Finally got my GM70 amp all done. Sounds just great! Could not be happier with how it turned out. Sounds even better than my Parallel 300B amp. Very good base control. It is driving into a JBL E140 in a 200 pound box tuned at 30 Hz.
The Hammond 167P18 (18v 5 amp) works perfectly for the filament supply. So perfect in fact it's 77% efficient with a linear regulator.
The Hammond 167P18 (18v 5 amp) works perfectly for the filament supply. So perfect in fact it's 77% efficient with a linear regulator.
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Thanks guys. Yes it is a fan on the back. It's running on the filament supply for the 7027 6SN7. That's the third fan I tried before I got one you could not hear. It doesn't need it. Never built a thousand volt amp before so I put it in. No measurements yet. Back to work tomorrow so it may be a few days.
You can get the cases from 8audio on ebay for $76. I actually wrecked one of the fronts and the guy sent me another one for $30 including shipping. If you use some fore thought you can slide boards in on the sides of the case.
You can get the cases from 8audio on ebay for $76. I actually wrecked one of the fronts and the guy sent me another one for $30 including shipping. If you use some fore thought you can slide boards in on the sides of the case.
Started some testing last night. Was looking at near perfect sine wave 40v peak to peak and my inrush current limiter had it's limit and went into melt down. Actually it cracked and opened up and turned into a 6.4K resistor.
I had a 6.8 ohm load attached so that is like 28 watts and looking good.
I also managed to sweep the low frequencies and it's dead flat and then at the upper end it's starting to drop at 18K. I just watched the sign wave start to fall a bit there but didn't write anything down. Humm that was with about a 14v peak to peak sine wave.
I have some 2.5 amp NTC's coming. The one that melted was a 1.5 amp. Which I thought would be fine. I must be pushing into A2???
I had a 6.8 ohm load attached so that is like 28 watts and looking good.
I also managed to sweep the low frequencies and it's dead flat and then at the upper end it's starting to drop at 18K. I just watched the sign wave start to fall a bit there but didn't write anything down. Humm that was with about a 14v peak to peak sine wave.
I have some 2.5 amp NTC's coming. The one that melted was a 1.5 amp. Which I thought would be fine. I must be pushing into A2???
Then you need to add a DC-coupled cathode follower between the present driver and GM-70.
Alrighty. I switched over to the 4 ohm tap and hooked up my 6.8 ohm 60 watt resistor and this thing is putting out a perfect sine wave 38 volts peak to peak. 26 watts! I mean perfect sine wave. That's pushing almost the max output on my cheap handheld BK wave generator so I don't know if the wave distortion above 38 volts peak to peak is the BK or the amp at this point. The sine wave is pretty much perfectly symetrical!!!
I have to use a 2.5 amp NTC (in rush current limiter) on the high voltage transformer anything lower cracks up at peak power. I have a 3 amp SloBlo circuit breaker in it now that does not trip so I feel pretty good about that.
The GM70 appears to be quite a nice tube, I must say.
I have to use a 2.5 amp NTC (in rush current limiter) on the high voltage transformer anything lower cracks up at peak power. I have a 3 amp SloBlo circuit breaker in it now that does not trip so I feel pretty good about that.
The GM70 appears to be quite a nice tube, I must say.
I guess I need to catch up with technology. And I thought I was cool owning an oscilloscope. TrueRTA a good one? I have a Delta 1010.
Latest circuits for those interested.
Huge improvement in sound using these:
940C20W1K-F Cornell Dubilier Electronics (CDE) | 338-1182-ND | DigiKey
Instead of these:
Copper Jensen .47uf oil capacitor 845 211 300B 2A3 45 PX25 6SN7 tube amplifier Q | eBay
for coupling caps. Just my opinion of course.
Huge improvement in sound using these:
940C20W1K-F Cornell Dubilier Electronics (CDE) | 338-1182-ND | DigiKey
Instead of these:
Copper Jensen .47uf oil capacitor 845 211 300B 2A3 45 PX25 6SN7 tube amplifier Q | eBay
for coupling caps. Just my opinion of course.
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