Elrog 300B vs Takatsuki 300B tubes

Thanks, George. I don't doubt that what you are saying is correct in most and perhaps nearly all cases. But without knowing the DC resistance or low frequency impedance of the filament winding of the particular transformer (which would enable calculation of the voltage that is dropped across it for a given current draw), and perhaps also the +/- tolerance on the transformer's turns ratio, I'm not certain we can say that for sure. Although I will state that I don't have a particular feel for what those numbers are likely to be for the kinds of power transformers that are used in audio components such as these.

Again, see the statement by Matthias of Elrog that I quoted in my first post dated yesterday (10-28-15).

10-28-15: Dracule1
So as far as Elrog 300B in Lampizator Golden Gate DAC is concerned, a rectifier that draws 2A/5V is fine (assuming GG DAC has a separate 3A winding for rectifier tube)?

10-29-15: Dracule1
Based on what George just said, I suppose the answer to my question is a yes.

Yes, certainly as far as the 300B is concerned, given George's point about the separate filament windings. And most likely as far as the rectifier is concerned, although per my comments above I for one am not sure we can say that with certainty.

FWIW, IMO, etc.

Best regards,
-- Al

It occurs to me that I should perhaps add some clarification to Matthias' statement I referred to just above, which I quoted in my first post of yesterday. That statement was:

If an EML 300B XLS is the right choice we have 1.5A heater current at 5V. There is no voltage regulation. A transformer a rectifier bridge and a CLC only. May be the XLS is underheated (so I hope) ore all other (right) 300B are overheated, because they draw 1.2A (some russians and chinese 1.25A)only. This would result a heater voltage above 5V...not so good for any 300B and very bad for an Elrog 300B, because the use of thoriated tungsten for filaments. Higher heater voltage will result a (much) higher anode current and a much lower lifetime...

What he is saying is that if the power transformer's filament winding is designed to provide exactly 5 volts to a 300B which draws 1.5 amps, if a different 300B which draws 1.2 amps is substituted the voltage applied to that 300B will be higher than 5 volts, to a degree that might be harmful over time. The reason for that increase in voltage is that the reduced current draw will result in a reduction in the voltage that is dropped across the resistance of the filament winding.

Note also that he is referring to a difference in current draw of only 0.3 amps.

In principle similar considerations may come into play when a rectifier rated at 2 amps is substituted for one rated at 3 amps. However I suspect that the sensitivity to filament voltage increases of the rectifiers being discussed is considerably less than the corresponding sensitivity of a 300B.

Best regards,
-- Al

I have measured this in my amp. Since my EML 300b XLS filaments draw 1.5 amps I have to adjust the dropping resistors so I still get 5 volts because voltage gets pulled below 5 volts. Other 300b tubes that draw 1.2 amps makes the voltage rise above 5 volts making me re adjust the dropping resistors. It's ohms law in practice. I heat my filaments with a/c. Jet

Thanks very much, Jet. Could you give us a rough idea of the magnitude of these voltage changes that you see in your particular amp?

I did a few minutes of research trying to find specs on the resistances of filament windings of transformers that would be used in these kinds of applications, and came up pretty much empty. It is surprising that such specs aren't commonly provided, which makes it hard to pin down the issues being discussed in any kind of quantitative manner. Which opens the door to speculation and differences of opinion.

Not to mention that it seems highly unlikely that data would be available for the particular tubes being discussed, or most other tubes for that matter, which would quantitatively indicate how their MTBF (mean time between failure) varies as a function of filament current, among other application dependent variables.

In fact the only conceivably relevant data I was able to find was for some military grade 60 Hz filament transformers specified in MIL-PRF-27 and its associated documents. For transformers intended for applications that are roughly similar in terms of voltage and current those documents generally indicated filament resistances in the area of 0.1 to 0.25 ohms. Which seems reasonably small **IF** the transformer and its turns ratio are chosen by the designer based on a loading assumption that is at least roughly in the general ballpark of the actual load.

Best regards,
-- Al

Al-
when I got home this evening I measured my Brooklyn line voltage with my fluke meter and got 124v which is more or less normal. My EML300b XLS filaments measured 4.97v and my Sophia mesh measured 5.06v. That's about a 2% increase. I am using 5v filament transformers that are over spec. They are rated at 3amps.