Hey folks,
Trying to sort out an HRD for a friend. I've repaired this amp in the recent past, and all seemed well for several weeks of regular use. Then a new symptom appeared: When played at volume, the sound would break-up, get choppy, sort of cut in & out.
While this was happening, the panel LEDs would flash in synch with the cutting out. After quizzing the owner, I found that this all began when he added a wah pedal.. or so it may be.
Now I know these amps use little board mount, logic-driven relays to control clean / drive channels. What are the chances that the wah is producing some harmonic that's setting up a resonance in the relay armature(s), causing the amp to act as if the channels are rapidly being switched? Sort of an anomalous gating effect..
I can't otherwise see how the wah could be responsible.. unless the HRD will do this, if it's catching DC or some sort of osc. from the wah. The wah is powered, uses a 9V iirc.
What do you think?
Trying to sort out an HRD for a friend. I've repaired this amp in the recent past, and all seemed well for several weeks of regular use. Then a new symptom appeared: When played at volume, the sound would break-up, get choppy, sort of cut in & out.
While this was happening, the panel LEDs would flash in synch with the cutting out. After quizzing the owner, I found that this all began when he added a wah pedal.. or so it may be.
Now I know these amps use little board mount, logic-driven relays to control clean / drive channels. What are the chances that the wah is producing some harmonic that's setting up a resonance in the relay armature(s), causing the amp to act as if the channels are rapidly being switched? Sort of an anomalous gating effect..
I can't otherwise see how the wah could be responsible.. unless the HRD will do this, if it's catching DC or some sort of osc. from the wah. The wah is powered, uses a 9V iirc.
What do you think?
Heya PRR,
Thanks for chiming in, sir.
Is the HRD considered 'recent'? Thought this piece was ca. 1993-96 or so..
Do you have any sense of how a flagging LV supply might cause this - specifically, when a wah pedal is in use? He didn't report this issue with high volume / less wah, but only at mid-high volume / with wah.
I can understand that the LV supply will sag with the HV under load (shared primary), but is this enough to wreck the LV supply integrity?
Thanks for chiming in, sir.
Is the HRD considered 'recent'? Thought this piece was ca. 1993-96 or so..
Do you have any sense of how a flagging LV supply might cause this - specifically, when a wah pedal is in use? He didn't report this issue with high volume / less wah, but only at mid-high volume / with wah.
I can understand that the LV supply will sag with the HV under load (shared primary), but is this enough to wreck the LV supply integrity?
> Is the HRD considered 'recent'?
Maybe depends who is saying.
To _me_, there's the "real" Fenders, 1947-1965, CBS' lame continuation, and then CBS made more changes. 1985 the employees bought Fender from CBS, their hearts were pure, but not all the products were lifetime-build. (And if it is a 1995 build, that's already ancient in modern-electronics years....)
I have a gut feeling the wah is not the cause. Or that something else happened. Users' stories, are clues, not facts.
Maybe depends who is saying.
To _me_, there's the "real" Fenders, 1947-1965, CBS' lame continuation, and then CBS made more changes. 1985 the employees bought Fender from CBS, their hearts were pure, but not all the products were lifetime-build. (And if it is a 1995 build, that's already ancient in modern-electronics years....)
I have a gut feeling the wah is not the cause. Or that something else happened. Users' stories, are clues, not facts.
Look at R78 R79 next to CR13 CR14.
That's a lot of heat in a small section of medium-grade PCB.
The LEDs (and many other things) are fed this +16V.
On some other model, a similar low-volt supply tends to heat-rot the solder joints and even the resistors. Poor connection, cut-out.
That's a lot of heat in a small section of medium-grade PCB.
The LEDs (and many other things) are fed this +16V.
On some other model, a similar low-volt supply tends to heat-rot the solder joints and even the resistors. Poor connection, cut-out.
Attachments
No the wah did not do...anything weird... to cause the issue.
Agree with PRR, it is most likely R78 or R79 has failing solder connections. Poke them with a stick while it runs and see if you provoke the symptom.
That one detail was a marginal design. If you ever replace those resistors, mount them up off the board a little for extra ventilation. The extra wire length on them also is a tiny bit of heat sink. On the foil side I bare the copper back from the pad a little ways, and I lay down the resistor lead along the trace and solder. That extra wire lead length plus the amount of solder also helps as a heat sink. SOme guys bite the bullet and use oversized resistors bolted to chassis and run wires back to the board.
Also whenever inside a HR Deluxe or DeVille, I always check the solder on the power tube sockets, it often forms cracks around the pins.
Agree with PRR, it is most likely R78 or R79 has failing solder connections. Poke them with a stick while it runs and see if you provoke the symptom.
That one detail was a marginal design. If you ever replace those resistors, mount them up off the board a little for extra ventilation. The extra wire length on them also is a tiny bit of heat sink. On the foil side I bare the copper back from the pad a little ways, and I lay down the resistor lead along the trace and solder. That extra wire lead length plus the amount of solder also helps as a heat sink. SOme guys bite the bullet and use oversized resistors bolted to chassis and run wires back to the board.
Also whenever inside a HR Deluxe or DeVille, I always check the solder on the power tube sockets, it often forms cracks around the pins.
Fair enough, just trying to get some definitions; leads to a more productive discussion.
Your skepticism isn't unwarranted. But it did take some careful questioning of the owner to extract the info that "Oh yeah, this only happened +after+ I had the wah plugged in! I never thought about that!". He didn't come to me with the 'story', so to speak.
So we'll see what we get. I'll report back when I know something worth mentioning.
Weird.
Correct me here, but aren't those diodes purportedly used as fail-safe devices?
I've read that they're used in case the output load opens up. The idea being that if the voltages go crazy enough (big signal, no load) the diodes' PIV will be exceeded and act to short out the fault voltage.
