The Tubes



Decades of International Business Travel had me walk into Valvolandia in 2001

This one of a kind Tube Store was located in Santa Ifigenia, Sao Paulo.

I struck up a nice conversation with Toninho who graciously determined

that I knew my stuff and allowed me into the shelves to pull the Tubes

that I wanted to purchase. Indeed a unique experience that I will treasure forever.

He had treasures beyong belief. AMPEREX, TELEFUNKEN, RFT, ETC.

NOS in Boxes with the cellophane covering.


There once was a Electronics Store on Fernandez Juncos Ave. in San Juan where

I used to visit as a Teenager and drool over McIntosh and AR Speakers. They closed down

but not before calling my Business Card to inform Me that all of their Tubes were going to

the City Dump. I quickly drove over and hauled out boxes and boxes of Tubes.

This Card was among the thousands of Tubes. I thought it was a unique glimpse into

the world of Punch Cards used to manage Tube Stocks and Customer orders.

Among the Treasures were 2 sleeves of NOS Coin Base 7591 GE & Sylvania Tubes.

Also two sleeves of 5692 Black Plates (a special 6SN7). This was an amazing

Store from an age where Audio Equipment Stores were abundant.

I still have at least 3 dozen Amperex SQ E80L/6227 Pentodes waiting for Me to make

a 10 Watt Push Pull Stereo Amp. I will nickname this amp Tiny Tim, in honor of

the Man who brought the Ukelele out into the World as He "Tiptoed through the Tulips"

I regret not shooting pictures of this amazing Electronic Store.

We also had LA ELECTRONICA near my house, and they sold Tubes

until they shut down in the early 90's.

Military Tube Handbook 1963




I will add many more links as I develop them from my store of documents.

The real "Tube Masters"

Thank you Mr. Lee DeForest

Thank you Mr. John Fleming

The Vacuum Tube Pioneers.

They lit the Lamp and made possible the Amp

The NOS "Stash" in my Lynchburg Garage

From New Electronic Center, they were going to the City Dump, I rescued these Tubes

in San Juan, now when I moved up North, they came along in the Move.

An assortment of TV, Radio & Audio Tubes

I gave most of them away years ago but still kept the useful Tubes.

Among these a stash of 6227/E80L SQ Pentodes AMPEREX

PL36/25E5 for the Sansui 1000 amp and plenty

of strange but good one's used in Vintage FM Receivers 6D11, etc.

If you need some Tubes, just ask, I only ask a few bucks each

and that you cover the shipping. This is a Hobby stash, I am not

in Business, just here to help other Hobbyists.

My Tube Testers

If you want to avoid frustrations, buy a basic Tube Tester

Below my operational Tube Testers, each one does something well

as there is no "Single" Tester that does it all, that is still a myth

Even the great AMPLITREX has some quirks on 4 pin DHT's

But its minimal, considering the power of the AMPLITREX Software

The AMPLITREX is an amazing tool for people who sell tubes

I want one.... some day.... will buy if I open a Tube Business

EICO667 - Pass/Fail Tester

A reliable tester for Portable, General Purpose use

I carry this on every Tube Road Trip, especially for Hammond Organs

Power ON, do the Settings, Install Tube, wait 5 minutes, Test

The EICO 667 does not test 4 Pin 2A3 or Rectifiers :(

There is an EICO 725 Adapter that creates an EBay bidding panic

when they come up for sale.....


Some Power Tubes do not measure correctly on the Eico 667

meaning if you have a set of new Power Tubes

especially 6.3V @ 1.5 Amp Filament

on the EICO 667 they may measure ?, or slightly into REPLACE

Make sure you compare against a known good tube

don't immediately assume the tubes are bad

Lots of Vintage Tube testers exhibit some of this

Just don't throw tubes away based on one tester result

(Also capable of Dual Triode relative balance testing)

MAXI PREAMP II - Noise and Triode Balance

At the price, you just cannot find a digital tester for Preamp Tubes

I always first test for Noise, then Triode Balance

If a small signal tube is noisy, I set it aside for other applications

OTTO-1 - Matching @ 250VDC

Good for matching up to four (4) small Audio Power Tubes

Nothing else really..... Russian made

I replaced 4 burned resistors and a bridge rectifier

I got this for $75 broken

Caveat: At 250 VDC, it does not prove that Tubes are matched

It gives you a relative notion, as most Power Tubes use more than 350V on the plates

Actually matching Power Tubes requires measurement at several plate voltages

to derive a matching curve


This amazing Tube Tester was donated to

Antique Wireless Museum, New York

May future generations enjoy this classic tester where it belongs, in a Museum.

