Hi Gabriel
I have done this myself in a pair of monoblocks. Each required half a triode, so I wired one monoblock to use one half (pin 1, 2, 3 and according heater) and the other to use the other half (pin 6, 7, 8 and acoording heater). When they are tired I can swap them between amps, so that the other half will be used!.
Erik
I have done this myself in a pair of monoblocks. Each required half a triode, so I wired one monoblock to use one half (pin 1, 2, 3 and according heater) and the other to use the other half (pin 6, 7, 8 and acoording heater). When they are tired I can swap them between amps, so that the other half will be used!.
Erik
Because the two sections together draw twice the current for the same grid voltage is is said that the effective GM doubles. On many tubes the noise is reduced.
Since the two sections are never completely matched the current sharing between the two sections will not be exactly the same, and may change over the operating range of the tube. This can cause the "loss of definition" that some users talk about.
i've been busy the past few days so i was able to browse the net just now. thanks guys for the reply.
does this mean that i may not have to wire the other half (of the dual triode) at all? also, am i right that by doing so my main transformer will be less stressed because of less current required by the half triode operation?
ErikdeBest said:
does this mean that i may not have to wire the other half (of the dual triode) at all? also, am i right that by doing so my main transformer will be less stressed because of less current required by the half triode operation?
Or, if you're keen, you can apply an antiphase version of the signal to the other triode (like that phase splitter I can't think of the name of). The other triode will be a dead end, byt your current's will balance and your transformer will hardly notice they are there.gabriel611 said:
Edit: paraphase.
If this interests you, it occurs to me that there is an easier way yet. Simply cascade into a cathode follower. You can use the cathode follower, making it your new output, or ignore it and leave its ouput alone. These two stages could share the one supply rail.
If your existing stage is (A) and the spare is (B). If you have your plate(A) sitting at around half of B+, simply connect anode(B) to B+, cathode(B) to a resistor of the same size as plate(A) resistor, and the other side of the resistor to ground. Connect grid(B) to plate(A).
Naturally, as one goes up, one goes down, and there is zero net current change in the stage.
If your existing stage is (A) and the spare is (B). If you have your plate(A) sitting at around half of B+, simply connect anode(B) to B+, cathode(B) to a resistor of the same size as plate(A) resistor, and the other side of the resistor to ground. Connect grid(B) to plate(A).
Naturally, as one goes up, one goes down, and there is zero net current change in the stage.
Bump!
I was looking for a thread to add this to.
I am testing a 6N1P dual triode for THD and noise, but am only working with one triode in it. At one time I was using the second triode as a cathode follower, but changed to using a FET so that when I switch to a 6N2P, 6N3P, etc I don't change the characteristics of the cathode follower.
Any way, I left the second triode anode floating. This evening I decided it was a bad idea for cathode poisoning if nothing else and connected the plate to B+ thorugh a 47K resistor, grid to gnd with a 1M, and red LED in cathode ckt. I noticed an improvement in S/N of the triode under test, and a slight reduction in THD (I'm measuring in the 0.05%thd range.).
Has anyone seen this before?
I don't have time tonight to try just grounding all three terminals but will try to remember to do that tomorrow night for comparison.
I was looking for a thread to add this to.
I am testing a 6N1P dual triode for THD and noise, but am only working with one triode in it. At one time I was using the second triode as a cathode follower, but changed to using a FET so that when I switch to a 6N2P, 6N3P, etc I don't change the characteristics of the cathode follower.
Any way, I left the second triode anode floating. This evening I decided it was a bad idea for cathode poisoning if nothing else and connected the plate to B+ thorugh a 47K resistor, grid to gnd with a 1M, and red LED in cathode ckt. I noticed an improvement in S/N of the triode under test, and a slight reduction in THD (I'm measuring in the 0.05%thd range.).
Has anyone seen this before?
I don't have time tonight to try just grounding all three terminals but will try to remember to do that tomorrow night for comparison.
SUMMARY:
Parallel identical triodes:
Mu stays the same
rp is halved
gm doubles
and noise reduces by root 2
Using just 1/2 of a dual triode, then wire cathode,grid and anode to 0V.Heater handling depends upon the particular dual triode.
The 12A_7 series tubes can usually be wired such that ONLY the heater for the used triode is functional.
That will typically save 6.3V x 150mA = 0.945 Watts draw from the power tranny BUT possibly more importantly it may prevent cathode poisoning of the unused triode.
Cheers,
Ian
Parallel identical triodes:
Mu stays the same
rp is halved
gm doubles
and noise reduces by root 2
Using just 1/2 of a dual triode, then wire cathode,grid and anode to 0V.Heater handling depends upon the particular dual triode.
The 12A_7 series tubes can usually be wired such that ONLY the heater for the used triode is functional.
That will typically save 6.3V x 150mA = 0.945 Watts draw from the power tranny BUT possibly more importantly it may prevent cathode poisoning of the unused triode.
Cheers,
Ian
A cascode uses the upper grouded grid tube as the load for the lower grounded cathode tube. Its properties are similar to a pentode, including include high gain and high OP impedance (but without the partition noise).
A cathode-coupled arrangement doesn't have these characteristics. It has gain about half that of a single grounded cathode stage and medium OP impedance.
A cathode-coupled arrangement doesn't have these characteristics. It has gain about half that of a single grounded cathode stage and medium OP impedance.
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