K47 with EF42 tube ?

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Gus

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A good part of the tube microphone sound final product is the design of the power supply.  That supply looks like it would work OK for a simple cathode biased, triode plate out, to transformer circuit

One thing don't believe the stuff you read on the web without testing or checking (ref books etc).

A good first build would be a cathode biased tube microphone.  Look for schematics on the web G7, AKG C28, ELA M250, Royers plate out circuit(I would add a grid to ground resistor), bulldog?, VM1, m49c schematics etc.

You seem to asking for design work from others please correct me if I am wrong.

IMO to "design" something as simple as a tube microphone well, one needs knowledge of of things like noise, how tubes work in circuits at different operating points, how to design a power supply correctly and what type of circuit for the supply, what parts to use, knowledge of transformers and a lot more.

 

boogietube

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Well, I won't lie Gus. I have spent many many hours researching the topics you mentioned.
It seems to me that I am looking for some design help here. Some help with the power supply in relation to the Oliver Archut U47 circuit.
Since I have three power supplies, and not a whole lot of money, I would prefer to modify the existing supply instead of building a whole new one.
It would embarrass the seller to post how much the studio purchased these parts for. I have seen on in other threads some remarkable people with incredible mathematical knowledge. It would seem to me that the right person could look at the ioaudio PSU and plug in different values to get 5.05v from that circuit. I would love to be in this class. I'm not. I know my 100 hours of research doesn't even scratch the surface. I will keep researching and learning.
The G7 will not fit in my mic body. It was what I wanted to do first, in fact. The others I will research. Thank you for your input.
On the diystompboxes site, many have shared their knowledge with each other. In fact, that's the only reason I am attempting to do this here.
I have paid for and shared schematics and layouts with everyone on that site. I will do the same here with my PCB layout.  Here, I'd like to document everything I do for these microphones, so that others may benefit from the knowledge and experience of the highly skilled forum members. It is a community here, is it not? I will post every schematic, picture, and modification, to save the "next guy" the incredible amount of research I have went through. Don't get me wrong....I appreciate every word and fragment of help here. It is enjoyable to learn about tubes, transformers, composition of components, capsules, biasing, PSU'S, voltage dividers, choke filtering, fixed bias. Cathode biased tube microphone technology is apparently my next read.
I would gladly pay someone to help me with this, but I cannot afford an engineers hourly rate. If someone can easily modify the ioaudio heater supply portion of the schematic for 5.05 operation with Oliver Archut's "Alternative Tube U47 Schematic", I would be happy to negotiate compensation. However, I will post it here for all to see. As well, I will generate a PCB layout of my own design and share it as well.
If my post seems callous, it's not intended to be. It is simply my wish to complete these microphones for the studio I am helping out. I am not being paid to do this. The studio owners are friends of mine who have built a nice small studio with their own hands on a very small budget. The studio wishes to promote local acts and just break even. Keep the lights on, so to speak.
It is in that spirit that I ask for help here.
Sincerely,
Sean Harris
 

Denyle Guitars

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Unless I'm missing something (& I usually am) IOAudio's heater supply should work for an ef80/ef12. The data sheet for the ef12 says 6.3v/240ma for heater supply. If anything, you might need increase the trimmer value. For ef80, you should be good as is.
 

hop.sing

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Hi Sean

Have a look at Ohms law, it is really essential to know it in cases like this. Read and learn about it, it is worth it! The ef800 needs 275mA for the heater supply which is very close to the ef86. How much resistance do you need to drop the voltages to your liking? Just calculate...
The IOaudio schematic has very nice voltages already written up already, where you can verify your own calculations.
But in any case, the variable 22Ohms resistor should be sufficient to drop the voltage to your 5.05 Volts. But the tubes will work well with heater voltages from 5 to 6.8 Volts, so you will not destroy anything in the case of an error there. The very low voltage of 5.05V is just there for noise and/or (maybe) sound reasons. By the way, I think it is a very low value for an ef80, not sure the tube lasts very long that way. I tend to prefer 5.5V, it is still pretty low noise and sounds good to my ears, but there is really room to experiment.... like gus says
Tobias
Oh, I forgot, the schematic of Oliver is fixed bias, so you better stay with 5.05 volts, if you want to be on the save side and don't want to change anything in the mic.
 

0dbfs

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I thought sean mentioned using an RFT EF14.

Either way, sean you should download the datasheets for the tubes used in Max's mk47 and the datasheet for the tube you want to use. Max has listed the currents and voltages in his schematics so using ohms law, you should be able to figure out how to get a certain heater voltage as well as the power ratings for the various resistors. I have found max's schematics to be a great learning tool.

If you complete the heater circuit on paper with the various tubes max has used, you can come up with a total resistance to gnd, notate the currents and figure the max power dissipation in watts so that your resistors don't burn up and fail. You should be able to sub in your tube and adjust values on paper before you start buying parts etc. It looks like the rft ef14 is rated to draw 450mA @ 6.3V.

Once you have come to a point of being able to sub your tube into max's circuit and get your 5.05V then you might be able to look at Olivers circuit and fill in some blanks regarding the voltages, resistances, and currents involved.

