench Power Supply.
Grid Dip Meter (GDM) / Grid Dip Oscillator (GDO).
The Neglected Q Meter.
The Vacuum Tube Volt-ohm Meter (VTVM).

Equipment Reviews

I have decided it would be helpful to viewers of this page
if I post reviews of currently manufactured test equipment.
I have not been given any of this equipment in exchange for
a favorable review. Nor did I receive any discount other than
what the dealer makes available to all customers. I do this in
the hope that I may save you from buying something that
doesn't meet your needs.
Circuit Specialists® CSI4810A Semiconductor Curve Tracer
Hantek® Model 6022BE
2 Channel USB Oscilloscope

Hantek® Model DSO5202P Digital Sampling Oscilloscope
MASTECH® Model MS8050A Bench Top True RMS DMM
MASTECH® Model MS8340A Hand Held DMM
RIGOL® Model DS1054Z 4 Channel 50 MHz Oscilloscope
SIGLENT® Model SDG810 Function Generator
SIGLENT® Model SDS2202X Digital Storage Oscilloscope

How To Do It.

Build Your Own Website with a KISS
Characterizing Transformers and Interpreting Lead Colors
Eliminating Ground Loops
What is LT Spice
And why should I care?
Learning LT Spice
It's not as hard as you may think.
LT Spice for the Blind
Yes, it is Possible.
Methods for Obtaining Scope Display of
Frequency Response of IF Transformers and Filters.
Reading Resistor and Capacitor Color Codes
Restoring Electrolytic Capacitors that Appear to be Dead.
Soldering and Unsoldering
Speaker box design and construction.
Links to Pages.
Testing Capacitors: Do You Really Know How?
Tips From Mac's Workbench

Construction Projects

When I retired in 2001 I was looking forward to building
all those things I had put off for years. I had accumulated
a closet full of parts and I was going to build things
almost for free. .

Then something called the www came along. As a result
I have spent no small amount of money buying parts that
are currently in production. My reason was to make it easy
to duplicate the project. Most people who build these items
are clever, knowledgeable, and web wise. Therefor I am
going to use the free parts I have on hand. I will give
specifications but you are on your own to find equivalent
parts. Where I have bought new parts I will give the source.

Granted, some of the projects below are silicon based.
These are test equipment and in this application, whether
we like it or not, silicon is more stable, easier to build,
smaller, lighter, and performs better, than tubes.

4 Ways to Breadboard: Only One of them is Any Good.
8 Simple Power Supplies For Your Workbench.
Audio Power Meter Has Linear Scale, is Arduino Based.
The Best Breadboard: Soldering Doesn't Take Much Longer and is More Reliable.
Filter Choke Analyzer: Test Filter Chokes Under Current Load.
An IC Socket for Tubes: Not Nearly as Good as it Seemed.
Inexpensive Line Voltage Changer
An Intermodulation Distortion Analyzer.
A Load Box for Testing Power Supplies
Low Resistance Adapter for a Digital Multimeter
Using the Low Resistance adapter to characterize Unmarked Power Transformers
Making AM IF Transformers for New Construction.
Making AM IF Transformers for Replacements in Older AM Radios.
Winding Your Own AM I F Transformers.
Modifying a Heath IG-18 Audio Generator For Ultra Low Distortion.
PLL Frequency Control For AM Band Receivers. Know Where You Are.
Power Supply & Amplifier: Complex but Very Useful.

Powering Mobile and Portable Tube Gear
by J. Ed.

Vibrator Power Supplies Part 1. Plate Voltage for Low and Medium power.
Vibrator Power Supplies Part 2. The Precursor to DC-DC Converters.
Vibrator Power Supplies Part 3. The Present and Future.

Radio and Detector Circuits.

How AM Radio Works: A Simple Description.
How FM and FM Stereo Works
Winding Coils: To Wind or to Buy. Only You Can Answer That Question.
Build a Crystal Set
Build De Forest's Audion: That's Right, You Can Build His First Version of the Audion.
Grid Leak Detector: Needs an Amplifier.
Plate Detector: Needs an Amplifier.
Infinite Impedance Detector: Needs an Amplifier.
Regenerative Detector: Needs an Amplifier.
TRF Receiver: Needs an Amplifier.
Simple Superhet Receiver: Discusses Principles of Mixing and Image Frequencies.
3-Tube Superhet: Needs an Amplifier.
4-Tube Superhet: Needs an Amplifier.
5-Tube Superhet: No Coil Winding, Complete.
Low Voltage Radio Tubes
by J. Ed.

