Tube Mic Power Supply Upgrade Help

[kimothebeatmaker]

try another tube

Ok I will.  Do you have any suggestions?  Is the tube I have bad? 

Also why did you ask about the voltage regulator and diode?  It's a LM317 and the diode is a 1N4007

 

[abbey road d enfer]

Also why did you ask about the voltage regulator and diode?  It's a LM317 and the diode is a 1N4007

The components are only part of the story. How they are put up is more important. And sloppy lay-out can ruin the performance of an otherwise sound design.

 

[Gus]

Ok I will.  Do you have any suggestions?  Is the tube I have bad? 

Also why did you ask about the voltage regulator and diode?  It's a LM317 and the diode is a 1N4007

With tube microphones you might need to try a number of tubes(more than 2 is not uncommon) until you find one with low noise.

Asking about the part numbers are to understand what type of filament regulation circuit you have.

 

[kimothebeatmaker]

Asking about the part numbers are to understand what type of filament regulation circuit you have.

Im really interested in this, it seems like you nailed the diode dead on guessing its the 1N400 series.  Do you have an idea what kind of circuit this is and how to improve it? 

 

[abbey road d enfer]

Im really interested in this, it seems like you nailed the diode dead on guessing its the 1N400 series.  Do you have an idea what kind of circuit this is and how to improve it?

1N400x diodes are here since the 60's; they're the go-to type for many designers.
As popular as the 1N914/4148 for small signal.

 

[abbey road d enfer]

Asking about the part numbers are to understand what type of filament regulation circuit you have.

Much more enlightening would be knowing the type of U1 - probably LM317...?

 

[kimothebeatmaker]

Much more enlightening would be knowing the type of U1 - probably LM317...?

Yes it’s a LM137

 

[kimothebeatmaker]

Just incase anyone needs this info for the AL-Y59 mic by Luke Audio

Here is the tube cable pinout for the Y59 mic.

1 - 120
2 - 6.3
3- none
4- gnd
5- audio +
6- audio -
7- gnd


He also verified the Luke T14 can be replaced with the AMI T14.

Also, if you're a DIYer, the empty headbaskets are going for 50 bucks! So you can make your own swappable headbaskets with whatever capsule you like. NICE!!!!!!

 

[Tubetec]

Regarding the heat created in tube mics , the fact that the mic is running some degrees above ambient is a good thing . It will drive off any moisture in the capsule and will also stop the tendency for the performers breath to condense on the membrane , that can often be the cause of crackles and pops in cold running transistor mics. Moisture on the membrane might also tend to attract dust particles which again will lead to poor performance after a while .

I'd second the others who suggest swapping out the tube , in tube mics the grid resistor is many megaohms while in typical circuits 1meg would be normal , not all tubes will perform satisfactorily with high grid resistances .

 

[rjb5191]

I also have a similar mic, the Luke Audio AL-Y56. I'd agree that the noise floor is higher than I'd like and I'm using a Mullard CV4024 that was selected by Bowie so hopefully, the tube is reasonably quiet. I do hear the white noise that is mentioned, which I'm guessing is mostly tube noise but could be resistor noise and other noise components, but I also hear moduating low frequency hum below that noise floor. I'm going to rebuild the power supply for the hell of it but maybe its a lost cause becasue the layout of the supply pcb might be total garbage. I know the lamp on the psu is fed off the same circuit that goes to tube heaters. Initially I measured that the heater voltage was fluctuating up and down up to 0.2V which seems out of spec for the LM317. The input voltage to the regulator circuit is 10.2V so this should be enough headroom. I added another capacitor in parallel to the large 10,000 uf output capacitor and this seemed to stabilize the output. Maybe these are crap parts and a fake ST regulator. Who knows, but they are coming out. I'm going to make sure that the regulator circuit is built to spec. All caps will be changed out, low noise resistors will be going in, and UF4007 fast recovery diodes will come in. Wiring will be twisted if needed. Is there a way to isolate the lamp from the heater circuit. I'm guessing its an LED. Can these dump noise back in to the circuit?

 

[abbey road d enfer]

Initially I measured that the heater voltage was fluctuating up and down up to 0.2V which seems out of spec for the LM317.

This is definitely not normal. Can you check the voltage with a scope? Seeing if there are traces of ripple.

Maybe these are crap parts and a fake ST regulator. Who knows, but they are coming out. I'm going to make sure that the regulator circuit is built to spec.

Regulators can be noisy, but the tube in your mic has the active part pretty well isolated from the heaters. I wouldn't expect too much inmprovement even with a perfect heater voltage.

. I'm guessing its an LED. Can these dump noise back in to the circuit?

No.

 

[rjb5191]

This is definitely not normal. Can you check the voltage with a scope? Seeing if there are traces of ripple.

Regulators can be noisy, but the tube in your mic has the active part pretty well isolated from the heaters. I wouldn't expect too much inmprovement even with a perfect heater voltage.

I believe you are correct. I didn't notice any difference now that the heater voltage is at a steady, pretty much perfect 6.3V

No

Thanks, I will check this further. I agree it is strange behavior. Maybe 4V headroom is not enough for a possible fake 317? The input and output caps certainly seemed sufficiently sized before I added the additional caps in parallel on the underside of the board.

 

[abbey road d enfer]

Maybe 4V headroom is not enough for a possible fake 317?

Is it really 4V? The actual voltage is certainly 4V +/- something (ripple). When the ripple is negative, the headroom is noticeably lower.

 

[rjb5191]

I just measured 10.3 VDC at the regulator input and 6.3 VDC at the output with my multimeter, not with a scope yet.

 

[Matt Syson]

A digital multimeter when set to AC will measure the ripple voltage (AC component) with the proviso that as it won't be a sinewave the meter will not give a true reading, although a RMS measuring meter should be OK. Also the aC measurement is likely to be incorrect partricularly on the putpur side of the regulator as AC meters often struggle to read only a few millivolts of AC. This said you get some idea of problems.

 

[rjb5191]

A digital multimeter when set to AC will measure the ripple voltage (AC component) with the proviso that as it won't be a sinewave the meter will not give a true reading, although a RMS measuring meter should be OK. Also the aC measurement is likely to be incorrect partricularly on the putpur side of the regulator as AC meters often struggle to read only a few millivolts of AC. This said you get some idea of problems.

Nice, Thank you, that makes sense. I could also just hookup my scope but that's a bit more work for the holiday . I strapped a small ceramic capacitor across the b+ and ground at the input connections on the microphone pcb and it seemed to knock the hash down a little just based on listening. Scientific, I know..