New 300B pre-amp?

[earwaxxer]

Sorry if this question has been asked! - I dont remember seeing it mentioned but, how long are the 300B's expected to last when being used in a preamp circuit? Similar to other preamp triodes or are they run at full power?
Thanks - Eric

[Paul Joppa]

They are run at very low power, about 6 watts plate dissipation. They are not likely to die from excess temperature. The filament is run at the full rated voltage and current, so it would probably have the same life expectancy with regard to breakage. The plate voltage is low, so any loss of emission due to cathode poisoning should be much slower than under power-amp conditions. Loss of emission due to exhaustion of the cathode coating from causes other than poisoning will probably be the same as under power amp conditions since the cathode current is high.

I think those are the Big Four for guessing the lifetime. Which one is most important depends on the tube's detailed construction and can be known only to the manufacturer - and if I'm not mistaken, only a few of them actually know very much along these lines.

[earwaxxer]

Thanks Paul

[Chris]

That means??? If you could guess.... 3,000... 5.... !0,000 hours? depending on quality like JJ or WE type....

[Paul Joppa]

At one time, WE said 20,000 hours except half that at maximum ratings. I think they stopped saying anything at all long before the tube was discontinued - there are just too may variables. Probably they were getting calls like "I only got 18,500 hours" or "my power line is only 140 volts, yet my tubes blow out after only 5000 hours"....

[Chris]

Yeah, I can imagine... But with this being a preamp, I would imagine maybe 5 ish at least.. Anyway, should last a heck of a long time.... Thank you Paul

[Paul Birkeland]

Just an update on where the Bee Pre is, the Bee Pre in the photographs on the website is constructed and running, and we received the incredibly important blessing from PJ. 

We also observed a reasonable decrease in the noise floor between the prototype and the production prototype. 

We made a few tweaks to the PC board design and the parts that go on them, and those will go into production shortly. 

Lastly, the chassis plate layout will be ever so slightly tweaked to provide a little more space for some parts that ended up being a tighter squeeze than we thought. 

When the revised chassis plates and PC boards roll in, we'll be in manual writing mode, but in the mean time, I will install the attenuator upgrade into our second production prototype for evaluation (we are using nicer switches than we used in the prototype).

-PB

[Jim R.]

PB,

What are the specs for the coupling caps?

Thanks,

Jim

[Paul Birkeland]

Howdy Jim,

There are four 10uF coupling caps and two 0.22uF power supply caps that could be upgraded. Voltages should be no less than 250V.

-PB

[Paul Joppa]

Two of the 10uF caps are not used unless you are using the balanced output.

These are ourput caps, and if you are driving a really low impedance load, (under 1K ohms) you would want to increase them; 27uF is (IMHO) the point of diminishing returns.

[corndog71]

Howdy Jim,

There are four 10uF coupling caps and two 0.22uF power supply caps that could be upgraded. Voltages should be no less than 250V.

-PB

Yikes!  That's gonna be a painful but I'm sure satisfying upgrade.

[Paul Birkeland]

The kit is coming with some pretty nice caps the attenuator upgrade may be a better investment.

[Chris]

Speaking of attenuators... anyone have experience or heard the Lightspeed attenuators? Wonder if they would work with an active preamp...Could be interesting...

[Paul Birkeland]

Wonder if they would work with an active preamp

We did consider this option, but hand-matching LDR's didn't seem to be such an attractive option, and the active circuitry options to keep them matched would require quite some development and additional costs.

[Chris]

I understand...  Have you heard one in a passive configuration before?... in your opinion, if someone was to tackle it as project, post bee pre build, as just a personal thing, do you think they are superrior to a dact2 type attenuator?? I think this bee pre kit, design wise, could be one of the very best sounding preamps on the market in decades. DHT OTL 300B type design , i think a design like that can use the very best type of attenuator possible.... It doesnt have to come from you of course.. I am just saying if someone wants to go to all the trouble, is an LDR attenuator possible (practical) for the bee pre, feasible and worth it for the bee pre?? Thank you for your reply...