Rode NTK with NOS Telefunken 6922. Where to get tube in US?

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Category 5

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First question is, has anyone tried replacing the Sovtek 6922 with a Telefunken CCa in the Rode NTK? Concensus says that the NTK's circuit is plenty good for the capsule, and overall about as good as one would need. However, I think an $11.00 Sovtek tube is hardly ideal.

I thought the overall best replacement would be a Telefunken or Siemens NOS 6922 type. What kind of performance improvement is logical to expect?

Also, where in the heck can I get NOS telefunken CCa tubes in the US? I can't seem to find them anywhere (except ebay which is shady to me). I would only need one. Anyone got a spare?

Thanks!
Shane
 
Man, you can't swing a cat without hitting a carton of 6DJ8s. They're not hard to find. They're the number one tube choice of the audiophile crowd.

Oh, and the first person who suggests cannibalizing them from old Tek scopes will be shot.
 
Have you heard or do you own a ntk?

Concensus? what Concensus? about the microphone don't believe the stuff you read on the web about a microphone untill you test it yourself.

A frame grid tube might not be the best for a microphone circuit.

That said, the specs lead me to believe it is a charge amp circuit for the tube section, that type of circuit uses feedback and the use of a tube in that can be a marketing device IMO it might sound the same with a FET. I don't think changing a tube will make much of a difference from my experiment with other microphones using charge amp circuits.

IMO some of the web reviews of microphones make me wonder if people even turned them on or have heard a good microphone. The more I learn and do the less impressed I am with alot of microphones.

A NTK might be a good microphone I don't own one and have not tested one.
 
I have a couple NTK's

I just got finished with this project. when doing the vocal I put up an NTK and an AT4050. The 4050 beat out the NTK hands down. The NTK sounded thin compared to the 4050. This is just on vocals but I bet the circuitry could be improved on. maybe the capsule isn't as good. I don't know.

I've been thinking about trying to reverse the NTK circuit for some time but I just have not got around to it.

I to have heard that the circuit is good for the capsule, but I don't know where.

I sure this will sort it self out pretty soon.

EDIT:

that said the NTK is pretty prime for modding. Its has alot of room and I would assume a high voltage power supply...
 
Bluebird

Could you take some pictures of both sides of the board in the NTK maybe I could spot some parts for upgrades. If I was to change the tube I might try rewiring the heater pins and using a 6072A/12ay7. If only 1/2 of the tube is used maybe rewire it for an EF86.

FWIW I have a nt1000 I bought because of web reviews(you live you learn) it was too edgy stock, when I changed a few caps it became usable IMO.

I do like the body grill design of the NTK and it LOOKS like it uses a 797 audio built capsule.
 
I had an NTK and sold it. The Nady TCM-1050 sounded a LOT better to my ears. The NTK had a really grainy sound.

I don't have any supermics to compare it to, though, so that's just my observation based on comparing the lower end tube mics.
 
[quote author="Gus"]Bluebird

I do like the body grill design of the NTK and it LOOKS like it uses a 797 audio built capsule.[/quote]

The NTK uses a capswule made in Australia by RODE. THe NT-1 and NT-2 used chinese capsules, but since the NTK and NT1000 Rode manufactures their own capsules in Australia. This could be seen as a good or a bad thing.

The NTK is a very good sounding microphone in it's own right. The main differences between the NT1000 and NTK (aside from cosmetics) are that the NTK uses a tube base preamp and the NT1000 uses a FET. If you want to know what the NTK will sound like rewired so as to not be a tube mic anymore, just listen to the NT1000.

Shane
 
Ok heres some pictures...
Once again, my camera sucks.

ntk1.JPG


ntk2.JPG


ntk3.JPG


ntk4.JPG


ntk5.JPG


ntk6.JPG


the 5 transistors bunched up by the big caps are all 2N5551 except for the middle one and its 2N5401. Q2 is 2N5401

I hope I didn't mess up the tention of the capsule by taking out the screw that held the positive wire :shock:

I guess its in the name of good science :green:
 
The brand electros on the board look like the same brand on my NT1000 that I replaced. I measured them and they did not have the reading I like. Is c10 in the signal path? The two cubes under C10 are they caps?(not the white blocks)

The capsule looks like a 797 style to me. I believe I read the nt2000 and k2 are the models that started using Rode made capsules.

Bluebird you should be fine with removing the screw.

I am going to try to trace the circuit from the picture.

First thing I would do is change the electros to better Panasonic,Elna,nichicon or rubicon. Next test to see what pins of the tube are connectted together,if any.

I think we can help this microphone it looks like the same capsule as the nt1000.

The grills of the nt1000 and NTK are different that will change the sound?
I have emailed ride in the past about the nt1000 capsule never did get a reply.
 
Looking at the pictures it looks to me only 1/2 of the tube is used pins 1,2,3 triode section and 4 and 5 heater 6,7 and 8 look unused.

I can't tell from the pictures is the tube setup as a CF or a plate out? If C10 goes from plate to grid and is about 100pf it would be one of the caps that makes the biggest difference in the sound. IIRC I measured about 100pf for the nt1000 capsule.

If you do cap upgrades another might be to move one heater wire and use a 12ay7 instead.
 
If I was to do anything I think I would just redo everything. I would think using a different tube and introducing a transformer would be the only thing worth the work. this seems like a good canidate for the G7...

what do you think Gus?
 
What are the voltages? you can build a tube microphone using 100V to 230V The higher the voltage the cleaner the sound. Look at a u47 105V PS circuit and a u67 210V PS circuit. Don't get to hung up on PS voltages remember you are working with tubes

For a tube microphone you want >=1.1Vdc fixed or cathode bias u47 fixed at 1.1Vdc u67 fixed at 1.6 to 1.8Vdc IIRC.

Look at the tubes used and the curves at the operating points on different microphone schematics there is some insight there.

I think I would upgrade the caps first. I like both transformered and transformerless microphones. This might turn out to be a very good transformerless microphone.

A few caps are cheap and possable very good mod IMO.

If you want to change to a transformer circuit the VM1 cardiod only would be a good one to try. It looks to be based off the u67 without the feedback network and cathode biased instead of fixed. But note the u67 the g7 and vm1 have alot in common.
 
Well this is weird.

The voltages are negitive.

-125 and -5.8 they work out to about -119 and -5.4 under load.

Could you point me in the directions of some schematics I could work from?

I guess I could try replacing some caps. I dont know what the silver blocks are...will try to find out.

Pins 3 and 9 are the only things connected.

The only reading between the wires from the capsule and the tube are like 100 megs...
 
Hitano web site.

http://www.hitano.com.tw/electrolytic.htm

Are they EXRs? or?
 
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