Sorry, Grogon, no, not exactly. Telefunken used their own numbering codes for special quality tubes, which is different from the more popular Philips code. In Telefunken's ECC803S the S means nothing else than »Spezial«, i. e. special quality, longevity etc. Telefunken ECC801S and ECC802S, their SQ versions of ECC81 and ECC82, resp., aren't frame grid constructions.
@ceylon.mooney: What makes you sure that these tubes aren't Valvo's. Personally, I'd not be able to decide, due to the photo quality.
@Magz: Perhaps you might want to search the Philips etch code that all tubes produced under this global player show, and tell us?
Best regards!
You can run them with low plate voltage and they will be very linear as well. BUT the internal resistance may be significantly higher (or lower) than for other 12ax7's and this will definitely affect the audio spectrum.
By running them at a higher plate voltage, they are of course still linear, but the internal resistance is more or less the same between makes (at least for those which I tested).
i already answered this in pics--see comment #74
after examining post #74 youll be able to decide.
the photo quality is more than enough to see clearly a horizontal halo getter.
Last edited:
Actually, they are frame grid tubes, and the S stands for "Spanngitter".
And they do sound good; I know, I have a few (not for sale).
And they cost 🙂
So which is it?
ECC803S have frame grids ("Spanngitter)? Or...
ECC803S are simply SQ version of ECC83?
Not that I care that much, since I can't afford to buy any ECC803S and I have several sleeves of good 12AX7As and 7025s from the old days.
and... It's "rongon" not Grogon. But it could be Grogon. That would be kind of funny.
ECC803S have frame grids ("Spanngitter)? Or...
ECC803S are simply SQ version of ECC83?
Not that I care that much, since I can't afford to buy any ECC803S and I have several sleeves of good 12AX7As and 7025s from the old days.
and... It's "rongon" not Grogon. But it could be Grogon. That would be kind of funny.
Last edited:
Telefunken ECC803S are frame grid construcions as well as SQ versions of ECC83.
Best regards!
Best regards!
Kay, tnx for the correction, you are right, the S stands for special quality, and that is probably why some other manufacturer could get away with labelling his tube as ECC803S although it has no frame grid at all.
Anode current changes Ri. Not Ua. If you keep grid voltage constant and increase Ua, Ia goes up (and Ri goes down) as well.
For 12AX7 and ECC83 types, linearity is generally better with higher plate voltages. Of course you will bias the tube to compensate for the different operating point(s). Usually you'll be using cathode bias, so at higher voltages you can increase the value of Rl (the plate load resistor) and the value of Rk (the cathode load resistor). The larger plate load resistor helps reduce harmonic distortion in the triode's output. (Rp is that much greater than rp, making for a flatter, more horizontal load line.)
The rp or Ri (internal plate resistance) will go higher with higher plate voltage and with lower plate current.
The tube constants (rp, gm and mu) are in a dance together, sort of like E, I and R in Ohm's Law.
12AX7A with Vp (Ea) at 100V:
12AX7A with Vp (Ea) at 250V:
See how the internal plate resistance is higher at 1mA Ip with 250V Vp, and lower with 1mA Ip and 100V Vp?
Conversely, gm is lower at 1mA Ip, 250V Vp, but higher with 1mA Ip, 100V Vp.
rp and gm go up and down, but mu stays pretty much the same, but varies less with 250V on the plate of the 12AX7A.
🙂
The rp or Ri (internal plate resistance) will go higher with higher plate voltage and with lower plate current.
The tube constants (rp, gm and mu) are in a dance together, sort of like E, I and R in Ohm's Law.
12AX7A with Vp (Ea) at 100V:
12AX7A with Vp (Ea) at 250V:
See how the internal plate resistance is higher at 1mA Ip with 250V Vp, and lower with 1mA Ip and 100V Vp?
Conversely, gm is lower at 1mA Ip, 250V Vp, but higher with 1mA Ip, 100V Vp.
rp and gm go up and down, but mu stays pretty much the same, but varies less with 250V on the plate of the 12AX7A.
🙂
But it does change a little, depending on operating points chosen.
In the bottom graph in Post #90 (250V plate voltage), the mu trace is flatter than in the top graph (100V plate voltage).
In the bottom graph in Post #90 (250V plate voltage), the mu trace is flatter than in the top graph (100V plate voltage).
