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Old 14th June 2004, 04:03 AM   #1
owel is offline owel  United States
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Default Need advice: Want to learn Vacuum tubes

Hello, I need some sort of push in the right direction. You see, I want to learn how to build, DIY projects that uses vacuum tubes. The folks here seems to be the experts at VT, so I'm throwing this question here.

I'v been reading the RCA receiving tube manual and looking for cheap kits... So far, the S5 amplifier seems to be the most cheapest true-tube/high voltage design out there. I might get this kit to play with.

My background: I'm not new to electronics and DIY. But all my life, I've built either discrete or IC based electronic projects. ... mostly audio stuff, preamp, mic preamp, amp, EQ, that stuff. Now, I want to venture to Vacuum tubes.

Questions:
1. When reading a VT schematic, I've come to the conclusion that you need to know the pin #s of the plate, grid, heater, etc of a particular tube model.... and this is where the RCA manual comes in handy. Right?

2. Knowing the right pin #, I can now do point-to-point wiring??? Is that right?

3. The RCA manual sometimes lists RC components for some of its design (in a table format)... but no voltage ratings (for caps) and wattage (for resistors) are given. If the B+ is say 300V, can I just use 450V rated caps, or should I go 2x at 600V? Should I use 2W for all resistors to be on the safe side?

4. How dangerous *really* are these voltages. IF you make a mistake (i.e. brushed them or touched them accidentally), would you instantly die? I mean, the amperage are very small. (Not that I'm planning on touching them, but I need confidence in this area)

5. Is it safe to poke around with an oscilloscope? Or is there some sort of adapter/protector I must use in my scope before I start poking around?

6. Typically, how much would the power transformers cost... i.e. 300V secondary, 6.3V, etc... what is the price range?

7. Any good VT books you can recommend for a total newbie like me? ...sort of equivalent to Dummies book. That's my knowledge of VT... zero. I'm more comfortable around transistors and solid states.

That's all for now. Thanks in advance!
Owel
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Old 14th June 2004, 04:08 AM   #2
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I got pretty much ashamed toady, so I would like to learn tubes as well.
Quote:
Originally posted by fdegrove

As if you'd know what to say anyway...
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Old 14th June 2004, 04:19 AM   #3
SY is offline SY  United States
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Let me try to attack a few of them:

1. The tube manual (data sheets in general) is indeed invaluable for this. It's also going to be your best friend once you start playing around with designing.

2. Yes.

3. You can generally figure out the voltage and dissipation ratings by drawing out the schematic and seeing what voltages to expect. For coupling caps, at least 1.5x the B+ voltage is a good idea. Two times is even better. 2W resistors in the plate circuits will work most of the time, but again, a few minutes with the schematic and Ohm's Law will get you the answers you seek. Grid resistors can generally be much smaller than plate resistors.

4. EXTREMELY. I wouldn't even CONSIDER working on tube circuits without experienced supervision your first few times through. Death is quite permanent, and among the ways to die, this is among the worst.

5. Subject to the caveat above, you'll want scope probes rated appropriately to the voltages you're looking at.

6. You're on your own here!

7. Assuming you've got a good grasp of Ohm's and Kirchoff's laws, I'd recommend Morgan Jones's book.
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Old 14th June 2004, 04:36 AM   #4
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Hi,

Quote:
I got pretty much ashamed toady, so I would like to learn tubes as well.
You'll be too busy with the kids/kits, Peter

OTOH...What took you so long???

Owel,

1/ A manual with tube specs, doesn't have to be RCA, is a must have especially when you want to work offline.

2/ Correct.

3/ No, here's where you'll need Ohm's law, loadlines, learn how to bias the grid of the tubes and sometimes even more complicated stuff.

4/ Very. Lethal in most cases in fact. This has been discussed extensively here, there must be a sticky thread about safety issues at the top of this page about this, I think.

5/ I'm no scope jockey. I'll leave that to the guys that do that on a daily basis, I don't.

6/ Check at vendors such as Hammond, perhaps?

7/ Is there a Tubes for Dummies? Dunno. There are some websites with the basic things you need to know though.
I'll try and post a document compiled by one of our members and post it in your thread later on.

Cheers and welcome,


EDIT: Dang, SY....you beat me to it...
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Old 14th June 2004, 06:11 AM   #5
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Hi Owel,

Welcome to a fascinating avocation, where
you can create wonderful amps (relatively)
cheaply from simple designs, and spend a
lifetime learning the subtleties.

