845 tubes for Cary 805 AE amplifiers

845Bs are indeed 100W dissipation. And sound quite good IMO.

SuperTNT 845Ms also handle 100W, but are rare.

I never heard an OS 845, and it's too bad the prices are preposterous, but the cheap 845B is pretty darn good in these amps or others. NOS 211s (GE) are not expensive and also very good in these amps.

Paulfolbrecht.

Thanks for the response. I've read conflicting reports on the 845Bs. Some are specified at 100 W dissipation, and some state more than 70W dissipation. As far as sound quality, IMHO the 845B sounds somewhat dirty compared to the 845M or the Cetron 845s I once owned.

I've spoken to Cary about this issue, and they claim that when you bias the 300B at 60MA, that the 845 has 100MA plate current with 950 Volts plate voltage. That equates to 95W dissipation. Strikes me as odd that a manufacturer would set up the amp to run so close to maximum dissipation as variations in line voltage or tolerance on parts values could easily push the amp beyond the maximum.

In addition, no one at Cary can tell me what happens to the plate current on the 845 if the 300B is biased at something less than 60MA. To me, it seems a poor design when you cannot bias the 845 directly so you don't ever know exactly what the dissipation is.

I was hoping that someone with Cary 805s might have had experience with some of the newer 845s such as the Sophia or the Psvane, and if so, where have they set the bias on the 300B?

Dean

Dean,

I have to say I think you were misinformed by Cary.

I currently own 805 AEs. I bias the 300Bs to 60 mA as instructed and run either stock Chinese 845s or Super TNT 845 Ms. If either were pulling 95WI think I would see both glowing plates and short tube life. I see neither. Furthermore, just about everybody with these amps, if they are running 845s, are running straight Chinese 845s or 845Bs. Like any tube, these tubes like no more than 80% of max dissipation - or 80W - for decent tube life. I think there would be many reports of 845 tubes lasting only dozens or hundreds of hours in these amps (when they should last thousands) if they were really dissipating 95W.

Also, I have never heard a single report of 845Bs with 70W max dissipation. Yes, 70W is the figure for several variants of new-production metal-plate 845s (845Cs and some 845Ms), but not the graphite-plate 845Bs.

I'd say I'm 90% sure on each of these counts - but not 100%!

The 845 graphite is NOT suppose to glow? ? ? Mine glow 15 minutes after I turn the amp off.

The 845 graphite is NOT suppose to glow? ? ? Mine glow 15 minutes after I turn the amp off.

That's normal. You should not see a red glow through the white light when powered up. 15 minutes for the red glow to last after powered down does seem long.

The 845B is RCA spec standard i.e. 100w dissipation