Running water sound in amp

razorrick1293 · 19th September 2011, 09:59 PM

Hi guys,
A while ago i built a 50 Watt 6L6GC Guitar amp. i havnt drawn up any schematics yet, but basically its a cross between the mesa boogie 2 ch rectifier and a soldano SLO (separate clean/drive channels, gain EQ and vol for each channel, crunch+bright switch on ch1) but every now and again i get a sound from the amp like water trickling through a pipe. i first thought it was a capacitor problem, checked them and one of them had been obliterated... but its still there.

Ive just finnished tidying up the heaters so they are elevated slightly and have artificial CT's i also recently rebuilt the rectifier and reservoir capacitor part. (standard bridge rectifier (no CT on HT transformer winding), no choke with standby switch) and its still there.

Anyone have a clue what it is? i have checked the tubes, and all are fine.

I tried this in instruments and amps forum but i just see it falling down the post ladder, im hoping i may get more help here?

GloBug · 19th September 2011, 10:06 PM

Did you use the LDR's or devise manual switching?

What's your B+ in relation to your cap's voltage rating?

SS or valve rectification?

Sounds like a nice amp.

razorrick1293 · 19th September 2011, 10:18 PM

Relay switching (switched using transistors in darlington pairs)

B+ when in standby rises to around 510v, reservoir capshould be good for 1Kv (2x 500v 220uf in series) 2nd cap total ratings come to around 800v (2x 68u 400v) the rest are 22u 500v (ive never had the voltages here rise over 450 even without power tubes in.

SS 1N4007 diode rectifier

Thanks, its pretty much how i wanted it, except this problem

GloBug · 19th September 2011, 10:58 PM

Well I guess it couldn't hurt to have some resistors across those power supply caps if you don't already.

You could try to jumper the relay(s) see what happens.

Aside from that chop stick it to see if you can reproduce the sound. Maybe a resistor is faulty or something is arcing out from time to time.

razorrick1293 · 19th September 2011, 11:03 PM

ive got some accross the power supply capacitors, and how can a relay cause problems?

Or.. what about the transformer? i went a bit wierd when i first built the amp, its rated 350v RMS but gives about 510 Peak. and the bias tap is rated 0-36v and gives around 108v peak... not sure what happened to it, and its worked just fine with an extra resistor to drop the voltage, (still saving for a new transformer).

gingertube · 19th September 2011, 11:38 PM

Caution:
I had a very similar sounding problem in a HiFi Amp - it turned out to be a microphonic tube - a replacement tube fixed the problem.
Tap each tube lightly to see if you can kick off that noise. If not, then it is probably something else.
Cheers,
Ian

GloBug · 19th September 2011, 11:45 PM

As far as the relay, just trying to figure out if the (noise) is in the a audio path or not, and if so which channel, helping to narrow down the fault.

Here in North America as you may already know our voltages are a little higher then before, giving higher then rated voltage readings. I'm assuming you have an older transformer.

Are your parts vintage for the most part?, resistors etc.

How about a picture of it, just curious.

GloBug · 19th September 2011, 11:51 PM

Quote:

Originally Posted by gingertube

Caution:
I had a very similar sounding problem in a HiFi Amp - it turned out to be a microphonic tube - a replacement tube fixed the problem.
Tap each tube lightly to see if you can kick off that noise. If not, then it is probably something else.
Cheers,
Ian

Good tip.

Also if your tube sockets and what not are vintage, a good cleaning with Acetone will work were fancy cleaners fail. (Deox-it) Acetone might dissolve or soften some plastics so be careful. Great for getting rid of weird noises.

razorrick1293 · 20th September 2011, 06:35 AM

This problem is on both channels, so it might slightly narrow it down. no parts are vintage, everything was bought new including transformers. all clean. il check the tubes again. though after a look yesterday im starting to suspect one of the 6L6's
as for the transformer, its rated for 220-230 so that might be why, (our voltage is generally around 240vrms even though its supposed to be 230...)
Il get a picture up soon (its not exactly the tidyest wiring ever but it has surprisingly low noise

)
Thank you for all the help!

dcgillespie · 20th September 2011, 07:25 AM

If tubes, sockets, and caps have all been eliminated, this sounds like an intermittently noisy resistor in one of the stages somewhere along the signal path. To isolate where it is, first operate the amplifier with just the output tubes in place and see if it will make the noise. If not, then install the next preceding tube in the signal path and check for the noise, then the next, and so on. When the noise first appears, it will be associated with the last tube you installed. It does sound otherwise like it's a great amp! Good luck with it!

