Phædrus Audio FAQs

Frequently Asked Questions

We hope that you find the following Frequently Asked Questions useful. Nevertheless, we accept that often there is no substitute to communicating with a human being! So please use these FAQs, and if you have follow-up question, contact

Dealing with Phædrus

Electronic tubes™ for microphones - General

Telefunken VF14 replacement tubes

Telefunken AC701 replacement tubes

Other replacement electronic tubes™

Studio equipment

Needle-drop equipment

Answers to FAQs

What is the price of (a Phædrus product)?

All our prices are given on this page.

International buyers, please note:

Phædrus Audio Terms and Conditions are here.

Sales to EU countries post BREXIT

Since the UK left the European Union, VAT prices are only applicable to customers in the United Kingdom. We no longer charge the VAT price to European customers. Instead we will charge you the basic price, but you will have to pay the equivalent tax (TVA in France, Germany, IVA in Italy and Spain etc.) when the unit arrives into the European Union. Carriers will normally ask you to pay this before they will deliver the goods to you. You are responsible for making this payment.

European distributor

As is widely reported, due to the implementation of the new customs arrangements due to BREXIT, some of our European customers have experienced long delays due to customs processing when the goods reach the destination country. In view of this, we have set up a European distributor inside the EU who holds a small stock of our popular Electronic Tubes™ and Supertubes™. European customers buying from this distributor avoids customs delays due to shipping from the UK. Contact our distributor for availability, prices and conditions.

Sales to UK customers

Note that these prices are ex-works. Postage and packing are extra. VAT will always be charged.

How do I order and pay for Phædrus Audio products?

We prefer payment by PayPal. When the goods are ready to ship, we will raise a PayPal invoice and we dispatch on payment of this invoice. We always invoice in UK Pounds Sterling (GBP) but PayPal makes it easy for you to settle the invoice in your local currency. To go ahead with an order, we simply need an email address to which we can send the PayPay invoice and a shipping address.

We can also accept electronic transfers; although we can only accept transfers in UK pounds (GBP), so there will be FOREX and other charges. PayPal works very well for small amounts. Remember it is the vendor (Phædrus Audio) who pays the PayPal charges.

Do you deal direct or through dealers?

Most of our sales of the electronic tubes™ and Gold Dot Supertubes™ are direct to end-users. However, we welcome trade enquiries, as we do from all customers.

Do you ship to my part of the world?

In principle, we ship to anywhere in the world. Some guide prices are here.

Customers in the following countries should check with us first: Afghanistan, Belarus, Burma (Myanmar), Central African Republic, Democratic People’s Republic of Korea, Democratic Republic of the Congo, Iran, Iraq, Lebanon, Libya, Nepal, Rwanda, Somalia, South Sudan, Sudan, Syria, Ukraine, Venezuela, Yemen, Zimbabwe.

What lead times do you offer on your products?

With most of our electronic tubes, we ship within 3 to 5 days of order. The preamplifiers and studio products depend on our present stock and you'd be best to contact Remember, we only invoice when a product is ready to ship.

What are your prices for shipping?

Electronic tubes™ and Groove Sleuth MICRO

If you wish us to deliver using a courier, please give us the precise delivery address and contact for a quotation. Prices change all the time, so we can't give a fixed price for this service. We will always endeavour to find the best price in the circumstances. To give you an idea, charges range from about £20 to £50 for one tube, depending on destination.

Our preferred delivery method for Electronic Tubes™ and the Groove Sleuth MICRO is by Royal Mail Service - Tracked and Insured. At least since the beginning of the COVID-19 pandemic, this has proved as reliable and reasonably fast. Here are the prices for postage and packing using this service (VAT has been applied where required):

P&P for Electronic tubes™/Supertubes™/ single GS MICRO from Phædrus UK in Pounds sterling

Royal Mail - tracked and insured £ (GBP) 1 - 2 tubes £ 3 - 5 tubes
UK address
Special delivery (insured)
£21.00 £21.00
European address
International delivery (insured)
£25.00 £35.00
ROW address
International delivery (insured)
£32.00 £45.00
USA address
International delivery (insured)
£32.00 £45.00

For LONDON Series products and PHUSION/ FAB-S preamplifier

Please give us the precise delivery address and contact for a quotation. Prices change all the time, so we can't give a fixed price for this service. We will always endeavour to find the best price in the circumstances.

Can I borrow a Phædrus product to try?