The All American Five: Millions Were Made.

Introduction and Power Supply
The Converter
The Intermediate Frequency Amplifier
The Detector
The Audio Section
Cautions, Precautions, and Troubleshooting

Communications Receivers

Image Rejection, IF Bandwidth, and Number of conversions
Block Diagram
Construction Tips
Power Supply
Audio Amplifier
RF Amplifier and Preselector
Converters, Mixers, and Local Oscillators
IF Amplifiers and Band-pass Filters
AGC (Automatic Gain Control) and S Meter (Signal Meter)

Ham Radio Corner

This is a new feature added to Fun With Tubes. Everything
under this heading may not be tube related but an
overwhelming majority of hams long ago traded tubes for
the efficiency and feature packed rigs that only silicon
construction can provide. I hope there will be some tube
articles here in time but I'll take whatever I can get.
Receive and Transmit on separate Antennas.
Transmission Lines and Standing Wave Ratio (SWR):
A Misunderstood Concept.
Free and Low-Cost Ways for Getting on the Air.
by Dr. Ron Milliman, K8HSY.

Audio Amplifiers: How They Work

Power and Output Transformers: The Basics.
A Basic Power Supply: Found in the Newcomb D10.
A Technical Discussion of Power Supplies: Not For the Faint of Heart.
Resistance Coupled Amplifier, A Basic Building Block
Magnetic Phono Preamp: With Two Examples.
Volume and Loudness Controls;
What the manufacturers don't want you to know.
Tone Controls: From Simple to Complex.
Balance Controls: The Good, the Bad, and the Useless.
Phase Inverters, Split Load Phase Inverters, and Drivers
Push-Pull Outputs
Overall Feedback, Pros and Cons
The FTC and Amplifier Power. Caveat Emptor.

Audio Amplifier Design.

How Much Power is Enough? It Depends.
Speaker Impedance: Did you know it isn't constant?
A Low Distortion Gain Block: Gain from 6.7 to 34, THD less than 0.060%.
How Does Removing the Cathode Bypass Capacitor Affect Distortion.
An Amplifier Test Bed: Low THD Driver,
Full Metering, & Regulated G2 Voltage.
Practical Tone Controls: Passive and Active.
Preamp Design.
Considerations for the Design of Inverters and Drivers.
Phase Inverters and Drivers: The Heart of an Amplifier
The Pentode/Triode as Amplifier/Phase Inverter.
Improving the Phase Inverter.
The Wise Linearized Williamson Circuit.
Experiments with Triode Power Amplifier Circuits.
Designing an Amplifier with Feedback. A Downloadable Program Helps.
How To Design and Optimize Feedback Loops For Best Performance.
Newcomb D-10, A Tough Nut, Cracked At last.
Optimizing Feedback Loops, a different point of View. Tim E. Smith.

An Amplifier Smorgasbord: Take Your Choice.

50 Watt Monoblock Amplifier: 6L6 GC.
The 70 Volt Line Amplifier
Contest Winning Amplifier: Results of the 2012 Amplifier Contest.
An EL34 Ultra Linear 50 Watt/Channel Amplifier.
Story of the Original Koss Headphones: Leads Into the Next Project.
A Dedicated Headphone Amplifier
Tim's Second Amplifier
Triode Monoblock: 6L6 GC.
Ultra Linear Monoblock: 6L6 GC.
A Unique Circuit Circlotron Amplifier: Probably Not Worth the Complexity.

Photo Gallery

The Hotel Radio: No Longer a Mystery.
Project Pictures Sent to me by Viewers of this Page.
Schematics of Viewers' Projects.
Tour My Kilowatt AM/SSB Ham Station
Tour My Old Tube hi-fi and Stereo Systems.

Operating Instructions

Silvertone Wire Recorder/Phonograph/Radio
MaxCAD Drawing Program Instruction Manual

Restoration Projects

1937 Philco Radio: This Radio Needs a Battery Eliminator to Work.
Heathkit Power Supply: The Fault Was a Most Peculiar Tube.
Harman-Kardon A-300: A Basket Case From eBay Plays Again.
Atwater-Kent Model 20: Restoring a 93 Year Old Radio Isn't Easy.

