Modify Simulcast to NPN

[neiltheseal]

Hey everyone

I'm thinking of making a Simulcast/Duocast but I don't have any germanium transistors and I have a couple of quesitons:

1. Can I use a PNP silicon transistor in place of the germanium one?
2. If no to above, can I modify the PCB to accept NPN transistors in q2?

Schematic is here

I've had a look around and found the narrowcast. It seems to me that an NPN is in Q2 and VCC/Ground are swapped. If I flipped orientation of Q2 (using a 2n3904) and swapped VCC (going into R7) and ground (r8) then this should work right?

I know I will probably have to mess around with resistors to bias it but to my small brain this seems like it should work.

Thanks in advance.

 

[finebyfine]

Before trying to adapt the Narrowcast circuit to the Simulcast PCB I would just try socketing Q2 and try using a low HFE silicon PNP transistor - such as 2N2904, 2N2905A, 2N3703, etc, and using trimpots for R7 & R8 in case OC71 leakage (unsure if this is the case, but rather safe than sorry) has an impact on biasing.

 

[neiltheseal]

Before trying to adapt the Narrowcast circuit to the Simulcast PCB I would just try socketing Q2 and try using a low HFE silicon PNP transistor - such as 2N2904, 2N2905A, 2N3703, etc, and using trimpots for R7 & R8 in case OC71 leakage (unsure if this is the case, but rather safe than sorry) has an impact on biasing.

Thanks for your reply.

As this is the simplest option it is also my preferred option!

I figured this would work but I just wanted other opinions. I’ll try out the trim pots if necessary.

 

[HamishR]

There are silicon models produced by Hudson. They use the 2N4033 which is a large PNP Si transistor - it looks rather like a Ge transistor. I have built a few Broadcasts with it and it requires no modification to work. I also prefer the sound of it over Ge - the difference is subtle. The 2N4033 is available at Mouser.

 

[neiltheseal]

There are silicon models produced by Hudson. They use the 2N4033 which is a large PNP Si transistor - it looks rather like a Ge transistor. I have built a few Broadcasts with it and it requires no modification to work. I also prefer the sound of it over Ge - the difference is subtle. The 2N4033 is available at Mouser.

Thanks for this. I might have to get one.

I have a 2n2905a lying around that is a pnp silicon transistor. Do you think that would work?

 

[HamishR]

No idea! Try it! I often use thos circular transistor sockets for Ge and larger Si Trannies so it's easy to try a few.

 

[neiltheseal]

Thanks. I’ll try out what I have. I can always order your suggested transistor next time I do a mouser order. It’s in my cart waiting.

Thanks for the input!

 

[neiltheseal]

I built this this afternoon and can confirm that a 2n2905a transistor works and sounds fantastic.

Thanks @HamishR for the suggestion. No need to buy a germanium transistor!

I’m not sure whether it sounds like the original or not but it sounds great nonetheless especially at 27 (or whatever voltage the switch gives). This thing is loud too!

 

[airbud]

There are silicon models produced by Hudson. They use the 2N4033 which is a large PNP Si transistor - it looks rather like a Ge transistor. I have built a few Broadcasts with it and it requires no modification to work. I also prefer the sound of it over Ge - the difference is subtle. The 2N4033 is available at Mouser.

this is intriguing, thanks for sharing.