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In Reply to: Life is funny sometimes...... posted by Vinnie on May 6, 2007 at 13:27:36:
Maybe it would be worthwhile to analyze the design in more detail. For instance, which OPT did you use? Have you posted a current schematic of the amplifier (maybe I missed it)? Also, you might consider a 211. Unlike the 845, the 211 was originally designed for audio service. There's a distinct difference in the sound. Assuming the OPT is in the ballpark (~10K), you might only need to reduce bias voltage to drop in a 211. With 1KV on the anode and -52 on the grid, the tube will idle at roughly 70mA. Just food for thought...
Follow Ups:
"Unlike the 845, the 211 was originally designed for audio service."Um... no. the 845 is more suited to audio output than the 211. By history and design it's that way. Both will work - the 845 will work easier IMNSHO. FWIW Neither were exclusively designed for a single particular purpose (same thing could be said for most tubes)
-Ed
I was sure I'd read that in several places, so I went to one of my few remaining older references following your post. The 11th edition (1947) of the Editors and Engineers' Radio Handbook shows the 211 specified for Class C telegraphy, Class C telephony and Class B audio. A GE 211 datasheet from '42 additionally specifies the 211 for Class B RF and Class A audio. I don't have an original datasheet for the 845, but the Handbook noted above specifies it only for use in Class A audio. Do you have an early 845 datasheet that specifies operating condition for RF?
The 845 is more suited to audio output than the 211. By history and design it's that way.Why?
Both types were "intended" for service in radio transmitters. However, the 845 served as a modulator. That makes it both a RF and an audio type.Some FINE sounding amps have been made with both 211s and 845s.
BTW, the only construction difference between the 2 types is in the grid. Everything else is the same.
Eli D.
I'm thinking about more power for my power-hungry electrostats and I'm still in doubt about which way to go. I'm thinking about either replacing my 300Bs with the maxed up variants like 320B etc or perhaps a 300B like I have now driving a 211 or 845 (push-pull). That should give enough power for sure.But as I said, I'm much in doubt and I fear that with the increase in power I might lose the subtle details/finesse that I have now. But I have no arguments to support that it's just a feeling.
The most involving sound I ever heard was a 45SE on some very peculiar looking horns, but I like the naturalness of my electrostats too much to say goodbye to them yet. Can't have it all :-)
driving ESL/line array combos. Much better than all of the PP amps I've tried. With SE you can maintain that involvement you speak about with a truly holographic soundstage, and the 845s have plenty of power. I know what you mean about ESLs, for all of their faults I wouldn't trade mine.Rgds,
Naz
Hi Naz,sounds interesting. How are you driving those parallel 845s? Or even beter, do you have a circuit diagram?
In an interesting but slightly complicated way. Driver is basically a White CF using a 6H30P DR running off both positive and negative supplies. It’s DC coupled to the 845 to get rid of the coupling cap and to drive into A2 on peaks. I get about 75W from the two tubes with very low distortion right up to max power ... very efficient, rivalling PP but sounding way better!The WCF is in turn driven by a Russian 1578 (6H8 / 6SN7 equiv but better), which is also DC coupled and runs from the same supplies. It is basically a mu follower but with an added choke which provides greater linearity for the high voltage swing needed to drive the 845. Bias for the 845 is set by a pot on this stage. The only cap is between this and the first stage, a Siemens Cca (6922 equiv but better). I've tried IT coupling here but was unimpressed. I aim to revisit this one day with a much better tranny but I'm in no hurry because these (monos) sound better than any commercial amps I've ever tried or DIY I’ve built.
The circuit is my own but I can email you a schematic if you are seriously interested.
Regards,
Naz
Thanks Naz, sounds like an interesting circuit. But as you say it's slightly complicated indeed. Four stages, two power rails and DC coupled does not seem like an easy project. But I like it and if I seriously start planning something like it then I know who to turn to. I'll probably have a dozen questions for you then :-)Thanks again,
Arend-Jan
> BTW, the only construction difference between the 2 types is in the grid. Everything else is the same.I'm not saying that you're incorrect, but the reference I noted in the previous post quotes different maximum anode currents. It specifies maximum anode current for the 211 at 175 mA, and the 845 at 120 mA. Unfortunately, there's no way to tell from the listing whether these numbers might be tied to different operating conditions.
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