Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TerryD on October 15, 2017, 08:55:42 pm
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I fixed my friends Hot Rod Deluxe amp with the two large resisters that over heat and cause havoc with the board. The solder joints were burnt to crap. I had to make a few external wires in place of using the traces/connections on the board.
I have the heat causing resisters up off the board now but they are not soldered totally firm in place. Any kind of local/hardware goop I can use that will stand the heat and hold these resisters "still". Thanks, Terry
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I fixed my friends Hot Rod Deluxe amp with the two large resisters that over heat and cause havoc with the board. The solder joints were burnt to crap. I had to make a few external wires in place of using the traces/connections on the board.
you've done about all you can do. use epoxy to hold the wires down. swap out with higher wattage resistors. try parts with at least double the wattage rating. BTW, which resistors? i'm guessing R78-R79....
--pete
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Check JB Weld
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My 2c will be to rise those resistor al least 10mm from the PCB
and to put between PCB and resistor some material that has heat shield capacity
Very good to use larger (in wattage) resistors as Pete say
Franco
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what i have done in the past, if a higher wattage resistor is not available and/or there are space constraints, i'll double the value of the same package and connect them in parallel stacked on top of one another. it's easier if they are the rectangular wire-wound ceramic/cement type and there is enough space to do so. another option is to use a chassis mounted (http://uk.rs-online.com/web/p/panel-mount-fixed-resistors/6835997/) resistor and extend the leads to the PCB.
--pete
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I used same value resisters but did raise them up. Still looking for something to stabalize them. I think JB Weld (which I always love) would be too permanent. Thanks, Terry Yes they are those resisters.
Kagliostro What kind of material could I use that would be "heat shielding" and non conductive? They are already up and that would stabalize them as well.
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One possibility is to use a very small piece of Glass Fiber Thermal Isoling Tape
Something like this
https://alexnld.com/product/25mmx15m-exhaust-heat-wrap-insulation-pipe-tape-titanium-glass-fiber-with-6-stainless-ties/ (https://alexnld.com/product/25mmx15m-exhaust-heat-wrap-insulation-pipe-tape-titanium-glass-fiber-with-6-stainless-ties/)
I think you can use similar tape planned to be used for wood stoves
one other chance, if there is enough space between the resistor and the PCB, is to use .... a sand resistor (only glued to PCB and not connected electrically it will act as a shield)
also a small piece of aluminium sheet with extremities bent to have a small space under it (2-3mm) will be a choice
there are many possibilityes, you must use your fantasy
Franco
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Leo Fender would not be happy with the poor design of these Fender PCB amplifiers.
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Thanks Franco.
Leo has been swirling like a top for some time now.
I wanted to add a joke about China but this says it was made in the USA. It might have been a little more honest and said "Made poorly in the USA".......Actually for these PCB units and stuff this one isn't bad. Useful features and some degree of bullitt proofing.
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Actually for these PCB units and stuff this one isn't bad.
Any design that puts input jacks on the PCB is crap in my opinion. I don't know how many modern Fender amps I have had to modify that setup to a wired jack on. Jacking in and out of a jack connected to a rigid PCB is bound to lead to a failed solder joints. That, ROHS compliant solder and thin PCB traces are the bane of amplifier existence today. There is a reason there is a huge after market hand wiring retrofit industry on these things. They are disposable manufacturing.
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You can't glue the body of a hot resistor. (JBWeld may be best if you must.)
You support a hot resistor by its leads and away from low-temperature stuff. In this case I would look to mount a terminal strip off-board where the heat does less harm, and run wires back. I dunno if that amp has space.
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You can't glue the body of a hot resistor. (JBWeld may be best if you must.)
You support a hot resistor by its leads and away from low-temperature stuff. In this case I would look to mount a terminal strip off-board where the heat does less harm, and run wires back. I dunno if that amp has space.
correct. i was stating for him to use the JB weld for the wire. secure the wires to the board. you can also use crazy glue. however, if you installed the same crappy underrated parts, all this advice is moot.
--pete
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Permatex Red RTV is rated for 600 Degree F...i have no idea how hot those resistors get.
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Permatex Red RTV is rated for 600 Degree F...i have no idea how hot those resistors get.
there is no adhesive made that will work for you if those resistors are getting hot enough to burn through board and traces. you can use some epoxy to help with new wire trace replacement to hold it in place but not for for support. if you need to support the parts themselves, then what PRR recommended or my previous post with chassis mount resistors are basically your only options, other than the obvious, which is to replace the entire PCB assembly.
--pete
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use GE Silicone II it's the non acid based version that won't etch components, and silicone can take super high temperatures. You could just build a bubble of it under the resistors. And I do agree, I've got a Blues Deluxe (original one) and had to move them up off the board, it was getting pretty dark on the pcb.
~Phil
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The resistors we are talking about here are meant to be air cooled. They don't need any gloppy stuff on them. If the board will no longer securely support the resistors then move them to a terminal strip or chassis mounted turrets and run wires back to the board. And leave plenty of air space around the resistors.
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Thanks a lot guys . I appreciate all the input. I think I'll leave them in the air and put a little JB Weld at the base of the wire for a little more umph and I think I'll be fine. Thanks for all the help. Terry
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Right. Air-cooled. Glop is bad for that.
Engine-glop may stand XXX degrees as a gasket between two bolted surfaces. It may get weak in a blob on/around a part. If the part shakes on the way to a gig, it will work loose.
I'm sure there is a glue to hold it together, and another glue that adds some thermal transfer. Not the same glue, probably.
Re-design for more than 30-day thermal life, or scrap and install a Hoffman Board.
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Re-design for more than 30-day thermal life, or scrap and install a Hoffman Board.
And enjoy the fantastic low noise incredible tone of that effort. :icon_biggrin: