[ARC5] Solid State 6AL5

[jeepp]

FWIW, I gave away a functional NC-88 years ago that had the 6H6 replaced with an octol base and two glass diodes. I do not recall the type diodes, but there they were.K3HVG


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-------- Original message --------
From: Richard Knoppow <1oldlens1 at ix.netcom.com> 
Date: 2/5/18  16:35  (GMT-05:00) 
To: arc5 at mailman.qth.net 
Subject: Re: [ARC5] Solid State 6AL5 

    I am a little confused, here you say that 
semiconductors are more linear than vacuum tube 
diodes due to the 3/2 law leading to poor 
_nonlinearity_ which to me means better linearity. 
Is this sentence supposed to read _poor linearity_ 
if so it makes more sense.
     Also note that semiconductors have a constant 
voltage drop, something like mercury vapor 
rectifiers. Ge is about 3/4 volt, Si about 1 volt. 
It is independent of current. Vacuum tube 
rectifiers have a voltage drop which is dependent 
on the current but is not like a linear resistor 
since it does not vary linearly with the current 
drawn, perhaps this is where the 3 halves power 
law comes in. For this reason the output voltage 
of a semiconductor rectifier is usually greater 
than a vacuum tube diode and can be corrected for 
only one value of current.
    BTW, some early detector circuits using solid 
state semiconductors had a source of bias voltage, 
usually a battery, to improve sensitivity. When I 
was making crystal sets in the dim, distant, past 
I didn't know about this and never tried it but it 
shows up in early books on "wireless".
On 2/5/2018 12:33 PM, Tom Lee wrote:
> Hi Peter
> 
> Assuming that impedances are matched, a vacuum tube diode will always be less sensitive than a semiconductor diode as a detector -- the 3/2-power law leads to poor nonlinearity. That more-linear characteristic is one reason there are some audiophiles who insist that tubes sound better.
> 
> The 1N34 is a good detector partly because matching impedances to it is straightforward. Even though a silicon device has a better slope near the origin, the extremely high impedance there can't be matched in practice, so that potential lies unrealized. Adding a tiny bias current helps, but purists dislike the extra bits.
> 
> Cheers
> Tom
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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