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Pilot Lamp [message #10384] Sat, 31 January 2009 11:50 Bill Messages: 64 Registered: March 2002 Location: Kansas Member Just passing along something I ran into, while chasing serious hum in my K200's....I had totally recapped and checked the amp and still had a hum. Discovered someone had put in the wrong pilot lamp. Replaced it with the proper 1829 lamp, and cured it! BillC Report message to a moderator

Re: Pilot Lamp [message #10386 is a reply to message #10384] Mon, 02 February 2009 01:48 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member That would make some sense, because of the load imbalance on the positive and negative side of the power supply. But that load seems inconsequential to the much larger load of the amp itself. That being said, perhaps that is only an issue while the amp is idling and a low level hum would be most apparent. Kind of like the Kustom Hiss, patent pending. Any other thoughts guys? Steve? ChicagoBill? Conrad Report message to a moderator

Re: Pilot Lamp [message #10388 is a reply to message #10384] Mon, 02 February 2009 06:21   stevem Messages: 4739 Registered: June 2004 Location: NY Senior Member i do not know, I have other bayonet type bulbs that I will try tonight and see if I get the same hum and report back. Report message to a moderator

Re: Pilot Lamp [message #10389 is a reply to message #10388] Mon, 02 February 2009 11:33 chicagobill Messages: 2005 Registered: April 2003 Senior Member I think that it would have to draw a lot of current to cause a big enough imbalance in the power supply to cause a big hum, especially with new filter caps. The 200 ohm dropping resistor must have been really cooking. In fact it probably should be checked for drift. What number bulb was in there? Report message to a moderator

Re: Pilot Lamp [message #10390 is a reply to message #10384] Mon, 02 February 2009 12:09   stevem Messages: 4739 Registered: June 2004 Location: NY Senior Member I have never did the caculation, but as it is that 200 ohm 5 watt gets so hot they must be running it at 4.5 watts. Report message to a moderator

Re: Pilot Lamp [message #10391 is a reply to message #10389] Mon, 02 February 2009 16:13 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member I thought the same thing. The power supply can handle that little bit of current at idle without causing ripple on the filter caps. Unless, the caps were't changed. I've seen amps where the caps were virtually non-existent and by the very nature of a push-pull amp, the hum was cancelled in the power stage. There has to be a better reason. Conrad Report message to a moderator

Re: Pilot Lamp [message #10393 is a reply to message #10384] Tue, 03 February 2009 06:02   stevem Messages: 4739 Registered: June 2004 Location: NY Senior Member Untill I find my other stach of bulbs to try in one of my heads, the only other guess I can make is that while he was in the amp fooling around at the same time he bumped into the offending input jack who`s switch was not closing well. So the hum was due to a open jack switch on a channel that was turned up. Report message to a moderator

Re: Pilot Lamp [message #10398 is a reply to message #10393] Tue, 03 February 2009 09:33 Bill Messages: 64 Registered: March 2002 Location: Kansas Member Gee, Maybe I'm lying.... Bill Report message to a moderator

Re: Pilot Lamp [message #10399 is a reply to message #10398] Tue, 03 February 2009 10:22 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member No, not lying but sometimes when you go into ANY electronic equipment, you disturb something you hadn't intended. The amount of current draw in any lamp that would fit into a bayonet socket is so small that it would be hard to upset the balance between the positive and negative power supplies. An imbalance in the current and added ripple would hardly be noticable in hum production. First off, the ripple would have to be almost completely unfiltered for the power amp to hum. Then the voltage is then reduced to 8 Volts and filtered again. The amount of unfiltered voltage would be in the microvolt region. Now, it is entirely possible that you disturbed something else, perhaps a cold solder joint and the hum appeared. But you never said if you just replaced the bulb from the outside or were inside the chassis when this occurred. I repair amplifiers and major electrical installations and there is nothing worse than troubleshooting a circuit, remove a plug in component, reseat the component and have it work. What did I do??? Unless I replace a defective component, I would never know what I did. Will that problem return? Don't be so defensive. Sometimes these questions just need to be asked. Everyone here is trying to help, but the solution to your problem doesn't quite fit. If Steve could reproduce the problem, then maybe we have an answer. I read your original message again and I only questioned if the 2 large filter caps mounted on the chassis were replaced. Stevem, ChicagoBill and quite a few others heve been together on this site since 2001 and we DO NOT insult anyone with a legitimate question or problem. This is just the first time that the problem of an improper bulb has had this result. Sorry for any misunderstanding. Conrad Report message to a moderator

Re: Pilot Lamp [message #10401 is a reply to message #10384] Tue, 03 February 2009 12:07   stevem Messages: 4739 Registered: June 2004 Location: NY Senior Member No no! I do not mean to imply that you are lying, Its just hard to get my head around this one without reproducing it myself. All too many times while working on a ampI have fixed one problem and created another, I just meant that this could be kind of the reverse thing. Report message to a moderator

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