TheRadioBoard

Norm_N_Tam · Joined: 19 Jul 2008 Posts: 252 Location: Connecticut

I've never actually had a genuine CK722 in my hand. If I ever manage to aquire one, I'd keep it aside as a collectors item anyway. When I've built a circuit in the past that called for a CK722, I've found that a 2N404 has worked as a substitute for me. Sure, the 2N404 has more gain and less leakage, but it worked. What transistor would you use?

Norman
KA1GUK

peeblesoriginals · Posted: Mon Mar 08, 2010 1:12 pm Post subject:

Norman,

You either want to keep the thing original, for nostalgic reasons,
or just go buy a cheap 6-transistor radio. Crying or Very sad

Just about any PNP/Ge transistor will work in the place of a CK-722.

Sure a modern silicon, cheap NPN transistor will work, but I thought
we all liked to play with vintage/nostalgic radio. . .Anyone can play
with cheap 6-transistor radios.

I guess their's no helping some. . . Wink

Mike
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Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

millwood · Joined: 26 Feb 2010 Posts: 59

millwood · Joined: 26 Feb 2010 Posts: 59

Norm_N_Tam · Joined: 19 Jul 2008 Posts: 252 Location: Connecticut

millwood · Joined: 26 Feb 2010 Posts: 59

KR1S · Joined: 06 Jun 2009 Posts: 750 Location: South Florida

Norm,

Fixing the bias such that gain is not dependent on beta makes good sense. Then, if I get a device from a different batch, or you use a 2N3904 and I have only 2N44401s, I can make the swap without headaches. That's simplicity. Circuits "morphed" because designers got smarter.

73,
_________________
Jim, KR1S

Just build it!
http://kr1s.kearman.com/
http://qrp.kearman.com/

Curt Reed · Posted: Tue Mar 09, 2010 10:46 am Post subject:

Going from memory here, but back in its heyday, the CK722 was often replaced with the 2N107 and 2N35 transistors. But finding one of them today would be as much of a problem as finding a CK722!
Curt
_________________
Curt, N7AH
CW forever
Connoisseur of the cold 807

millwood · Joined: 26 Feb 2010 Posts: 59

in general, you can replace a Ge transistor with a Si transistor, or vice versa.

That replacement, however, can get tricky, if the circuit in question relies on some unique characteristics of the devices.

For example, Ge transistors have high and thermally sensitive leakage current. Si transistors don't exhibit that behavior (for the most part). So it would be very difficult to replace a Ge transistor with a Si transistor in a circuit where such a character is exploited, without some major redesign.

I had a circuit that used a Ge transistor as a light sensor - the top of the transistor's metal can was chop'd off. a replacement Si transistor has much higher turn-on/off behavior (not enough transition). The code used to adc the output of the light sensor had to be re calibrated to account for that.

exray · Joined: 30 Apr 2007 Posts: 1806 Location: Vieques, PR

There's a few Ge types still existing in the NTE line of subs. Are any of those basically equal to a CK722? I guess it might depend on the circuit.

Norm_N_Tam · Joined: 19 Jul 2008 Posts: 252 Location: Connecticut

exray · Joined: 30 Apr 2007 Posts: 1806 Location: Vieques, PR

Ah the good old days! I used to find old surplus PCBs loaded with 2N404s. I put them in all sorts of circuits. Seems that now even that 'junk' is scarce.
Side story - I stumbled on a couple of old Hammarlund HK-1 electronic keyers several years ago. They used some 404s. I actually had to find and BUY some to repair the units.

The CK722 is a tad before my time. They used them in the circuits in the (older) books I had access to but they had already become scarce for this boy builder in the mid-60s.

peeblesoriginals · Posted: Wed Mar 10, 2010 6:57 pm Post subject:

Here are all the CK-722 substitutes, found in my substitution book:

2N60, 2N60A, 2N61, 2N61A, 2N188A, 2N270, 2N270+, 2N320,
2N363, 2N4148, 2N414C, 2N422A, 2N610, 2N611, 2N1175,
2N1192, 2N1313, 2N1348, 2N1349, 2N1350, 2N1351, 2N1372,
2N1383, 2N1414, 2N1415, 2N1681, 2N1383, 2SB89,
2SB156A, 2SB185, MM380, NKT214, NKT224, SF, T322, T352,
PTC102, GE-2, TR-05, HEP253, SK3004, AT20M, ECG102, WEP631,
276-2004, RT-120

All are listed as: Ge, PNP, AA: Which means they are;
"Germanium, PNP, Audio Amplifier".

The above means that just about any Germanium, PNP,
Audio-Amp units will work.
Which means, just about any Germanium PNP Transistor
will work in place of a CK-722. Most will likely work better,
since the CK-722 was a very early, experimenter,
low-cost transistor, prior to the designs of better units.

2N404 crosses to a GE-53, which is also a Ge, PNP, Audio Transistor.
2N2048 crosses to a GE-51, which is a Ge, PNP, RF/IF Transistor.
I find it works well as an Audio Transistor, also.

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

Norm_N_Tam · Joined: 19 Jul 2008 Posts: 252 Location: Connecticut

Curt Reed · Posted: Thu Mar 11, 2010 8:17 am Post subject:

Mike- an no mention of the 2N107? That amazes me, so maybe it was a simple omission. But looking back thru all the magazines of the early 1960's almost all of them that used a CK722 in the parts list also show a 2N107 as being useable. I know for a fact that the 2N107 worked good in my sets that mainly called for a CK722 as the primary choice.

When one of the leads broke off my treasured CK722 and rendered it useless, I had to resort to the 2N107, and in some circuits, it actually performed better than the CK722 did.
Curt
_________________
Curt, N7AH
CW forever
Connoisseur of the cold 807