Fender BF amp temp too hot?

[jc4yr]

Hey guys,


My blackfaced Fender amp seems to get pretty warm when it's been powered up for a bit... is this normal and do you have similar experience?

I have a Vibrolux.

thanks!

 

[jazzguitar]

It depends on where it gets hot and how much!

Obviously, the tubes are too hot to touch. The back panel (metal) above the power tubes and rectifier may be too.

The front panel should not get really hot. The power transformer can get pretty warm but should not be too hot to firmly grip it a few seconds.

A typical Vibrolux issue is some honko followed the 70% hype and biased the amp to the point of the power tubes idling at 70% of their max.

The Vibroluxes are built with a little less plate voltage than Pros Supers and Twins so this ends up at a higher idle current than the amp was made for. Hence it gets pretty hot.

 

[Thin69]

In the interest of longevity I always add small quiet cooling fans to keep my amps from getting overly hot. Inverted tubes really do heat up a chassis and components. The old rule of thumb is that for every 10 degrees C the life of electronics is cut in half. I prefer not to let my amps run too hot.

 

[jc4yr]

It depends on where it gets hot and how much!

Obviously, the tubes are too hot to touch. The back panel (metal) above the power tubes and rectifier may be too.

The front panel should not get really hot. The power transformer can get pretty warm but should not be too hot to firmly grip it a few seconds.

A typical Vibrolux issue is some honko followed the 70% hype and biased the amp to the point of the power tubes idling at 70% of their max.

The Vibroluxes are built with a little less plate voltage than Pros Supers and Twins so this ends up at a higher idle current than the amp was made for. Hence it gets pretty hot.

Thanks for the reply! That sounds like a good sign then and that everything is probably ok. I mostly notice the heat when i go to flip the amp off. I can feel the heat on my hand from the back panel and it made me curious. it's not too hot where i can't touch the panel but i just wanted to make sure all is well.

When i bought the amp (transformer, recapp and other odds and ends), i've asked every tech to be pretty conservative with the work theyve done it. I'll ask my guy about the hype and bias!

 

[jazzguitar]

When i bought the amp (transformer, recapp and other odds and ends), i've asked every tech to be pretty conservative with the work theyve done it. I'll ask my guy about the hype and bias!

I have written an article about this issue in the hope of addressing some common myths. You will find it here
http://www.blueglow.de/TechPaper/Debunk.html

 

[Silverface]

I mostly notice the heat when i go to flip the amp off. I can feel the heat on my hand from the back panel

It's very normal.

BUT - never back the amp up to a wall without at least a few inches of clearance for ventilation purposes.

Fans are unnecessary in Fender amps, which are well-ventilated ; The wrong type can also cause noise. Adding one is something for a qualified tech to do, not someone unfamiliar with tube amps.

Is your Vibrolux a reissue/custom model or a vintage amp? If vintage did you ensure it had been serviced prior to using it, or did someone just tell you certain work had been done?

If the tech was being "conservative" and is not a guitar amp tech (or is following directions based on what knowledgeable players tell them) he may have done only a partial cap job. It's not uncommon. You might check and make sure ALL the filter caps are fairly new - otherwise you could have a very expensive failure without warning.

Regarding bias settings, good techs want you there. The bias can be set arbitrarily by a calculation - but that doesn't always result in the best tone. The bias can be set in a range, and various players like it set differently - some hotter for a warm tone and earlier breakup; some colder for more clean headroom.