What 300b's are you running?
- Thread starter debk
- Start date
Paul Joppa
Moderator
Thanks, Aaron. I see 0.6% difference in the regulated voltage, 0.6% different and within spec since the voltage-set resistors are 1% parts. The means the voltage loss in the wiring is very small, and the solder joints are good.
The A tube is getting 4.83v, and the B tube is getting 4.44 volts (by subtraction). Both of these might go up as the tube comes to full temperature. You can swap the tubes and see if the difference moves with the tube. If it moves with the tube, then the B tube is drawing more current - 1.36 amps if the 8 ohm resistors are spot on and your measurements are exact. If it doesn't move with the tube, then either the 8 ohm resistors are off a bit (they are supposed to be 1% parts) or there's a questionable connection. Most meters can't measure low resistances with sufficiently reliable accuracy so I don't suggest making that measurement.
The A tube is getting 4.83v, and the B tube is getting 4.44 volts (by subtraction). Both of these might go up as the tube comes to full temperature. You can swap the tubes and see if the difference moves with the tube. If it moves with the tube, then the B tube is drawing more current - 1.36 amps if the 8 ohm resistors are spot on and your measurements are exact. If it doesn't move with the tube, then either the 8 ohm resistors are off a bit (they are supposed to be 1% parts) or there's a questionable connection. Most meters can't measure low resistances with sufficiently reliable accuracy so I don't suggest making that measurement.
Paul Joppa
Moderator
Hard to go wrong with Mills; good choice. I'm quite interested in any measurements, since we have very little experience with this "in the field" as yet. I was startled at the high current/low voltage at first, but as I thought about it I realized that the filament doesn't come up to full temperature until the plate has had enough time to radiate its heat to the filament - and the filament resistance increases with temperature.
I plan to be at BottleHeadquarters next week, and will try to get some data on Doc B's preamp.
I plan to be at BottleHeadquarters next week, and will try to get some data on Doc B's preamp.
johnsonad
New member
Today's data with 20 mintues of warm up:
EH Gold Grid tubes
B4: 9.88
B1: 5.02
A4: 9.82
A1: 4.98
After reviewing my notes from yesterday I messed up on the B1 voltage. The previous thread has been edited. There is very little difference from the intial results after a couple of minutes and at the 20 minute mark.
EH Gold Grid tubes
B4: 9.88
B1: 5.02
A4: 9.82
A1: 4.98
After reviewing my notes from yesterday I messed up on the B1 voltage. The previous thread has been edited. There is very little difference from the intial results after a couple of minutes and at the 20 minute mark.
Grainger49
New member
At 5 minutes everything should be settled out. Then listen for half an hour. See if the measurements moved. I doubt they will move by as much as 2%.
Paul Joppa
Moderator
Thanks, Aaron - good data. The tubes seem to be getting 4.84-4.86 volts which is 3% low, well within the usual +/-10% and the more strict +/-5% that premium tubes often specify.
EML specifies +/-4%. For a quick estimate, let's assume your Mills resistors are exact and that your meter is also exact. Then averaging the two tubes, your actual current would be 5.00v/4 ohms, or 1.25 amps. If you increased to 1.3 amps, the resistor drop would be 5.2 volts, leaving 9.85-5.2=4.65 volts which is 7% low - below the EML spec.
As you can calculate, a 56 ohm resistor in parallel with the two 8-ohm resistors would, in this case, give 5.00 volts on the 300B filament. I am not recommending this, at least not yet, and I won't be making any recommendations until we have a greater variety of data on the variability from one build to another. But you can see where I'm headed. I expect this will prove to be better than adjusting the regulated voltage, which is a delicate balance between the available voltage and the heat wasted in the regulator.
EML specifies +/-4%. For a quick estimate, let's assume your Mills resistors are exact and that your meter is also exact. Then averaging the two tubes, your actual current would be 5.00v/4 ohms, or 1.25 amps. If you increased to 1.3 amps, the resistor drop would be 5.2 volts, leaving 9.85-5.2=4.65 volts which is 7% low - below the EML spec.
As you can calculate, a 56 ohm resistor in parallel with the two 8-ohm resistors would, in this case, give 5.00 volts on the 300B filament. I am not recommending this, at least not yet, and I won't be making any recommendations until we have a greater variety of data on the variability from one build to another. But you can see where I'm headed. I expect this will prove to be better than adjusting the regulated voltage, which is a delicate balance between the available voltage and the heat wasted in the regulator.
debk
New member
I just got a pair of KR 300b and am listening to them now. Compared to the Psvane the KR's sound a little more open/spacious and more accurate. The bass is about the same, but the highs are more clear. I prefer them to the Psvane.
The only drawback is that the top is a little wider than the Psvane so the lead damper rings don't fit as well.
I am very glad I spent the money to get them. They are on sale at TubeDepot for $599 a pair
Debra
The only drawback is that the top is a little wider than the Psvane so the lead damper rings don't fit as well.
I am very glad I spent the money to get them. They are on sale at TubeDepot for $599 a pair
Debra
debk
New member
I have about 5 hours on the KR's now. They have "opened" up more, very spacious and detailed sounding. I am very happy I bought these, the best sounding 300b I have tried in the BeePre.
The data sheet that came with the tubes say the filament current is rated at 1.2A. The actual test data included with the tubes are 1.11A and 1.12A.
I have not had a chance to make any measurements myself. When I get a chance I will drag it down to Lab (Ok, Basement but Lab sounds better) and make some measurements
Deb
The data sheet that came with the tubes say the filament current is rated at 1.2A. The actual test data included with the tubes are 1.11A and 1.12A.
I have not had a chance to make any measurements myself. When I get a chance I will drag it down to Lab (Ok, Basement but Lab sounds better) and make some measurements
Deb
Paul Joppa
Moderator
So, they don't meet their spec, do they? But it's close. When I have more voltage data, I'll have some thoughts....johnsonad said:
The voltage variation is about half the current variation, so 1.13amps is 6% low and the voltage would be 3% high, close enough. Do the numbers, and you'll see that 1.1 to 1.3 amps is a nominally safe range - if we ignore variations in component values and build resistances in individual amps. So I am looking to learn what the build variations may be, and what the tube variations may be, before making any recommendations.
Ignoring the other variations as above, you might think you could say that a 1.3A tube will work. But you can't say a tube model with 1.3A +/-0.5A current draw will work - half of them will draw too much current.
johnsonad
New member
I tried the TJ 300B mesh this weekend. I enjoyed this tube in my Paramounts but it wasn't the best combo for my BeePre and speakers. Too light weight, no body or soul. I only gave them an hour or so but to my ears and system, the EH 300B Gold Grid have been the best sounding tube so far.
