6072 in Parallel Dual Triode Mode

[JessJackson]

I've seen a couple mics use both side of the 6072 tube in parallel with a 200k plate resistor and 12.7v on the heater.

What benefit would this give? A friend informed me it helps lower noise and increased gain.

Cheers.

J

 

[Matt Nolan]

It reduces noise overall. It actually reduces stage gain a little in a condenser mic as the Miller Capacitance goes up, but it does lower the plate resistance so, potentially, you can use a lower ratio output transformer and thus get your gain increase.

 

[JessJackson]

It reduces noise overall. It actually reduces stage gain a little in a condenser mic as the Miller Capacitance goes up, but it does lower the plate resistance so, potentially, you can use a lower ratio output transformer and thus get your gain increase.

Thanks Interesting,

I like how Adele vocals are captured which got me researching the rode classic ii.

So in theory we could use nice 6:1 output tx with a 200k plate resistor. I'm gonna try it in a elam build with a utc 24 transformer and see how it differs. Would you keep the B+ at 110 or would that need doubling like the rode.

J

 

[TLRT]

I have here a C12VR which has this configuration, when made tests against my clones,almost everybody preferred the clones with Tim Campbell capsules. The real advantage is that you don't need expensive tubes, the C12VR can go easily with a "standard" TAD selected tube (JJ or EHX,which are not so good in the single anode-follower circuit)

 

[JessJackson]

I have here a C12VR which has this configuration, when made tests against my clones,almost everybody preferred the clones with Tim Campbell capsules. The real advantage is that you don't need expensive tubes, the C12VR can go easily with a "standard" TAD selected tube (JJ or EHX,which are not so good in the single anode-follower circuit)

The C12 vr isn't a C12 and not worth comparing to any half decent microphone to be honest with you mate. The only nice thing about that mic is the Bodywork.

I took a look at that schematic. It looks like the default for this mic is single triode mode unless you reconfigure the internal switch to utilise the other size of the tube (+10db)

The Rode classic is a pure and simple parallel circuit, literally bridging the tube pins with no circuit between.

Cheers.

J

 

[OPR]

The lucas Cs1 also  runs a tube similar to the 6072a in Parallel .. it also has a Haun CK12 style capsule  and is a pretty amazing sounding mic!! I have a very lucky neighbor who owns one.

 

[JessJackson]

The lucas Cs1 also  runs a tube similar to the 6072a in Parallel .. it also has a Haun CK12 style capsule  and is a pretty amazing sounding mic!! I have a very lucky neighbor who owns one.

hmm interesting... the rode also uses ck12 type capsule.

 

[Matt Nolan]

So in theory we could use nice 6:1 output tx with a 200k plate resistor.

No. I wouldn't go so low with the transformer ratio. You can come down by root 2, not by 2.

 

[Banzai]

Never understood why the C12VR gets this much hate... Only around $2K s/h for a monster of a mic.

 

[Bowie]

Never understood why the C12VR gets this much hate... Only around $2K s/h for a monster of a mic.

Though they're much more than that these days (at least, in the States), I think it can be a wonderful mic in the right applications.  I remember picking one above vintage U67s, a 47, and several other classic mics on a certain female pop vocal I was tracking.  It's not exactly a C12, and yes it's quite expensive, but I do think it's a nice sounding mic that seems to have been made for pop vox.

 

[JessJackson]

So in theory we could use nice 6:1 output tx with a 200k plate resistor.

No. I wouldn't go so low with the transformer ratio. You can come down by root 2, not by 2.

Why, can you explain Matt.

So 8.4 : 1? I don't even know a tx thats at this ratio

 

[Matt Nolan]

So in theory we could use nice 6:1 output tx with a 200k plate resistor.

No. I wouldn't go so low with the transformer ratio. You can come down by root 2, not by 2.

Why, can you explain Matt.

So 8.4 : 1? I don't even know a tx thats at this ratio

You have halved the output impedance of the triode stage (more or less). Transformer impedance ratio is turns ratio squared.

With a single side of a 6072, biased for mic head-amp operation, the output impedance is around 20kOhm. You want the output impedance of the mic to look like 150 ohms or so. Square root (20k / 150) = 11.5 so 12:1 transformer or similar.

With a parallel 6072, output impedance is around 10kOhm. Square root (10k / 150) = 8.2.

There are all sorts of transformers with a ratio around 8. Cinemag and Sowter to name but two brands. AMI too, I think.

 

[granger.frederic]

about noise improvement : 20*log (n^0.5) where n is the number of paralleled devices
don't expect more than 3 db !
on the other side, the added miller capacitance causes a noise increase and other issues !
in theory you should bias the two halves independently
you can expect a higher distortion as well,  and higher microphonic noises

i'm still not a big fan with paralleled tubes in headamp mics...

in a C12VR the tube is paralleled only when the internal switch is activated

 

[Matt Nolan]

in a C12VR the tube is paralleled only when the internal switch is activated

Not quite. A whole second triode gain stage is added when the switch is activated, not a parallel triode.

I agree though that the sonic gains are questionable from paralleling up the triodes. Sometimes it can help though. Case by case listening needed.

 

[granger.frederic]

yes !  your right for the C12VR , it's just a second stage ...
my memory was faultly !

 

[JessJackson]

in a C12VR the tube is paralleled only when the internal switch is activated

Not quite. A whole second triode gain stage is added when the switch is activated, not a parallel triode.

I agree though that the sonic gains are questionable from paralleling up the triodes. Sometimes it can help though. Case by case listening needed.

I think the question i was trying to ask would be more in line with are there any sonic differences. Noise floor and specs aside, is there any kind of sonic benefit to this.

When I listen to Adele vocals recorded with this circuit, they have more of a u47 sound than a elam / c12 sound, bare in mind the rhode is utilising the same capsule and tube.  By them using a 610 > 1176 and in combination with the plugin chain loans itself to a lesser hyped and mids richer sound.

Jess

 

[Tim Campbell]

Jesse, the Røde capsule really isn't a CK12 type. It's an edge terminated K67 type.
The original CK12 capsules built within the first year can have a more K47 midrange than later versions.
I had 2 Siemens SM204's in for repair. They were among the first 50 C12's made. They had Henry Radio transformers
and sounded like a blend between a C12 and U47.

 

[JessJackson]

Jesse, the Røde capsule really isn't a CK12 type. It's an edge terminated K67 type.
The original CK12 capsules built within the first year can have a more K47 midrange than later versions.
I had 2 Siemens SM204's in for repair. They were among the first 50 C12's made. They had Henry Radio transformers
and sounded like a blend between a C12 and U47.

Hi Mate, hope your well,

Thats interesting, so its basically a ck12 with k67 backplate holes? it would be interesting to see what sonic difference this has over against center terminated k67.

Also interesting about the Henry Radio Transformer, was it the same ratio as a t14?,  the Røde utilises a custom Jensen.

These capsule images are published on Rødes website for the NT1, Loving the patented Lyre technology mount from Rycote by the way. I assume its the same capsule in the classic II

And the attached image from the Classic II Booklet

Jess

 

[JessJackson]

for interest