If you are reading this, chances are you already know there is nothing quite like the warm and smooth sound of an LA-2A compressor. However, what you may not know is that your LA-2A is a great instrument for trying different tubes, and you can improve the sound of any unit for relatively little dough by replacing your device’s preamp tubes.
Whether you have fallen in love with a vintage LA-2A unit or a modern clone, here is Fuzz Audio’s list of the best vacuum tubes to improve the performance of your LA-2A leveling amplifier.
There are four tubes in the LA-2A, but only two of those tubes, the 12BH7 and one of two 12AX7s, directly influence the quality of the audio signal. Most of the tonal quality in your unit is attributed to one 12AX7. This means that when deciding on which tubes to upgrade in your amplifier, most of your budget should be directed towards one premium long plate 12AX7.
In 1958 leading into 1959, Jim Lawrence, the inventor of the LA-2A and founder of Teletronix, developed and produced the first LA-1 leveling amplifier, which contained RCA black plate preamp tubes. During the next five years, many things changed in design from the LA-1 to the LA-2A, but the choice of preamp tubes did not. For that reason, RCA black plate 12AX7’s are a must try for any serious user as they are the original stock option and were preferred by Lawrence and Teletronix.
1. RCA Black Plate – Warmest tube with most depth of tone. Excellent low and high end. Preferred by Teletronix and used in original LA-1 and LA-2A units.
2. Telefunken Ribbed Plate – Sacrificing some warmth for lots of smoothness. This is the second tube to try if you have already tried a black plate.
3. RCA Long Grey Plate – Like the RCA black plate but cheaper!
4. GE Long Grey Plate – Best Budget Option
5. CBS – Second Best Budget Option
If you are considering replacing the 12BH7 in your unit, it really comes down to budget versus how much of a “tone snob” you are. Vintage 12BH7 tubes can be somewhat pricey and hard to find from trustworthy online tube sellers. Pricing and supply, mixed with the fact that 12AX7s influence tone more, means that you should focus on finding a nice 12BH7 only once you have nailed down your preference in 12AX7.
For serious “tone snobs,” users who have original vintage units, and folks not hindered by budget, we recommend a vintage RCA black plate 12BH7. This was the valve found in the original units and is what we endorse for those looking to get every ounce of warmth out of their device. Alternatively, an RCA 12BH7 grey plate is another great choice.
Spending $100 on an RCA 12BH7 may make sense if have an original LA-2A hardware worth $10k (or if you are Jeff Bezos), but if you are on a budget and trying to improve the sound of a more reasonably priced unit like a Warm Audio WA-2A, we recommend GE or Sylvania grey plate 12BH7s. These two tubes can be found at around a fifth the cost of the RCA black plates and are still a huge upgrade from any modern-made tube.
1. RCA Black Plate – Stock for Vintage LA-1 and LA-2A
2. RCA Grey Plate
Both the 6AQ5 and the remaining 12AX7 do not influence tone and thus should only be replaced if you are trying to return a unit to 100% stock condition or are replacing a bad tube. The only advantage to using a vintage 6AQ5 is longevity and because you can find a NOS RCA 6AQ5 for $15 this is what we recommend.
Although, there is a lot of great information about Jim Lawrence and the history of Teletronix on the web, articles rarely talk about the vintage tubes used in original units. While it would be foolish to attribute the magic of these leveling amplifiers to anything other than Lawrence’s ingenious use of the T4 optical attenuator photocell, the vintage tubes Teletronix used in the early days pushed the already legendary sound over the top.