Ivantheterrier
New member
Reposted from the general questions cause I somehow completely overlooked the troubleshooting heading. Sorry
So I just finished up a Duocast build. Only to find out it has a rather wierd quirk. I think the problem centers around the germanium transistor.
Anyways here’s the deal. If I set the low cut to 0. I get no sound. More low cut = more volume. The gain control doesn’t seem to do much right now and it seems the transistor may be gating a bit. also changing the voltage selector in either direction causes a momentary massive boost in volume. Tried pulling the 1054 chip. No change.
I’ve checked the values in the low cut filter and everything seems up to spec. Tried re touching the solder joints as well. Also in a last ditch effort. Tried swapping the transistor around 180 degrees. And even tried a spare metal can instead of a red dot oc75. And it seems to behave the same in either direction….
ive previously built a simulcast. And own a dual foot switch broadcast. So I have a pretty good idea something is very wrong. Any ideas where to go from here? Haven’t pulled the board from the case as it’s quite late and I was hoping a retouch of solder would fix this thing…
Addendum. Continued working on this some more today. Been testing the pots for bad connections and values. Socketed a new bc549. And checked the components in the low cut filter. Even lifted the 330u cap for good measure. Same wierd behaviors. Plugged it in through a real amp and it sounds like it’s always on high gain mode. Low output volume overall. And the low cut seems to act like a volume control… like it’s affecting the bias of the transistor or something.
And for good measure some transistor voltages. All measured to ground
Bc549
1: 7.84
2: 3.01
3: 2.49
germanium
1: 7.98
2: 7.84
3: 7.96
And if I pull the germanium. And measure at the sockets
1: 8.98
2: 6.49
3: 7.92
I’m no expert here. But shouldn’t these values at least follow a similar pattern?
So I just finished up a Duocast build. Only to find out it has a rather wierd quirk. I think the problem centers around the germanium transistor.
Anyways here’s the deal. If I set the low cut to 0. I get no sound. More low cut = more volume. The gain control doesn’t seem to do much right now and it seems the transistor may be gating a bit. also changing the voltage selector in either direction causes a momentary massive boost in volume. Tried pulling the 1054 chip. No change.
I’ve checked the values in the low cut filter and everything seems up to spec. Tried re touching the solder joints as well. Also in a last ditch effort. Tried swapping the transistor around 180 degrees. And even tried a spare metal can instead of a red dot oc75. And it seems to behave the same in either direction….
ive previously built a simulcast. And own a dual foot switch broadcast. So I have a pretty good idea something is very wrong. Any ideas where to go from here? Haven’t pulled the board from the case as it’s quite late and I was hoping a retouch of solder would fix this thing…
Addendum. Continued working on this some more today. Been testing the pots for bad connections and values. Socketed a new bc549. And checked the components in the low cut filter. Even lifted the 330u cap for good measure. Same wierd behaviors. Plugged it in through a real amp and it sounds like it’s always on high gain mode. Low output volume overall. And the low cut seems to act like a volume control… like it’s affecting the bias of the transistor or something.
And for good measure some transistor voltages. All measured to ground
Bc549
1: 7.84
2: 3.01
3: 2.49
germanium
1: 7.98
2: 7.84
3: 7.96
And if I pull the germanium. And measure at the sockets
1: 8.98
2: 6.49
3: 7.92
I’m no expert here. But shouldn’t these values at least follow a similar pattern?
