MK47 PCB tube mic kit - build thread
- Thread starter ioaudio
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MK burning for several days.
Intermittent crackling is not what I would attribute to noisy tubes, but it may be a first.
The popping and crackling is violent, clipping the signal. I'll post some audio clips, both of what I hear as normal tube futzing and this crazy violent popping.
The microphone will be quiet for even long periods of time, and then it will go on for several minutes of the popping.
jordan s are you still around, is your microphone still behaving well after the resistor swap?
Intermittent crackling is not what I would attribute to noisy tubes, but it may be a first.
The popping and crackling is violent, clipping the signal. I'll post some audio clips, both of what I hear as normal tube futzing and this crazy violent popping.
The microphone will be quiet for even long periods of time, and then it will go on for several minutes of the popping.
jordan s are you still around, is your microphone still behaving well after the resistor swap?
Quick datasheet observation while hunting down an aluminum chassis mount 1.5K (aluminium for you folks across the pond ;D )
Temperature Coefficient:
Power Resistors Wirewound Aluminum Housed 20 PPM / C
Power Resistors Wirewound Inorganic Potting Compound 300 PPM / C
Temperature Coefficient:
Power Resistors Wirewound Aluminum Housed 20 PPM / C
Power Resistors Wirewound Inorganic Potting Compound 300 PPM / C
Category 5
Well-known member
MicDaddy said:
Sounds like the trouble I've had with some Western Electric tubes. What kind are you using? Are you using the cement style dropper resistor?
JAN Philips and what looks like the cement resistor that came with the kit.
The thing will work fine for hours on end and then blasts of popping, it's not like fizzy futzing in the noise-floor, it's like fireworks.
The thing will work fine for hours on end and then blasts of popping, it's not like fizzy futzing in the noise-floor, it's like fireworks.
Category 5
Well-known member
MicDaddy said:
Yeah. If you are using the cement resistor than that is likely the problem. A good quality aluminum sinked resistor has solved the issue for more than a few MK47s.
Current kits are already including the newer resistors, that's why I asked.
I've got a bunch on the way. I was curious as I'd seen IOaudio recommend replacing yet the photo for the mk kit at Chunger's place still shows the cement type..
Thanks guys! I'll follow up with the audio and when the new 1.5K show up.
Thanks guys! I'll follow up with the audio and when the new 1.5K show up.
ioaudio
Well-known member
Hey,
yes the aluminium resistor should solve that problem - there was a batch of cement resistors showing the fireworks you describe.
-Max
yes the aluminium resistor should solve that problem - there was a batch of cement resistors showing the fireworks you describe.
-Max
Swapped through a few sets of tubes just to exhaust that possibility, popping followed the mic.
Swapped the 1.5k with a 10W aluminum, no more popping... 8) thanks everyone for your help hunting that down!
Sad news, now my mic is stuck in omni... did I kill the relay (how to test?), break a trace swapping tubes?
I'm seeing ~90VDC before the output cap, this seems very high? Thanks for any tips
Swapped the 1.5k with a 10W aluminum, no more popping... 8) thanks everyone for your help hunting that down!
Sad news, now my mic is stuck in omni... did I kill the relay (how to test?), break a trace swapping tubes?
I'm seeing ~90VDC before the output cap, this seems very high? Thanks for any tips
Thank you duy_hoang, so you say you had a trace go open?
I suspected I had broken one/several of the 90* solder pads where the main and daughter board meet from the stresses of swapping tubes. Would ideally like to secure that daughter board with something supplemental to those 90* solder joints.
From which contact to which did you apply the jumper? (I suppose I could try to figure it out from the schematic but I don't have the mic in front of me.)
If I'm looking at the diode, would it be cathode to polarity, or anode to ground that was disrupted?
When switching the pattern, I hear the normal pwop but no polar change...(can you hear the relais inside the mic?)
I'll chime those two traces with the DMM and see if one is open. Thanks again!!
I suspected I had broken one/several of the 90* solder pads where the main and daughter board meet from the stresses of swapping tubes. Would ideally like to secure that daughter board with something supplemental to those 90* solder joints.
From which contact to which did you apply the jumper? (I suppose I could try to figure it out from the schematic but I don't have the mic in front of me.)
If I'm looking at the diode, would it be cathode to polarity, or anode to ground that was disrupted?
When switching the pattern, I hear the normal pwop but no polar change...(can you hear the relais inside the mic?)
I'll chime those two traces with the DMM and see if one is open. Thanks again!!
Category 5
Well-known member
Did you test the mic without the pattern wire connected? just disconnect it inside the PSU and see if that changes anything. You would normally be stuck in cardioid in such case.
Excellent points and tips guys! So sounds like my relais is stuck on/closed/shorting (term?)...
I'll try to both disconnect the polarity rail at the PSU and inside the mic (should go cardioid?) If that works to get the mic to cardioid I'll hunt for a short, or replace the relais? I suppose I could check the relais powered down for open/short?
I'll measure my switch for correct operation, perhaps it failed?
What else might cause the relais to not shut down... if the above fails I'll disconnect the rear diaphragm just for sanity check. ;D
I'll try to both disconnect the polarity rail at the PSU and inside the mic (should go cardioid?) If that works to get the mic to cardioid I'll hunt for a short, or replace the relais? I suppose I could check the relais powered down for open/short?
I'll measure my switch for correct operation, perhaps it failed?
What else might cause the relais to not shut down... if the above fails I'll disconnect the rear diaphragm just for sanity check. ;D
ioaudio
Well-known member
If it's stuck in omni, it means the relais is active /turned on.
Search around the pattern switch, maybe it's not correctly connected.
90 V is very high, what's your B+?
Search around the pattern switch, maybe it's not correctly connected.
90 V is very high, what's your B+?
B+ at the PCB under load (mic) ~104+
I will double check.
I will double check.
:'( what a stupid problem... the tubes which I was testing in the mic (northern electric) have some nasty white corrosion underneath.
Swapped the tubes back for the JANs and my patterns are working, no crazy popping. Working.
Thanks again guys!
Swapped the tubes back for the JANs and my patterns are working, no crazy popping. Working.
Thanks again guys!
tonycamp
Well-known member
MicDaddy said::'( what a stupid problem... the tubes which I was testing in the mic (northern electric) have some nasty white corrosion underneath.
Swapped the tubes back for the JANs and my patterns are working, no crazy popping. Working.
Thanks again guys!
I bought a 10 piece lot of northern electrics, about 1/2 of them are noisey, when you find a good quiet pair, they are quite nice.
interesting you say that tonycamp, I immediately found the "timbre" of these tubes more pleasing than the JAN, but the wooosh is much much higher than the noisefloor of the JAN, which are quiet yet microphonic
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