I am new to this site, so I hope I am posting this in the right place. I have a USA Hot Rod Deluxe that is cutting out and making noise on the Drive channel only. The clean side works fine. When switching to Drive, the amp will cut out unless the input is hit with a strong signal, but even then you hear the sound of the guitar along with some cruddy hashiness. The tubes are all brand new. I replaced them first, thinking it might be the source of the problem. The weird thing is, the amp operates just fine on the clean side. Any thoughts? I am confident I could erform the repair if I had an idea as to what to look for. I appreciate your help and thank you all in advance.
A common issue in older Hot Rods. This may help.
Remove all chicken head knobs, washers, the black screws holding the PCB down, and the green ground wire behind the input jacks. Gently remove the main PCB so that you get under it to replace the remaining plate loads.
Locate R4, R11, R16, and R22. Unsolder and replace them. Reconnect everything and go for it.
Remove all chicken head knobs, washers, the black screws holding the PCB down, and the green ground wire behind the input jacks. Gently remove the main PCB so that you get under it to replace the remaining plate loads.
Locate R4, R11, R16, and R22. Unsolder and replace them. Reconnect everything and go for it.
Thanks for the quick reply. Do you have a schematic for this amp? I need to know what values to replace those resistors with...
One issue many people overlook in these amps is failed power supply capacitors. When they go, you can get this exact same effect. Plays reasonably good till you hit the overdrive,t hen you loose most of your sound and the thing sounds like crap. I have run into this a couple times on Hot Rod DeVille amps and in both cases, replacing the power supply capacitors fixed the issue. Not saying this is always going to be the case, but there was a bad run of these power supply capacitors a few years ago and many found them selves inside Fender amps of this type. Basically what happens is that the decoupling between stages in this amp is via the power supply capacitors. When they fail, this decoupling is no more and you get what amounts to a lot of inverse feedback between stages via the plate circuit. This causes the drop in gain and the increased instability of the preamp sections of the amp.
Still having issues... Help please!
I replaced all the plate load resistors, the crackling is gone, but the distortion channel now intermittently cuts out unless being hit with a strong signal. If I palm mute the strings, about every 3rd or 4th time the sound will cut out completely. Only on the distortion side. Clean side works with issue. Again, the crackling is gone, but the cutting out is still there... Thoughts?
I replaced all the plate load resistors, the crackling is gone, but the distortion channel now intermittently cuts out unless being hit with a strong signal. If I palm mute the strings, about every 3rd or 4th time the sound will cut out completely. Only on the distortion side. Clean side works with issue. Again, the crackling is gone, but the cutting out is still there... Thoughts?
Finally resolved the issue, was not easy... Figured I'd let you all know what the final fix was.
As mentioned above, problem first presented as a loud crackling on the Drive channel only. The clean has always worked without incident. As I was advised, I replaced the plate load resistors.
Reassembly and testing revealed 2 new issues. (1) Drive channel would intermittently cut out and (2) Reverb not working, on either channel. Hmmm...
Well, I thought I was conquered so I took it to a tech. His solution was to reinstall R103 (1.5Kohm) which I removed per the instructions that came with the Fromel upgrade kit. Mind you, the reverb worked fine (as did the entire amp) for more than a year after the kit was installed. Furthermore, he was not able to get it to "cut out". Whee.
After spending $50, which I may as well have just balled up and tossed out the window of my car, I got the amp back. I didn't even bother to test it. I let the holidays pass and then went back to diagnosing.
Upon closer inspection, I noticed some goo leaking from the ends of the 470ohm/5w resistors in the +/-16V supply. Some web research indicated that these can cause all kinds of problems, including disappearing reverb!! Per Justin Holton's writing, I replaced these with 330ohm/5w resistors and high temp RTV sealer to insulate them from the board. While in there, I also removed the $50 dollar R103.
Reassembly. Test. No cutting out!!! Yay! No reverb... Boo...
Tested the verb tank cables and other connections. All good. Hmmm...
Decided to inspect the traces near where R103 was. You see, I originally just clipped it out. In order for the other guy to install a new one, he had to heat the holes to get the leads pieces out. Put on the cheaters and, lo and behold, a broken trace where one of the leads protruded. Scraped of some insulation, soldered on a jumper. Reassembly. Test. Reverb!!!
What a long strange trip it's been.
As mentioned above, problem first presented as a loud crackling on the Drive channel only. The clean has always worked without incident. As I was advised, I replaced the plate load resistors.
Reassembly and testing revealed 2 new issues. (1) Drive channel would intermittently cut out and (2) Reverb not working, on either channel. Hmmm...
Well, I thought I was conquered so I took it to a tech. His solution was to reinstall R103 (1.5Kohm) which I removed per the instructions that came with the Fromel upgrade kit. Mind you, the reverb worked fine (as did the entire amp) for more than a year after the kit was installed. Furthermore, he was not able to get it to "cut out". Whee.
After spending $50, which I may as well have just balled up and tossed out the window of my car, I got the amp back. I didn't even bother to test it. I let the holidays pass and then went back to diagnosing.
Upon closer inspection, I noticed some goo leaking from the ends of the 470ohm/5w resistors in the +/-16V supply. Some web research indicated that these can cause all kinds of problems, including disappearing reverb!! Per Justin Holton's writing, I replaced these with 330ohm/5w resistors and high temp RTV sealer to insulate them from the board. While in there, I also removed the $50 dollar R103.
Reassembly. Test. No cutting out!!! Yay! No reverb... Boo...
Tested the verb tank cables and other connections. All good. Hmmm...
Decided to inspect the traces near where R103 was. You see, I originally just clipped it out. In order for the other guy to install a new one, he had to heat the holes to get the leads pieces out. Put on the cheaters and, lo and behold, a broken trace where one of the leads protruded. Scraped of some insulation, soldered on a jumper. Reassembly. Test. Reverb!!!
What a long strange trip it's been.
In closing, those 5w resistors are a real problem. Any thoughts on how one might attach some type of heat sink?
One alternative is to lift the resistors up off the board by leaving the leads longer when soldering the replacements in. This allows air to circulate on all four sides of the resistor, most importantly under it which will dissipate more heat. This eliminates the need for a heat sink. Also, don't bend the leads down right next to the resistor. Put some kind of a spacer next to where the lead connects to the resistor, then bend the lead around the spacer so the lead comes straight out about 1/8" or a little more before it bends down.
EDIT:BTube was quicker on the keyboard! ;-)
The most common technique is to elevate the resistor from the PCB by leaving the leads longer and just soldering in place - if you have the room to do that. (No sealant/insulation). If the amp is being transported a lot, perhaps this isn't the strongest assembly method.
Can you get a 10W resistor into the same area?
You can get metal-bodied resistors which will bolt to the chassis or a heatsink, but long leads on some components can cause all sorts of oscillation/hum/etc. problems.
Can you post a schematic (or part of it) showing the resistors in question? Perhaps they are dissipating more heat than designed because of another problem?? (Not at all familiar with that amp....)
It takes quite a bit of power to burn out a ceramic (aka sand) resistor, IME.
Here is a schematic and layout. It is resistors R78,79. On the layout, it is the ones labeled +16v and -16v. On the schemo, they are on the bottom right of the power supply.View attachment Fender_hotrod_deluxe.pdf
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