[ARC5] Solid State 6AL5

[John Watkins]

I have the metal case off of one of my mil 6AL5s, it is encased in an amber colored epoxy.  I could remove enough to see exactly what is in there and provide a few pictures if it would be of interest.

John WD5ENU 

Sent from my iPad

> On Feb 7, 2018, at 09:15, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> 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
> 
> 
> 
> Sent from my Verizon 4G LTE smartphone
> 
> 
> -------- 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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