Vanguard Audio Labs

Building out one of our custom patent-pending V14 Variable-Voltage Tube Condensers. Every time I use our laser engraver it makes me feel like an astronaut 🧑‍🚀

The V14's patent-pending Variable-Voltage tech allows the engineer to change the tube supply voltage on the V14, resulting in very interesting THD and frequency response characteristics. Between those 9 settings, the 9 polar pattern settings, and the 3 selectable voicing settings ("12", "251", and "ribbon" modes), the V14 is about as close to an analog modelling microphone as we've come!

LEARN MORE HERE: vanguardaudiolabs.com/v14

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Today's repair - an AKG SolidTube from the late 90s! These were one of the first "affordable" tube mics for the home studio, coming in around $1500. They had some clever design ideas, as well as some baffling design choices that make the power supplies incredibly unreliable.

Let's start with the good - a clever electret-style cardioid capsule using very similar mechanics to the "nylon CK12", but with better chambering. the capsule actually sounds pretty nice and has a clever shockmounting arrangement.

The baffling - an all-plastic internal structure to the microphone. An AKG special, which is using proprietary components - in this case, the power transformer, low-cut inductor, and low-cut switch are all specially-made components. A "NATIONAL" brand Chinese 12AX7 is at the heart of the microphone, which makes for an easy upgrade path - although extracting the tube is a bit tricky.

The unreliable - the power transformer supplies an insanely unnecessary 23V heater winding. That means that after rectification and diode bridge voltage drops, there's 30V heading into the heater regulator. That means the regulator is sinking 18V! Additionally, the transformer is undersized for the amount of current and voltage its supplying - including a 400V(!) high voltage secondary after rectification, which is subsequently dropped to 205V for the tube plate. Long story short - it pulls a LOT of power and then has to dissipate that power as heat. Heat is NOT GOOD for components and reduces their usable lifespan.

The transformer is potted into an epoxy, making it even less able to dissipate its own heat load. The PSU transformers fail with regularity, and often take several other components with them when they do.

Unfortunately their $500ish used value makes repairing them almost not worth it, especially since AKG no longer supplies replacement transformers. Fortunately Electronic Music Services in the UK has manufactured replacement transformers, and I have exactly one of these transformers left on my bench. If your solidtube isn't working, I can fix exactly one more of these, so shoot me a DM.

Today’s repair project is a Sony C800G. These things eat tubes like candy, and this one is exhibiting the “campfire” noise of a crapped-out tube. Fun fact - Sony sorts and relabels inexpensive 6J4P tubes and sells them for $487 each as replacements. I’ll be putting in a nicer low-noise long-life Phillips-made tube that will hopefully keep the microphone tube happy and healthy for longer.

Note the power supply in this unit uses a dual-triode 12AT7 instead of the original pair of 6au6 pentodes. I’m replacing that as well to be on the safe side. They also use two 1-farad super capacitors that have a short life expectancy in the power supply.

If you own a C800G expect some tube maintenance costs as you move forward. The design of the mic tends to chew through them. I found one Sony tech quoted as saying each tube had an expected useful life of 100 hours. Probably low-balling it, but still insane.

As always if you have any sick mics that need some TLC, email me at [email protected] !

The Vanguard Roadshow will be in Laramie, Wyoming on August 29, 2026 at Timber Canyon Studios for a day of recording and exploring.​ Vanguard Audio Labs' Chief Everything Officer and mic mystic, Derek Bargaehr will be on hand, so stop by and say hi!

Timber Canyon's Jim Roberts will be hosting us for a day of tracking with some of the finest Americana players in Big Sky country, all captured with Vanguard Audio's full line-up of exquisite, non-clone studio condenser microphones.

Don't miss out on this opportunity to see and hear Vanguard Audio Labs in action.

​This event commences on August 29, 2026 at Timber Canyon Studios at high noon. Light refreshments and a splendid time are guaranteed for all!
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​Space is limited, so you must RSVP to:
[email protected]