Hi - I have an old amp that used to have an optocoupler in an auto mute circuit to operate during a 2 minute warm up.
This is the component:
https://www.tubesandmore.com/sites/default/files/associated_files/r-vtl5c1_2019.pdf
I have been chasing hum and thought it might be one of these so I removed from the circuit, the hum did not change much ( a little bit) but the sound improved so I kept it out of circuit.
I now wonder if I need to put in some sort of equivalent resistor in the controlling / driven side of what is now a circuit missing a component in a circuit.
To be honest I really have no idea what I am talking about, but I have a problem of instability that is occasional and worrying and it's just a logical question - have I left an unstable circuit with a gap!!
Circuit is here https://www.arcdb.ws/Database/SP8/ARC_SP8_manual.pdf
This is the component:
https://www.tubesandmore.com/sites/default/files/associated_files/r-vtl5c1_2019.pdf
I have been chasing hum and thought it might be one of these so I removed from the circuit, the hum did not change much ( a little bit) but the sound improved so I kept it out of circuit.
I now wonder if I need to put in some sort of equivalent resistor in the controlling / driven side of what is now a circuit missing a component in a circuit.
To be honest I really have no idea what I am talking about, but I have a problem of instability that is occasional and worrying and it's just a logical question - have I left an unstable circuit with a gap!!
Circuit is here https://www.arcdb.ws/Database/SP8/ARC_SP8_manual.pdf
Removing the optocoupler should be just fine. The driver circuit certainly won't care. However, the mute circuit is designed to engage on brief mains outages. That function may be good to have as tube amps can be have a bit oddly on power glitches and on startup in general.
Tom
Tom
thanks,
We don't get many outages here, and it sounds a LOT better without so I think I will live with the risk....hopefully not regretting it!!
We don't get many outages here, and it sounds a LOT better without so I think I will live with the risk....hopefully not regretting it!!
also it hummed and buzzed like crazy on auto mute, necessitating the manual mute on warm up anyway! (which is why I hoped removal might help)
Oh, is that the amp you're having hum issues with? Has the hum always been there or has it developed over time? If the latter, I would look at the power supply caps (C14, C15). Measure the AC voltage across those caps. I'd expect a few volt, maybe 10 V AC of ripple voltage. If you have more, I'd replace the caps.
Tom
Tom
What is the difference with and without ? Any level change ?
any change in distortion ?
As for the hum, i think finding the cause of hum would be better then
removing functionality . The most probable source of hum should be
some of the many DC powersupply sources could be bad.
Hum always been there since and endless effort to remove, I have it down but not out.
C14 and C15 just been replaced as has C12 and C35.....
I will check the AC across the caps
Use the sound card in your computer with software Visual Analyser 120Hz would mean you have bad filtering. Set your meter to AC and measure the main B+ voltage.
You get a scope, thats a very good tool for problems like hum-hunting.
out of interest the last repair guy (who also fitted the wrong FETs that were under rated and gave me my elusive hiss when they went fizz) replaced R87, not sure why.
the 12BH7A gets REALLY HOT not sure this is normal, but maybe I am hunting a fault in the PS somewhere as the route of the hum?
the 12BH7A gets REALLY HOT not sure this is normal, but maybe I am hunting a fault in the PS somewhere as the route of the hum?
As others have suggested: Find out what the frequency of the hum is. Measure the spectrum of the output voltage with a sound card and show us. We can provide better help then, unlike now where the blind is leading the blind. 🙂
Tom
Tom
+200
Fix first. Then mess with. Messing first will leave you with a brick. Just saying.
Tom