[ARC5] Solid State 6AL5

[J Mcvey]

This thread has been long on speculation and short on building.It would be simple to build a suitable solid state replacement with a series zener and diode combo.Why do a before/after comparison of the sensitivity? No radios will be harmed in this experiment !
I suspect that A Schottky type would be better than a silicon diode but either one would be better than a 6aL5.The levels are high enough in the IF that a near zero knee is not necessary but the conduction curve will be much sharper than the tube.However, simulating the forward voltage drop may be key in not adversely affecting the original design function.Try it with and without the zener to check the premise...




 

    On Wednesday, February 7, 2018 9:37 AM, jeepp <jeepp at comcast.net> wrote:
 

  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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