Another thing to do would be to trace out your PSU pcb and turn it into a schematic so that you can better understand how it is working now and come up with some modifications to get it where you want it to be.

I am definitely not an expert like some of the guys around here so please don't take my word as gospel.

Best,
jonathan
 

boogietube

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A little convoluted my posts seem to be.
I'm building this:
K47 / EF14 / BV8/
As per this schematic:
http://www.tab-funkenwerk.com/sitebuildercontent/sitebuilderfiles/AMIU47alttubeschematic.pdf

Wow. I did not notice the wiper on the resistor. A 22 ohm wire wound variable resistor. I'll just see if I can splice this into my PSU.

Layouts and pictures to follow. Give me a week or two.
Thanks!!
Sean


 

Sredna

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Dont forget that voltage from the transformer could vary a bit depending on manufacturer, rating and load.

The calculations brings you in the ballpark but you should be prepared to fine adjust the values afterwards. 
 

Gus

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I am the same Gus at Aron's page.  The beginner project is from me.

With the supplies you have cathode bias is what I would build.  If you want to use the Oliver circuit, I would build at least a proper heater supply.  The 5.05 volt part is easy, read NS power supply app notes, but that is not the problem.

I have built a few circuits like the linked circuit and learned on my own what to do to make them work correctly

Read the mk7 threads.
 

rodabod

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For that PSU, I'd either try to add some additional filtering to the 7806 lifted to 6.7V with a diode (not sure if I can ballpark how much noise you'd be able to drop with CRC filtering though).

Or, I'd see if I could shoe-horn something akin to Max' heater section onto the original PCB whilst still keeping things neat, and more importantly, safe.

Measure your heater winding, and you can work from there. I'm glad you've got the cheaper capsule, etc. to work your prototype with; keep the expensive stuff in the box first!

 

Gus

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rodabod

The voltage listed 6.7VDC and the picture seems to indicate the heater is a 6VDC reg with a added diode in the ground leg.

Again read the MK7 threads.

 

rodabod

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Gus said:
Again read the MK7 threads.

I'm guessing someone said that you can't get that 6.7V from a standard supply clean enough for the MK7 with additional filtering. However, it's not the same; this mic requires ~5V at the heater which does qive you some additional scope for filtering. Just a thought.
 

boogietube

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I have decided it prudent to splice the heater portion of the MK7 PSU circuit into my PSU.
It took me a while to read through all of the MK7 threads.
Parts are on the way.
I'm going to make a daughter board and run it off of the same transfomer. I will disable the original PSU circuit.
I need a new box! Not enough room.
This will work:
http://www.princessauto.com/search-products?keyword1=ammo+box
And, it's local. 
Updates and PCB layouts to follow.
Thanks for the input!
I appreciate everyone here!
SEAN
 

Gus

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That type biasing is very sensitive to any noise, hum, click in the heater supply.  I have built a number of circuits biased kind of like that or like that.    It is hard to say from pictures if the stock transformer will work with a heater power supply circuit without trying it or measuring the transformer parameters.  When I built the 6au6 circuit fragment like in a c800g I found I needed to add super caps to the heater section to help and that microphone is cathode biased, it was an earlier build of mine and I would build the supply different now.  The B+ part should be fine with the stock supply adjusted to 105VDC at under 1ma

The honeybear microphone has a circuit like that with a submini tube and a modded Royer Supply.  I had to use a 2amp rated transformer and a changed heater circuit to make it low noise.

You really need to build a few microphones or microphone circuits to learn IMO.  The power supply is a part that the DIY world seems to missing (ioaudio has posted some circuits)

 

boogietube

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Awesome info Gus.
The first thing I will have to do is measure the current and voltage off of the transformer secondary.
I had surmised that. I also believe that I can just drop the voltage of the first output to 105v and it will be fine.
Like I said, I have ordered the parts for the 5.05v section from the rectifier to the output. (choke, caps, resistors, rectifier variable resistor)
I respect your opinion, but I'm up for this challenge.
Looking at the other PSU'S / tubes and capsules, IMO this may be the simplest build.
With the others, I'd like to get all 9 polar patterns available, and I haven't found a schematic on how to do this with the available parts I have. 
I've contacted Peluso to maybe buy their boards/ transformers/tubes, but I haven't heard back from them yet.   
Could you expand on "Super Caps"? The info I can find is:
An electric double-layer capacitor, also known as supercapacitor, supercondenser, pseudocapacitor, electrochemical double layer capacitor (EDLC), or ultracapacitor, is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor. For instance, a typical D-cell sized electrolytic capacitor will have a capacitance in the range of tens of millifarads. The same size electric double-layer capacitor would have a capacitance of several farads, an improvement of about two or three orders of magnitude in capacitance, but usually at a lower working voltage. Larger double-layer capacitors have capacities up to 5,000 farads as of 2010[update].[1] The highest energy density in production is 30 Wh/kg,[2] below rapid-charging Lithium-titanate batteries.

EDLCs have a variety of commercial applications, notably in "energy smoothing" and momentary-load devices. They have applications as energy-storage devices used in vehicles, and for smaller applications like home solar energy systems where extremely fast charging is a valuable feature.

Interesting.

Thanks, Gus.
 

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