t.bone Retro Tube II AK12-Mod Pattern Voltages

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t.bone Retro Tube II AK12-Mod Pattern Voltages

Postby Ewlman1 » Tue Oct 20, 2020 1:46 pm

Hi,
years ago I bought a Apex 460 Mod-kit and then stuff happened and I kind of forgot about it...
Anyway, I'm currently modifying a t.bone Retro Tube II (same as "Alctron BV300" with a "Stellar CM-2"-PSU), so it's is basically an Apex 460 with -10dB pad, 100Hz Lo-Cut running a 12AT7 and a couple other changes/addons to the Microphone & PSU circuits*.

My question is:
Are my pattern voltages too low/out of balance compared to the backplates?

Measured at Microphone*
Backplates : 61.75VDC
Front : 0VDC
Back Omni : 0VDC
Back Cardioid : 52.9VDC
Back Fig-8 : 108.6VDC

Should I make changes to the polar pattern voltage drop resistors and if so what values would you recommend?
-------------------------------------------------------------------------------------
The modifications I've done so far are:
Advanced Audio 460 Mod-kit
Microphone:
- Capsule : AK-12
- OT : BV-11
- C8 : 2.2uF, Film
- Tube : 12AY7A / 6072A
PSU:
- D5,D6 : 1N4759A, 62V

Other Mods (Microphone):
- R7 : 2.2k (closest value on hand, had no 1.8k, will change later)
- C6 : 22uF/50V, Elna Silmic II
- C3,C5 : 5000pf/250V, Polystyrene**
- C4 : 1000pF/250V, Polystyrene**

* See attached schematics. Found these in really poor resolution so I upscaled/cleaned them up and made corrections relevant to the particular unit in front of me.
** I just happend to have a good range of values of these so more a choice out of convenience when experimenting...

Plans:
- keep the CCDA
- keep the cathode biasing (at least for now)
-------------------------------------------------------------------------------------

Any other mod suggestions and their benefits while I'm at it?

/André
Attachments
the t.bone Retro Tube II - PSU - AA-Forum_b.png
PSU
the t.bone Retro Tube II - PSU - AA-Forum_b.png (197.5 KiB) Viewed 9308 times
Ewlman1
 
Posts: 2
Joined: Mon Jun 08, 2015 4:18 am

Re: t.bone Retro Tube II AK12-Mod Pattern Voltages

Postby Ewlman1 » Tue Oct 20, 2020 1:48 pm

And here's the Microphone Schematic... :)
Attachments
the t.bone Retro Tube II - MIC - AA-Forum_b.png
Microphone
the t.bone Retro Tube II - MIC - AA-Forum_b.png (218.47 KiB) Viewed 9307 times
Ewlman1
 
Posts: 2
Joined: Mon Jun 08, 2015 4:18 am


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