i have built a couple of preamps to date, all based on either the 6922 or the 5687(6900).
i find that i have only improved the clarity aspect of my preamps. one sounding more clean and defined than the previous one. all still lacking warmth in the mids. i find this is a little odd.
any thing i can take to increase the warmth factor?
i find that i have only improved the clarity aspect of my preamps. one sounding more clean and defined than the previous one. all still lacking warmth in the mids. i find this is a little odd.
any thing i can take to increase the warmth factor?
I haven't tried the 5687, but I like the 6bk7b much more than the 6dj8 or 6922, which I think sound rather sterile by comparison. With a little rebiasing, you can usually get a 6bk7b to work where a 6dj8/6922 would. I wonder if the frame grid construction has something to do with this.
Has anybody tried the Svetlana 6N1P which is supposed to be similar but also not have frame grid construction?
Has anybody tried the Svetlana 6N1P which is supposed to be similar but also not have frame grid construction?
It all depends on what you mean by "warmth". If you decrease the value of the anode load resistor, you reduce the ratio of RL to ra, and 2nd harmonic distortion rises, perhaps sounding warmer. If you remove the cathode bypass capacitor, this increases ra, reducing the RL/ra ratio, but it also introduces local negative feedback, so the effect is not quite so predictable (it also significantly reduces rejection of power supply noise, increasing mud).
Frame grid valves such as the 6922 were designed for use at HF and can easily oscillate at UHF. HF oscillation can often produce a subjective "steely" effect. A 1k carbon film grid-stopper resistor soldered directly in series with the valve grid pin usually stops UHF oscillation, although cathode followers are more intransigent, and may require 10k.
Frame grid valves such as the 6922 were designed for use at HF and can easily oscillate at UHF. HF oscillation can often produce a subjective "steely" effect. A 1k carbon film grid-stopper resistor soldered directly in series with the valve grid pin usually stops UHF oscillation, although cathode followers are more intransigent, and may require 10k.
Hi, EC8010 -
Sounds like a good suggestion. Someone should try that & see if that corrects the sound of those frame grid tubes. I should mention in passing that the 6BK7B's (which were sort of a precursor of the 6DJ8 for RF cascode applications) I'm using in the phono preamp as SRPPs show no signs of RF misbehavior when looked at with a 500 Mhz scope.
Btw, I just ordered some 6N1P's and maybe I'll try 'em in my home brew phono preamp instead of the current 6BK7B's or perhaps my old Carver CD player where I currently have some Amperex 6DJ8 Bugle Boys (the best I've heard of that type). It turns out, though, that the transconductance spec of the 6N1P's is a bit on the lowish side at around 7000 uMho (7mS?) compared to the other two types.
Sounds like a good suggestion. Someone should try that & see if that corrects the sound of those frame grid tubes. I should mention in passing that the 6BK7B's (which were sort of a precursor of the 6DJ8 for RF cascode applications) I'm using in the phono preamp as SRPPs show no signs of RF misbehavior when looked at with a 500 Mhz scope.
Btw, I just ordered some 6N1P's and maybe I'll try 'em in my home brew phono preamp instead of the current 6BK7B's or perhaps my old Carver CD player where I currently have some Amperex 6DJ8 Bugle Boys (the best I've heard of that type). It turns out, though, that the transconductance spec of the 6N1P's is a bit on the lowish side at around 7000 uMho (7mS?) compared to the other two types.
Hi,
It's easy enough to check and it's well known to work too.
With careful choice of operating points and layout you'll hardly ever have to resort to gridstoppers but, as EC8010 suggests, some tubes can be rather hard to tame.
BTW, I don't think it has anything to do with the tube being of the grid frame type of construction.
Cheers,
It's easy enough to check and it's well known to work too.
With careful choice of operating points and layout you'll hardly ever have to resort to gridstoppers but, as EC8010 suggests, some tubes can be rather hard to tame.
BTW, I don't think it has anything to do with the tube being of the grid frame type of construction.
Cheers,
fdegrove said:
Hello, thoriated. But can you afford probes that maintain that 500MHz bandwidth to the probe tip? (I can't.)
As Frank says, grid-stopper values are heavily dependent on layout. I recently had to resort to 10k on a point to point layout (great for audio, less great for RF), whereas the PCB equivalent got away with a few hundred Ohms...
6dj8 vs 6922
Hi Hacknet.
Actually these two tubes are somewhat different, so don't get too confused by them.
The 6DJ8 was designed for RF tuner service in which the gain needs to change with varying signal levels so as not to overload in high signal areas, near the transmitting tower as an example.
