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Help - Orange AD200 - Can hear the hum but no power

Plastalmonus

Plastalmonus

Apr 22, 2017
1,177
2,862
Melbourne, Australia
#1
I was playing a gig on the weekend and when I was setting my amp up I switched it on but no light came on. At first I thought it was the power cable so I swapped that out with another but still, no light.

So the sound guy and I decided to run it to a different power point but still nothing. In the end I switched the power point off and on again and then suddenly I had a working amp. It didn't miss a trick for the rest of the show.

Anyway... I was a bit suss about it so I plugged it in again the next morning. Nothing. I try different points in the house and different cables... nothing.

When I switch the power on I can hear the slight hum of the transformers getting power but no light comes on and, from what I can see, no tubes glow. It just seems dead.

I checked the mains fuse and the HT1/HT2 fuse and they look fine (admittedly fuses looking fine isn't always indicative of them working but I didn't have any replacements). I even swapped the mains fuse out with a new one. Still nothing.

So it is going into the shop next weekend but in the meantime I thought I'd see if anybody had experienced something like this before. I am dreading to think it is the PT that has died. It was recently serviced and re-tubed and worked fine the last 3 weeks. When I went to plug in at rehearsal the week before I thought I felt the IEC connector move more than it should but when I opened the amp up everything seemed fine (possibly something has broken there that I didn't notice...).

Anyway, I'm at a bit of a loss. It seems rather strange that it is intermittent enough at first to allow it to run fine once power is actually achieved but as of yesterday be completely dead in the water.
 
#2
If no pilot light and no heaters in the tubes I would have looked for a bad connection in the heater string. I don't recall if these amps have a fuse on the heater line but I likely wouldn't suspect that for an intermittent issue anyways. Orange uses spade connectors from the PT so it's possible one came loose.
 
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#4
Proper troubleshooting using a (volt) meter, signal generator and scope sure beats gussing it's the power transformer.
 
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#5
Plastalmonus said:
I was playing a gig on the weekend and when I was setting my amp up I switched it on but no light came on. At first I thought it was the power cable so I swapped that out with another but still, no light.

So the sound guy and I decided to run it to a different power point but still nothing. In the end I switched the power point off and on again and then suddenly I had a working amp. It didn't miss a trick for the rest of the show.

Anyway... I was a bit suss about it so I plugged it in again the next morning. Nothing. I try different points in the house and different cables... nothing.

When I switch the power on I can hear the slight hum of the transformers getting power but no light comes on and, from what I can see, no tubes glow. It just seems dead.

I checked the mains fuse and the HT1/HT2 fuse and they look fine (admittedly fuses looking fine isn't always indicative of them working but I didn't have any replacements). I even swapped the mains fuse out with a new one. Still nothing.

So it is going into the shop next weekend but in the meantime I thought I'd see if anybody had experienced something like this before. I am dreading to think it is the PT that has died. It was recently serviced and re-tubed and worked fine the last 3 weeks. When I went to plug in at rehearsal the week before I thought I felt the IEC connector move more than it should but when I opened the amp up everything seemed fine (possibly something has broken there that I didn't notice...).

Anyway, I'm at a bit of a loss. It seems rather strange that it is intermittent enough at first to allow it to run fine once power is actually achieved but as of yesterday be completely dead in the water.
Click to expand...

I don't have an official schematic for this amp. I do have some unofficial schematics that show fuses on the primary of the transformer, and also the B+ and screen taps. No fuse is shown on the bias supply or heater circuit.

If the transformer is humming, it suggests the main fuse is good and AC it getting to the primary.

Most likely the pilot light is driven directly off the heater taps. If the pilot light is out and the heaters do not light, either the amp has lost continuity somewhere in the heater circuit or the heater tap is dead.

The heater circuit is very low voltage, but very high current. If the broken connection makes contact while the power is on, it can weld shut temporarily.

Are you absolutely certain it's not just a bad pilot light? It's not unusual for a bad pilot light to self repair and work for a few hours.
 
#7
Wasnex said:
I don't have an official schematic for this amp. I do have some unofficial schematics that show fuses on the primary of the transformer, and also the B+ and screen taps. No fuse is shown on the bias supply or heater circuit.

If the transformer is humming, it suggests the main fuse is good and AC it getting to the primary.

Most likely the pilot light is driven directly off the heater taps. If the pilot light is out and the heaters do not light, either the amp has lost continuity somewhere in the heater circuit or the heater tap is dead.

The heater circuit is very low voltage, but very high current. If the broken connection makes contact while the power is on, it can weld shut temporarily.

