6cg7 instead of 12bh7

[pro_crip]

I noticed that in the schematic that a 6cg7 is used for the shunt regulator instead of the 12bh7 called for in the instructions. Can I go ahead and use the 6cg7 instead, and if I do what sort of changes, if any, would need to be made? Thanks for listening.


Rich

[Paul Joppa]

The heater power connection is different. Otherwise, it was designed to work with either tube.

However, the Eros shunt regulator dissipates 2.25 watts per plate, the 6CG7 is rated 2.5 watts maximum, vs. 3.5 watts for the 12BH7. I would expect a 12BH7 to last approximately twice as long.

[pro_crip]

Thanks Mr. Joppa, can I ask 2 more related questions then? One is on the heater change, also valid for my 6cg7 conversion on the FP3. Would I just connect the red lead from the STP to terminal 4 on the tube socket and the black lead to terminal 5 on the socket. That 9 terminal is connected to the electrostatic shield between the two sections, would attaching that to ground help in lowering noise? Sorry, this is turning into 3 questions. Is there a way to raise the plate dissipation max of the shunt regulator, maybe even stick in a muffin fan, or do I just live with the shorter life. Finally, I swear, is there enough of a performance gain to go through the bother? Thanks for helping to educate a brother.

Rich

[Doc B.]

FWIW I like the sound of the 12BH7 better.

[Paul Joppa]

Thanks Mr. Joppa, can I ask 2 more related questions then? One is on the heater change, also valid for my 6cg7 conversion on the FP3. Would I just connect the red lead from the STP to terminal 4 on the tube socket and the black lead to terminal 5 on the socket. That 9 terminal is connected to the electrostatic shield between the two sections, would attaching that to ground help in lowering noise? Sorry, this is turning into 3 questions. Is there a way to raise the plate dissipation max of the shunt regulator, maybe even stick in a muffin fan, or do I just live with the shorter life. Finally, I swear, is there enough of a performance gain to go through the bother? Thanks for helping to educate a brother.

Rich

Your understanding of the heater wiring is correct.

Grounding the shield is always good practice, but it does more to reduce crosstalk than noise. In a regulator, crosstalk is not a big issue since there is no signal voltage in that tube.

There are ways to cool tubes, including PEARL tube coolers and IEC tube shields; it's not clear how effective they are in terms of extending the life of a tube. The easy way is to replace a 6CG7 with a 6SN7-GTB which has a higher rated dissipation.

Doc B has already answered the performance question.

[pro_crip]

12bh7 it is then. Does brand really matter in a regulator position?

Rich

[Doc B.]

I have an interesting story to share, though not strictly about 12BH7s. We have been doing some development on a new circuit that uses a 5687 as the tube element in a hybrid shunt regulator. Yesterday we changed the tube from a Sylvania 5687 of unknown pedigree to an Amperex PQ series 7119. The improvement was not subtle. I will file this under the same "I don't know why, I just know it sounds better" category as the new power cord.