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Last week while playing through my hrd, i noticed the power light was flickering. finally, sound stopped coming from the speaker. the first thing i did to fix this was buy new 6l6 power tubes. i installed them, and it worked great for a week. Last night however, the light started flickering again. The amp is stil making sound, but the light is basically all the way out now. ANY ADVICE AS TO WHAT IS GOING ON?
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Been there, seen that.
I see two amp models for repair more than any other: HRDV and Kustom Coupe. (I assume "hrd" is Hot Rod Deville?)
There is a reason they call it "hot rod." What happens when you make a car into a hot rod? More power and it breaks a lot. Same goes for amps. They can sound good, but there is a tradeoff.
As the symptoms could be serious, I suggest you proceed carefully.
It is entirely possible the flickering jewel lamp is unrelated to the power problem. Sometimes the holders get intermittent. Or the bulb could be loose or burned out. Check that out with the standby OFF and resolve that question before doing anything else. Unscrew and remove the jewel lens and you can get to the bayonet bulb without any disassembly. That 6.3 Volt bulb you can buy in lots of places. -
90% or better of all the problems I see on Hot Rod DeVille, Blues DeVille, and their Deluxe cousins have their root in solder problems, especially if it's intermittent.
I always like to approach these amps by initially retouching solders at: all controls, switches, jacks, multipin connector pins, tube sockets, LED's, and large and/or heat-producing components. I do this under magnification with lots of light and while hitting all the aforementioned spots I am constantly scanning for and retouching any other joint that looks ring-cracked or solder-starved.
After that, if there is still a problem (and like I say 90% of the time it's gone), I feel like I have at least eliminated the mundane stuff and can set about some real troubleshooting while also knowing I have probably extended the time-between-failures future of the amp. It's kind of like replacing the spark plugs, cap & rotor on a car before REALLY starting the tune-up. (If you're old like me add adjusting the valves & replacing the points & condenser...)
Additionally I would re-tension all of the tube sockets.
Helpful pages can be found here:
http://studentweb.eku.edu/justin_holton/
http://www.hotrodamps.com/
On my own Blues DeVille 4x10 I immediately took it apart after buying it (used) and retouched every single solder joint on the PCB. I've been gigging it for 6+ years now with no problems other than a failed power tube.
Good Luck!Comment
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circuital reference
"points and condenser..." what nostalgia, not to mention a killer cosmic circuital reference to the hot rods!!
my compliments.Comment
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In fairness, the Hot Rod DeVille is not a hopped up something else, it is just a plain old vanilla 50 watt amp with as pair of 6L6 like any other. It is hot rod because they added a dirt channel. A crappy dirt channel, but dirt nonetheless. SO compared to the usual Fender fare it is spicier.
ANyone tells you to replace the 470 ohm resistors feeding the zeners with 330 ohm, DON"T DO IT. The 330s will run hotter and push more curren tthrough the zeners so THEY will run hotter. If the solder is OK under them, I suggest a squirt of silicone between and under them to reduce movement.Education is what you're left with after you have forgotten what you have learned.Comment
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HRDV
The concern I have, two actually, with the Hot Rod Deville are
1.) the method of channel switching uses a large number of diodes, transistors, 4560's, etc... IMHO, this is a Rube Goldberg. My guess is it was more cost effective to have a machine punch all these into the pcb before hitting the wave solder and thereby allow use of a plain stereo cable. (Peavey used a 6-pin format instead for a similar function, and thus required more hands on labor expense.) Troubleshooting that section has taken me anywhere from 30 seconds to several hours. For some reason, I have to find "the" bad component before repair. Truly, though, it is usually broken etching or a faulty solder joint. Test equipment: magnifying lens.
and
2.) the gain on the extra-extra-extra-extra drive is over the top.
This is what I see as "hot rodded" about this amp. It is so high that the socket or the shielded grid leads themselves are often microphonic, as, apparently the capacitance of the shielding is sensitive such that acoustic deformations in the dielectric yield essentially the same thing as a ribbon bridge pickup on an acoustic guitar. I'm open to other theories out there on this one.
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Actually I very seldom have to repair the actual foot switch circuits. I think it is pretty clever really. They apply an AC voltage to the FS line and the switches out there switch in diodes and zeners to lop off the tops and bottoms of the waveforms. The series of voltage comparators then either turn on or off depending upon whether or not the voltage crosses their thresholds. Very elegant.
This allows a plain old vanilla guitar cord to connect the pedal to the amp. No special cord. Whewrever you go, if teh FS cord goves out, you can find something to take its place. AS much as I like the PV folks, those 7 pin DIN cables are not on the shelf most places.
