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magnetman 2nd February 2013 09:43 AM

Tubelab SE buzz and crackle
Hi all,

So I have had the tubelab SE up and running for a while now all was good. Until I turned it on too soon after turning it off.

At the time there was a bright flash from the 300b's.
After much wailing and gnashing of teeth I went through the usual checks, and all was ok.

However after a warm up of roughly 30mins i can hear a buzz and a course crackle in both channels I is present when volume is all the way down as well as up the volume does not change.

could this be the pq5ev5 volt reg?

you thoughts would be appreciated.



MelB 2nd February 2013 01:15 PM

When you flipped the switch back on right away your negative grid voltage was either not present or very high. Your B+ caps were still charged or charged quickly and since the filaments were still warm on the 300b's they conducted right away. As their was not enough negative grid voltage you had an electrical arc in your 300B's. Sorry to say you may have damaged them.
My thoughts on what happened anyhow.

wicked1 2nd February 2013 04:49 PM

I agree..
You could easily check the 5v reg by being sure you have a steady 5v at the 300b filaments..
otherwise, yeah, I'd pop in another set of 300b's.

magnetman 2nd February 2013 10:01 PM

Ok, so I have changed the valves, all was good then i started my computer and what do you know there is the crackling again in sync with the hard drive, that's an easy fix.

buzz is still present, after the amp warms up it starts. its constant. Its reasonably loud i.e. i can hear it 6m away with vol down, but not very noticeable whilst music playing.



wicked1 2nd February 2013 10:10 PM

Buzz in both channels, w/out the computer? And you checked all the voltages and bias and everything, and it all appears to be working? And exactly 5v at the 300b filaments?

If that all checks out, my next guess would be power supply caps. I am just guessing, though.

I had 2 failures in my tubelab se over the years.. one was a failed diode and then recently, after several years, a 10m45 failed. The diode caused a trace on the PCB to completely vaporize and took out PS caps too. The 10m45 failing didn't do any damage, but that channel was very quiet. That probably doesn't help....

magnetman 3rd February 2013 07:51 AM

So, I have spent the day checking and testing.
HT 367V
pre tubes 175V on both
300B bias 600mV
heater 5.17V

Temps inside box roughly 40 deg C.

I have had the amp running for about an hour. For the first 30-40mins the amp ran silently. then the buzz creeps in and the crackle starts (sounds similar to a Geiger counter getting slowly closer to a radioactive compound) infrequent cracks then gradually becoming more 'crackly'.

voltages remain stable.

the volume of crackles remain the same. Simultaneous in both speakers

The power caps seem to be ok, HT Voltage would fluctuate if damaged wouldn't it?

still nutting it out


MelB 3rd February 2013 02:28 PM

Could be a cold solder joint? Or rectifier tube or other tube not making proper contact in socket? Since it is both channels start in power supply.

rmyauck 3rd February 2013 02:52 PM

Could be the rect. tube have got damaged with what you did, as I read a good mod which George is or has added to the SE amp is UF4007 SS diodes in series with the PS Trans. secondary wires to pins 4 & 6 of the 5AR4/GZ34.

The banded end goes to pin 4 & 6 and you can use heat shrink over the diodes.

It will help the tube last longer also besides helping in a power outage where the power flashes off and on quickly. It won't hurt the sonics either.


j.michael droke 3rd February 2013 02:53 PM


Originally Posted by magnetman (
Hi all,

So I have had the tubelab SE up and running for a while now all was good. Until I turned it on [too soon] after turning it off.....At the time there was a bright flash from the 300b's, could this be the pq5ev5 volt reg? your thoughts would be appreciated....cheers Luke

Hi there L: Out of curiosity, how long is "too soon" on turn on-after shut off?......... regards,Michael

rmyauck 3rd February 2013 03:01 PM

I read somewhere you should wait till everything cools down inside the tube which may take a while depending on room temp and how enclosed the tubes are etc. You may get away with less but I always wait. So back to room temp to the touch for sure.


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