Useful Information

Verifying My Test Equipment: Making Accurate Measurements is not Easy.
Resistors' Behavior At HF and VHF. When is a Resistor Not a Resistor?
Tube Cross-reference and Selection Guide
Catalogs of Discontinued Parts
Free Programs You Can Download
Other things you can download.
Textbook, Electronics for Non-Engineers
Textbook, Troubleshooting Techniques.
Email me

Off Topic Pages

Fun With Wood. A piggybacked Site.
The Total Solar Eclipse of 8/21/2017.
The Lawnmower House, The Teddybear Cottage, and My Woodshop.
A New Workbench and Other Revisions to my Electronics Shop.
It Isn't Finished. Work on the Electronics Shop continues.

I've Never Lost the Wonder.

As I have said elsewhere on the web I became hooked on electronics when I saw a film on what was then known as educational television which contained animation illustrating how a vacuum tube worked. Memory of the exact year has grown a bit dim but it should have been 1951 or 1952. After that I would look into the back of my radio at night and think about the processes that were going on inside those glowing tubes and a sense of awe and wonder would come over me. The smallest things in nature, as known at that time, were being controlled inside those tubes to capture music from the air and deliver it to the speaker so I could hear it. As I began to understand radio my wonder only increased. I could hear a record that was being played on a turntable more than 1000 miles away as clear as if it were being played on my own phonograph. Actually clearer because the "needle" and record were in much better condition than my own. Over the past 66+ years I still haven't lost that sense of wonder.

It is also true that I have the same feelings about electrons and holes flying around inside the tiny crystal of a transistor. Think of it, I can hold in the palm of my hand a working computer that has more power than those first vacuum tube computers that would have filled a rich man's mansion.

The whole field of electronics encompassing audio, radio and digital systems still motivates and inspires me to wire up circuits. I still feel the same when it all works. I hope to share some of it with you.

Email Tube Man.  SHA ZAM!
Everything you always wanted to know about
vacuum tubes but didn't know who to ask.

Ask Tube Man.

Would you like to tinker around with tubes but don't know what to do? Want to fix up that radio that belonged to your great-grandfather but don't know where to start? Are you experienced in working with tubes but you just came across a problem which has you stumped? Tube Man knows all and tells all. Just click on the super hero's picture to email a question to him. See questions submitted to Tube Man and his answers.

Who and What.

This web site is owned and operated, as a hobby, by Max Robinson. As time goes by I will post tutorials on the fundamentals of electricity and electronics, interesting circuits you can build with vacuum tubes and op amps, and I will share some of my experiences restoring antique radios and early electric phonographs.

I have a master's degree in electrical engineering from the University of Florida 1966. My early EE classes covered vacuum tubes so I know what I am talking about and doing. If you have any questions or suggestions feel free to email me.

If I Don't Answer...

I scrupulously answer all emails sent to me. If you send me one and you don't hear from me in a reasonable amount of time maybe something went wrong.

On a number of occasions I have received emails from people seeming to be asking legitimate questions. When I attempt to answer them I get back one of those "Mail System Error" messages saying that there is no such address or my email address has been blocked by the sender. Some anti spamming programs are quite strict and maybe you forgot to enter my address as "allowed". Check your antispam list to be sure my reply will be given to you instead of being bounced back to me.

On the other hand maybe this is someone's idea of juvenile fun. No doubt the people who have done this (you know who you are) think this is very funny. To me it's just a minor annoyance. Even though it's a small thing I could do without it. Just because you're not having fun don't spoil it for the rest of us.

Going all in with NVDA.

I have uninstalled JAWS and NVDA now starts upon boot up. If you download NVDA the first thing you will discover is that JAWS key plus 2 doesn't initiate reading. Some may become frustrated at this and give up on NVDA. The read all command is numpad 0 (JAWS key) + down arrow key (not the number 2 key.). This is an easy reach with third finger on the 0 key and first finger on the down arrow key. The middle finger just hangs there and does nothing. For some configuration tips that make NVDA better for me and possibly for you click here.

With reference to the above, NEVER SAY NEVER.

To learn more click here.

The people who run the website EE Web have
interviewed me and written a very
nice article. Here is the link.
EE Web article.

An Observation.

If I worked on radios the same way doctors worked on people whenever a capacitor, resistor, or tube, failed I would just take it out and throw it away. Yet the radio would be expected to work as well as when it was new. So far I am down my tonsils, adenoids, about one and a half feet of large intestine, and a gall bladder. My power output is down and my distortion percentage is up.

My Favorite things.

Thank you for visiting my page at Angelfire.
Please come back and visit again!

This site begun March 14, 2001

This page last updated Wednesday, November 03, 2021.