The pedals are sturdy, with most repairs being a switch replacement. That is the case with ANY form of FS. SOmetimes I have to resolder or even replace an LED too. I don't like those jacks they use, but they work well enough, and I could stuff a CLiff jack in there if I wanted.
The amp end of it rarely fails, but like most circuits, when they fail, 90% of the time it is the components exposed to the real world that fail rather than something out in the middle of the circuit. That helps focus the search.
ALmost always when I get a FS complaint or a channel switching complaint, and especially on the HR series, it is not the FS circuit anyway, it is those damned resistors for the +/-15V zeners.
When you understand the circuit, it is not at all difficult to spot the bad part. Each op amp attends to a particular function, and I can connect the FS and toggle them while monitoring the voltages at their output pins.
And as you point out, if there is a problem in the amp it is most likely solder under the FS jack anyway.
Be it Marshall or PV or anyone else, those multipin DIN connectors are FAR less reliable that a good old 1/4" jack. I think Fender was going for sturfy, reliable, and versatile. (They can configure the same basic circuit to handle quite a few functions on one single cable conductor.)
When that system first arrived, Fender noted that the diodes had to be 1N4448 in stead of 1N4148. SO I ordered 10 of them. (I usually buy 1N4148 by the hundred.) That was like what 10-12 years ago? I just looked, there are still 5 in the drawer, and they also use that part in some SS power amps.Education is what you're left with after you have forgotten what you have learned.Comment
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[QUOTE=Enzo;16756]Actually I very seldom have to repair the actual foot switch circuits.
That is very, very interesting, from a probability viewpoint. I've seen a slew of them: failed zeners, failed op amps, failed transistors, detached etching and bad solder joints mostly at the power resistors for the Vcc.
You are so right about the PV design. I must concur that between these two, Fender wins...but it's like comparing the chicken pox with the mumps.
I do understand the circuit and I agree they were clever in using the ac, etc. etc. But I come from the design school where simplicity is elegance and tantamount to improved reliability; and simple the HRDV switching ain't. I recall one from last year that was heck to resolve. Found one bad zener and one bad op amp to start with. Took me hours. The voltages would not quite get to where they needed to be to make a switch. Oddly, I don't remember the cure. I may have had a bad batch of 4560's in stock for repairs.
I really do enjoy these discussions, and it's great to have an opportunity to challenge my thinking and reasoning. I do appreciate your posts.Comment
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As a wannabee amp designer, I've experimented with a bunch of different footswitch designs. The most complex one I ever did used a 3-pin XLR cable, the pins being ground, 12V supply, and serial data with an encoder chip at one end and a decoder at the other. That allowed any number of buttons with just 3 connections, and it could have been got down to 2 by putting power and data along the same wire.
Nowadays I just use plain switches, with a mono 1/4" jack for a single function, a stereo one for two functions, and I just avoid having more than two footswitch functions. I try to make sure all the functions of the amp are still accessible if you only have a one-button footswitch to hand or none at all."Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"Comment
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Maybe use a USB port...infinite switching.
But a very simple way to get zillons of on/off signals is to use your idea of a serial connection and use a bit-oriented protocol, and you wouldn't need microprocessors, proms or any of that.Comment
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Amen.Originally posted by Enzo View Post
The use of power resistors and zeners to make +/- supplies for opamps is intrinsically silly these days. I've seen HRDs and BDs run these resistors so hot they melt their soldered connections and fall out.
What makes sense is to replace the zeners with TO-220 regulators for +/- 12 (or is it 15?) in there and diddle the resistor values a bit.
Zeners are shunt regulators. They only way they work is to have the max current going through them all the time. The zeners can eat whatever the circuit they're supplying doesn't need. It's like having full flow on a car throttle all the time and regulating the car speed by dumping mixed air/fuel out of the manifold when you want to go slower than max. There is a time and a place for shunt regulators but this is not one of them.
Three terminals like the 7812/7912 supply only the current actually needed. In addition, the TO-220 package can dissipate more power than the zeners. The resistors should be cooler because the zeners are not keeping them going 100mph all the time.
When I saw the schemo for this amp, I could hardly believe they did that.Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!
Oh, wait! That sounds familiar, somehow.Comment
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Yes, you are so right.
Sadly, there are disturbing circuit designs in guitar amps as far back as the oldest schematics I've seen. For example, the 5E3 takes plates to ground for volume control. Sure, only the non-dc signal would be shorted, but, really, Leo/Don?
Recently I've been looking at early radio receivers, and was amused to learn that some TRF receivers, such as the RCA Radiola 18, attenuated the antenna as a means of volume control.
But that was around 1928.
No excuses, Fender.Comment
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