You are in fine hands with Frank and SY,
and let me add just a couple of things:

1. An indispensible online tube reference is:
http://tdsl.duncanamps.com/tubesearch.php

4. Unfortunately, the safety thread is *not* on
this page. Here it is:
Safety Practices, General and Ultra-High Voltage
(in case the link doesn't work, it's in the Everything Else forum.

7. I started with Morgan Jone's book (Valve Amplifiers,
I'm looking at it) too, and recommend it. Excellent
as it is, it unavoidably skips over some stuff, and
I find myself collecting books (and loving it).

Check out audioXpress.com for a great selection,
and do not miss their Audio Classroom articles:
http://www.audioxpress.com/resource/audioclass/

They are an excellent introduction. If you take
your time and absorb those articles, you will
be well on your way. Besides, they're free
(one of my favorite words), and you can start
right now.

Also, check out the FAQ over at AudioAsylum.com
It's Tubes section has some links to great intros,
including how a tube works and stuff.

Welcome, be safe, and have fun.

Best,

George "I Loves Me Some Tubes" Ferguson
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Old 14th June 2004, 07:10 AM   #6
SHiFTY is offline SHiFTY  New Zealand
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I second the duncanamps.com recommendation. Download the database software and the power supply designer- incredibly useful.

As for safety, start with low voltage projects first. 250V won't kill ya, 400V still unlikely, 1000V pretty likely.

For caps use a decent margin, eg 450V caps for a 350V project.

Wattage for resistors- just find how much voltage they are dropping, divide by the resistance to get current, times the current by the voltage drop to get power dissipated. Make the resistor 50-100% bigger power rating.
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Old 14th June 2004, 07:31 AM   #7
dhaen is offline dhaen  Europe
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Quote:
250V won't kill ya,
Incorrect: 250v can easilly make you (permanently) dead.
But Shifty's sentiments are correct: The lower voltage projects are lower risk.
Brushing past high voltages is unpleasant, but you are more likely to damage yourself from the muscular reaction, that from electrocution.

**The golden rule, is to keep one hand behind your back, or in your pocket**

Such things as insulated shoe soles, and non-metalic bench, are essential for any electronic testing.

I too recommend Morgan Jones Valve Amplifier books.

Cap ratings: SY says 1.5x +B. That's correct unless a reactive load such as a choke is used, then go for 2.5x. Also, cathode bypass cap ratings should be calculated individually.

Resistor values: we often use higher wattage resistors, not for the power dissapation, but for their higher voltage rating.
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Old 14th June 2004, 09:37 AM   #8
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In addition to Jones' writings, Principles of Power by O'Connor and Basic Electronics for Scientists by Brophy are good references.

If you understand FET circuitry, you have the beginnings of understanding tubes. FETs, like tubes, are voltage controlled high impedance devices. The characteristic curves of FETs and pentodes are remarkably similar in appearance.

The warning about working with only 1 hand can't be over emphasized. Even with careful work habits, an occasional shock will occur. In the hand, a shock is UNPLEASANT. A shock across the heart can be, and frequently is, deadly.

BTW, people UNDERESTIMATE the danger of SS equipment. A 200 W. SS power amp has rail voltages > 40. Several Amperes at 40+ V. can easily burn you very badly.
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Old 14th June 2004, 12:56 PM   #9
owel is offline owel  United States
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Default Thanks!

Excellent replies. A very big thanks to all.

I've bookmarked the sites and links you've given and will start reading them. I subscribe to Audioxpress, and sometimes visit their website. I'm surprised I didn't see their free VT tutorials (their website can be confusing to navigate sometimes).

>Morgan Jones's book

What is the complete title of this book? Valve Amplifiers?


>BTW, people UNDERESTIMATE the danger of SS equipment.

Funny story, when I was 16 (many decades ago) I was trying to check how my DIY SS amp was doing, checking for heat, and with moist hands I reached in the back and put my two fingers on the case (i.e. the collectors) of the NPN and PNP power transistor. I got a SHOCK there!


I'll come back again for more questions. Thanks.
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Old 14th June 2004, 01:01 PM   #10
SY is offline SY  United States
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Quote:
What is the complete title of this book? Valve Amplifiers?
Yes.

And as a safety warning, consider this as a reminder to always keep one hand in the pocket and don't play with high voltages without supervision from an old tube guy (hams are a great source here).
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