I dragged out my old Kelvin Electronics Solid State AC Operated Superheterodyne Receiver Kit Stock No. 137-19 that I built in high school about a century or two ago.

Believe it or not, I still have the original builders guide and schematic.

I'd like to get it working again.

For starters I can see it is missing one 2n410 transistor. I have not gone through it yet but I would bet there are other bad transistors in the set too.

So the complete list of transistors is:

2N412
2N410
2N408
2N3638

Can anyone tell me a good source to purchase these parts or their replacements at a reasonable price?

What would their replacements be?

I really have not touched electronics for years. I hope I can recall some of my basic troubleshooting skills.

For example: A simple ohm meter check should be reasonably good enough to check the transistors. Correct?

 

this has some of those transistors:
http://www.kelvin.com/Merchant2/merchant.mv?Screen=CTGY&Category_Code=ELPCTO

 

I dragged out my old Kelvin Electronics Solid State AC Operated Superheterodyne Receiver Kit Stock No. 137-19 that I built in high school about a century or two ago.

Believe it or not, I still have the original builders guide and schematic.

I'd like to get it working again.

For starters I can see it is missing one 2n410 transistor. I have not gone through it yet but I would bet there are other bad transistors in the set too.

So the complete list of transistors is:

2N412
2N410
2N408
2N3638

Can anyone tell me a good source to purchase these parts or their replacements at a reasonable price?

What would their replacements be?

I really have not touched electronics for years. I hope I can recall some of my basic troubleshooting skills.

For example: A simple ohm meter check should be reasonably good enough to check the transistors. Correct?

Probably the best source is Joel Ballek's garage. Let me look.

 

Probably the best source is Joel Ballek's garage. Let me look.

Yikes and I thought I was a pack rat!

Well to tell you the truth, I think I still have some old vacuum tubes around here.

 

this has some of those transistors:
http://www.kelvin.com/Merchant2/merchant.mv?Screen=CTGY&Category_Code=ELPCTO

Funny I did a search on their site and it came up with nothing.

I was going to email them, they might get a kick out of the fact I still have one of their old radio kits.

 

Yikes and I thought I was a pack rat!

Well to tell you the truth, I think I still have some old vacuum tubes around here.

I have HUNDREDS of vacuum tubes. Three tube testers.....and a partridge in a pear tree!

 

Funny I did a search on their site and it came up with nothing.

I was going to email them, they might get a kick out of the fact I still have one of their old radio kits.

Those are all germanium transistors.

Eric

 

Welcome back to electronics.

It would make a good addition to the project to find out a bit about these transistors (and transistors in general) while you are about it.

The 2N4xx transistors are very low voltage, low current germanium jobs (PNP). However they are relatively high frequency What was the range of your superhet? Did you have a 4.5, 6 or 9 volt battery?

The 2N3638 is a bog standard silicon pnp low power transistor, probably used for a simple output to headphones or high impedance speaker.

 

Welcome back to electronics.

It would make a good addition to the project to find out a bit about these transistors (and transistors in general) while you are about it.

The 2N4xx transistors are very low voltage, low current germanium jobs (PNP). However they are relatively high frequency What was the range of your superhet? Did you have a 4.5, 6 or 9 volt battery?

The 2N3638 is a bog standard silicon pnp low power transistor, probably used for a simple output to headphones or high impedance speaker.

It's an AM radio. Powered by a DC power supply 18.6 V.


I checked all of the transistors. The RF stage transistor and first stage IF seems fine. The second stage IF is missing (2N410). Looks like both audio amp transistors (2N3638) are completely shorted.


I am including a schematic.

Since the audio transistors are shorted, do I need to worry about any of the other components?

 

If you don't find any subtitute transistors, and it could be for just a couple, you will have to bias the transistors a little differently with the resistors. This will ensure nearly the same performance just like the old transistors performed; except you have different transistors and different component values.

Austin

 

Have you tested the audio transistors out of circuit? With all those tramsformers they might appear shorted to an ordinary ohmeter.

Incidentally older ohmeters have an output battery of 22.5 volts on the high ohms range. This would kill those germanium transistors, with a rating of 13 volts. The silicon ones are rated at 25 volts.

do I need to worry about any of the other components?

I don't understand. The germanium transistors would be the most expensive and hardest to replace or substitute. Any general purpose silicon pnp one will substitute for the 2N3638

 

Have you tested the audio transistors out of circuit? With all those tramsformers they might appear shorted to an ordinary ohmeter.