We don't do loans. It's impossible for us to administer and enforce. We regret that. But history has shown us that, too often, a product loaned is a product lost. We're sure that wouldn't be true for you, but it's been our experience often enough that it has made us adopt a fixed policy of no loans.

What's the latest news from Phædrus Audio?

Our latest news is on this page.

Who are Phædrus Audio?

Phædrus Audio is a manufacturer of handmade tube and solid-state audio equipment. Inspired by great accomplishments of audio engineering, we are devoted to preserving and re-capturing the optimism, magic and energy of the past with modern materials and techniques and innovative electronic circuits. See more about us.

Do Phædrus Audio have a Privacy Notice?

Phaedrus Audio is committed to safeguarding your privacy and ensuring that you continue to trust Phaedrus Audio with your personal data. Read our Privacy Notice.

Has Phædrus Audio closed? Has the company been bought?

Phædrus Audio hasn't closed, and the company has not been bought. This rumour may have resulted from a Companies House search which does indicate that a Phaedrus Audio Ltd. was dissolved on 26 July 2022, having been incorporated in 2012. Search further and you will see that this legal entity has not been used as a trading company since 2015. We set this company up for a while, but changed how we operate after a couple of years. In a recent spell of housekeeping, we decided that filing accounts for a dormant company was a waste of time and money and closed this company. But, to be clear: the dissolution of Phaedrus Audio Limited does not affect our warranties or our trading conditions.

It's sad to say that the people circulating this rumour never checked with us. We'd have been happy to clarify the situation. As we will again should anyone wish to contact us: Address all mail to

What are your electronic tubes™?

You can read about them here.

What is the difference between standard and Red Dot electronic tubes?

During initial tests of the VF14M, EF14M, and AC701 electronic tubes™, we select the best 10% of tubes in performance terms and soak-test them, after which each tube is re-tested, certificated and marked with a RED DOT. These are our premium quality electronic tubes and carry a three year warranty. More importantly, these tubes are covered by Phædrus Lifetime Care

GOLD DOT Supertubes™ are only selected types and all are guaranteed to the highest standard. These are all premium quality tubes. They carry a three year warranty and are covered by Phædrus Lifetime Care.

You can read about the difference between the standard and the Red/Gold Dot tubes here and follow a link to the Lifetime Care page.

Do Red Dot tubes sound different?

The truth is that we always try to avoid saying this because we do NOT select Red Dot tubes on the basis of what the tubes "sound like". (We couldn't expect the test technicians to do this.) We do however base the selection on best headroom and lowest noise, so - insofar as those qualities correlate with better sound - the tubes must "sound better".

What are Gold Dot tubes?

Gold Dot tubes are our premium tubes and employ our second-generation SupertubeTM electronic-tube technology. All Gold Dot premium quality, selected tubes and carry a three year warranty and are covered by Phædrus Lifetime Care service level agreement.

Is it true that Phædrus Audio Electronic Tubes are "just a FET"?

We're not sure where this idea comes from. But, if you think that you can drop a FET in instead of a VF14 or a AC701 in a Neumann microphone, we'd suggest you try it. It won't work for several reasons: Firstly, few FETs will tolerate the anode volts designed for a tube: neither is the bias arrangement suitable.

You could take the approach of using a cascode transistor to hold-off the anode volts from the FET. This works, but the output impedance of a FET in a common-source amplifier is much too high, and increased still more in a cascode arrangement. An alternative replacement for microphone valves uses this arrangement. But the circuits fails to drive the transformer correctly, and the entire sound of the microphone is changed.

A FET behaves much more like a pentode valve than a triode, and it is a triode we need accurately to model in these old microphones. Phædrus Audio Electronic Tubes not only correctly emulate the input and output impedances of a triode, but also emulate the coupling (Miller capacitance) between them.

Tell me more about your various VF14 tubes

For replacement tubes in vintage microphones we recommend the premium VF14M product called a Gold Dot Supertube™.

A cheaper (but still excellent alternative) is the VF14M Red Dot model. Alternatively, we have a cheaper variant of the VF14M which we developed principally for DIY projects. All our prices are given on this page.

Lastly, we have the VF14T which uses a more modern thermionic device in place of the original Telefunken tube. This is the same device offered in VF14 replacements from other vendors.

Are your VF14 electronic tubes plug and play in the U47/U48 microphone?

Yes, all our VF14 products require no modifications to the microphone.

Which of your VF14 electronic tubes sounds best?

Top studios who have taken the time to evaluate the Red Dot and the Gold Dot version have always chosen the Gold Dot as the "best sounding" of the tubes. If we had to sum it up, we'd say the top-end of the Gold Dot VF14M is a little bit more open (especially around the 7kHz mark) compared with the first generation device. Certainly, the electrical performance is better. The VF14M Gold Dot was a complete re-design. The main differences are:

Does the thermionic VF14T sound different?

The VF14T is based on one of the last commercial tubes (for under-water amplifiers for Atlantic telephone cables!) We use the same tube that other manufacturers do for their VF14 replacements. The Western Electric tube we use (from an ex-NATO stockpile) is a great device, but it doesn't match a Neumann selected VF14(M) exactly and it gives the microphone a different sound which some people seek.

The WE tube has a greater grid-current than a Neumann selected VF14M and this drops the bass response. And it's less linear. Now, people tend to use the U47 much nearer the talent these days than was the case in the 1950s. (Take a look at the Frank Sinatra pictures with the U47, he's a yard away!) So, working closer tends to increase the bass via the proximity effect. It also drives the tube harder into a "tubey" sound.

The original tubes (and our VF14M) give a much better bass response which means the microphone can be used more as it was originally intended.

For thermodynamic reasons (it's hotter!), the tube VF14T is also noisier than the VF14M which matches the original, big, German tube. The combined advice is therefore:

The tube VF14T is suitable for close-miked work (where the noise level isn't an issue, but a "tubey" sound is sought and where proximity effect makes up for a falling LF response); the VF14M, or the VF14M Gold Dot are better choices for more general duties.

The demo on this page is a comparison of the tube based competitor's tube (based on the same device as our VF14T) and the VF14M, so it gives a good idea of the different "shading" the two devices give.

I have a U47 with the Nuvistor modification, can I fit your VF14M?

The Phaedrus Audio VF14M (all models) needs to be installed in the original (tube) U47/48 circuit. The installation of the Nuvistor required a change to the power supply, and the refitting of the 29ohm resistor in the original U47/48circuit.

In our manual for the VF14M, you will find Appendix 1 is the original Neumann instructions on the modification to the PSU for the Nuvistor. These modifications needs to be reversed when you install the VF14M; just as you would need to do if you went back to an original tube.

What models of microphone are compatible with the AC701 electronic tube?

There are many microphones which rely on this miniature tube; including: Neumann KM54, KM56, M249, M49 (a,b &c), M50, SM69, M269c, Schoeps M211b, M222 and the SM stereo microphones. The Phædrus Audio AC701 may be used as a replacement in all these microphones. In some (late) versions of the M49 circuit, you may experience stability issues, in which case there is a simple fix.

The Phædrus Audio AC701 is not compatible as a replacement in circuits where the valve is used as a cathode-follower. For example, the AKG C60.

Can you tell me about your EC8020 Supertube™?

Because of its enormous transconductance, the Telefunken EC8020 is the best valve for low-noise phono or microphone preamplifiers. Today, it's impossible to get. The Phædrus Audio EC8020-pH is a modern replacement for this tube for low-noise phono or microphone preamplifiers. Click for more information on the "best valve ever made".

Can you tell me about your SPRIT phantom-powered Supertube™?

The Phædrus Audio SPIRIT is designed to operate as a tube impedance converter in microphones supplied solely with 48V phantom power. Heater current is reduced to 400µA so that the nominal 6V heater may be supplied from the 48V via a 100k resistor. Click for more information

Do you do an EF14 tube replacement?

Yes. For replacement tubes in high quality microphones we recommend the EF14M Red Dot model.

Do you do an EF12 tube replacement?

As of March 2022 we now manufacture a direct EF12 replacement electronic tube.

Contact for the latest news on this project.

Can you tell me more about your 6072 tube, will it work in my microphone?

For replacement tubes in vintage microphones we recommend the 6072M Gold Dot model. Here is a link to the datasheet for the 6072M Supertube. Note that you will (almost certainly) need to make some changes to the connections on the tube base of your microphone. For various reasons, the 6072M is not "plug and play".

Will your 6072 work in the AKG C12VR?

The AKG C12VR is a different microphone to the original C12. In the original, only one half of the 6072 tube was used in a one-stage amplifier. In the contemporary C12(VR) both sides of the tube are used in a two stage amplifier. Our 6072 only has one-half of the full 6072 and works well in the original circuit. But it won't work in the C12VR circuit. The good news is that - by using a two-stage amplifier - the choice of tube is less critical. Therefore, a good standard 6072 (12AY7) tube, which are very widely available, will work well with your microphone.

