[R-390] Tube Class 101 for 3TF7 substitutions

Fri, 18 Jul 2003 09:06:30 EDT

Since Phil ran across a 3TF4 in his R390A recently, I thought this "oldie"=20
from the archives would still be relevant.

Les Locklear

From: [email protected]
Date: Thu, 13 Apr 2000 18:39:42 EDT
Subject: [R-390] Tube Class 101 for 3TF7 substitutions
Message-ID: <[email protected]>

To the group,

Concerning the replacement of the 3TF7 with the 3TF4.

1. ballast tubes have two ratings, a voltage range where current regulation=20
takes place, and the regulated voltage.

=A0 3TF7 8.6 - 16.6 volts 200 - 300 milliamps
=A0=20
=A0 3TF4 4.3 - 8.3 volts=A0=A0 280 - 320 milliamps.

2. If you substitute a 3TF4, it will be operated beyond its recommended=20
operating voltage rating. and the two filaments it regulates will operate=20
beyond their recommended or maximum voltage ratings.

3. Sure it will work, but rather than replacing a 3TF7 with an improper tube=
,=20

sub one of the resistor or other mods.

Just my 3 cents worth.

Les Locklear

--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---