John Broskie's Guide to Tube Circuit Analysis & Design

Letters to the Editor
The Tube CAD Journal welcomes letters from its readers. Please share your views, opinions, design ideas, and critiques with us. Letters should be brief and accompanied by your name, email address (please indicate if you do not wish us to publish your letter), city and country
(it's fun to know where you are from). All letters become the property of Tube CAD Journal and will be edited for length and clarity. No one's email address will be published. If you wish to correspond with another reader, send me the email to forward on.

Before you email me...
Tube CAD Journal has a devoted readership, as many are looking for more information on tube circuits and new ideas for tube-based projects. Consequently, I receive many emails, which I greatly enjoy reading. Unfortunately, I easily fall behind in answering the email. (I used to limit myself to two hours a day for replying, as I could easily spend eight hours.) One famous tube guru whom I know and whose name everyone would recognize once grew red in the face and looked as if we was going to suffer a stroke at the mention of email. At the time, I thought he was being overly sensitive; but then, at the time, I wasn't receiving gobs of email. To make things go more smoothly for all of us, please follow the rules below.

Begin the subject line with "Tube"
Most of the email I receive is spam (about 6,000 a day). If I see an email subject line beginning with "Tube" I will not delete it, whereas no subject line or one that begins with "Hey" or "Hi" or "Want to see something great?" will be deleted.

Only one question per email
I have received emails that held ten questions. These emails more closely resemble an electrical-engineering final exam than a brief exchange. (Speaking of exams, a friend of mine, who sells tube-related products, once got email asking for explanations of his electronic product's fundamental operation. He replied and received more email asking for other un-product-related fundamental electronic explications. After several days of emailing, he grew exhausted trying to keep up with this pleading e-mailer, and he finally asked just what was going on. The answer was that the email came from the other side of the world, from a student in high school who routinely emailed his homework questions around the globe until he got all the answers he needed.)

In answering email, I perform a quick triage evaluation: Just long will it take to answer this email? If the answer is over half an hour, the email is shoved to the back of the pile and the pile can be huge. (Questions like "Can you teach me all there is to know about tube amplifiers?" although they qualify they as "one" question, are deleted on the spot.) So, please if you have three questions, send three separate emails.

No secrets
Let's suppose that you have used a NI-CAD battery in lieu of a cathode resistor or say that you used an 11k plate resistor instead of the 10k resistor I had specified. Do not email me telling me of your invention/discovery if you do not wish to share it with others.

Provide schematics
"In your circuit, what wattage should the 12k resistor be?" What circuit? Which 12k resistor? If the circuit in question is from the Tube CAD Journal or another web page, then give me the exact URL and page directions (for example, the schematic on the top of the page). If the circuit is your own creation or from a magazine or book, then scan the schematic and save the file as a GIF or JPG, not a BMP (bitmap). No schematic deserves to be 8M big.

Provide words
We are not sending telegrams to the South Pole; you are not being charged by the individual character. More detail is always welcome. Imagine that we are on the phone: How would you describe the same message with your voice instead of your keyboard. Additionally, I do not read any newsgroups or forums, so do not expect me to know what the current abbreviations are or what is the present circuit of the day ("Wild Bill's line stage" means nothing to me). If you are trying to fix a broken tube circuit, then provide all the useful information: when the circuit last worked, expected B+ voltage, actual B+ voltage, measured resistor values, measured currents.

Do not use me as a search engine
I get emails asking if there are any single-ended amplifier circuits in the Tube CAD Journal web site. Use Google ("Keyword").

Do not expect me to fight your fight
I get emails from those who are losing a battle on some forum and want me to rescue them, although the emails are seldom honest about motive. I have unknowingly replied to such email only to receive many more stating that I had posted on some site I have never heard of, such as or, that 2A3s are terrible tubes or that transconductance is the same as plate resistance Sorry, I do not read any newsgroups or post on any forums for a reason: I do not want to. Please respect this wish.

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