Tell me more about your EF86 Supertube™ replacements

We have two models of EF86 Supertube™.

The Phædrus Audio CV4085 Supertube™

This Supertube™ matches the dimensions and performance parameters of the CV4085 tube, which is a high performance EF86 type. It is supplied as a standard B9A substitute device and has a wide range of “plug-and-play” applications in: microphone preamplifiers; hi-fi equipment; and guitar amplifiers. In fact, almost anywhere a low-noise, low-distortion and zero microphony EF86 type pentode is required - see more information here.

EF86M Supertube™ for U67 microphone?

The Phædrus Audio EF86M Supertube™ is modelled on the early, Silver Cage Telefunken EF86 with the Hilumin (nickel-plated steel) screen. This tube is widely considered to be the best EF86 for use in microphones. The Phædrus Audio EF86M Supertube™ is designed as a drop-in replacement for the EF86 tube. A second-generation Phædrus Audio Electronic Tube™, the EF86M guarantees, maximum headroom, excellent linearity and low-noise performance from the U67.

Is FRANCINSTIEN stereo enhancement still available?

Very much so! We still sell the small FRANCINSTIEN Actif domestic matrix (with the revised Bride of FRANCINSTIEN parameters). We also offer the SHUpHLER studio processor which contains both the original and the later EMI Stereosonic stereo shufflers due to Alan Blumlein.

And, we have the third generation stereo enhancement, the FRANCINSTIEN WARP (WAvefront Reconstruction Processor).

Finally, the Blumlein shuffling algorithms, and the FRANCINSTIEN processes are all available in software in the Stereo Lab product.

Is the PHAMULUS compressor still available?

Sadly, we don't think we shall ever be able to say the PHAMULUS is back in production. We were forced to stop production because several of the critical components went obsolete. Worse, the manufacturers gave us no notice of this so that we could last-time-buy. Essentially, the product is no longer manufacturable

Is the HYDRA preamplifier still available?

The HYDRA four-headed microphone preamplifier is no longer in production. We were forced to stop production of the HYDRA because several of the critical components went obsolete. Essentially, the product is no longer manufacturable. The idea of the "four-headed" preamp' did make it into the PHUSION product.

Can you tell me more about the Groove Sleuth preamp's?

Our precision Groove Sleuth Mk. II preamplifier is our original product and was designed to be used with Pspatial Audio's Stereo Lab software. It is our laboratory standard solution for needle-drop recordings for collectors and achivists.

The diminutive Groove Sleuth MICRO is our entry-level, non-equalising preamplifier for those who don't require all the features of the Groove Sleuth II.

The Groove Sleuth LOCKDOWN is our flagship, DC-couped, low-noise, wide-bandwidth, version of the Groove Sleuth Mk. II preamplifier, designed to support either top-end moving-coil cartridges or the PHLUX-II active phono cartridge for both listening and needle-drop recording applications.

To help navigiating the various Phædrus Audio Groove Sleuth products, this matrix will help you decide which unit is most appropriate to your needs.

Can you tell me more about the Groove Sleuth adaptors?

Phædrus Audio Groove Sleuth Adaptor preamplifiers were developed to convert the XLR socket microphone inputs on commercial computer sound cards to non-equalised phono cartridge inputs. Three versions exist: for moving-magnet cartridges; for moving-coil cartridges; and for Phædrus Audio's PHLUX active phono cartridges.

Please tell me more about the PHLUX active phono cartridge

The Phædrus Audio PHLUX active phono cartridges represent a new development in phono cartridge technology in which the electrodynamic motor system is buffered by a miniature, internal impedance-converter thereby securing excellent electrical performance with excellent tracking. PHLUX-II is the second generation product and replaces the original PHLUX. The PHLUX-III will be released in 2022.

What is Stereo Lab?

Stereo Lab is a Macintosh High-Resolution Audio App. The software has developed over several years and, now with the addition of equalisation and noise-reduction for all shellac-era records, Ambisonic decoding and Quadraphonic decoding, 5.1 up-conversion and full implemention of loudness measurement and adjustment to ITU BS.1770-3.

The software has value to mastering, broadcast and recording sound engineers as well as sound-archivists working with media which might range from phonograph cylinders, to analogue-cassette tape, to high-resolution digital files. More information.

Paying for Stereo Lab is very simple thanks to an in app purchase mechanism.

How do I get hold of the Phædrus Audio cartridge alignment protractor?

The Phædrus Audio cartridge alignment protractor is available FREE with Pspatial Audio's Needle-Drop Handbook.


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