That would be a good OPT for a bass amp but wouldn't expect it to have the FR for much above that if it was designed just for bass. Wouldn't call it a problem or sub par.
@Tube Radio You may want to consider the Heathkit AA-100 output transformers as another choice of an output transformer that would work well with a 6V6 push-pull amp. I built such an amp a few years ago. Works well. As I recall, the AA-100 transformers are 7.6K primary impedance. Just a thought anyway.
The one difference of course is they wouldn't be suitable in a parallel push pull scenario since they have 7.6k primary, unless you run them in half impedance mode.
The one difference of course is they wouldn't be suitable in a parallel push pull scenario since they have 7.6k primary, unless you run them in half impedance mode.
Not to beat a dead horse, really, I just want to make one more point about my comment that I thought you were overthinking this ''stability'' test result so I'll quote the thread again you posted.
''...Any practical value of capacitance would not cause instability when loaded into a 4 Ohm resistive load. Under conditions of no load however, less than .01 uF connected across the output terminals would cause sustained oscillation. This is not inconsistent with other power amplifiers of more prominence.''
Your test used .1uF, correct? 10x Dave's test. The point being instability with 1/10 was consistant with power amps ''of more prominence.''
Folks looking for problems can always find them and promote a cure.
''...Any practical value of capacitance would not cause instability when loaded into a 4 Ohm resistive load. Under conditions of no load however, less than .01 uF connected across the output terminals would cause sustained oscillation. This is not inconsistent with other power amplifiers of more prominence.''
Your test used .1uF, correct? 10x Dave's test. The point being instability with 1/10 was consistant with power amps ''of more prominence.''
Folks looking for problems can always find them and promote a cure.
Last edited:
I'm thinking he told me to use .1uF, but I will check again to be sure.
However doing the stability testing did get the 10kHz square wave looking better at 4 8 and 16 ohms and the output is flat from 20Hz-20kHz. Plus it doesn't oscillate with nothing connected to the input and output.
However doing the stability testing did get the 10kHz square wave looking better at 4 8 and 16 ohms and the output is flat from 20Hz-20kHz. Plus it doesn't oscillate with nothing connected to the input and output.
Last edited:
I had to correct my math.... 10x not 100x.
Dave's improvement... ''Used in conjunction with a new step network added to the plate of the AF Amplifier stage, HF stability is greatly improved, with the amplifier now being able to handle capacitive only loads of at least .03 uF''
Went from .01 to .03. That's 300%!!!
Dave's improvement... ''Used in conjunction with a new step network added to the plate of the AF Amplifier stage, HF stability is greatly improved, with the amplifier now being able to handle capacitive only loads of at least .03 uF''
Went from .01 to .03. That's 300%!!!
Last edited:
I do have a small mono TDA2050 amp kit that was fine when the speaker cable was 3-4 feet, but started to go unstable when the speaker cable was about 24' and I fed a signal to the amp. That one drove a 16 ohm load. It's likely a combination of a capacitance and inductance caused by the longer speaker cable.
So I can see why a stability test needs to be done and maybe a capacitor somewhat simulates the effects of a longer speaker cable. That said the load would be a mix of inductance, resistance and capacitance though, not just pure capacitance.
So I can see why a stability test needs to be done and maybe a capacitor somewhat simulates the effects of a longer speaker cable. That said the load would be a mix of inductance, resistance and capacitance though, not just pure capacitance.
I should stick a 25' lenght of #16 ripcord on my cap meter and see what it reads. I've done that to check phono cable but not speaker wire.
I could do that with my DATS V3 speaker tester as well since it measures capacitance.
Last edited: