[musclecars4ever]

Hi guys and gals, I decided about a year ago to get back into a good stereo system again. After upgrading on several fronts I now have a pair of modded MK III Dynaco amps, which except for some hum coming out of the transformers sound great. I tried the DC blocker from Emotiva which did make the amps sound better (tighter bass) but did little for the hum. I'm open for any suggestions to reduce it as I can hear it from several feet away. Thanks for any help, Ron.

[underdawg]

Did the transformers remain originalto the amp? The few pairs I had that problem I ended buying new manufacture transformers which helped. I think there was differences in the originals as far as some were quieter than others.

[medium jim]

Also check the caps for signs of leakage.  If they are leaking it will be obvious.

Jim

[Mark Korda]

Hi Musclecars,I have a Dynaco St-35 that sounds flawless. When you go near it, with the music real low, I could detect a humming sound. I'm sure there are better scientific answers,and the more I hear, the more I learn, but I did this; I put a 5 pound cast iron York dumbell weight on the top of the protective cage and the hum vanished! I think it also helps to dissipate heat and works with the same princible as the VPI brick. After you check all the grounding and tighten the transformer mounting screws, try it as an experiment and let me know if it works,it did for me, my hum was not audible in my listening position 7 or 8 feet away at low and normal levels to begin with..........Take care...Mark Korda

[musclecars4ever]

Hi guys, thanks for the tips. The amps have the original transformers I think. They were modded with all new caps. about 5 years ago by the previous owner (Triode driver and cap boards). I tightened up all the bolts and it did help, except for one output transformer. I put a weight (about 5 pounds) on it and it did quiet it down some. After doing a search some people use rubber washers between the case and the transformer to quiet them down. I'll try that this weekend or is there something else I should try? Except for the one output transformer I could live with what I have. Thanks for any help, Ron (musclecars4ever).

[musclecars4ever]

Well I tried the rubber washer tweak and it didn't help. In fact all of the transformers in the system are still humming to some degree including the power supplies for the preamp and the turntable. I think I'm down to either a grounding problem or a problem with the power company. Thanks for any help, Ron (musclecars4ever).

[NIGHTFALL1970]

Have you checked out this thread?


http://www.audiocircle.com/index.php?topic=114316.0

[Mark Korda]

Musclecars,it looks like Nightfall solved your problem. I know this,if you described or showed this forum question to Frank VanAlstine and that Humdinger didn't work,I know he would refund your money.It sounds like another way to troubleshoot with out risking money,Oh,if it works your out 125. I'd do it...Mark K.

[avahifi]

Your transformer hum is being caused by one of two things.

First, your very old transformers may simply have internal loose plates.  This happens.  The 60 Hz AC in acts like a shaker table and anything loose vibrates.  The fix is to first make sure the mounting hardware is secure and tight.  If that does not help see thing two below.

The second thing is that something in your electronic circuits after the transformer is pulling too much power from the transformer, more than it was designed to handle.  This could be a leaky power supply capacitor, a defective rectifier tube, audio power tubes pulling too much current, or even possibly circuit modifications to the unit that were not well thought out and now demand more energy from the transformers than before.  In any of these cases, the transformers can hum in protest.

Note that the AVA HumDinger will not help these situations unless the hum is actually being caused by low level DC on your AC power lines.  This is not a likely situation with a vacuum tube power amplifier with big standard iron transformers. However, we do use an old working Dyna St-120 with its original conventional iron power transformer here to test the HumDingers, along with a hair drier at half power on the same AC circuit.  Without the HumDinger the old St-120 hums so bad it wants to almost leap off the shelf.  With the HumDinger it is dead quiet.

Regards,

Frank Van Alstine

[musclecars4ever]

Thanks guys for the advice, I tried the DC blocker from Emotiva with no luck. But I will try your unit because every transformer in my stereo has some hum, so I kind of think that is where it originates from. I have a boom box elsewhere in the house that also buzzes when I listen to AM. I'll call tomorrow about your DC blocker and also a Dynaco Ultimate70 that I bought used but lost the left channel shortly thereafter. That amp sounded great so I'd like to get it up and running again. Thanks for the help guys, Ron (musclecars4ever).

[musclecars4ever]

Hi Guys, sorry for the delay (it's been a busy month). Anyway a local tube amp guy told me how to check the AC mains with a scope. Talk about a ragged sine wave, the peaks are really bad. It looks just as bad through the Emotiva unit. When hooked to a signal generator I get a perfect sine wave so the scope is fine.  My next move is to talk to the power company, but I'm open for suggestions. Thanks for any help, musclecars4ever.

[doctorcilantro]

Any developments Musclecars?

[musclecars4ever]

Hi guys, I think my problem may be with the power coming into the house. The local electric company stopped by to check things out and found a bad neutral connection in the meter. They suggested I upgrade to a 200 amp service which would include replacing everything from the weatherhead to the breaker panel. So I got a price on the job and was hoping to get it done in the fall but it looks like the spring now. Also when the electrician looked things over he said the original grounding of the house needed to be upgraded. Among other things the plastic water meter that was installed a couple of years ago should have been jumped with a ground strap. I picked up a powerline noise analyzer (dirt cheap) and when I plug it into the outlets around the house I pick up an AM radio station out of NYC 50 miles away. When I plug it into the Emotiva  filter I get dead silence. So if anyone has a suggestion for me with regards to upgrading the service I'm all ears. Thanks, musclecars4ever.