This one had a full set of Western Electric Cards, plus a new set of regular Tube cards that

I purchased. Just as well the Calibration Plug was re-created by a retired Hickok

Engineer who had the original Calibration data from the Hickok Factory.

Long live Hickok Testers, the clunk of the solenoid is just Priceless....

Duncans Amps

A must have bookmark

My reference for more than 20+ years and counting 21, 22, 23....

You cannot find a better Tube Reference Website

Since 5/8/96

Audio Power Tubes - limbic system activator

KT-88/6550 - Cavernous lows & very polite highs, trash metal crunchers, surprisingly good with Horns and Lowthers

KT-66/6L6/5881* - Layered, tonal, great for both HiFi & Guitar Amps, many nice variants, a chameleon of Tones

SPECIAL HONORABLE MENTION: 7355 TUBE (RIP) - Small 6L6 variant, brilliant design, out of production, the 7591XYZ was a great 7355 sub, until SOVTEK production ceased

KT-77/EL34/6CA7 - Midrange Guitar "screamer", with a nice leading edge, crystal clear HiFi, very nuanced, KT77 smoothest

EL-84/6BQ5 - Musically engaging, great for Classical Music, a smooth operator, vocals are crisp and clean

7591/7591A/7868/6GM5 - Sweet sound, deceivingly smooth at high power, can kill speakers, current production is Russian

7027A (RIP) - Nice Warm & Detailed Sound, used when Tubes roamed the market

8417(RIP) - Audio Power Pentode, late bloomer, akin to a V8 and Oil Price Hikes, long out of production

6F6 Metal / 6F6G Glass (Russian 6F6S Glass) - Think old Tube Car Radios, fabulous tonality, best kept DIY secret, listen here on 16 Ohm PSV-2

6V6/7408 - Lighter version of 6F6 but different sound, filaments are not as hungry as 6F6, can be bright, glassy-clear

6AQ5 (RIP) - Out of production, have a few on hand, will made a prototype amp, with plans to enjoy later

6CM6 - (RIP) also out of production, fantastic Jazz and Vocal, listen... a small 6V6, similar sound character, glassy-clear

E80L/6227 (RIP) - European 9 Pin Pentode. 10,000 hour PQ version, on my short list of Tubes to use, uncommon

2A3 - Single Ended Holography, Fine Bourbon & Single Malt Scotch, look for the Single Plate Sovtek today. NOS usually worn/used

300B - The trusted voice of DHT Class A - the golden S.E. standard - Expensive but Musical, used in Preamps as well

Special Mention RF Power Tube;

6146B - Commonly used for Radio Transmitters, seen in Audio Amplifiers, bully of the block. Easily capable of 75W in PP

Small to Medium Signal Tubes

Line Stages, Tone Controls, Phase Splitters & Buffers

ECC83/12AX7 - High-Mu, Dual Triode everyone knows something about, it is very common in Audio

ECC81/12AT7 - Medium-Mu Dual Triode, common in Guitar amps, seen less in HiFi amps (Fisher SA300)

ECC82/12AU7 - The true 9 Pin chameleon, Low-Mu, versatile, ubiquitous, handy, the toolbox of small signal tubes

12DW7/7247 - Half of a 12AX7 plus Half of a 12AU7 cool tube, (Dynaco ST35, EICO 2036)

ECC88/6DJ8/6922 - Frame Grid design, a Love/Hate HiFi reputation, I love'em Hot and Bothered (Audible Illusions)

ECC85 - Used sparingly in Audio, very sweet, much more common in German Amps (Grundig)

EF86/6267 - A small Pentode Tube, everyone needs to listen to, most never have (Mullard 5-20)

6C4 - This is half of a 12AU7, small and petite, very cute, used in Acrosound Preamp & Hammond AO-28 (RIP)

6SN7/5962 - The Bulldog of Small Signal Gain Stages, robust and musical (Cary Audio SLP-5)

6J5 - This just half of a 6SN7 (think 6C4/12AU7), killer tone, a best kept secret, out of production (RIP)

6N7 - Rare metal audio tube, Stromberg Carlson Theater Amps (Stromberg Carlson APH50)

