audio-talk

I know its a bit defeatest, but I would ask the question, just what is the problem with a TX, that makes it worth using non linear valves, large number of devices in parallel, loads of solid stage CCS, high current and heat dissapation a output stage with a gain of less than one, and unless feedbac...

Thanks Nick, I thought I was going mad there :) So as in any OTL the obstacles to overcome are tremendous. The dissipation is quite nice but an output impedance of 13R is fricking useless! What might the feedback incorporated in the design be likely to reduce this to? So let's say, for the sake of a...

Cheers Nick

It seems I'm missing something important here. How does one go about paralleling up a set of valves whilst keeping the cathodes seperate?

Steve

OK Here is my take on the output stage. The first is with self biased Cathode Followers. Second is with self bias and CCSs. I don't know whether that is right or not as I have never used CCSs. Comments would be appreciated. http://homepage.mac.com/scress1958/.Pictures/SelfbiasCF.gif http://homepage....

Thanks Andrew. I thought CCSs might work to keep the valves in line. These would have been difficult to implement in 1952 when this output stage was designed. However that is no reason not to fit them now. Thanks for the link Philip, These look to be just the job. I'll post my take on the output sta...

Hi Andrew Yes. It's terrifying isn't it? I'm currently drawing up something to try to address this. I'll post the diagram when I've finished it, which will be tomorrow. I'd like plenty of feedback from the panel on it if poss. Just a thought meanwhile. Could a series of LM 317 regulators or somethin...

Yeah, it doesn't make a lot of sense to me, which is why I posted the diagram to get some other views. Personally I would be wary of operating the 6AS7 in an OTL configuration at anything over 150V. I would operate it at 145V with -60 grid volts, which is 75mA draw. This gives a cathode resistor of ...

OK.

This is the best I could get it. This shows the output stage as they had it drawn with the single valve.

Might be my interpretation at fault Nick.

I'll see if I can enhance the original scan and post the relevant bit . It only shows the one 6AS7 and asks the builder to multiply that by 4 so I could have cocked something up.

Be back in half an hour or so.
Steve.

Now then, Thinking about OTLs, which you do when you have heard (however fraught the circumstances) one in operation I looked long and hard for a really simple one to start with, rather than the Rozenblit Transcendent T8. That amp taught me plenty, burned my fingers and sounded very nice on four cyl...

OOPS! Sorry Nick
I missed this emoticon off the end of my last post.

Steve.

Nick wrote:
I couldn't be arsed with people telling me I had done it wrong on the WD
site.

Come come Nick! surely you can't mean that. Nobody on there is in the slightest bit opinionated or a know-it-all.

Paul Barker wrote:
In short extreme complexity and cost for what? Where is the need?

Yeah in the cold light of this morning, I'm of the same opinion. What's the point? I think I'll just enjoy what I've got and think about the OTL breadboard like I was supposed to be doing. That might be a bit more sensible.

Steve

Here is the silly circuit I worked out for driving a 300B or 2A3
I stuck it here to avoid hijacking Dave's thread.



Steve

Thanks Guys for your generosity.

I think I'll go with Simon's offer as he is nearer to me.
Off I go to experience the worst of both worlds.

Steve