AT4060 Tube Mic & AT8560 PSU

[maxwall]

Objective : PSU for the AT4060 tube mic (cardioid only) , 6922 tube.

AT4060 PSU Link HERE , but the document is unreadable unfortunately.

Looking for a At8560 tube mic psu pcb layout or detailed pics would be a big help.

Original Thread HERE , referenced from Lab discussion.

Possibly a schematic like this can be used to create a new psu for the At4060 with minimal circuit changes in B+ (120vdc) , since the At 4060 mic accepts 120vdc Plate voltage and 6.3vdc Filament voltage. Plate voltage below would be single output Mosfet (IRF740) regulated at 120vdc with current requirement from 5-10ma min. The 6922 tube for the filament has a current requirement of ~ 300-365ma. Also regulated by NPN pass transistors found the original AT8560 PSU schematic, but in this case LM317 is used , in some instances as a current source regulator as illustrated below in PSM169 heater supply. The NTK heater supply below is voltage based regulator. Yes, there is a difference.

Having the PSM169 psu that originally powered a 6205 sub-mini tube filament supplied ~ 100ma, However , I'm tying to convert the LM317 CCS ( constant current source) filament circuit in this supply to deliver more current for a 6922 tube , but having difficulty stabilizing the filament voltage to 6.3v (+/- 10%) after changing the 15ohm 5w resistor to 3.9ohms 3w (R1). CCS Calculator HERE This resistor is positioned on the adj (pin 2) leg of the LM317 regulator - see circuit below. I have also tried different small power transformers ranging from 8vac up to 16vac from 400ma to 1amp. Apparently, the filament transformer must be 5v higher than what is required on the Vout according to LM317 operating specs. I do not have access to a schematic for the PSM169 and will have to draw one out - now added. As a Dummy load,rather than a large power resistor, and without placing a costly 6922 tube at risk, I test only using one 12au7 tube tapping only the filaments in parallel (pin 4,5 tied & pin 9) configuration which simulates a ~300ma load, close enough . Note : HV AC not applied to the HV section of the psu pcb for B+ during bench test - filament only. PSU circuit below is Rode NTK tube mic which powers a 6922 tube. Closest circuit I could find that used the 6922 tube, and I like the modern Mosfet regulator pass transistor regulator rather than a BJT NPN pass transistor. The Audio Technica At4060 tube mic utilizes a 6922 tube, not a 6DJ8.

 

[McIrish]

I have one. Let me see if I can take some pictures..not sure I have time for a full disassembly but I might get something helpful

 

[McIrish]

Here is a link to pictures of both the top and the bottom of the PCB of an AT4060 power supply. Hopefully the pictures are clear enought to get what you need from them.
This won't be a permanent link so let me know once you have grabbed them.
AT4060 supply pics

 

[gyraf]

I don't like the heater regulation there - if switch fails open or 'ish, which it will over time, heater goes to 17V and kills tube quickly..

 

[Khron]

I don't like the heater regulation there - if switch fails open or 'ish, which it will over time, heater goes to 17V and kills tube quickly..

Can't quite figure what the 9V option is for. Severe underheating of 12.6V / series'd up 2x 6.3V filaments?

 

[gyraf]

[email protected] plus some for the cable?

 

[RuudNL]

6922 (=ECC88) has a filament voltage of 6,3 V. (Pins 4 and 5)
So no split filaments, connected in series.

 

[gyraf]

IIRC, AKG had something like this on a tube mic psu for activating when using specific extra-long mic cables..? (can't find reference.. And it was not this much..)

 

[Tubetec]

Even in the usual 15 foot of tube mic cable expect to loose a couple of hundred mV at the far end .


The Alctron or TBone tube mic PSU looks the same as the sterling , you'd only need to add the patern switching components and rewire to what ever pinout the AT uses ,
Some of the series resistors in the HT might need adjustment .

Theres a few here who made their own replacement PCB for that style of supply ,

 

[RuudNL]

IIRC, AKG had something like this on a tube mic psu for activating when using specific extra-long mic cables..?

See the attachment. They did this (among others) with the N12VR power supply.

 

[maxwall]

Many Thanks McIrish , downloaded it. love this forum , and all the replies.

* Added redrawn PSM169 tube mic psu heater supply schematic for reference. Just need to dial in the circuit to get it to feed the AT4060 mic the correct heater current and voltage , the HV section is already regulated to 120vdc.

 

[maxwall]

Can someone help me identify the 5 pin SIP IC in this AT8560 power supply ? IC outlined in yellow.

 

[Khron]

Can someone help me identify the 5 pin SIP IC in this AT8560 power supply ? IC outlined in yellow.

So is your goal to make a 1:1 clone of the AT power supply, or just to make *A* power supply that works with your AT4060?

 

[McIrish]

It's an M5231 regulator. It was tight to the heatsink but I was able to bend it over enough to read it .

 

[maxwall]

Thanks again, McIrish, I owe you a McGuinness

Would be nice to build a replica AT8560 for personal use, but not sure its practical , have to weigh in on parts availability , some of the parts may be hard to source or cost prohibitive as with many japanese transistors. In any case, its important to study the design, IC datasheets and possibly implement a modern version with easy to source parts that reach the same objective. There might be other DIY'ers in the same fix. However , considering Audio Technica offered to sell me a replacement PSU for $1K , I think the answer is clear.

I think the PSM169 PSU just needs some corrective component changes in the heater supply section ,namely the resistors sitting off the LM317 regulator, the B+ section is already there at 120vdc regulated and measured.