41

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« Last post by MRMNW on May 20, 2026, 05:57:34 PM »

Thanks, what do you mean by sequenced?

It's one of your 501 Chassis, but does the same in my API lunchbox too.

42

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« Last post by JPK on May 20, 2026, 05:47:34 PM »

The voltages are OK.
Check that the 2 voltages are sequenced and come up after a few seconds.
Check that it is not the chassis that is loaded too much. What brand is it? Did you add more modules recently?

43

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« Last post by MRMNW on May 20, 2026, 01:56:41 PM »

I get 222v and -5v

44

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« Last post by JPK on May 19, 2026, 04:14:54 PM »

Can you do the high and low votages check in the test guide, steps 3 and 4?

45

SK49 Multi-patern Tube Microphone / Re: SK49 pair on a live orchestra

« Last post by JPK on May 19, 2026, 04:09:22 PM »

The recording sounds fantastic, thank you so much for sharing!
We love seeing our kits built so well and put to such great use. Thanks for the support, and happy recording!
Kind regards,

46

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by JPK on May 19, 2026, 03:58:57 PM »

VO to V- 0.817 volts
Problem here: you have no negative -16V rail.
Check again after unpluging the U5 module.
Check if R53 is OK (1 ohm).

47

MP566 Tube microphone preamplifier / 5.66 Problems

« Last post by MRMNW on May 18, 2026, 08:37:45 AM »

Hi, 
built this a month ago and it has worked fine,
Now when switching the chassis on it clicks on and off before eventually working after switching it off and on again.
There is also a very low and thin sound. I think it may have overheated. 
Any help much appreciated.
Thanks

48

SK49 Multi-patern Tube Microphone / SK49 pair on a live orchestra

« Last post by Alex Harmer on May 18, 2026, 06:09:45 AM »

Hi,

I thought you would like a sound sample of what the SK49s can do on orchestra. I built these mics, but I had to buy extra long 7-pin XLR cable to hang them from the ceiling of the auditorium. 

Last week I recorded the Christchurch Symphony Orchestra live in the Town Hall, Christchurch, New Zealand.

There is no reverb, EQ, or processing. 

They are absolutely fantastic microphones! Thanks Sound Skulptor!

https://soundcloud.com/harmerny-productions/sk49-in-ortf-on-a-live

49

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by spurton@gmail.com on May 17, 2026, 08:48:14 PM »

I found 2 bridges which I fixed. 1 was between 2 joints that connect the main PCB to the tube support PCB. The other was on the HPF pot connection. I hooked up a signal generator at 1k 0.020v and used my oscilloscope to trace the signal after I fixed the bridges. I was getting no signal from TP3,4,5,6. TP2 had a slight signal. I replaced the U2 and U3 op amps and no signal. Here are the DC test values. So something is messed up somewhere. 
VO to V+ 16volts
VO to V- 0.817 volts
V- to B+ 13.8v
H+ to H- 18.96v
V0 to TP2,3 14.58v
VO to TP1 -0.003 v
VO to TP4 0.04v
VO to TP5 2.25v
VO to TP6 1.38v

😞

50

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by JPK on May 08, 2026, 08:46:01 AM »

Can you tell me which pins were shorted?
What results do you get from the voltages checks in the test guide steps 2 to 5?