M8162

Bad Tubes – Bad Bad Tubes

Bad Tubes - Bad Bad Tubes

Well, I finally had some tubes go “bad” on me or “become microphonic”. When I purchased my Doge 8 one thing I didn’t like was that it used 4 12AT7 tubes for the line stage. I liked the idea of 12AT7 because they can really change the music. However, it is tough to get a quad of matched tubes. Originally I was going to get a quad of Bugle Boys from VTubeAudio but only 3 of the 4 matched. I passed on them and wish I hadn’t.

Amperex Bugle Boy 12AT7 / ECC81
Doge 8
Amperex Bugle Boy Halo Getter

After talking with www.VTubeAudio.com we decided the quad didn’t match and I passed on them and decided to try my luck on a cheap set to get me by from another company until VTubeAudio had something I really wanted that matched. 

Brimar 12AT7

Pay attention kids because here is the lesson in this post. Do not buy cheap tubes. I found a quad that was said to be a matched and NOS Brimar 12AT7 quad. The price was right and I purchased them.

I rolled them in and gave them some warm-up time before running some Sade on vinyl through them and seeing what they were made of. I was happy enough with them. After some time to burn in and settle they really had the same sound as when they were first rolled into the preamp. I was skeptical about them being true NOS tubes at this point though. Usually, true NOS tubes will adjust and change through the first 10 hours at least before they settle down, or that has been my experience with tubes. I purchased a pair of Mullard 12AT7 / CV4024 ( Rebranded BEARD M8162) tubes from VTubeAudio a while back and it was awesome listening to them change and finally settle in. Now they don’t leave the amplifier they are in.

Mullard CV4024

After 2 weeks with the Brimars, I noticed one afternoon that I could hear the volume being adjusted through the speakers. I don’t mean the music playing louder and softer I mean the actual volume pot being adjusted. It had a mechanical sound that took me off guard. Initially, I thought It must be the tubes adjusting and it would go away, but it continued to get worse. Word to the wise: shut your system down if you have anything sounding odd. I did have a bit of panic as this has been the first major problem I’ve had with my tube equipment. So I powered everything off and decided to start with the preamp. Logical starting point since I could hear the volume and nothing else had changed in the amplifier it was feeding. 

Removing the Doge 8 Cover

Immediately the problem was obvious. You could see the 3 tubes that had the white haze all over the plates. I removed the tubes and put the stock tubes back in to make sure that was the only problem in the chain. Luckily no damage had been done to the preamp by the tubes becoming microphonic.

First 3 tubes Microphonic
Triplett 3444 Testing Siemens ECC82

I feel like I really dodged a bullet. I haven’t had this happen yet and no components of the preamp were damaged so I feel very lucky. While tubes can go bad there are a few things to remember. Cheap tubes sometimes mean cheap tubes. You know the ole “you get what you pay for” saying. Buy from a dealer that is known for quality tubes, tests the tubes, and shows results for those tests.

Every set I’ve gotten from VTubeAudio has come with a sheet showing the results of the test for each tube. It’s seriously awesome to know what they read before you put them into your tube equipment. It’s peace of mind and will save frustration when you are listening to your music.

Test Results Sent With Tubes

I’ll be patient next time. I should have waited for the right quad of 12AT7 to come along. I feel like everyone has a story of an amp being affected by tubes going bad. I would love to hear your experiences with tubes that didn’t live up to your expectations, and then catch up on past posts by clicking below.

Tips on identifying a NOS Mullard M8162 tube

Beard M8162 vacuum tubes

NOS tubes are a great way to improve the sound your system produces. If you are going to purchase quality NOS tubes there are things to look for to make sure you are getting what you expect.

This post is going to focus on the Mullard M8162 that is rebranded by Beard. You’ll discover over the course of this blog my favorite flavor of tube is the Mullard, so of course I like these!  I’ve got a set of them currently in my main tube amp that I just can’t get enough of. So let’s dive right in!

The M8162 will be called different names: CV4024, ECC81, but must most commonly the 12AT7 (WA). Many NOS tubes were made by one manufacturer and then branded/re-branded by another. Besides the silk screening on the outside of the glass everything else is 100% Mullard.

Model Code

You’ll also notice the code on the glass 654. This signifies it is an M8162 or CV4024.


halo getter

They have a halo getter that some will swear changes the sound. I’m not in that group. I think the getter does its job, but really only helps to confirm the era it was made when identifying tubes.


cross seams

These also have the Euro style cross seams on top of the tubes.

Ladder Plates

If you look at the picture you can see the double ribbed ladder plate that these tubes are known for having.

Plant/Year Code

For me, the numbers R3A2 on the tubes are the most important. They signify what plant they were made in and the year of production. In this case Mullard, Mitcham Plant year 1983.

The plant/year makes a big difference when selecting tubes. A different year means different runs of tubes. Quality of work and quality of materials can vary and can change the sound of a tube even if it is from the same plant and a different year.  Something I really like about Mullard tubes is a pretty consistent quality and tone from the Mitcham plant tubes.  If you’re interested in a bit of history on the plant here is a great video to give some insight and a side by side comparison of a Mullard label and BEARD branded Mullard.

My personal take on these tubes falls in line with how most people feel about Mullards. They have a nice thick midrange, and the highs are extended but not harsh. I run horns in my system so harsh highs are something that can happen easily, but not with this tube. They are very non-fatiguing even at high volumes. Of course, the lows are solid, accurate  and typical of Mullards of this quality.  Click on the picture below and grab a pair from VTUBEAUDIO!

Just remember tubes were relabeled/rebranded by plenty of companies. Know what you are getting before you buy. Make sure it’s from a reputable source and that the tubes are tested before you buy.  VTubeAudio has been my go to for tubes.  Here is a picture of my BEARD M8162 in my system.