As Glass Audio pointed out, the transconductance and gain of the 6DJ8 varies quite alot with voltage and current.
As also pointed out by Glass Audio, the 6922 has the same high transconductance in the "high current region", but the transconductance and gain do not drop off nearly as much in the "low current region". This translates to much lower distortion, as I have confirmed in my own testing/measurements.
The result is a different sound, although brand makes a large sonic difference.
Hope this helps.
Hi Hacknet.
Actually these two tubes are somewhat different, so don't get too confused by them.
The 6DJ8 was designed for RF tuner service in which the gain needs to change with varying signal levels so as not to overload in high signal areas, near the transmitting tower as an example.
As Glass Audio pointed out, the transconductance and gain of the 6DJ8 varies quite alot with voltage and current.
As also pointed out by Glass Audio, the 6922 has the same high transconductance in the "high current region", but the transconductance and gain do not drop off nearly as much in the "low current region". This translates to much lower distortion, as I have confirmed in my own testing/measurements.
The result is a different sound, although brand makes a large sonic difference.
Hope this helps.
Steve, if the GA article you're referring to is the one called "Is the 6DJ8 suitable for audio?", there has been some talk that what the author was testing were actually 6ES8s that a supplier had illegitimately relabelled. Real 6DJ8s do not have the remote cutoff characteristics that he described.
my testing
My testing/measurements confirm there is a substantial difference in distortion between major brand 6DJ8s and 6922s.
If these major brands had relabeled tubes then my apologies. I wonder if they knew? And why relabel them? Simply ran out of stock and needed some to sell?
Take care guys.
My testing/measurements confirm there is a substantial difference in distortion between major brand 6DJ8s and 6922s.
If these major brands had relabeled tubes then my apologies. I wonder if they knew? And why relabel them? Simply ran out of stock and needed some to sell?
Take care guys.
Often, yes. Also, it's tempting when you run across a large stock of 6ES8s for a few pennies per to just relabel them and reap the rewards. Not necessarily a stock situation, more like dishonest opportunism. Shocking to say, that actually happens in the high-end audio industry!
BTW, examination of the grid structure can give you a clue about the actual pedigree of the tube. The 6ES8 has a variable pitch to the grid spacing; the 6DJ8 is quite even.
BTW, examination of the grid structure can give you a clue about the actual pedigree of the tube. The 6ES8 has a variable pitch to the grid spacing; the 6DJ8 is quite even.
Yes
Hi Sy,
"Often, yes. Also, it's tempting when you run across a large stock of 6ES8s for a few pennies per to just relabel them and reap the rewards. Not necessarily a stock situation, more like dishonest opportunism. Shocking to say, that actually happens in the high-end audio industry!"
I didn't make myself very clear Sy. I didn't mean in the recent past, audio stashes etc although you are certainly correct.
I mean 60s vintage. I tested old tubes out of TVs (got alot of different tube types), and maybe a NOS or two, have to look closer. Looks like even back then, some pretty big wigs must have been dishonest.
"BTW, examination of the grid structure can give you a clue about the actual pedigree of the tube. The 6ES8 has a variable pitch to the grid spacing; the 6DJ8 is quite even."
I may investigate further, maybe "open" one tube up and inspect closer. Be interesting if that long ago, we had some crooks pulling the same stunts.
Take care Sy and thanks.
Hi Sy,
"Often, yes. Also, it's tempting when you run across a large stock of 6ES8s for a few pennies per to just relabel them and reap the rewards. Not necessarily a stock situation, more like dishonest opportunism. Shocking to say, that actually happens in the high-end audio industry!"
I didn't make myself very clear Sy. I didn't mean in the recent past, audio stashes etc although you are certainly correct.
I mean 60s vintage. I tested old tubes out of TVs (got alot of different tube types), and maybe a NOS or two, have to look closer. Looks like even back then, some pretty big wigs must have been dishonest.
"BTW, examination of the grid structure can give you a clue about the actual pedigree of the tube. The 6ES8 has a variable pitch to the grid spacing; the 6DJ8 is quite even."
I may investigate further, maybe "open" one tube up and inspect closer. Be interesting if that long ago, we had some crooks pulling the same stunts.
Take care Sy and thanks.
Steve, the other thing to keep in mind is that in any triode, gm changes with ip. More so in high gm tubes, since you're starting at a higher value. But rp also changes, and in tubes that aren't designed for remote cutoff (variable mu), the product of the two parameters stays remarkably constant. That's the other way to separate the wheat from the chaff.
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