I'm in the planning and parts ordering stage of my first amp, it's based on a GEC 912 amplifier. Here are the schematics:
The transformer that I have is rated at 375 volts, but according to the duncan power supply designer software, after the the rectifier it will only supply 289 volts. The schematic shows the high voltage line at 350 volts. How would the reduced voltage affect the amplifier, and is there something I can do to compensate for it?
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The transformer that I have is rated at 375 volts, but according to the duncan power supply designer software, after the the rectifier it will only supply 289 volts. The schematic shows the high voltage line at 350 volts. How would the reduced voltage affect the amplifier, and is there something I can do to compensate for it?
Hi mossmamc,
This valve line-up is the same as Gingertubes' Baby Huey and requires about 200ma for a stereo amp.
This valve line-up is the same as Gingertubes' Baby Huey and requires about 200ma for a stereo amp.
The valve rectifier will have a significant voltage drop, and C11 (the reservoir cap) is quite small at 8uF so there will be a big ripple voltage at this point, which will depress the average value. Better to design a modern power supply which will supply the amp's needs. We have access to bigger capacitors than they had in the 1950s.
What do you mean by this? I've never designed a power supply before, so I could use some direction.
Ah, looks like you're building a guitar amp. It would help to point that out, most people assume hifi unless otherwise told.
A 5Y3 and small caps are probably what you want; they'll get you a vintage sound with plenty of sag.
First thing: did you model the whole PS in PSUDII? You should be modeling the transformer, 5Y3, 8 uF, choke, 16 uF, rough 100 mA load, 10K, 8 uF, rough 5 mA load. Then check voltages and ripples at the current taps to see what those look like.
No, the intended use is as a hifi amp, but I only want to build a monoblock amp and then build a second one later.
Oh wow, that's a pretty mediocre design, how set are you to build that model? It's got noticeable weaknesses: high NFB to burn off unneeded gain, 12AX7 makes a bad concertina, high PS ripple from small caps. If you want a PP EL84 there are much better choices: Bevois Valley, Red Light District, Baby Huey, Tubelab Simple PP, etc.
I'm not that set on it I guess, I actually picked it because the tubes it uses happen to be the ones that I was able to get for free.
When you sim'ed in PSD did you use the unloaded voltage? If you put in rated voltage your results will likely be low. You need unloaded voltage and DCR. PSD has tools to help you estimate these if you don't have them on hand.
Ok, I'm learning a lot of new things here, what is unloaded voltage, and how to I calculate its value?
The secondary voltage with no load (unconnected). Manufactures specify voltage at rated load which is lower. PSD needs the no load voltage and secondary DC resistance. In PSD if you hit help in the input dialog it will help you calculate an estimate of these. If you have the transformer in hand of course you can just measure them.
As a rule of thumb the output voltage of a transformer will drop by about 10% when put to work.
For example if you measure your heater voltage without the valves in you might see 7v
Once you put the valves in the heaters light up and are doing work.
If you measure the heater voltage again the voltage should drop down to 6.3v
HTH Bill
For example if you measure your heater voltage without the valves in you might see 7v
Once you put the valves in the heaters light up and are doing work.
If you measure the heater voltage again the voltage should drop down to 6.3v
HTH Bill
OK, I had a look at the baby huey amplifier design, and I do like it better than the one I was originally talking about. Im changing directions and Im going to follow the baby huey schematic.
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