Naked Alctron GT-2B
Following on from the MXL 990 mod, I am now starting on modifying an Alctron GT-2B. This is a chinese built tube condenser with the standard format of PSU that allows a stepped nine-position sweep though omni, cardioid and figure-8 polar patterns. For the capsule swap, I have again turned to Microphone Parts and have selected an RK-67 capsule.
Valve soldered to PCB
It currently has a chinese 12AX7 tube soldered directly to the PCB, so the first job will be to remove that and install a B9A valve socket in its place. I am hoping I can arrange it so that the socket is installed on the underside of the PCB so that the valve is installed through the PCB into the socket as this will allow more space for the tube to fit inside the mic body where space is at a premium. Having researched this model (which also sells as a Nady TCM-1050), it becomes clear that the 12AX7 is the wrong tube for this circuit and a more appropriate model would be the 6072 / 12AY7 / ECC88. To this end, I have managed to get hold of a few suitable replacment candidates including a NOS Telefunken ECC88 and a NOS Philips JAN ECC88, hence the desire to installl a valve socket!
GT-2B PCB component side
I am also intending to replace a few of the key PCB components with higher quality equivalents, most certain capacitors, but this will again require some more research on my part I’ll be seeking advice from those with more knowledge of this circuit than I have at the moment.
Alctron GT-2B
As with the previous modification project, I have made a spoken word reference recording to compare the sound before and after the upgrade. I found I had to tap the mike once or twice as the gain inexplicably dropped by around 24dB more than once during the recording session… most likely a dodgy joint somewhere – not all that surprising having inspected the quality of the soldering!
Here is the “before” recording:
Stock GT-2B dry
Stock GT-2B LA2A
Hi,
I saw Matt’s post on Twitter of your success with the APEX 460 mod kit. (We designed that one) Since you bought a K67 capsule I thought you might want to check out my recent article on how to handle that capsule. You need to add an EQ cap in parallel with the 100K plate resistor of your GT-2B. You can play with that value to your taste, but it definitely isn’t a “u67” style mic without EQ. I found 1000pF gave me a flat response like the Neumann. YMVV.
Love the look of your site.
Brian Fox
Thanks Brian. I am over the moon with the auccess of the Apex 460 mod kit… it’s now made the HST-11a my “goto” vocal mic. Thankyou ever so much for sharing the mod tip on the GT-2B, I will go have a good read! I will most definitely be employing that when I continue this mod.
Thanks!
Dave.
Hello,
I just purchased one of these mics, with the intention of modding it. Were you able to successfully mod this one?
Hi Dan, unfortunately, no, it has become one of those projects that is sitting on the back-burner long-term.
You need to smash out the tube and desolder the pins individually… It’s a shit job
I reckon I could desolder it without smashing the tube if I used my hot-air rework tool and a desolder pump.
I know this is an olde post, but in case anyone stumbles onto this hoping to mod a GT-2B, K&K audio sells individual “socket pins” that can be inserted into the existing PCB to act as a socket for the tube. This requires carefully drilling out the holes and soldering the individual socket pins in place. I’ve successfully done this with 4 mics.