ARC VS115 Power Transformer Buzzing

My ARC VS115 power transformer will make a mechanical buzzing noise after playing for 1 hour. My ARC VS115 was manufactured in 2012 which came with the KT120 tubes. Anyone has the same problem? Please share your experience with me. Thanks.

I have contacted ARC service and according to them that the new KT120 tubes draw more current than the original designed 6550 tubes which caused the power transformer overworked and ran hotter and eventually making noise.

Since I did not buy my VS115 from an authorized dealer, the best they can do for me is to offer me a 50% discount on a brand new transformer. Also, they recommend me to use 6550 tubes instead and even offer to send me a new set of 6550 tubes for free if I buy the transformer from them. What a sweet deal and best service from ARC!!!

Next I will confirm if the 6550 tubes make the transformer run cooler and whether it will sound as good as KT120. So, please stay tuned on this. Thanks for listening.

Keep us posted & Happy listening!
My informal study of this has indicated that nobody has EVER had an issue with transformers being disturbed by 6550 to KT120 to KT150 swapping. Nobody. My relatively modest Jolida 502P came with 6550s, ran 120s for 3 years, and now uses 150s for over a year…sounds brilliant, works beautifully with no noticeable transformer heating, and it’s buzzless. I, of course, noticed the warnings about current draw hazards but the Jolida dudes told me not to worry…so I don’t. I do use a PS Audio Humbuster III but mostly since another amp (SS for occasional outdoor speaker driving) I plug into the thing had a transformer hum at times and the Humbuster has 2 outlets. This could be a first for my informal study but somehow I doubt it. I’m staying tuned!

I hope you are right. I wished my case is just a bad transformer and hope the new one will fix my problem since I like the way KT120 sounds now.

The reason I posted it here is to see if other ARC VS115 owners experienced the same problem with KT120 or even 6550 tubes. If you do a Google search, you will notice at least 1 VS100 and 1 VS115 owners complained the same problem.

Here is ARC response: "Over the course of time with KT120 use in the VS115, Audio Research has observed an accelerated rate of failure in the power transformer for the VS115. The power transformer start to buzz loudly. This is most likely due to the large increase in the heater current requirements of the KT120 output tube which causes the power transformer to run extremely hot.  Due to this increased risk of power transformer with KT120 use,  Audio Research now recommend customers use only the 6550 output tube in the VS115. Moving forward, Audio Research will only warranty future power transformer replacement with the use of the 6550 output tube. "

Finally, I got the parts from ARC last week. I need to find time to replace the power transformer. Before I do that, I went ahead to conduct a preliminary comparison between the 6550 and KT120.

My initial impression is the 6550 sounds a little bit mellower while KT120 sounds a little bit bolder. Surprisingly, I found some music sound more musical and better with 6550 to my ears. However, KT120 will give you more snap and weight in bass and certainly it does look more sexy. The bottom line is I would stay with KT120 and use 6550 as my backup.

Next, I will replace the transformer and measure the temperature difference between using 6550 and KT120 to verify ARC's theory that KT120 will run the transformer hotter. Thanks for listening.

I purchased a new VS115 from my local dealer in 2009. It came with 6550 tubes. In 2011 I switched out the tubes to the KT120's. I was very happy with the improved sound. In 2012, one of the transformers began buzzing. My dealer determined the transformer was going bad and ARC replaced the transformer. Recently, after 3800 hours, one of the KT120's failed along with a resistor. It was quite a pyrotechnics display. A 6 foot linear orange arc along with resistor shrapnel. I took the amp to my local dealer for service and planning on getting new KT120 tubes. He informs me that ARC is no longer recommending putting KT120's into the VS115 because they are encountering a number of long term transformer failures with the KT120's in the VS115 amps. They are now recommending going back to 6550 tubes. I still have my original 6550. The amp is currently at the shop. I'm anxious to hear what it sounds like with the 6550's reinstalled. I have grown very fond of the sound the KT120's produced for the past 5 years. 

The best sounding 6550 I found was the mil spec GE-6550 with green writing, and the glass was so much thicker than the others I remember, they had a real heavy dead sound when flicked with the fingernail.

Cheers George