The Tube CAD Journal, Heater Concerns

From: "Saved by Internet Explorer 11" Subject: The Tube CAD Journal, Heater Concerns Date: Wed, 8 Apr 2015 11:38:20 -0700 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01D071F0.832F0190" X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.17609 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01D071F0.832F0190 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.tubecad.com/july2000/ =20 =20 =20 =20 =20 The Tube CAD Journal, Heater Concerns =20 =20

= =20 =20


	Circulation: =20

59072


	since=20 July 2000

Heater=20 Concerns

This=20 Issue

Subject: 6.3v or 12.6v
=20 I am well aware of the virtues of the regulated B+ be it = split rail=20 or single ended, but what about an article on a few good heater = supply=20 schemes. All this emphasis on circuit topologies and so forth and = so on is=20 useless without proper heater control and decoupling. Over heated = or under=20 heated cathodes cannot maintain the proper emission level for the = tube to=20 operate at its specified rating, especially in the preamp stage. A = fancy=20 circuit without a good heater supply scheme is like a muscle-bound = man=20 with extraordinarily skinny legs. Can you prove me=20 wrong??
Rowan

I agree wholeheartedly. Thus, this = month's=20 topic: tube heaters. We will look at both directly heated and = indirectly=20 heated tubes, current sources, and fixed regulators for the=20 heaters.
Remember, if you have a request or = suggestion of=20 your own for either an article topic or circuit explanation, = please=20 e-mail:
= =20 = =20 Editor

"I like everything about tubes, the = history, the=20 sound, the look, the glow, everything actually, except dealing = with the=20 heater." This is what a friend once told me was his view on tubes. = He=20 argued that the heater was the single=20 largest liability to the vacuum tube. He then listed hum, heat, = high=20 current demands, failure, heater-to-cathode voltage limits, and = the sonic=20 imprint imparted by the choice of heater supplies. I did not argue = with=20 him. Taking the headache out of the heater is the aim of the = following=20 topics.

Getting the Right Voltage
The heater is a low resistance length of = wire that=20 is either coiled or folded upon itself inside the cathode = structure. When=20 attached to a voltage supply it conducts enough current to heat to = a=20 glowing hot state. This is necessary to bring the cathode's = temperature up=20 to what is needed to ensure electron emission. Once this point has = been=20 achieved, however, any further voltage increase will only shorten = the=20 tube's life expectancy.
You might say: true = enough, but=20 since the heater string is usually attached to a 6.3 or 12.6 AC=20 transformer winding, what is the issue? The problem is that the = 6.3 volt=20 winding often puts out more than 6.3 volts! How is this possible? = Two=20 factors join together to increase the 6.3 to as much as 7 volts. = The first=20 is that historically wall voltages have been slowly on the rise in = the=20 United States. If you scan old schematics you will see sometimes = 110 VAC=20 or 112 VAC or 115 VAC specified. Today, 117-120 VAC is the = standard the=20 power company aims for and usually it is closer to 122 VAC or 123=20 VAC.

In This=20 Issue

1
3
5
6
7
9
10
11
=20

Heater Concerns
Free=20 DC Power Supply
Free=20 Transformers (Sort of)
Current=20 regulation for Heaters
Using=20 a 6SN7, 8SN7, or 12SN7
Directly=20 Heated Filaments
Voltage=20 regulators for the 2A3
E-mail
Publishing=20 Information
Glossary=20 of Audio Terms
Glass-Ware.com=20 Articles
Classic=20 Magazine articles
=


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	www.tubecad.com Copyright =A9 2000=20 GlassWare All Rights Reserved =

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