In one sense they're asking them to act like ~1kV zeners..
Last edited:
What type of fault could ever cause either opt. tube plate circuit to be driven negative wrt ground?
So here's an update on this situation. As I suggested, the owner tried the amp +with the wah pedal, but at relatively low levels+. He reports no recurrence of the previous fault(s) when played at these lower levels.
I'm sticking with my original thought, that this problem is due to vibration of the board & chassis. Some less than perfect connection(s) are being perturbed by the particular tone the amp is producing. Again, this could be the relay armatures, but other weak contacts in this circuit could produce the same results.
Any comment? At this point, I'm going to apply some damping compound to the relay cases.. it can't hurt, that's for sure. I have some 3M stuff that's a thin sheet of metal (stainless?) with a viscous elastic adhesive on one side. It's intended as an externsional damping material.
I'm sticking with my original thought, that this problem is due to vibration of the board & chassis. Some less than perfect connection(s) are being perturbed by the particular tone the amp is producing. Again, this could be the relay armatures, but other weak contacts in this circuit could produce the same results.
Any comment? At this point, I'm going to apply some damping compound to the relay cases.. it can't hurt, that's for sure. I have some 3M stuff that's a thin sheet of metal (stainless?) with a viscous elastic adhesive on one side. It's intended as an externsional damping material.
I would sweep the amp with a sine wave generator and see if at a certain low freq the problem rears its ugly head. This would indicate a cold solder joint somewhere.
The two power resistors EnZO mentioned are sure culprits. Also check the tube socket pins as mentioned.
I would also seriously suspect the IC capacitors used in these amps.
The two power resistors EnZO mentioned are sure culprits. Also check the tube socket pins as mentioned.
I would also seriously suspect the IC capacitors used in these amps.
No, they are only supposed to conduct if either output anode drops below zero volts (indicating the other anode is at twice B+, because of the symmetrical push-pull transformer). So the hope is to limit maximum voltage excursion of the anodes to no more than twice the B+ voltage.
If these protection diodes do conduct, they are in normal forward bias, not in Zener mode. The idea is to bleed off the stored energy in the transformer primary, by allowing the current already flowing in the transformer primary to die down quickly to zero by letting it flow through the power supply via the protection diodes.
This way, we hope that stored energy doesn't find a much more destructive way to escape - such as, by flashing-over the transformer insulation and charring it into uselessness.
Enzo said as much, he just used fewer words.
-Gnobuddy
The power resistor and tube socket joints were touched up when I last serviced the amp, roughly three months ago. They didn't look bad, but I went ahead and reflowed them anyway, with SN63.
Just about any component can become vibration sensitive (microphonic), either from bad solder joints or internal failure. Damping the relay cases is just a simple, sensible first step - if that doesn't solve it, there are plenty of other places to look. Anyway this is mostly all conjecture, things might change once the unit is back on the bench.
True. I hope you find the problem. Intermittent problems can be so aggravating to trouble-shoot!
-Gnobuddy
Any update?
I have been battling a mechanical resonance in a Hot Rod Deluxe. There were several actually. One was the output transformer, it seemed to really go nuts around F#, I removed it and mounted it with nylon washers and that noise is now gone. The second was the little board where V1 is by itself, I removed it and remounted it with o-rings as shock absorber/dampening. There is still one last resonance that sounds like the speaker but I have tried two speakers and the same noise persists. It's only on the low E string open note (82 Hz), it goes away if you sit on the cabinet while playing. Very frustrating, I have spent countless hours taking this thing apart and putting it back together. Fender made a giant POS when they created these amps, I truly hate them.
I have been battling a mechanical resonance in a Hot Rod Deluxe. There were several actually. One was the output transformer, it seemed to really go nuts around F#, I removed it and mounted it with nylon washers and that noise is now gone. The second was the little board where V1 is by itself, I removed it and remounted it with o-rings as shock absorber/dampening. There is still one last resonance that sounds like the speaker but I have tried two speakers and the same noise persists. It's only on the low E string open note (82 Hz), it goes away if you sit on the cabinet while playing. Very frustrating, I have spent countless hours taking this thing apart and putting it back together. Fender made a giant POS when they created these amps, I truly hate them.
Last edited:
Any amp by any maker can have a cabinet buzz.
First V1,V2. V1 by nature of the circuit will be a little microphonic in most amps. In later production, Fender included a block of dense foam, I assume silicone, with a couple holes in it to fit over the tubes. You shoved it over the first two tubes to dampen vibration.
CALL Fender and ask how you can get one of those foam blocks because your amp is too sensitive,. They MIGHT even send you one free.
The cab buzz could be anything, you eliminated the speaker, but the baffle board could be buzzing, the chassis could be buzzing against the cab. Does it still buzz with the rear cover panel removed? There could be a loose joint in the cab corners. There could even be a void in the plywood.
Sitting on it works, fine, does turning the amp on its side either way matter? Upside down? Finger pressure on each side top or bottom panel? Etc.
First V1,V2. V1 by nature of the circuit will be a little microphonic in most amps. In later production, Fender included a block of dense foam, I assume silicone, with a couple holes in it to fit over the tubes. You shoved it over the first two tubes to dampen vibration.
CALL Fender and ask how you can get one of those foam blocks because your amp is too sensitive,. They MIGHT even send you one free.
The cab buzz could be anything, you eliminated the speaker, but the baffle board could be buzzing, the chassis could be buzzing against the cab. Does it still buzz with the rear cover panel removed? There could be a loose joint in the cab corners. There could even be a void in the plywood.
Sitting on it works, fine, does turning the amp on its side either way matter? Upside down? Finger pressure on each side top or bottom panel? Etc.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.