Author Topic: EL84/6BQ5 consequences of repurposing pin1 "spare" socket-pin position  (Read 369 times)

Offline marantz123

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Some manufacturers of the EL84/6BQ5 tube have bridged pin 1 to G1 (pin 2) internally. The likes of Matsushita is one of them. (I assume Mullard is another ?). There are other manufacturers who have not practiced this and left pin 1 "spare/disconnected" internally. Such an example is the  Russian 6N14P and JJ.  Effectively this results in G1(pin 2) being shorted to pin 1 or not. I have had a look at some tubes through a magnifying glass, hence leading to this post.

There is some known practice where amplifier builders tend to take advantage of "spare" pin positions on a tube socket, using these points as termination points for eg. a grid stopper resistor. This wouldn't pose a problem for a tube where pin1 is not connected to pin 2 internally, however if a tube of the internally shorted type (pins 1 & 2) is placed in a socket where the pin 1 socket position has been purposed as a termination point, can the tube be damaged if run under these circumstances ? (Discuss for 15 marks).

As an example..(to satisfy my curiosity) I have tried to get a look at the Dynaco SCA35 wiring diagram as a reference to the track layout on the power tube board wrt this however I'm not much closer to finding out how pins 1 and 2 are configured there..maybe someone here knows.. (possibly not the ideal example to look at ..but lets see.)

I did find some references about this subject on the web however its noisy without informed experiences.

As a side note, on close inspection of the 6N14P-EV, its remarkably well built mil spec, with double layer mica wafers, better internal support, thicker wire bonds and a thicker glass envelope compared to another manufacturers product I looked at.

« Last Edit: June 10, 2021, 01:59:21 PM by marantz123 »

Offline Mars

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I have also wondered about this aspect and decided to leave pin 1 open on projects, and only use pin 2.
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Offline Steerpike

Original data sheets usually designate such pins as " I c" (= internal connection), which means it may or may not be attached to anything, but should not be regarded as floating and not available for tag-strip use.

Offline Ampdog

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As above!
Also often pertains to pin 1 on an octal socket for the likes of American power valves.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)