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Old 24th December 2002, 08:02 PM   #61
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Default FOR INFO

Hi,

And does anyone care to explain how that could could possibly happen?

Common Peter,you seem a little biased here.

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Old 24th December 2002, 08:08 PM   #62
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OK, I bite It could happen with any number of fault conditions. Just as happens with SS stuff every day
The cure? Put a fuse in series with the output. And if you're one who worries about daming factor, enclose it in the feedback loop.
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Old 24th December 2002, 08:13 PM   #63
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Hi Frank

I am not biased at all. Just know that worst case scenario always happens to beginners. And not only. Are failures in o/p tubes in DC coupled OTLs really uncommon? Most such curcuits require a protection circuit at output more than a SS amp. All this i admit is plain conjecture - always wanted but never built such a beast. Well, it does go a bit against the grain - all the effort to replace coupling caps with iron and at the end - lose the only really essential iron?

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Old 24th December 2002, 08:16 PM   #64
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Hi,

That's not even necessary.

Just fuse the rails of the output tubes,use a CT powerxformer and you're done.

In any fault condition: no DC on the output.

It never happened with the circuit I use since 1986 and it never happened with the Rozenblitt OTL design either.

This is just a myth caused by the unreliable Technics A20 OTL.
Just by looking at the circuit you can already tell it's bound for trouble.

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Old 24th December 2002, 08:32 PM   #65
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Default OTL SEQUEL

Hi,

Quote:
I am not biased at all. Just know that worst case scenario always happens to beginners. And not only. Are failures in o/p tubes in DC coupled OTLs really uncommon?
Tubes can fail.
When you have a classic design it may blow a bypass cap and cathode resistor.
And a blown bypass cap is a pretty awfull mess let me tell you.

In an OTL you don't have those since you don't use self-bias.

The beauty of the 6080/6AS7G family of tubes is that they're fused internally.
From experience though I can anly tell that the fuses in the rail blow first (as they should).

I'm the last person to say that OTL amps should be the first thing you start with as a beginner,hell one wrongly sized cap can cause oscillation and take out a tweeter or a woofer but soundwise they're very hard to beat.

One last thought,if you don't need to transform impedances you don't need the expensive iron and you will have much more extended bandwith at both frequency extremes.

Mind you,I've got nothing against xformers at all.
I just use them where they're most useful.

Cheers,
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Old 24th December 2002, 08:38 PM   #66
dhaen is offline dhaen  Europe
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Quote:
you don't need the expensive iron
True enough, but you'll pay in the end with running costs (valves and electricity)
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Old 24th December 2002, 08:45 PM   #67
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Default AS THEY SAY...

Hi,


Quote:
True enough, but you'll pay in the end with running costs
You can't have your cake and eat it too.

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