Are you absolutely certain it's not just a bad pilot light? It's not unusual for a bad pilot light to self repair and work for a few hours.
Click to expand...

Would a bad pilot light cause no signal to come out? I thought it would have a redundancy built in to bypass it if the globe goes. Also I assume we are both meaning the big Orange light on the front.

EDIT: an auto-correct typo
 
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#8
Plastalmonus said:
Would a bad pilot light cause no signal to come out? I thought it would have a redundancy built in to bypass it if the globe goes. Also I assume we are nothing meaning the big Orange light on the front.
Click to expand...



The amp should work as normal if the pilot light is blown. Sorry it wasn't clear if you had tried to play the amp or not. The schematic I have doesn't show where the pilot light is connected, but typically it's parallel across the heater taps.
 
#11
Plastalmonus said:
Yep sorry I should have been more specific.

No signal at all.
Click to expand...

Hopefully it's something simple. The first thing to check would be the mains fuse.

Here's a gut shot, so you can see how easy it might be for a connection to fall off the IEC plug.
AD200B Gut A.jpg
 
#12
Wasnex said:
Hopefully it's something simple. The first thing to check would be the mains fuse.

Here's a gut shot, so you can see how easy it might be for a connection to fall off the IEC plug.
View attachment 3520062
Click to expand...

Yep checked all the spade connectors and visually checked the fuses. The next step would be to check them with a meter but at this rate I'm fast approaching the level of comfortable I feel working on high voltage equipment. My usual domain is pickups and building pedal circuits :D

The only fuse I've confirmed with testing so far was the mains.
 
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#13
I'll post my observations and 'sorta' problem with my AD200B in the Orange thread... as not to hijack your thread...
My pilot light comes on upon power up, then after half an hour, it's almost off, or so dim it's hard to see.
Amp still works great tho...

As I said, I'll post this in Orange thread, so please @Wasnex et al, feel free to impart your knowledge to a electronics simpleton
 
#17
rodl2005 said:
I'll post my observations and 'sorta' problem with my AD200B in the Orange thread... as not to hijack your thread...
My pilot light comes on upon power up, then after half an hour, it's almost off, or so dim it's hard to see.
Amp still works great tho...

As I said, I'll post this in Orange thread, so please @Wasnex et al, feel free to impart your knowledge to a electronics simpleton
Click to expand...

I couldn't find your post in another thread.

Going dim is sorta weird behavior. As I mentioned I don't have an official schematic for this amp. But from the image I posted, it looks like the light is tapped off at the same point as the heaters.

The first thing I would do is check the bulb to see if it has any markings and replace it. I believe the bulb is a #47 which is a bayonet mount miniature bulb rated for 6.3V, 150mA, 1W. While you have the bulb out, check for any corrosion on the base and in the tube socket as this could cause the symptom.
[Invalid or Expired Link Removed]
If you have the skills to open and work on the amp, measure the voltage on the light socket. My assumption is it uses the same supply as the heaters, so it should be around 6.3-6.5V. If the voltage is stable around this level, replace the bulb. If the voltage is dropping significantly lower, check the voltage on the heater pins at the tube sockets and also trace the wires from the light harness to make sure they tap into the heater circuit. If they do, measure where the transformer heater taps attach to the circuit board.

If the heater voltage is actually dropping, it's indicative of a more serious problem. Possibilities that come to mind include an intermittent short somewhere in the circuit, one of the tubes has a bad heater winding, or your transformer's heater winding is bad. If there is a short or one of the tubes is pulling excessive current, it will eventually burn out the heater winding in the transformer. So if the voltage is actually low, the problem needs to be fixed ASAP.
 
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#18
A bit more forum digging has shown that there is an issue that is found in the AD Series where the plastic splice connector for the heater/lamp circuit is a bit dodgy, causing the heaters to fail. The solution in the past has been to hardwire the heaters.

Definitely will be just passing this on to my tech. I don't want my amp to be a casualty of a misplaced optimism brought on by an enthusiastic amateur :D
 
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#20
Plastalmonus said:
A bit more forum digging has shown that there is an issue that is found in the AD Series where the plastic splice connector for the heater/lamp circuit is a bit dodgy, causing the heaters to fail. The solution in the past has been to hardwire the heaters.

Definitely will be just passing this on to my tech. I don't want my amp to be a casualty of a misplaced optimism brought on by an enthusiastic amateur :D
Click to expand...

Here's hoping for an easy (and low cost) fix! :thumbsup:
 
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