Elrog 300B vs Takatsuki 300B tubes

Charles, it sounds like you may have to do this resistor change to make the 300B last longer. If they do tweak this tube you may want to wait for that replacement. If you just get another one from this batch I probably would do the resistor change. It can always be taken out in the future.

Jeff,
George is only going to use the modified tubes from this point going forward, so these will be my replacement Elrogs(when they're ready). The resistor swap option seems simple once I know which one to change(you think Doug could help?). I'm very encouraged and hopeful.
Charles,

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