Mixing makes of 6DJ8 tubes in preamp, and how to ascertain best position.

[spiritofmusic]

I've had some ongoing noise/hash issues with my Nat Audio Utopia preamp. Stock current production Teslas and Electro-Harmonix tubes are generally quiet, but bland sounding.

I've moved onto Voskhod Rockets and Reflektor Silver Shields 6N23P tubes, and every pair fails within weeks of install re rising levels of noise, an issue w my 101dB/1m efficient Zus.

Bazelio kindly put me onto Brent Jesse who has sent me a couple of 60s and 70s Mullards and Mazdas 6DJ8 tubes.

My Q is re positioning of different tube makes in my preamp. Is it simply a case of experimentation, or do I choose a symmetrical layout left to right?

Ie A-B-B-A or B-A-A-B

I don't really have any schematic on my amp, my dealer and the company are of zero help.

 

[LL21]

Hey Spiritofmusic,

In my own experiences with Brent's most excellent tubes...i would find one absolutely dead silent if put into the left CJ channel...but slightly noisy if put into the right...and sometimes vice versa. Maybe minute differences in voltage or some other such inconsistency.

I am going to guess you will want to experiment and symmetry based on location is probably not the answer...it is probably VERY socket-specific.

 

[spiritofmusic]

Sure Lloyd, I assumed things needed to be mirror image.
But possibly one random arrangement will work best.

 

[LL21]

I am the last person who should speak about technicals...all I can say is that the same tube is silent in one socket and noisy in another. Which suggests to me that each tube is different...and thus symmetry can only be done if you measure each tube...and know what to measure...and can actually find identically measuring tubes to create that symmetry. Or more likely...pick a customized arrangement since who knows, maybe even each socket is ever-so-slightly different as well.

 

[spiritofmusic]

So, four tubes...sixteen permutations?

 

[LL21]

So, four tubes...sixteen permutations?

Actually, 4 tubes (1,2,3,4) is 24 permutations?

 

[spiritofmusic]

I guess I can count myself lucky I'm not running 24 tubes Lol.

 

[spiritofmusic]

And there was me before, reluctant to try reverse orientations of fuses.

 

[BruceD]

Marc-I may have mentioned this before--but I've had excellent service from

Derek Rocco
Watford Valves & Speakers Ltd
Tel: 01923 893270

He may be able to assist

BruceD

 

[spiritofmusic]

Hi Bruce, all good here. After a couple of install teething issues, Brent's mix of these tubes has been a slam dunk success.

I've decided not to go too far down the rabbit hole in comparing 24 permutations. Life is too short, and I've hit on a musical permutation right off.

I didn't go too far down the hole on re reversing fuses on my big SR fuses upgrade episode.

Although of course any sane person would look at me and say I'm already in a dark place, wearing my audiophile sunglasses is biasing my outlook Lol.

 

[Direct Drive]

I'm already in a dark place, wearing my audiophile sunglasses is biasing my outlook

should that not be..... biasing the tubes.

 

[spiritofmusic]

Is that a euphemism like bashing the bishop?

 

[Direct Drive]

Is that a euphemism like bashing the bishop?

No Marc, me just being naughty......adjusting the bias for optimal performance dependent on circuit design.

 

[bazelio]

Marc, as we discussed, without knowing the circuit topology, you're left with trial and error. If there is a PCB in the unit, then possibly the tube sockets are labelled on the PCB itself. The label names might give us a clue as to what the topology is. Did you look for PCB tube socket labels?

If all four tubes are in series (unlikely to me, unless this is a high gain phono), then any order is acceptable, and you can move them around at will, listen for a while, and choose the most pleasing result. And, you don't really have 24 permutations since you have two pairs of presumably identical tubes (for all intents and purposes).

If there are two tubes in series per channel, then you will want one tube of each make in each channel and in the same order. E.g. Input->Mullard->Mazda->Output in both sides. Or Input->Mazda->Mullard->Output. Two choices only.

When I recommended to you the split of Mazda and Mullard, I also noted that generally I prefer Mullard on the input side and Mazda on the output side. But you'll need to listen and determine what you prefer. But again, without knowing circuit topology, it's going to be a little error-prone.

 

[spiritofmusic]

No Marc, me just being naughty......adjusting the bias for optimal performance dependent on circuit design.

DD, I think you've inadvertently come up with a new one..."biasing your tubes"
I mean, when a woman asks what you do upstairs on your own in the dark in all that sweltering tube heat, wearing just yr pants...
Lagonda the go-to guy here.

 

[spiritofmusic]

Marc, as we discussed, without knowing the circuit topology, you're left with trial and error. If there is a PCB in the unit, then possibly the tube sockets are labelled on the PCB itself. The label names might give us a clue as to what the topology is. Did you look for PCB tube socket labels?

If all four tubes are in series (unlikely to me, unless this is a high gain phono), then any order is acceptable, and you can move them around at will, listen for a while, and choose the most pleasing result. And, you don't really have 24 permutations since you have two pairs of presumably identical tubes (for all intents and purposes).

If there are two tubes in series per channel, then you will want one tube of each make in each channel and in the same order. E.g. Input->Mullard->Mazda->Output in both sides. Or Input->Mazda->Mullard->Output. Two choices only.

When I recommended to you the split of Mazda and Mullard, I also noted that generally I prefer Mullard on the input side and Mazda on the output side. But you'll need to listen and determine what you prefer. But again, without knowing circuit topology, it's going to be a little error-prone.

Brian, I will look but cursory glance shows no labelling on the amp. And getting a schematic from Nat is like getting a 100% effective vaccine for Covid.

 

[Lowrider75]

It's very possible your preamp uses 2 tubes in a gain stage and 2 in a cathode follower (driver position). They are usually the same tube type. They have very different functions, but designers like to keep things organised. Are the tubes positioned 1234 in a row, or 2 in front with 2 behind them?
If 1234, typically 1& 4 are the same circuit, 2 & 3 are the other circuit.

Due to the high sensitivity of your speakers, next time ask Brent to noise test the tubes.
FYI for the future, 6922 is an equivalent of the 6DJ8 and are of superior build quality.

 

[spiritofmusic]

Lowrider,
Left to right, 12 34
With 6s19p-v tubes at extreme right and extreme left
So, you would suggest one type at 1 & 4, the other type at 2 & 3?

 

[tima]

Perhaps ask the manufacturer which positions have the greatest sonic impact.

 

[spiritofmusic]

Tim, there's my issue. Nat Audio are in Belgrade, almost never answer emails, noone speaks fluent English.

Tbh, I'm not sure what I should be asking...the stock tubes are all one brand. The last thing I was expecting Brent to recommend was two brands of 6DJ8 tubes. Hence my quandary.