Elrog 300B vs Takatsuki 300B tubes

I find it fascinating that changing the cathode resistor value from 1K ohm to 1.2 K ohm has such an impact, that's all it takes? Almarg, where are you my friend? LOL.
Charles,

The franks have a very high operating point!?

- 525V operating voltage with some drop (25V) over the OPT
- Makes 500V at the Anode
- because the 1kOhms cathode resistor we have 86.8V at the cathode
- results about 413V across the plate of the Elrog.

If that's the case its way too high for the Elrog. Its probably too high the the Tak's and any other standard 300b tube. It could make for a very sweet operating point for the EML 300b XLS.

Its hard to believe that is the actual operating point for the Franks since Israel Blume has said he runs the franks conservatively.

If there was actually a 525V operating voltage coming from the power supply there would have been a warning to only use 300b tubes that could handle a plate voltage of 400 to 425v. Something is not quite right here -Jet

Hi Charles,

You are absolutely right...No problems for EML XLS tubes.
They are designed for 55W anode dissipation, not for 36(40)W only. For this tubes the "Frank" is easy. ;-)
You can read something about that here:
http://www.emissionlabs.com/datasheets/EML300B-XLS.htm

Yes, we work on modifying the tubes to improve the compatibility for some "special amps"...but this needs time.

For now we will replace failed tubes with selected tubes, tested at the same conditions as this amps are working(plus 10% safty margin)...

Regards, Matthias

Charles you may want to call Israel Blume. I find that this operating point would be hard to believe. It would fry any mesh plate tube and push any standard 300b to its limits:

"1kOhms cathode resistor we have 86.8V at the cathode at anode current of about 87mA."

Jet,
I am a bit confused to some extent. Israel says the Frankenstein MK II is a "easy on the tube" design, heat dissipation is 25 watts and overspec transformers that operate at only 30% capacity. I can say that the amplifier is cool to the touch. The power transformer is only warm to touch when left on the entire day (never hot). I didn't have tube durability problems with my former Shuguang black treasures.i could have sworn at one time Israel said the Frankenstein ran relatively modest plate voltages(I could be mistaken). Bottom line, the amp sure sounds superb when good quality 300bs are used.

If the cathode resistor change settles the problem then this is very good
news. Matthias I'm assuming there's no adverse affect on the circuit (or other amplifier parameters) with this resistor change.
Charles,