Alctron BV300 (T.Bone Retro Tube II) to half of AKG C24 mod

Ideas to improve the PSU design? Anybody?

Ok, now my

-B+ is 121,6v

-heater 6,2v

-Pattern voltages are:0v-51,6v-105,8v (but i'm aiming at 0v-60v-120v) coming from the PSU.

The question is, as i'm trying to clone the AKG C24, should i change all those 51M and 1G reasistors to 200M too, as in the C24 schematic?

All help would be greatly appriciated!

telefunk said:

Ideas to improve the PSU design? Anybody?

Click to expand...

You could get rid of the zeners and the (possible) switching noise, and use bigger value R5 to achieve the right B+. That may lead to capacitor popping voltage unloaded though.

Changing the 1G grid to ground to 200M -> less (sub)bass.

Measurements done with a load?

You could get rid of the zeners and the (possible) switching noise, and use bigger value R5 to achieve the right B+. That may lead to capacitor popping voltage unloaded though.

Changing the 1G grid to ground to 200M -> less (sub)bass.

Measurements done with a load?

Click to expand...

Yes, all measurements done loaded. (pun intended)

Actually the grid to ground is 200M originally here, as it is in Apex 460 too.

But the question i'm wondering is, if using the CK12 capsule and T14/1 transformer, original B+ and pattern voltages, should i also use all original resistor values?

That would make sense?!

Anyway, tuhannet kiitokset!

If you're aiming for a clone you should use the original values for all the resistors and capacitors but then you should also use an original brass ring CK12, correct head basket, body etc... I would just try to build a good mic and use the resistors that are already there or experiment with different values, maybe try a smaller grid to ground value.

Good read: http://www.groupdiy.com/index.php?topic=28519.0

BTW, I'm not sure if it fits the capsule mount in your mic but I highly recommend Tim Campbell's CT12.

pasarski said:

BTW, I'm not sure if it fits the capsule mount in your mic but I highly recommend Tim Campbell's CT12.

Click to expand...

I believe it's going to fit, one way or another. I'm waiting for Tim's CT12 already!

Nice, with that capsule I think you'll be satisfied with any decent electronics. Interested to see how it fits. Lykkyä tykö!

Thanks,

if it doesn't fit with the original 4 point silicone strap thing, i'm going to do some metal work with the lollipop head assembly and then it fits with Tim's own mount for sure.

Good thing is, that Alctron BV300 35mm capsule has exactly the same dimensions as CT12.

Thanks for the link, btw, it was a good read!

Together with AMI T14 it should rock. The head assembly is the only question mark...

Pidetään sormet ristissä, as we say.

telefunk said:

-Pattern voltages are:0v-51,6v-105,8v (but i'm aiming at 0v-60v-120v) coming from the PSU.

Click to expand...

shouldn't really make a big difference... maybe a little less volume, but imho should be fine. could be fixed though, but I wouldn't worry about it.

Howdy!

Since Retro Tube II is really cheap now I have bought 2 that I will try to improve.
I would apprechiate help identifying problems with my plan.
See attached schematic.

evil grill said:

Howdy!

Since Retro Tube II is really cheap now I have bought 2 that I will try to improve.
I would apprechiate help identifying problems with my plan.
See attached schematic.

Click to expand...

What's the diode for?

abbey road d enfer said:

What's the diode for?

Click to expand...

Saving the life of the tube at start-up.
www.valvewizard.co.uk/dccf.html

The values for resistors connected to the capsule are copied from http://www.tab-funkenwerk.com/sitebuildercontent/sitebuilderpictures/C12-Alternative-for-AMI-PSU.jpg


I was thinking of copying that schematic but I don't know if rebuilding the heater supply is worth the trouble + I would like to keep the cathode follower and I do not know how to design it if I change the first triode.

> Saving the life of the tube at start-up.

Not with 51k in series. 98% of stray current flows in grid, 2% in diode. Stray current is a mA at most which won't hurt the grid.

What is in fact wrong with the mike as-is? If you just want a change to have a change, paint it purple. Color can have a large effect on sonic perception. (I wish I still had my brass microphone but it needed constant buffing.)

PRR said:

> Saving the life of the tube at start-up.

Not with 51k in series. 98% of stray current flows in grid, 2% in diode. Stray current is a mA at most which won't hurt the grid.

What is in fact wrong with the mike as-is? If you just want a change to have a change, paint it purple. Color can have a large effect on sonic perception. (I wish I still had my brass microphone but it needed constant buffing.)

Click to expand...

Purple would contrast nicely against my green room, but I won't paint it purple. Might do dark green.

The mike is actually really good for the money. I would like to hear a microphone that can sound nice after EQ and compression. Also I would like to solder some audio stuff. I have'nt had the time or lust to do DIY for over ten years and all of a sudden I wan't to turn something electric into something better.  I have no experience with microphones. Apart from repair and maintainance I've built fuzz-boxes and simple guitar amps and upgraded components in audio gear. Right now I have inspiration to learn.

I measured the Retro Tube II power supply. Not 120 V but 180 on B+. 
VAC not measured but taken from marking on transformer.
Edit: Microphone connected during measurement.

Edit 2: Got suspicious. Measured with calibrated meter at work. B+ is 150 V without load. My voItmeter is broken.
I removed the image.

I'm modding my Retro Tube and wonder what R11 is for, the apex 460 don't have it and the Rode NTV have a 0.22uf cap + 200R resistor there. Is it filtering something?
And why C11 is there and not after cathode? Is there no difference where to place the HF roll of?

Thanks!

LevinGuitar said:

I'm modding my Retro Tube and wonder what R11 is for,

Click to expand...

Where is R11 in the schemo? Do you have a better schemo than this one, which has several mistakes.

LevinGuitar said:

the apex 460 don't have it and the Rode NTV have a 0.22uf cap + 200R resistor there. Is it filtering something?

Click to expand...

Please post a schemo when you ask such a question. We don't have all the schematics in teh world.

LevinGuitar said:

And why C11 is there and not after cathode? Is there no difference where to place the HF roll of?

Click to expand...

Where is C11?

Sorry, here it goes:
R11 is between the plate of first stage and grid of the second stage. C11 from R11 to ground. I have increased the value of C11 to 390pf (from cathode of the second stage to ground), and now have better response for speech. Is there something I'm missing because of moving it?


Here is the similar Apex 460 (no R11)

And the NTV

LevinGuitar said:

R11 is between the plate of first stage and grid of the second stage. C11 from R11 to ground. I have increased the value of C11 to 390pf (from cathode of the second stage to ground), and now have better response for speech.

Click to expand...

C11 acts in conjunction with R11 and the internal impedance of teh tube to produce a roll-off starting at about 10-12kHz. I'm not sure it has much perceptible effect, but it it sounds good to you, it's OK.

LevinGuitar said:

Is there something I'm missing because of moving it?

Click to expand...

Moving it from where?

LevinGuitar said:

Here is the similar Apex 460 (no R11)

Click to expand...

Yes, many mfgrs keep the sibilant response because customers are attracted to it when the test the mic. Only to find out later that they would like it less sibilant.

LevinGuitar said:

And the NTV

Click to expand...

This one is very different in many respects. You just can't compare.