Groove Tubes MD1B Mica Capacitor values

[dude24man]

Hello, I have a Groove Tubes MD1B. I'm in the process of tracing down the lovely AC background noise. I Replaced the original gt6205 tube with a NOS 5840. Still the same noise. So I'm looking to replace the Mica Capacitors, (1) is 33pf and the other one is 5 D. I'm not sure the value of 5 D. Thank you

 

[Dylan W]

Hello, I have a Groove Tubes MD1B. I'm in the process of tracing down the lovely AC background noise. I Replaced the original gt6205 tube with a NOS 5840. Still the same noise. So I'm looking to replace the Mica Capacitors, (1) is 33pf and the other one is 5 D. I'm not sure the value of 5 D. Thank you

Pretty sure it’s just 5 pf. D means +/-0.5pf, so in this case +/-10%.

https://www.electricaltechnology.org/2022/01/capacitor-color-codes.html

 

[dude24man]

Dylan W, Thank you. I will update as things go

 

[Tubetec]

Those dipped silver mica caps are extremely reliable components , there often rated at 500vdc .
If you have a mains AC hum appearing in the audio it points towards a psu issue .
The first thing you need is a schematic , with voltages , then you can cross check ,rather than randomly swapping things .

 

[dude24man]

Tubetec, thanks. Trying to find a schematic is difficult. the sound is not a hum, its like a ocean sound. the mic still passes signal but has that sound in the background. I'm gonna double verify voltages from the B+ and A+

 

[Tubetec]

Ok,
have you checked the capsule for contamination ?
there might also be moisture behind the membrane ,
Putting the mic in a warm dry place for a day or two might help .

Theres also the possibility that the PCB ,components or tube socket has been contaminated , swab everything down with cotton buds and isopropyl alcohol and allow to dry before applying power .

 

[rock soderstrom]

Ok,
have you checked the capsule for contamination ?
there might also be moisture behind the membrane ,
Putting the mic in a warm dry place for a day or two might help .

Theres also the possibility that the PCB ,components or tube socket has been contaminated , swab everything down with cotton buds and isopropyl alcohol and allow to dry before applying power .

+1

 

[dude24man]

Thanks, I'll give that a try. I'm measuring 6.1v heater. 122v B+ at the power supply after being warmed up for 15 min.

 

[dude24man]

I fixed the mic, It was the 33pf, 5pf Mica caps. I figured I'd share this for other folks with similar problems. thanks for all the help.