Hum from 5E3 after adding USB thermal fan more when using A/B switch to change from channel 1 to channel 2

Johnnydoright

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Seattle, Wa
Hi folks. I have 6 or 7 5E3 Deluxe clones. Started by building a kit from Stuart Mcdonald, because it was a complete kit with instructions. I got brave,(cheap/stupid) and bought an inexpensive kit on EBay from China. Got it together and struggled for quite some time but finally got it sorted out. From there I put together a couple from parts mainly acquired from the Hoffman amplifier store. I found his layouts to be very good. The pricing for his parts was good, and his website includes parts lists for many different amps. Not too long after I happened across Rob Robbinette's Deluxe page and built my first one of those. It was magic. The amp is the one I play through almost always. All of these amps have a couple things in common. First they all sound incredible! Second, they all have a very low noise floor, in fact, there have been a few times after turning one on for the first time, I was not sure it was working, it was that quiet! Third, and this is why I am writing this post, they all get very hot! Now this was brought to my attention by a friend of mine who has been coming by to jam with me and my buddies on Friday evenings. Of course, I decided to investigate this phenomenon, and so set to work trying to do research. The consensus is yes the 5E3 does get very hot. All the ones I have get hot enough to cause me to be concerned, although I have had no failures after 7 or so months of playing through them. However, being concerned with possible spotainious combustion I decided to try to figure a way to cool things down. I swapped out the 250 ohm cathode resistor for a 500 ohm, but found the tone was ruined. I settled at 270 ohms (264 ohms when measured) the 250 ohm resistor measured 246 ohms. The amp still gets very hot. When I measured the bias, I was a little uneasy to find the tubes are running 44 and 46 milivolts. Quite a bit more than recommended for the little 6V6 tubes. Still, there have been no failures, so I decided to install a fan, and was pleased that this cooled things off quite admirably.
I wired the fan using a desktop outlet with 2 120 volt outlets, and 2 USB outlets. Being old and forgetful, I decided to install a thermal switch to control the fan, so I would not have to remember to turn them on and off. At this point, I now have developed a very annoying hum, particularly on channel 2, which is the 5E3 channel. I use an A/B switching box to switch from channel1 to 2, as channel1 is voiced like a Marshall and is very pedal friendly. This problem presented after the thermal switch was installed. I am hoping that somebody can provide a little insight into my dilemma. Thanks for listening.
 

TunedupFlat

Tele-Meister
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Ground loop maybe? Have you tested what happens with the thermal switch removed?

What type of thermal switch? Thermal Reed switches use a magnetic field that could create emi and cause hum
 

unixfish

Doctor of Teleocity
Silver Supporter
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Apr 20, 2013
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No idea. You might get a better response posting in the Amp Tech Center forum?

I would love to build amps - but this is just another hobby I have not made the time for.
 

Johnnydoright

TDPRI Member
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Jul 18, 2022
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Age
66
Location
Seattle, Wa
Ground loop maybe? Have you tested what happens with the thermal switch removed?

What type of thermal switch? Thermal Reed switches use a magnetic field that could create emi and cause hum
I did unhook the switch, but I need to remove it completely and test again.
 

archetype

Fiend of Leo's
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Jun 4, 2005
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Western NY
Welcome to TDPRI! The beer's in the fridge, over there.

Never in my life have I heard or read that a 5E3 circuit operates at a higher temperature than other amps. Unless your amp has a specific, quantifiable problem that's generating excessive heat, you broke it trying to fix a problem that didn't exist. Post in an appropriate amp forum, here, and you'll get expert advice.
 

Chester P Squier

Friend of Leo's
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Jan 16, 2021
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Welcome to the TDPRI!

Make yourself at home!

I don't mess with amps. I hope you have presented your case to the amp people on this forum. Lots of great info.
 




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