Transistor Pinouts [resolved]

[adamlmac]

Greetings,

I am looking for the pinouts for the transistors on the Eros 2 C4S board. 2N2222A, MJE350 and PN4250A.

If it helps, the issue I am having is excessive hiss on the right channel. I have ruled out anything upstream and tubes. I have reflowed all joints on the right channel C4S. Voltage on the OkC and OkD is 0.57V and 1.18V. All other voltage is basically right in the middle and very close to matching right to left. When I originally finished the build, OkC and OkD were 1.41V and 1.63V. Those were different tubes, but the point is that there was a decent delta between right and left already.

Anyway...
Thanks for the help.
Adam

 

[Paul Joppa]

You can usually find data sheet links on vendor websites like Mouser and Digikey. They will have pinouts.

In a properly operating Eros, those voltages are the bias (cathode) voltage for the EF86 tubes, which depend on the individual tube's emission. The voltage decreases as the tube ages. For a good classic EF86, fresh but fully broken-in, it's about 1.5v. But many on the market don't meet that spec - which is why there is a servo bias arrangement instead of an LED. I'm away from my notes, but IIRC anything below 1.0v indicates a worn-out cathode.

One test is to swap the EF86's between channels and see if the voltage follows the tube.

 

[adamlmac]

You can usually find data sheet links on vendor websites like Mouser and Digikey. They will have pinouts.

In a properly operating Eros, those voltages are the bias (cathode) voltage for the EF86 tubes, which depend on the individual tube's emission. The voltage decreases as the tube ages. For a good classic EF86, fresh but fully broken-in, it's about 1.5v. But many on the market don't meet that spec - which is why there is a servo bias arrangement instead of an LED. I'm away from my notes, but IIRC anything below 1.0v indicates a worn-out cathode.

One test is to swap the EF86's between channels and see if the voltage follows the tube.

Thanks, Paul. I'm not sure which manufacturer makes the transistors in the kit. I am asking because I have found different pinouts in the data sheets for the 2N2222A. There doesn't seem to be a standard. This was specifically for the 2N2222A - metal can type, but I figured if I was asking for one, might as well ask for all. Granted, I'm new to this, so there might be something else in the 'extended designator' that I don't understand that makes the difference obvious to the trained eye.

I swapped tubes and listened for the hiss, but it stayed in the right channel. I didn't check voltage, but the noise didn't move, so I assumed not tube related. These are Tung Sol EF806 and are only a few months old.

 

[Paul Birkeland]

0.57V on OKC is way off spec, what are the rest of the voltages on that front C4S board?

Any old 2N2222 will do, I have never observed a pinout difference, but some manufacturers will show the pin diagram top down, and others bottom up

 

[adamlmac]

Ok, I’ll just go ahead and order parts.

The rest of the readings are:

IA 218.8
IB 218.9
OA 161.6
OB 161.2
OC 95
OD 94
OkA 97.3
OkB 96.2
OkC 0.57
OkD 1.18

Thanks again, Paul.

 

[Jameson]

Ok, I’ll just go ahead and order parts.

The rest of the readings are:

IA 218.8
IB 218.9
OA 161.6
OB 161.2
OC 95
OD 94
OkA 97.3
OkB 96.2
OkC 0.57
OkD 1.18

Thanks again, Paul.

We’d be happy to ship some to you. Shoot Jean an email at Jean(at)Bottlehead(dot)com

 

[adamlmac]

We’d be happy to ship some to you. Shoot Jean an email at Jean(at)Bottlehead(dot)com

Ok, awesome! Thank you! I was going to order some LEDs anyway, so that will save me some shipping.

 

[Paul Birkeland]

Can we see some build photos? Do the OKC and OKD voltages switch places if you switch EF86s?

The super low voltage at OKC would make me think that possibly the heater wiring going to pins 4/5 on the EF86 on that side aren't 100% solid, which would reduce cathode emission, and decrease the bias voltage like that, but otherwise things might look OK. That's about the only way I can think of to get the voltage set that you're getting, other than having one weak EF86 (which would swap the OKC/D voltages).

 

[adamlmac]

Can we see some build photos? Do the OKC and OKD voltages switch places if you switch EF86s?

The super low voltage at OKC would make me think that possibly the heater wiring going to pins 4/5 on the EF86 on that side aren't 100% solid, which would reduce cathode emission, and decrease the bias voltage like that, but otherwise things might look OK. That's about the only way I can think of to get the voltage set that you're getting, other than having one weak EF86 (which would swap the OKC/D voltages).

Well, I had some extra time so I swapped the tubes. The voltage switch channels. Not sure what I was doing before when I swapped them. Must have gotten distracted or something… lol. Anyway, I went back to stock tubes and both channels are dead silent.

Thanks again for the help. You saved me a lot of heartache.