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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Tube amp debugging - Hum posted by Ron B on March 13, 2006 at 16:43:09:
Hi Ron,Amateur here as well and I too built the same amps and using 97.5db Altec Valencia's the hum was simply unbearable. I tried several approaches to getting the hum down, including redoing all of the wiring, redoing wiring again using shielded wire, tracing down external noise problems (outside merc light with bad transformer), regulating my wall power with a high end 1500va Liebert UPS, and using a regulated DC supply on the 300B filaments.
What was odd was that with the DC supply, the hum was nearly gone. However, after a few weeks, the hum seemed to get louder and I just could not figure it out. I noticed the DC supply was generating a bunch of heat (no wonder I was feeding it around 9 volts and regulating down to 5 volts). The lm317 was just getting too hot and shutting down (I guess). Anyhow, I found some 5 amp LT1084 regulators on Ebay and modified my supply to use these instead of the lm317s. I also swapped out the 9 volt transformers for some Hammond 166L6 6.3 volt trannys. I put all this back together and powered it up and well, the hum was still there. The combination of lower voltage transformer and better regulator (something like a one volt drop) got my heat problem under control, however, I still had that madding hum.
I was about to rebuild the power supply using different caps and chokes when I was looking over my dc supply schematic. Will it was just a hunch, but I replaced the 2200uf cap after the diodes with some 4700uf caps and pressed the on button.
Well nothing, no sound, must have blown a fuse. At least that is what I thought until I noticed the filaments glowing. I quickly powered off the amp thinking something must be wrong. But after pondering about it for a moment I turned the amp on again. Still dead quiet and this was on a high efficient test speaker out in the shop. I’m guessing that 2000uf was not enough filter in the supply, however I also wonder if I did not cook the 2200s from my earlier attempts.
I can now put my ear right up to either the woofer or the horn in my Altec and I hear absolutely nothing. This is as it should be from what I have read about DC supplies.I figure, in a year or two I will give DC current regulation a try, but for now, am very happy about my amps.
I am no expert on this but I guess my point is don’t give up and if using DC supply, the amps should be dead quite unless something else is wrong.
Bright side, I learned a lot, got a new outside light, rewired shop (where outside light was located), got a UPS, and got dead quite amps :)
Sorry for the ramble,
Danny
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- Re: Tube amp debugging - Hum - Ciscokid 20:34:21 03/13/06 (0)
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