Dave

19th September 2011, 09:59 PM	#1
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	Running water sound in amp Hi guys, A while ago i built a 50 Watt 6L6GC Guitar amp. i havnt drawn up any schematics yet, but basically its a cross between the mesa boogie 2 ch rectifier and a soldano SLO (separate clean/drive channels, gain EQ and vol for each channel, crunch+bright switch on ch1) but every now and again i get a sound from the amp like water trickling through a pipe. i first thought it was a capacitor problem, checked them and one of them had been obliterated... but its still there. Ive just finnished tidying up the heaters so they are elevated slightly and have artificial CT's i also recently rebuilt the rectifier and reservoir capacitor part. (standard bridge rectifier (no CT on HT transformer winding), no choke with standby switch) and its still there. Anyone have a clue what it is? i have checked the tubes, and all are fine. I tried this in instruments and amps forum but i just see it falling down the post ladder, im hoping i may get more help here?

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19th September 2011, 10:06 PM	#2
GloBug Banned Join Date: Jun 2011	Did you use the LDR's or devise manual switching? What's your B+ in relation to your cap's voltage rating? SS or valve rectification? Sounds like a nice amp.

19th September 2011, 10:18 PM	#3
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	Relay switching (switched using transistors in darlington pairs) B+ when in standby rises to around 510v, reservoir capshould be good for 1Kv (2x 500v 220uf in series) 2nd cap total ratings come to around 800v (2x 68u 400v) the rest are 22u 500v (ive never had the voltages here rise over 450 even without power tubes in. SS 1N4007 diode rectifier Thanks, its pretty much how i wanted it, except this problem

19th September 2011, 10:58 PM	#4
GloBug Banned Join Date: Jun 2011	Well I guess it couldn't hurt to have some resistors across those power supply caps if you don't already. You could try to jumper the relay(s) see what happens. Aside from that chop stick it to see if you can reproduce the sound. Maybe a resistor is faulty or something is arcing out from time to time.

19th September 2011, 11:03 PM	#5
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	ive got some accross the power supply capacitors, and how can a relay cause problems? Or.. what about the transformer? i went a bit wierd when i first built the amp, its rated 350v RMS but gives about 510 Peak. and the bias tap is rated 0-36v and gives around 108v peak... not sure what happened to it, and its worked just fine with an extra resistor to drop the voltage, (still saving for a new transformer).

19th September 2011, 11:38 PM	#6
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	Caution: I had a very similar sounding problem in a HiFi Amp - it turned out to be a microphonic tube - a replacement tube fixed the problem. Tap each tube lightly to see if you can kick off that noise. If not, then it is probably something else. Cheers, Ian

19th September 2011, 11:45 PM	#7
GloBug Banned Join Date: Jun 2011	As far as the relay, just trying to figure out if the (noise) is in the a audio path or not, and if so which channel, helping to narrow down the fault. Here in North America as you may already know our voltages are a little higher then before, giving higher then rated voltage readings. I'm assuming you have an older transformer. Are your parts vintage for the most part?, resistors etc. How about a picture of it, just curious.

20th September 2011, 06:35 AM	#9
razorrick1293 diyAudio Member Join Date: Nov 2010 Location: England Hertfordshire	This problem is on both channels, so it might slightly narrow it down. no parts are vintage, everything was bought new including transformers. all clean. il check the tubes again. though after a look yesterday im starting to suspect one of the 6L6's as for the transformer, its rated for 220-230 so that might be why, (our voltage is generally around 240vrms even though its supposed to be 230...) Il get a picture up soon (its not exactly the tidyest wiring ever but it has surprisingly low noise ) Thank you for all the help!

20th September 2011, 07:25 AM	#10
dcgillespie diyAudio Member Join Date: May 2010 Location: Ball Ground, GA	If tubes, sockets, and caps have all been eliminated, this sounds like an intermittently noisy resistor in one of the stages somewhere along the signal path. To isolate where it is, first operate the amplifier with just the output tubes in place and see if it will make the noise. If not, then install the next preceding tube in the signal path and check for the noise, then the next, and so on. When the noise first appears, it will be associated with the last tube you installed. It does sound otherwise like it's a great amp! Good luck with it! Dave