6SL7/5961 - Less seen in amps, Cary Audio used them in the 90's (CAD SE300)

12BH7 - Robust dual triode, awesome & beefy, great driver tube (Hammond AO-28)

ECC99 - The new kid on the block, speaks with an accent, nouveau 12BH7 (JJ Electronik)

6C45P - Best kept secret for Phono Stages, used in DIY for those in-the-know (Transcendent Sound)

6N1P - More robust than a ECC88/6DJ8, great driver for DHT Triode Tubes (ShermanAudio Kismet)

7199 - Out of production tube (RIP), Pentode/Triode, Russian version hit-miss (Dynaco ST70)

6AN8 - Out of production tube (RIP), Pentode/Triode (Dynaco MK3, some Japanese Amps)

Tube Rectifiers, unsung heroes from the engine room

"An unfair reputation" when it comes to Music, Tube Rectifiers absolutely rule the tone department

Tube Rectifiers are gentle on their fellow Tubes, fairly slow turn-on, no voltage slam

GZ34/5AR4 - 5V/2A Superman of tube rectifiers, general purpose (Dynaco ST70)

GZ37 - A somewhat filament hungry 5V/2.8A variant of the GZ34, British, rare & expensive

Type 80 Globe - Paleo Rare Tube Rectifier, too much for me as well, for museums

5Z3 - Also rare, museum stuff, not for DIY, unless there is extreme nostalgia

5Y3/5Y3GT - Neutral 5V/2A, very reliable when operated within their maximum ratings, quick-on

6X4 - Lighter 6V/.6A version rectifier, mostly used in Preamps (Scott LC21)

6C4 - Small sized rectifier common in the 60's, Silvertone Guitar Amp, also Hammond Preamps

6CA4/EZ81 - Common small 6 volt rectifier, used in vintage preamps and Euro Tube equipment

5V4 - Rare now, 5V/2A sweetie, nice for medium powered amps 20 to 30w

12X4 - A 12V/0.6A version of a 6X4, same tube, different filament (Dynaco PAS)

6CA4/EZ81 - Like a 6X4, but not as popular, 1amp, think VOX (Leslie Reverb Cabinets)

5U4/5U4G - Robust Rectifier 5V/3A, tall, dark and handsome (US Navy)

5R4GY - That Sexy glass bottle, 5V/3A often seen with Brown Shorts (JAN)

5R4WGB - Potato Masher Rectifier, totally ready for Dinner and Battle (Military Grade)

6AX5/6X5GT - Popular 50's-60's 5V rectifier, similar to 5Y3 in ratings, 5V/0.6A from the 50's

274B - Western Electric, high end tube, available today, must be nice, Expensive as F, $$$

Tube Datasheets

I will now walk through a Tube Datasheet to explain how to pick out the essential electrical

characteristics of the Tube, and correlate these to the DC operating point to check if the Tube is operating

in the Safe Zone. It is with this information how you can do a check for "Power Tube Hypertension".

I will also look at a 12AX7 tube as well so it becomes clear that both Power and Small Signal tubes share

a common electrical situation, despite their different 'roles' in the amplification, gain stages and output stages.




An EICO 667 is a great "Pass/Fail" Tube Tester.

Albeit, with some limitations, as it will not test for Noise.

Portable EICO 667

Yes, other Testers abound, but this EICO is simple, easy to use and

does not have a single Tube inside. Be careful when buying Tube Testers

online, make sure they come with a return clause. It is not the Testers You should worry about.

It is the Person selling the Tester, read carefully.

The prices on EBay are beyond reason, the name EBay should be changed to SPeculay.

Spending good money on an old Classic Tube Testers is better spent

on a modern Digital Tester. Tube TV's and Tube based Testers are always hit and miss

Most of the Time, a huge miss.

Meter needles wobble, some Tubes that are perfectly fine, measure poorly.

Do not expect any type of real calibration accuracy on old Tube testers.

If a Tube Buzzes in your amp, no old tester can test for Noise.

Unless they are highly modified, and the Techs who did this are

now almost if not all deceased.

Old Tube testers are really just pass/fail.

Even the fancy old Hickok Cardmatics and the Kilobuck EBay listings

that test each tube with Cards for identical settings

their calibration is almost as frustrating

as setting keeping an old Engine in proper Timing

with a wobbly, worn out Distributor shaft and Points Cam.

