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

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telefunk

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Feb 16, 2010
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This Alctron BV300 tube mic, A/K/A T.Bone Retro Tube II or Maroon MT100.

specs:
http://www.alctron-audio.com/encpShow.asp?id=1717

Just bought this out of curiosity, and a platform for mods. Tested it briefly and while it's really nice for a 240€ mic, it's certainly not a Neumann, but this shoudn't be a surprice to anyone.

Anyway, as i said it sounds nice but more detailed and especially less hyped high end wouldn't hurt.

The chinese 12at7 is going to be changed first but what then? New capsule maybe? Better transformer? Any suggestions?

I know that Avantone used this as a platform to build their BV1 that had Cinemag transformer and 34mm capsule.

EDIT: ok, to be more exact: if i want to change the transformer, how do i know what Cinemag/Lundahl transformer to use?
 

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pucho812 said:
Test out the transformer which will get you the ratio and then find one that fits

Sorry, but how exactly should i measure the transformer? Sorry if this is a total noob one...

As this mic uses 12AT7, doesnt that tell something about what kind of a transformer it should be?
 
10:1....Then Cinemag CM-2480 would work.

Can anybody make any suggestion based on the pictures as what classic circuit this mic is more or less based on?

This mic looks outside like Trion 8000 but at least the pcb looks very different and this has different valve in it.
 
zebra50 said:
With a body like that, I would be tempted to build a DIY CMV563!

I was just comparing the two a couple weeks ago and considering the same. Funny how the forum works sometimes...
 
zebra50 said:
With a body like that, I would be tempted to build a DIY CMV563!

Hmm...interesting idea!

Even the tube is already there since the ec92 is the other half of the ecc81.

Here's one already made: http://www.groupdiy.com/index.php?topic=18890&highlight=

...with Cinemag CM-2480 transformer, i think CJ once measured that the original CMV563 had 1:9 transformer in it, correct?

here: http://www.groupdiy.com/index.php?topic=9310.0

I think the Alctron PSU gives 120v which would be perfect (I have to check that)

Then the capsule should be changed to M7/K47-type.

But what about the different directional pattern, those i would like to keep. What changes would need to be done to the CMV563 schematic?
 

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telefunk said:
I think the Alctron PSU gives 120v which would be perfect

If you're wanting to stick with a fixed bias heater, you may want to consider a different supply or add filtering to quiet things down. For more reading, I believe this particular issue was discussed in the MK7 thread.
Alternatively, there is a UM57 mod floating around that includes a cathode biasing scheme.
 
telefunk said:
10:1....Then Cinemag CM-2480 would work.

Can anybody make any suggestion based on the pictures as what classic circuit this mic is more or less based on?

This mic looks outside like Trion 8000 but at least the pcb looks very different and this has different valve in it.

I'll answer my own question: I compared the Apex 460 schematic and The BV300 and i must say i wasnt too surprised to find that it is EXACTLY the same mic. Only with added low cut and -10dB options. JFYI.

Of course, just making the typical Apex mods (capsule, transformer, tube and bit tweaking the PSU) could make this mic more usable.

Anyway, what might be the best capsule (C12 or k47 type) for this type of lollipop head assembly, regardless of the circuit that is going to be used?
 
I would go for the CK 12 capsule but then I am partial to the C12 & ELAM251. I owned a pair of U47's back in the 60's & prefer the AKG sound.
 
Ok, I thought i should update, if somebody needs the info.

I made some measurement on the stock Alctron BV300 aka T.Bone Retro Tube II aka Maroon MT100 etc.

Basically, as i said before, it's an Apex 460 circuit with low cut and -10dB pad added. And the capsule is 35mm, K67 variant.

PSU gives out 151v. Pattern voltages for the capsule are 0v-64v-132v. Heater 6.1v.

Schematic is identical to Apex 460 except R7 is 4.7K instead of 2.7K!!! (from cathode to ground) Doesn't that mean no low end at all?

I'm thinking of changing this to a C12 clone with Peluso CK12 capsule, Cinemag C-2480 transformer, 6072A tube and identical circuit values with CF removal. I'm just having hard time founding the correct PSU voltages for C12...anyone?
 
MagnetoSound said:
C12 B+ is 120v.

EDIT: found the plate voltage of C12. It is supposed to be 68VDC.

EDIT 2: I keep answering my own questions: Pattern voltages for C12:

Cardioid: Front = 0V Center = 60V Rear = 60V
Omni: Front = 0V Center = 60V Rear = 0V
Eight: Front = 0V Center = 60V Rear = 120V

 
Ok, the PSU.

As mentioned it's the basic Alctron PSU. (I attached the schemo).

There are few differencies to the schematic:

The value of R15 (should be 20R but is 2R) just before the L7806 heater regulator.

And the value of R6 (Should be 150k but is 1,5M) just before the output cap of the pattern volages.

Could it be accidental? Just reading one colour (the multiplier) wrong?

Anyway, to get the B+ voltage from 151v to 120v, should i just replace the last two zeners (they are probably 100v and 54v zeners) with two 60v diodes?
 

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