300b lovers

@lynn_olson 

The Mark I Karna's thrived on a matched quad of Emission Labs 320B-XLS, but that was also a serious investment. The European super tubes are something else

Agreed.

I had early production Elrog 300b tubes that sounded wonderful but had reliability issues. Fortunately that has all been sorted out with the current production Elrogs under the ownership of Thomas Mayer.

I have used the EML XLS 300b tubes over a 9-10 year period and they are utterly rugged reliable workhorse tubes that sound absolutely splendid. Expensive but worth every dime.

Charles

Considering that each Blackbird B+ regulator can crank out 500 mA peaks, and 400 mA steady-state, there’s plenty of current the super tubes can use. The only thing limiting the Blackbird is peak emission from the 300B filaments ... nothing else.

400 mA might not sound like much until you realize it’s at 480 volts, and the output transformer multiplies the current 28.7 times (on the 8-ohm tap).

(The 4-ohm tap has 40.2 times current multiplication, for those with current-hungry electrostatic speakers.)

@lynn_olson 

400 mA might not sound like much until you realize it’s at 480 volts, and the output transformer multiplies the current

To give context to these stated  parameters is the Blackbird easy, average or hard on the 300b tube? How is tube longevity affected by the circuit’s operational points?

Charles

The operating points are conventional, well within standard 300B specs, with the plate at about 75% of max rating (which typically gives maximum life). But if you really want to slam the amplifier, well, you can. There’s nothing stopping you. The amplifier gradually turns into a limiter, with the output current saturating on peaks. If you treat it like a guitar amp, running into heavy distortion for hours at a time, the output tubes will wear out more quickly (the same as a guitar amp). Momentary overload, as in music playback, is benign.

If peak power, and particularly, peak current, is important to you, the enhanced-rating European tubes are the best choice. Instead of 40-watt plates of the classic 300B, they have 65-watt plates, and peak current emission is 50% higher, or even more. Although they are related to 300B’s and bias the same, they are in the KT120 class, not EL34 class. Unlike the 845, which relies on voltage to deliver more power, the super tubes provide more current thanks to higher emission, and plates are more generously sized, keeping them cooler.

(User note: Not recommended or guaranteed for guitar amp use. 300B’s are physically fragile and can be damaged by high vibration, excess heat, or operation with a tilted chassis. If you own an electric guitar, get the right amp for the job.)

Unlike the 845, which relies on voltage to deliver more power, the super tubes provide more current thanks to higher emission, and plates are more

Thank you Lynn for your reply.

The EML tubes are a bit larger and heavier compared to my other 300b tubes. The glass envelope is thicker as well. It does possess a heavy duty aura and appearance.

Charles