The MaxiPreamp II

Here we have a marvelous compact, Portable Digital Tube tester with optional adapters

and none of the hassles, this is the Rock Star of Preamp Tube testers.

This one is 100% mine, and I do not lend it out to anyone.

I cannot recommend any other Digital tester as I have not evaluated them.

Every single thing I say, describe and document is real, not invented, not an opinion.

There is a saying in Spanish, that talks about People

who lend out precious equipment to unappreciative friends/strangers;

"No se sabe quien es mas pendejo, el que presta, o el que devuelve"

The only reason my 1995 Toshiba HI-8 Video Camera still works flawlessly,

I never lent it out to anyone, not even my Cousin.

buying tubes online - A REALITY check

After unboxing your expensive purchase of NOS/Used/New Tubes

Always visually inspect and test them before using or putting them in your stash.

Tubes are just like a dozen Eggs

If You don't open the Box at the Grocery Store,

You never will know the truth until Breakfast time.

Here are some of the pitfalls of not opening Tubes and placing untested Tubes on your Shelf

or in Your Amplifier. Yes those brand new $420 Quad of Tested 6550's can damage your Amp.

Signs of trouble....

Tubes that do not deflect the Tube Tester Merit test (D'Arsonval Meter) - DOA, send them back.

 Tubes that do not light-up - Open filament, DOA send them back.

Tubes with loose Bases, not good - Send them back

Little pieces that fall out of the Tube Box - Investigate that, look carefully.

Tubes with a Milky White Top or Side Getter - DOA, send them back

Brand new Power Tubes that go Cherry Red in a known good Amp - Defective, send them back

When testing any Tube

Sometimes, non measuring Tube needs a slight jiggle/move on the Tube Tester, it may wake them up.

Metric Tube Pins can clash with Classic US Sockets.

Euro/Russian/Chinese pins can also be thinner/thicker, be careful when forcing a Tube into any Socket.

I have noticed a few 1/4" Guitar Cables, brand new as intermittent

this is likely that the O.D. (outside diameter) of the 1/4 Plug is off causing

intermittent operation of the Guitar Shield, usually the Tip is pressure connected in the Socket.

Sometimes, Tube Pins do not make sufficient electrical contact with a Socket.

Do not move Tubes around on a live amplifier

circuit that is connected to a Speaker, bad idea.

If you want to risk this test, move the Master Volume to Zero

 Mute your Audio system.

It is never good practice to use your Tube Amp as a Tube Tester.
Also I see some people on YouTube, tapping tubes with a pencil eraser


Likely, they are like a Monkey, who sees and does.

NEVER Tap a Tube in a Live Amplifier.

I would never Pet a Tiger through a Cage in a Zoo, NEVER.

If you do stupid, stupid does to you.

Just isolate your Tube equipment from physical vibrations.

There are plenty of great products for this purpose.

All Tubes make horrible noises when tapped in a live Audio amplification Stage.

Tapping Tubes is like the Roof Snow that falls on You, as you slam your front door.

The internet is full of good hacks, tapping tubes is not a good hack.

I have special mention to any EF86 Miniature Pentode, to the guy on

YouTube who taps them, is only warning us about His Channel.

Just like the cranky old Ham, who says not to worry about VSWR.

He says High VSWR does not harm the Finals?

Is this genius an RF prophet with a breakthrough discovery; No.

An Engineering Degree and/or a Self-Taught Elon Musk are similar.

How many Elon Musk's are out there - One.

How many EE's with Degrees, could not explain a Power Supply - Too many.

Well meaning, in his legendary mind, Yes He believes He is a genius.

These YouTube's claim RF Antenna Tuners will optimize any Antenna?

I don't think they knows about

Smith Charts

Reactive Components

 Impedance, Admittance, Susceptance

Maybe heard of Resistance, but cannot calculate Ohms Law.

How about Phasors?

Symmetrical Components?

Vectors, Scalars?

Sine, Cosine, Tangent?

Hyperbolic of the above?

Diff Eq., Calculus, Tensor Analysis?

STEM degrees are no laughing matter, I suffered through mine.

 Student Loans for a STEM degrees are perfectly justified.

Taking out a Student Loan for Classic Greek Literature or Cooking, is not a good product vs. value ratio

Charlatans abound, and some even speak Tax Free on Podiums

Others speak with a Holy Books in their hands, and Tax Free blood money in their accounts.

When Flood Victims knocked on Joel Osteen's Church, He turned them away.


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