05-08-2020, 09:39 PM
(This post was last modified: 05-08-2020, 09:40 PM by Mike Watterson.)
At power on, after it's been off for a while there is 0V at junction of TR5 and TR6 (to the + rail, which is 0V). That rises to the 4.45 V eventually.
So I took out TR3, the AC128. It shows as a P-JFET on the Chinese tester. Does nothing sensible on the simple Hfe tester. On diode test both junctions are about 165mV.
But on Ohms, with + to emitter, base to emitter and -Ve lead to the collector it reads about 150 Ohms. This gradually rises to about 4K and then it goes much higher. It then stays "working" for a while. Eventually it "resets" and the characteristic is repeated.
The construction does look like a soldered cap on metal ring base. I can't imagine how this relates to a tin whisker, but I shall use the fine cutting disk on the Dremmel tool with can well heatsinked and examine the insides.
Somewhere I have an AC128, but meanwhile I found a pnp Germanium "T7" in an OC71 style black case that has similar to AC128 gain. The radio worked perfectly.
I'll be curious to see inside the can, though not tonight. I've been opening alarm clocks, valves and transistors for a long time.
So I took out TR3, the AC128. It shows as a P-JFET on the Chinese tester. Does nothing sensible on the simple Hfe tester. On diode test both junctions are about 165mV.
But on Ohms, with + to emitter, base to emitter and -Ve lead to the collector it reads about 150 Ohms. This gradually rises to about 4K and then it goes much higher. It then stays "working" for a while. Eventually it "resets" and the characteristic is repeated.
The construction does look like a soldered cap on metal ring base. I can't imagine how this relates to a tin whisker, but I shall use the fine cutting disk on the Dremmel tool with can well heatsinked and examine the insides.
Somewhere I have an AC128, but meanwhile I found a pnp Germanium "T7" in an OC71 style black case that has similar to AC128 gain. The radio worked perfectly.
I'll be curious to see inside the can, though not tonight. I've been opening alarm clocks, valves and transistors for a long time.