Incidentally older ohmeters have an output battery of 22.5 volts on the high ohms range. This would kill those germanium transistors, with a rating of 13 volts. The silicon ones are rated at 25 volts.



I don't understand. The germanium transistors would be the most expensive and hardest to replace or substitute. Any general purpose silicon pnp one will substitute for the 2N3638

Yes I pulled them out of circuit. All the transistors are in sockets so it is easy to do.

I have a newer digital multimeter. A cheap Radio Shack model. I tested with that. At first I tested with the K Ohm range. I hope I did not blow them. Then I realized it has a diode checker so I used that mode for the remaining ones.

Should I test them again?

 

Have you tested the audio transistors out of circuit? With all those tramsformers they might appear shorted to an ordinary ohmeter.

Incidentally older ohmeters have an output battery of 22.5 volts on the high ohms range. This would kill those germanium transistors, with a rating of 13 volts. The silicon ones are rated at 25 volts.



I don't understand. The germanium transistors would be the most expensive and hardest to replace or substitute. Any general purpose silicon pnp one will substitute for the 2N3638

NTE semiconductor lists replacements for them at there website:
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search
A source for them could be mouser electronics, www.mouser.com

 

Yes I pulled them out of circuit. All the transistors are in sockets so it is easy to do.

I have a newer digital multimeter. A cheap Radio Shack model. I tested with that. At first I tested with the K Ohm range. I hope I did not blow them. Then I realized it has a diode checker so I used that mode for the remaining ones.

Should I test them again?

Transistors are different from diodes. You might not have it on a cheaper multimer, but a adequate test would be a transistor tester. They should have these little holes four pins on each side. Take a look at the attachment, you'll find the transistor tester circled in red. This actually measures the gain of the transistor.

 

Transistors are different from diodes. You might not have it on a cheaper multimer, but a adequate test would be a transistor tester. They should have these little holes four pins on each side. Take a look at the attachment, you'll find the transistor tester circled in red. This actually measures the gain of the transistor.

I don't have a transistor tester on mine. I was just worried blowing the germaniums. Could I have blown them with this meter?

I was able to test the audio amp transistors. Those are obvious, they are completely shorted.

 

NTE semiconductor lists replacements for them at there website:
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search


A source for them could be mouser electronics, www.mouser.com

NTE does not come up with a price. Do you need to call them?

I also fond some here

http://stores.sacelec.com/sacramentoelectronics/detail.jsp?y=0&x=0&find=2n410&-skipRows=0

and here

http://www.galco.com/scripts/cgiip.exe/wa/wcat/itemdtl.r?listtype=&pnum=2N410-RCA

The packaging on the second one looks nothing like the ones I have (mine look more like the first). Does that matter?

 

I don't have a transistor tester on mine. I was just worried blowing the germaniums. Could I have blown them with this meter?

I was able to test the audio amp transistors. Those are obvious, they are completely shorted.

No, you certainly wouldn't blow them, and they shouldn't make any strain on the transistors. Meters use low value sources (current, voltage, and resistance) to take measurements so that they don't have much effect on the part under test. Your method just won't have much effect for accurate measurements. Put the transistors back in the radio and check to make sure if they have the voltage drop (around 0.3-0.4V for a gernamium). If they don't, then they are bad transistors. Also, you can calculate what voltages the transistors are operating at and then measure what the true voltage really is at those points. So simply start from the main voltage source and work your way down to what voltage the transistors should have, then see if they are under the correct conditions.

Austin

 

Would you like to sell your Kelvin Superheterodyne Receiver Kit, including the Builder's Guide and Schematic? If not, would you be willing to copy the Builder's Guide and Schematic for me and send it to me for a fee?

Thank you VERY much for considering my offer.

 

It's an AM radio. Powered by a DC power supply 18.6 V.


I checked all of the transistors. The RF stage transistor and first stage IF seems fine. The second stage IF is missing (2N410). Looks like both audio amp transistors (2N3638) are completely shorted.


I am including a schematic.

Since the audio transistors are shorted, do I need to worry about any of the other components?

I'd say TR1, TR2, TR3 = AF114 / AF116
TR4 = AC 126
TR 5, TR 6 = AC128 / AC188

Ramesh

 

Please note how many years old the original post is.