Transistor Conversion of Tube Amplifier

raises collector load reactance at rf to increase stage gain.

any modern jellybean tr capable of the frequency being used. The base bias Rs seem high at 220k on 3v.

I do suspect it's self oscillating. I don't see the point in building it.

NT

Perhaps. Or maybe the output coil and input coil are lightly coupled by distance and maybe it is a metal detector?

That is admirable.

I think Tabbypurr explained the function.

Values. Hmmm. Well, the dia is .25" and the length is .75". No magnetic core is indicated so that's pretty much all we have to go on. Maybe it is air-core? What wire size shall we use for an estimate? Let's start with #30 AWG.

I calculate the inductance could be 10uH with 75 turns on, say a wooden dowel.

That's difficult. My bet is that the 722 did not have much HF gain so using some other device may have its consequences.

You can buy (for collector's prices, link below) the original transistor. Otherwise, I suggest you search for germanium PNP transistors. If it were me, I'd just try it with a jellybean PNP, (whatever you have on hand) just to see what happens. That's your aim anyway, yes?

You have a larger problem facing you. There is nothing to indicate the "Well" and "Plate" coil characteristics. Also, there seems to be no indication of value for the "Rate" cap variable capacitors nor the pot below them.

Good luck. Please report back with your success.

Maybe go for the original transistor?...

If it's a converted valve circuit they'll almost certainly be coils wound on varnished card with air core.

nor what the connection to the 'radiator' is

Maybe my haul's worth a bob or 2 then.

You could probably sub the 3 stage amp with an LM386. Whatever you do just ensure any oscillation occurs out of licensed rf bands.

NT

Thanks for the pointers. My suspicion is that it functions as both an amplifier and transformer in the RF range.

I will build it using air coils and substitution PNP's as suggested.

The loose coupling idea makes sense. The tuning caps were probably the old half plate variety.

Kevin Foster

Put some flexible leads on them so you can move them around. Seems like a fun experiment to me.

Use any small-signal transistor you want; if NPN reverse the polarity of supply an electrolytics. Helpful if ft is not excessive (well under 1 gHz).

No clue as to frequency; try 100uH first; their impedance should be high WRTR2 to maximize signal coupling. .

• Really? crude i=e/r gives 3V/0.22Meg or 14uA which is decent for the CK722. Remember that their leakage current can be in that region.

OK, i give up; where in the heck did you get those dimensions?

My guess is those were section wound ferrite* chokes of 5-10mH. Since they are in series with 10k resistors that puts a slight gain peak at

Was the app underground potholing/mines communications repeater?

piglet

• Like ebay item "Vintage J.W. Miller CO. #6302 Ferrite Choke 2.5 MH 200 MA New Old Stock"

Low current doesn't help the tr's hf response - which presumably is lousy at the best of times.

From 1952 CK722 datasheet - which is rather brief: Abs max: Vce 20v, Ic 5mA. Pdiss 30mW @ 30C amb. Tamb max 50C. Average gain characteristics: Vc 1.5v, Ic 0.5mA, Ib 20uA, beta 12, power gain 30bD, NF 22dB@1kHz. With 1k source, 20k load.

NT

On the drawing he linked to.

There are tons of ex-Soviet germanium PNPs on eBay for cheap, and it should be possible to find a cross-reference. Many Soviet active components were spec-copies of US devices anyway..

Judging by the layout below, it seems the chokes are individual, and probably air core.

The final cap value chosen appears to be 70pF.

Any further assessment of the circuit based upon this would be most appreciated.

Keven Foster

In 1955 one paid a heavy premium for transistors, so the finished device must need portability & low power consumption.

All the chokes oriented the same means some coupling is inevitable. I don't know if it's worth looking at which paths create nfb & which pfb. Low frequency might make this minor, I don't know.

NT

Reminds me of this with different transistors:

from here:

I don't think it does anything. Please report back if you find out otherwise.

Mark L. Fergerson