You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

I'm pretty sure the Svetlana "4CX400" is the military "GS-36b" tube with a new brand on it. The military spec sheet says the control grid is rated for 2/10 of a Watt. Svetlana's 4CX400 spec sheet says 2 Watts, same as a 4CX250B.

Not sure who to believe. Could be the lower rating reflects a more-conservative set of rules to rate the same tube for military service? Don't know.

The control grid's gain factor is higher. You'll need to turn down the grid-bias voltage a lot to make the 4CX400 perform, compared to a '250B. And you'll need a larger chimney to fit the anode ring. Bear in mind that if you use a blower that was sufficient for a 250-Watt tube, you need more air to get the 400-Watt rating from the larger tube.

A control grid that uses a lower bias voltage has the wires closer together, as a rule. When you space them closer, you have to make the grid wires thinner, or they block the electron path to the tube's anode. Thinner grid wires tend to have a lower power rating.

Just color me skeptical.

I have some GS36b tubes I promised myself I would try to adapt, or at least learn how to use effectively.

Too many irons in the fire, never have done that. Not gonna be this week or next.

73

<blockquote data-quote="nomadradio" data-source="post: 673282" data-attributes="member: 22">I&#039;m pretty sure the Svetlana &quot;4CX400&quot; is the military &quot;GS-36b&quot; tube with a new brand on it. The military spec sheet says the control grid is rated for 2/10 of a Watt. Svetlana&#039;s 4CX400 spec sheet says 2 Watts, same as a 4CX250B. Not sure who to believe. Could be the lower rating reflects a more-conservative set of rules to rate the same tube for military service? Don&#039;t know. The control grid&#039;s gain factor is higher. You&#039;ll need to turn down the grid-bias voltage a lot to make the 4CX400 perform, compared to a &#039;250B.&nbsp; And you&#039;ll need a larger chimney to fit the anode ring. Bear in mind that if you use a blower that was sufficient for a 250-Watt tube, you need more air to get the 400-Watt rating from the larger tube. A control grid that uses a lower bias voltage has the wires closer together, as a rule. When you space them closer, you have to make the grid wires thinner, or they block the electron path to the tube&#039;s anode. Thinner grid wires tend to have a lower power rating. Just color me skeptical. I have some GS36b tubes I promised myself I would try to adapt, or at least learn how to use effectively. Too many irons in the fire, never have done that. Not gonna be this week or next. 73</blockquote>

[QUOTE="nomadradio, post: 673282, member: 22"] I'm pretty sure the Svetlana "4CX400" is the military "GS-36b" tube with a new brand on it. The military spec sheet says the control grid is rated for 2/10 of a Watt. Svetlana's 4CX400 spec sheet says 2 Watts, same as a 4CX250B. Not sure who to believe. Could be the lower rating reflects a more-conservative set of rules to rate the same tube for military service? Don't know. The control grid's gain factor is higher. You'll need to turn down the grid-bias voltage a lot to make the 4CX400 perform, compared to a '250B. And you'll need a larger chimney to fit the anode ring. Bear in mind that if you use a blower that was sufficient for a 250-Watt tube, you need more air to get the 400-Watt rating from the larger tube. A control grid that uses a lower bias voltage has the wires closer together, as a rule. When you space them closer, you have to make the grid wires thinner, or they block the electron path to the tube's anode. Thinner grid wires tend to have a lower power rating. Just color me skeptical. I have some GS36b tubes I promised myself I would try to adapt, or at least learn how to use effectively. Too many irons in the fire, never have done that. Not gonna be this week or next. 73 [/QUOTE]

Top Bottom