[gary o]

Two tubes in parallell in mic circuits.....what are advantages and disadvantages ...... would two tubes produce more noise ? I have Maxes brilliant MK47 with the two 6028 tubes, mics sounds great but much more noise than other tube mics iI have built I tried lots of 6028s ......wondered if it was a parallell thing....

[maq3396]

Hi Gary

Cant comment of the theory of one vs two tubes but I just put my Mk47 'on line' yesterday.
Without the body on there is a fair bit of hum.
However with everything together it is quieter than my Telefunken AK-47
There have been a few comments through this build on hum and the common culprits seem to be either grounding issues or the tubes.
Have you tried a few different sets of tubes by chance?

[gary o]

Hi Maq3396  yes tried loads of tubes & pairings of tubes......I dont have any hum its just general white noise mush, its useable I actually dont think theres anything wrong I only notice it when I A/B other sigle tube mic builds, I even build the circuit minus the board out of spare parts, it sounds the same....... so thtas why I was curious about the tube parallelling, wondered if noise is doubled when in parallell.....

Thanks for your thoughts.

[RuudNL]

If you use two tubes (with the same characteristic!) in parallel, they will amplify the input signal in the same way.
The noise produced by the tubes is random. In theory: the signal will add (in phase) but the noise will be 3 dB lower.
Try to clean all components that belong to the Hi-Z circuit. (Input from the capsule, coupling cap, grid resistor.)
Even a fingerprint can cause a higher noise level!

[moamps]

...... so thtas why I was curious about the tube parallelling, wondered if noise is doubled when in parallell.....

Hi,
you can check that yourself easily by removing two jumpers on the tubes board.
Regards,
Milan

[gary o]

Yes cleaned board & components & as I say I rebuilt the circuit without a board noise level was excactly the same I dont think anythhing wrong the noise is exceptable just higher than my other DIY mics I guess its circuit design & or the tubes I know Max 6028 is a compromise to a V14.... Im comparing noise to 6072 circuit like Ela & 5840 in M49 as I say its not terrible....

Milan I forgot , I did that a while back, I had a bad capicitor in the circuit popping, was trying to track down the pops if I remember correctly output level including noise just dropped....

Thanks for your thoughts guys.

[Pip]

I have built the MK47 and really not a noisey mic at all compared to some other tube mics and even some FET mics. The AKG 414 P48 comes to mind as does the KM54 both beautiful mics that I love and own but not what I would call noiseless.

When you say you tried many 6028/408a tubes do you mean of the same manufacturer or of different manufacturers. Because so far I have noticed vast differences between just the the Phillips ECG JAN and the Western Electric USA branded tubes. Not so much noise but timbre and voicing for sure. I would say the Western Electrics are my favorite so far.

What body and capsule are you using also what cable? All of this comes into play, especially the cable.  I like the Gotham stuff.

I will also state that the 6028/408a tube has a pretty high distortion % and is not considered a good tube for low microphonics. So many tubes to find the right ones is not surprising. But it sounds like the noise you are talking about is steady hiss not an intermittent popping or handling noise or oscillation and ringing. I would blame hiss more on the signal path than on the mic.

I have noticed that this mic has a distortion component that does not flatter some vocalists, the comment was it has a mushy quality,  but that is the same for any mic voice combo! There is no one mic!

All this being said the MK47 and Max's work is amazing and I love this mic and would recommend it to anyone as an awesome build!

See attached PDF for tube info:

[gary o]

Hi Pip I 2nd what you said about great mic kit ! I would buy again.... the tube I have are the pair that came with kit & I vought a stash of JAN tunes as well.... using same cable on a AKG Ela M251 type circuit now that is much quieter then the MK47 side by side I was just thinking is a noisier mic as I say it doesnt sound bad doesnt sound like a fault no popping & cracks as I said I built another MK47 point to point with two of the JAN tube sounded excactly the same body Im using is Skylars the sound is nice either with Tim cambel TC12 or a Violet vin 67 ( meant to sound like a U67) sound crap with RK47 cheapy tho

Thanks

[micaddict]

I have noticed that this mic has a distortion component that does not flatter some vocalists

Same with the real thing IMO.
Great mic, though.

[gary o]

Little update I re re built the Mk47 circuit point to point no circuit board used maxes tran  same 1uf pio & same heater dropper resistor same tubes & its quieter, still same low mush just lower level I did before after recording diffinate improvment, still not as quiet as 6072A 5840 & 6AK5 mic circuits I have tried but better..... So I guess the it would be dirty board, the point to point version now lives in its new skylar apartment U47 case with views overlooking my desk & my many DIY projects

[Melodeath00]

I wanted to bump this thread. What effect does running two tubes in parallel have on output impedance? I figured that was another reason to run two 6028 tubes in parallel in the MK47.

[Matador]

I wanted to bump this thread. What effect does running two tubes in parallel have on output impedance? I figured that was another reason to run two 6028 tubes in parallel in the MK47.

All other things being equal:  twice the current, same plate resistance means half the output impedance.

[evil grill]

I modified two T.bone Retro Tube II mics  to work with two triodes in parallell. 
No apparent noise and decent sound. Less overtones than stock I imagine.
Have gotten  some ECC81's with balanced triodes to put in them too.  Will maybe change capsules later on.

Had alot of fun doing this. Very easy modification but I could not have made it without this forum and all of your posts. Thanks!