TheRadioBoard

While looking around the internet at tube radio circuits that can run on 12 volts I came across this one:



It got me to realize that this little tube (about the size of a 50C5) can be used in most '1D8' circuits, can use just one 12 volt power source, and it is fairly cheap, too:

http://www.tubedepot.com/nos-14gw8.html

One example of a 1D8 circuit that the 14GW8/PCL86 can be used in is this:



In this case, both 14GW8 cathodes can be connected to ground. One reason that I picked this one is that it uses an external semiconductor diode, rather than the diode that is built into the 1D8. It's a nice circuit for a 14GW8 that does not have an internal diode section. Daves 1D8 circuit will work nicely, as will many others. Just remember, if you pick a circuit that uses the 1D8's internal diode, you will have to use an external diode instead, if you use a 14GW8 in place of the 1D8.

Norman
KA1GUK

I think I need a drink after looking at this one!

Well, here is a 1D8 circuit where the 1D8 diode section IS being used in a somewhat similar reflex circuit to the one I posted the first time. I'd think that this would cause your head to spin even more, ....or maybe not:



Now, if you were going to use a 14GW8 in place of the 1D8 in this circuit, you would need to use an external diode. This would make it more similar to the circuit in my previous post. Does this help?

Norman
KA1GUK

Bottoms up!

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

I've been trying to make my posts more clear. After having a couple of beers last night, I admit it was a little difficult keeping my thoughts together. BTW, here are the pinouts for the 14GW8/PCL86:



Norman
KA1GUK

Norm,

Your posts are clear! I wonder how this tube would work used as an untuned triode rf amp and pentode regen detector?

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

I haven't thought of that idea, but I think it would work fine. The 14GW8 is a triode - power pentode tube that was originally developed as an audio output tube for TV sets in the 1960's. I've seen plenty of circuits that used power tubes as regenerative detectors. Dave's 1625 receiver is just one example. Also, I've seen circuits where a 14GW8 has been used in an amateur transmitter, so the pentode side can work at RF frequencies. One idea I did think about is taking Dave's dual triode shortwave circuit and using the 6GW8's triode section as the regenerative detector. The power pentode stage could then be used to allow it to drive a speaker or provide more headphone amplification. This would be especially nice if you are using low z headphones, since they tend to be much less efficient than high z headphones. Then I realized that you can't have 6C4 and 6GW8 heaters in series because the 6C4 draws 150ma on the heater and the 6GW8 draws 300ma. I suppose a 6C4 with a voltage dropping resistor on the heater and a 14GW8 with the heaters in parallel would work.

Norman
KA1GUK

Howdy Norm,

I'm with Jim, nothing wrong with your presentation but I'm still trying to wrap my head around the original 1D8 circuit and its now coming to me. It's reminiscent of my 3A8 reflex which took me a LONG time to figure out! Once I did it made perfect sense.

73,
Bill

It's a shame they couldn't center-tap the heater.

How much power were they getting out of it as a PA?

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

A little rum goes a long way, eh Bill?

That schematic is a mess, due to cramming the circuit into a tiny box. Was going to re-draw it in TinyCAD but I ran out of scotch.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Picture says 1000 words...my brain hasn't been right since figuring this one out

Hi ex,
Two data sheets for 3A8GT show the diode on pin 8 and the fil c/t on pin 1.
Guess it doesn't matter when both are commoned though.
Don't know which would be correct.

Info only.
...........................

My espresso machine blew a gasket the other morning. Discovered my reflexes are still pretty good, even before coffee!

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

It looks like you can get 4w max out of the pentode section when run as class A. I would think you can get a bit more power for a PA circuit. I don't think you would need class A for that....

http://www.r-type.org/pdfs/pcl86.pdf

Max. pentode side plate dissipation looks to be 9w.

Are you thinking about building a tube type PA, Jim?

Norman
KA1GUK

You could probably get 13 W out of the thing on CW or SSB, then. With good air circulation.

I'm afraid there isn't enough coffee or scotch in the world to induce me to build a tube-type anything, but it's interesting to speculate. Safer, too!

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/