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Old 21st January 2002, 08:37 AM   #11
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Congrats on your 45 amp! Surprising how much bass you can get out of a couple of little watts. As far as small value coupling caps I have had good luck with WIMAs though they are a pain because of the circuit board length leads. I don't think I paid much for them and it took a long time to get around to them but so far I like them untill I like something better. If you are happy with your caps see if you can get some of the WWII 6SN7s labeled VT231s. They are supposed to be the best, and are lots easier to install than new caps.
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Old 21st January 2002, 03:23 PM   #12
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Default 45 diy tube amp

Thanks!
I was really surprised that the bass was so good. Both in terms of low frequency extension, and especially impact. When the drummer really laid into his floor tom on one disc, you felt the low pressure wave hit you, and It sounded very real and close to live sound. I play a set of Yamaha acoustic drums on weekends with a 6 pc. working band, and am familiar with how drums sound live.
Having 104 db/1w Lascalas helps with that 2 watts also.
I expected a great midrange, and got it, but bass was a nice surprise.
I thought most tube amps rolled off the top end, but the highs seem to go well beyond my hearing ability.
I built the amp in 3 sections, testing each section before continuing the build process.
I first built and tested the main power supply,B+, and 3 filiment supplys . Measured voltages with my Wavetek meter. All the voltages,(except the rectifier filiment), were on the high side, which I attributed to the fact that the power supplys were unloaded .
After I wired and mounted the 6sn7 driver circuitry, I powered the amp up, and fed a 1vpp triangular wave input signal to the input jacks, and looked at the output with an oscilloscope.
I was going to measure the -3db rolloff points. I couldn't find one at the low end. It was flat with a voltage gain of 10.6 from a few hertz, out to over 150,000 Hz. The triangular wave stayed very clean across the band.
6SN7 is a great ,wideband, amplifying tube.
I then hooked up the opt's, and plugged in the 45's, but didn't measure the final output at the speaker terminals, as I was too anxious to listen to it.
Later I'll put a 20 watt, 8 ohm, non-inductive wire wound resistor across the output terminals, and take some measurements using the scope, with square wave, triangular wave, and sine wave inputs.
Right now, I don't want to pull the amp out of my system.
Thanks for the tip on the vt231. I will definately try some tube swapping down the road.
mg16
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