I've used 2 of these in series in humbucker arrangement for DHTs like 26 and 01A. I no longer use these tubes, more like medium size drivers with 16mA current.
Spec is 8mA, 150H, 3700R.
So before I build up something with two of these in parallel, how is it likely they'll function? I should get 16mA, 1850R, 75H. But what of the doubled capacitance? I don't have measuring equipment to check the frequency response, so can somebody hazard a guess at the results - maybe a loss of treble?
Spec is 8mA, 150H, 3700R.
So before I build up something with two of these in parallel, how is it likely they'll function? I should get 16mA, 1850R, 75H. But what of the doubled capacitance? I don't have measuring equipment to check the frequency response, so can somebody hazard a guess at the results - maybe a loss of treble?
First of all, it is not double the capacitance, it is 4 X the capacitance.
C1 = C2
C1 in series with C2, C total = 1/2 x C1
C1 in parallel with C2, C total = 2 x C1
1:4 ratio
Consider the rp of the 26 and of the 01A.
What high frequency response did you get with 2 chokes in series?
Was it good enough?
The rp of the new tube type you select is going to have to be only 1/4 of the rp of the 26 or 01A.
And if slewing the capacitance is an issue, you need to stand 4 times the current in the new tube you select, versus the current you stood in the 26 or 01A.
C1 = C2
C1 in series with C2, C total = 1/2 x C1
C1 in parallel with C2, C total = 2 x C1
1:4 ratio
Consider the rp of the 26 and of the 01A.
What high frequency response did you get with 2 chokes in series?
Was it good enough?
The rp of the new tube type you select is going to have to be only 1/4 of the rp of the 26 or 01A.
And if slewing the capacitance is an issue, you need to stand 4 times the current in the new tube you select, versus the current you stood in the 26 or 01A.
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Yes, thanks for that. I was meaning twice the capacitance over a single choke, but I take your point. I should really hook the things up and listen. I just want an idea in advance of what the increased capacitance would affect.
75H anode choke is only usable for -medium- low output impedance (2-3k) tubes.
156C winding capacitance is enough low (if I remember correctly 30pF), so doubling it doesn't significantly affect HF behaviour.
156C winding capacitance is enough low (if I remember correctly 30pF), so doubling it doesn't significantly affect HF behaviour.
Ah, thanks. Very helpful. What I have in mind is tubes around 2-3k as you say. May work OK. I have a few of these chokes doing nothing.
Try (anti parallel connected) chokes with triode connected D3a, C3g or lower output impedance tubes (12B4a, 6N30P, 6C45P) or trioded 4P1L at lower anode current.
That's more or less my ballpark. Tubes like 6V6, KT61 etc in triode. Medium power pentodes/tetrodes around mu=10-20. I like these sorts of tubes. Some of them sound excellent. 4P1L doesn't really like less than 25-30mA. Sound gets a bit thin.
By anti parallel what do you mean? Like a hum bucker - back to back and connected in opposite ways?
By anti parallel what do you mean? Like a hum bucker - back to back and connected in opposite ways?
Thanks for that, interesting. I really should build a Salas reg.
I don't have any 76 - sold them all. This is for a driver for 300b. Something like a KT61, EL41.
I don't have any 76 - sold them all. This is for a driver for 300b. Something like a KT61, EL41.
euro21,
Unless you magnetically couple 2 chokes, there is no such thing as an Anti-Parallel connection.
It is either parallel, or series, when there is no magnetic coupling between them.
Right?
If you connect pin 1 on the first choke to pin 2 on the second choke,
and then connect pin 2 on the first choke to pin 1 on the second choke, Then . . .
You will have connected one chokes start of winding that is on the laminations,
to the outer windings on the other choke.
Now, let's ground both sets of laminations.
That will reduce the capacitance to ground of the parallel pair by about half (only one choke's inner winding to the laminations to ground).
That is all that "anti-parallel" connection will do (again, unless the chokes are magnetically coupled).
Hints:
The inductance of a choke is non directional.
The capacitance of the choke's 2 winding ends to the laminations are not equal to each other.
Right?
Unless you magnetically couple 2 chokes, there is no such thing as an Anti-Parallel connection.
It is either parallel, or series, when there is no magnetic coupling between them.
Right?
If you connect pin 1 on the first choke to pin 2 on the second choke,
and then connect pin 2 on the first choke to pin 1 on the second choke, Then . . .
You will have connected one chokes start of winding that is on the laminations,
to the outer windings on the other choke.
Now, let's ground both sets of laminations.
That will reduce the capacitance to ground of the parallel pair by about half (only one choke's inner winding to the laminations to ground).
That is all that "anti-parallel" connection will do (again, unless the chokes are magnetically coupled).
Hints:
The inductance of a choke is non directional.
The capacitance of the choke's 2 winding ends to the laminations are not equal to each other.
Right?
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"Right?"
No.
You completely misunderstood the problem.
Andy want to use two -individual- open frame choke paralleled as plate choke.
No magnetic coupling, no capacitance problems.
Even using only one open frame choke is a nightmare (hum, radiated electrical noises, EMC/EMI etc.), paralleling its doubling this problems.
The anti parallel connection reduces this anomalies.
BTW I never grounded plate choke's frame, installed its isolated.
No.
You completely misunderstood the problem.
Andy want to use two -individual- open frame choke paralleled as plate choke.
No magnetic coupling, no capacitance problems.
Even using only one open frame choke is a nightmare (hum, radiated electrical noises, EMC/EMI etc.), paralleling its doubling this problems.
The anti parallel connection reduces this anomalies.
BTW I never grounded plate choke's frame, installed its isolated.
euro21,
You are correct, I missed this important point (a reason for anti-parallel).
Anti Parallel will reduce external magnetic fields from interfering with the signal.
But
The distributed capacitance across the windings will be 2x that of a single choke.
Xc is 2X the Xc of just one choke. More loading of the plate at high frequencies.
And
The inductance of the pair of antiparallel chokes is 1/2 the inductance of a single choke.
Xl of the pair is 1/2 of just one choke. More loading of the plate at low frequencies.
If you are going to insulate any magnetic part, choke, power transformer, output transformer from the chassis (with the laminations not grounded), then be sure to enclose them under a cover. Sometimes windings short to the laminations.
Example: I had a brand new, unused, very well known output transformer that had one end of the primary shorted to the laminations.
Kids like to touch things. Wow.
And, Prevent Surviving Spouse Syndrome.
Safety First!
You are correct, I missed this important point (a reason for anti-parallel).
Anti Parallel will reduce external magnetic fields from interfering with the signal.
But
The distributed capacitance across the windings will be 2x that of a single choke.
Xc is 2X the Xc of just one choke. More loading of the plate at high frequencies.
And
The inductance of the pair of antiparallel chokes is 1/2 the inductance of a single choke.
Xl of the pair is 1/2 of just one choke. More loading of the plate at low frequencies.
If you are going to insulate any magnetic part, choke, power transformer, output transformer from the chassis (with the laminations not grounded), then be sure to enclose them under a cover. Sometimes windings short to the laminations.
Example: I had a brand new, unused, very well known output transformer that had one end of the primary shorted to the laminations.
Kids like to touch things. Wow.
And, Prevent Surviving Spouse Syndrome.
Safety First!
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