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?
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?
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.
What's your B+ in relation to your cap's voltage rating?
SS or valve rectification?
Sounds like a nice amp.
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 🙂
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 🙂
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.
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.
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).
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).
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
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
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.
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.
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.
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!
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!
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
Dave
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