EF1 was common for 5 watt amps of that vintage. I’d use ones rated for 4A, but that’s just so the beta holds up at the 1 amp or so current that you’d actually see. BD139/40 would work, and not blow up unless the speaker wires short.
A pair of Ge PNPs in totem pole with a driver transformer usually sounded better, and always put out a bit more power, with a given limited supply voltage. These were a step backward. It got even worse when everything went to the single-IC solutions. Those lost 6 to 10 volts of the available output swing, where the discretes fared much better.
A pair of Ge PNPs in totem pole with a driver transformer usually sounded better, and always put out a bit more power, with a given limited supply voltage. These were a step backward. It got even worse when everything went to the single-IC solutions. Those lost 6 to 10 volts of the available output swing, where the discretes fared much better.
The transistors need to withstand full rail voltage plus a safety margin to avoid something called 'secondary breakdown'. So if it had a nominal 25 volt rail a rating of 35 volts or more would be fine. In practice any common parts like BD's and TIP's would be more likely in the 60 to 100v region.
As you increase Bvceo, with all else equal, gain falls. And it falls faster at low Vce. With only a 25 volt supply, you can’t afford to have performance fall off radically below Vce=5V. It’s too big a fraction of the available swing. Lower voltage types (say 40 to 60 volt) tend to do better in these low voltage applications than their 100 or 160 volt counterparts.
The second breakdown issue is quite real, and annoying as hell. What it boils down to is that a transistor needs to handle its FULL power capability at the half-rail point. On a 25 volt single supply (or split +/-12.5 volt rails) you require full power handling to 12.5V. It can fall above that, because any current that does exist above that Vce in operation will be limited to one quarter of a cycle in duration and falling below the maximum the whole time as well. That’s not too big of an ask for any bipolar transistor. On +/-80V rails it can be.
The second breakdown issue is quite real, and annoying as hell. What it boils down to is that a transistor needs to handle its FULL power capability at the half-rail point. On a 25 volt single supply (or split +/-12.5 volt rails) you require full power handling to 12.5V. It can fall above that, because any current that does exist above that Vce in operation will be limited to one quarter of a cycle in duration and falling below the maximum the whole time as well. That’s not too big of an ask for any bipolar transistor. On +/-80V rails it can be.
I checked the resistors out of circuit with an ohm meter.
The first time I measured the voltage at the diodes I measured from the transformer side of the diode to ground and got 7 volts and change on AC multimeter. Second time I measured between the two diodes on the transformer side getting double my first measurement of 15 vac on same multimeter
"Put your black lead on ground and measure DC red lead on kathode D2/D3 junction.
If this is 22V continue with below."
This is 10 volts dc
The first time I measured the voltage at the diodes I measured from the transformer side of the diode to ground and got 7 volts and change on AC multimeter. Second time I measured between the two diodes on the transformer side getting double my first measurement of 15 vac on same multimeter
"Put your black lead on ground and measure DC red lead on kathode D2/D3 junction.
If this is 22V continue with below."
This is 10 volts dc
Somehow, you’ve developed a very unique failure mode in that transformer. I just can’t see you getting only 7-0-7 out of it and it not getting blazing hot at the same time.