It does change. I also see this on my eTracer when going through different operating points, but the change is so minimal that at least to me it seems it can be ignored?
Yes, that's one of the "secret sauces" ARC used in the 70's to make their SP3 sound better than their competitors from the 60's, the like of Marantz or McIntosh. The topologies are generally similar, but ARC ran their B+ at 440V instead of the 250V or so of the other guys.
Of course you'll need to replace your tubes often, but if you're an owner of ARC gears, you're familiar with this. 🙂
Why would you need to replace tubes more often if the operating points are well chosen?
12AX7/ECC83 is a high impedance device. It has very high internal resistance (rp or Ri). That means it wants to drop a lot of volts across itself.
Granted, the plate dissipation of 12AX7 is low at only about 1.2 watts, but that shouldn't be a big deal.
Let's say you have a B+ of 440V.
Choose a 300k ohm plate resistor.
Bias the 12AX7 to Ip of 0.86mA.
That means 258V will be dropped across the plate load resistor Rl. Make sure you choose a 2W rated resistor for that.
440V - 258V = 182V on the 12AX7 plate.
182V(0.00086A) = 0.1565W plate dissipation. Not anywhere near the maximum.
For the needed cathode bias of 1.5V, you'll choose a Rk of 1.744k ohms (standard value of 1.8k will be close enough).
Load line for that:
That should be a pretty linear spot, and as long as the power-on voltage spike isn't crazy, there should be no problem for the 12AX7 with its max plate voltage spec of 330V.
Right?
12AX7/ECC83 is a high impedance device. It has very high internal resistance (rp or Ri). That means it wants to drop a lot of volts across itself.
Granted, the plate dissipation of 12AX7 is low at only about 1.2 watts, but that shouldn't be a big deal.
Let's say you have a B+ of 440V.
Choose a 300k ohm plate resistor.
Bias the 12AX7 to Ip of 0.86mA.
That means 258V will be dropped across the plate load resistor Rl. Make sure you choose a 2W rated resistor for that.
440V - 258V = 182V on the 12AX7 plate.
182V(0.00086A) = 0.1565W plate dissipation. Not anywhere near the maximum.
For the needed cathode bias of 1.5V, you'll choose a Rk of 1.744k ohms (standard value of 1.8k will be close enough).
Load line for that:
That should be a pretty linear spot, and as long as the power-on voltage spike isn't crazy, there should be no problem for the 12AX7 with its max plate voltage spec of 330V.
Right?
The famous McIntosh Mc240 uses a (originally Telefunken) ECC83 as push-pull cathode followers driving the output valves. With original spec line voltage the anodes sat at +430VDC and the cathodes sat at output valve bias voltage, maybe -35VDC. It's not uncommon to see the original valves still in service. Still strikes me as an interesting data point - not sure what it means, but it's dramatic.
All good fortune,
Chris
All good fortune,
Chris
Right: good analysis, I guess that's what the ARC guys said after the design phase was done.
But wait, there were still cases of failure... Oh well, these were the cathode followers: they didn't like the full voltage at turn on. Easy enough to fix, diodes were added in the subsequent revisions, to be replaced with FET during the SP6/SP8 era.
@Chris Hornbeck
Yes, the MC240 had the same ailment, but the effects were milder: I bought mine fresh out of the Mac Clinic in 1978, all NOS tubes, etc. I didn't like the sound, so I messed with it quite a bit, most importantly I upped the bias to 55-60mA instead of the original 20mA, but I left the followers alone. Fast forward 34 years of normal use, the year was 2012, time for a re-tube. Surprisingly, most of them were withing specs at around -10% to -16% Gm re. nominal, except for these followers which were -34%/-31% and -36%/-33%.
You're a kind person.
The verb "chose" implies a conscious, responsible act, perhaps after running some what-if scenarios.
Me think they've been doing it since the days of the MC30, and made a lot of money, so why bother?
Yes, I'm evil 🙂
The verb "chose" implies a conscious, responsible act, perhaps after running some what-if scenarios.
Me think they've been doing it since the days of the MC30, and made a lot of money, so why bother?
Yes, I'm evil 🙂
Remarkably, the MC-275 in it's early versions uses the 12AZ7 as drivers for it's KT88's 😉.
Best regards!
Best regards!