Phaedrus VF14M and VF14T

Hello all,

This is my first post here. I have been reading this forum for a while and I do appreciate all the great information and technical help that is available here.

I'm going to be building a D – EF47 tribute mic pretty soon. I have chosen my capsule and transformer (Thiersch blue line and AMI bv8r). I am still up in the air about tube and circuit selection though. I was going to go with Olivers EF800 circuit, but I have also been looking at the phaedrus VF14M and VM14T. There is loads of information on the various tube circuits, but I haven't seen much on the phaedrus solid-state and tube replacements, just random mentions here and there. The audio samples on the Phaedrus website sound encouraging, but I was wondering if any one has had any direct experience with these replacements. If so, I would appreciate any feedback  you would have to offer.
Thanks a bunch,
Randy

Short answer yes!

I have built a U47 copy around the VF14M Phaedrus solution and I am very happy with the results. The company support is awesome as well! Check my posts and go to my website for more details look at blog section.

I have used both their AC701 and VF14 substitutes. Results are good.
With the AC701 I had a problem when I used it in a M49 microphone.
I got in touch with Phaedrus and they were very helpful.
After some experimentation I found the solution for the problem and they used my information in a 'service sheet', to inform other users who want to replace the AC701 in a M49 microphone.

I've no experience with them yet, but I do have their VF14M and a new Telefunken VF14K waiting to compare with a Neumann capsule and 4 BV8 style transformers to compare; one being AMI of course... Probably another month before that happens though.

I am interested in their AC701 for some 49s for sure. I'd love to hear the difference compared to the 6947s I'm using now... Now that BeesNeez's 49 bodies are done and I will be having my 49s converted to those bodies, now would be the time to compare!

Thanks y'all for your replies. I did check your website Pip and it looks like an awesome build. Hearing everything so far sounds like all positive reviews, though only from a few. Even though I never had a chance to correspond or speak to Oliver, I have the greatest respect for him and his legacy. I am assuming that these Phaedrus replacements must have come out after he passed away. I do wonder what he would have said about them.......
I'm spending a lot of money on quality parts, so I will not be able to do more than one build right now. I would eventually like to compare the VF14M using the original U47 circuit with Olivers EF800 circuit. For all the research I have done, these seem like the two most viable alternatives. Anybody have thought or comments, please let me know.
Thanks

The biggest difference between the EF8-- Series build and the VF14M-T etc... Is that the the VF14M is true to the original powering scheme and uses a single supply voltage with a drop-down resistor for the filament voltage where-as the EF14-12-13-80 etc... require a separate supply for the filament voltage.

As part of your research go to:

http://moxtone.com/mU47_U47.html

Actually,  I was just reading the moxtone website as you were writing your reply. I like his ideas about pattern switching and adjustable voltages.  The metering is nice but not essential since, with the stable line voltages in the US, it would only be necessary to  check the  anode and the heater voltages from time to time. This is the closest  I have seen yet to a "universal" power supply.  It could be used on mics with both single and dual power requirements, depending on how the connectors are wired.

jumpstart said:

Actually,  I was just reading the moxtone website as you were writing your reply. I like his ideas about pattern switching and adjustable voltages.  The metering is nice but not essential since, with the stable line voltages in the US, it would only be necessary to  check the  anode and the heater voltages from time to time. This is the closest  I have seen yet to a "universal" power supply.  It could be used on mics with both single and dual power requirements, depending on how the connectors are wired.

Click to expand...

Did you look at the research he did regarding tubes and heater voltages?

RuudNL,
I’ve got two AC701 ”Electronic Tubes” and I had the same problem as you had in my M49c circuit. The “tube” started to oscillate after a few seconds.  So far I’ve only used them in my test rig to check noise and distortion.
I knew that could happen after reading your post, and Phaedrus was very open about it and warned me when I bought the tubes. After removing the feedback resistor everything was ok.
The noise level was low and had a dark character (that’s a good thing), compared to the best of my 5840 tubes (I don’t have a real AC701).
The distortion looks very much like the 5840 tube, with mostly second harmonics. That’s also a good thing.

All seems positive on the Phaedrus AC701... It's sounding like it'd be a worthwhile effort to compare one to the 6947 I have in my M49b-types!

Wonder what they are selling these for? Real AC701s are not that expensive if you know where to look.

Can I buy you a beer, Mike?


Henk

Phrazemaster said:

Real AC701s are not that expensive if you know where to look.

Click to expand...

Tell us more... 

Pip said:

Did you look at the research he did regarding tubes and heater voltages?

Click to expand...

Yes I did, and he was very thorough in  the research that he did on those tubes.  I am definitely going to try Phaedrus

Recording Engineer said:

I've no experience with them yet, but I do have their VF14M and a new Telefunken VF14K waiting to compare with a Neumann capsule and 4 BV8 style transformers to compare; one being AMI of course... Probably another month before that happens though.

I am interested in their AC701 for some 49s for sure. I'd love to hear the difference compared to the 6947s I'm using now... Now that BeesNeez's 49 bodies are done and I will be having my 49s converted to those bodies, now would be the time to compare!

Click to expand...

I'm sure we would all be interested in hearing about your experience when you have a chance to build these mics.

Phrazemaster said:

Wonder what they are selling these for? Real AC701s are not that expensive if you know where to look.

Click to expand...

I would love to know where to look? I have several AC701K tubes NOS there is nothing that guarantees they are mic grade as they are unused. I am afraid to part with them as the low noise K's are like hens teeth as far as I know. Every time I fire up my KM54 and SRM64 I cross my fingers for fear that the day has finally come when the tube has given up the ghost.

Pip said:

I would love to know where to look? I have several AC701K tubes NOS there is nothing that guarantees they are mic grade as they are unused. I am afraid to part with them as the low noise K's are like hens teeth as far as I know. Every time I fire up my KM54 and SRM64 I cross my fingers for fear that the day has finally come when the tube has given up the ghost.

Click to expand...

Here's a hint. Non-K's may actually conform to "K" specs. If you know this then you can find non-K tubes that may be cheaper.

Here's a copy/paste from a site I ran across:

"...Since 1965 Telefunken only made frame grid AC701 (same as the "K" version) so there was no need to specially mark them since they were all "K" versions by that time. Also, these tubes have the red indicator mark on them. Telefunken also sold RFT made AC701 under the Telefunken name and those can be rather noisy and more microphonic than the Telefunken ULM made AC701. RFT made AC701 had a white dot versus a red indicator dot applied only by Telefunken ULM.

The date code shows these were made by Telefunken ULM post 1965. In the date code, if you have U for Ulm and then two letters sometimes with two numbers it is made before 1965. If you have a U and seven numbers then it was made by Telefunken ULM after 1965. All of ours have the same date code of "U4109203".
Finally, the last two digits in the date code represent the design revision number, with 03 being the final version for the AC701. All tubes with the 03 revision level match the AC701 ’K’ specs."

PS - many AC701K's are so robust, and have been in operation since inception - for thousands of hours, way past their expected life. They are an incredibly hardy tube, provided you don't go over 4.00V on the heaters. I run mine between 3.85V-3.95V. So I get your fear in turning on your mics but unless you are somehow unlucky, those tubes should last forever.