Please help me - New amp failing light bulb limiter test

[shaunf]

Guys, please help me. I finished wiring up my amp last night, checked everything as best I know how, and tried to power it up just now. Just switching on the On switch (standby still off) with the bulb limiter and the limiter light glows brightly.

Amps indicator light does light up at all.

Bummed, as I am now officially out of my depth.

[Colossal]

Guys, please help me. I finished wiring up my amp last night, checked everything as best I know how, and tried to power it up just now. Just switching on the On switch (standby still off) with the bulb limiter and the limiter light glows brightly.

Amps indicator light does light up at all.

Bummed, as I am now officially out of my depth.

Hi Shaun,

Bummer. Now is a good time time to just stop, don't do anything, and take a deep breath. Exhale (and now pass to a friend). To get this sorted, you might be sorely tempted to succumb to randomly trying things. This is a sure fire way to compound what could be (and likely is) a simple oversight. Do not do anything to the amp. You have to identify and confirm all of your assumptions. To this point, you have worked under the assumption that you followed the schematic exactly. So there is either a mistake in your work, a bad part, or both, with the first being the most likely case.

DISCLAIMER: Before starting this procedure, make sure that you have a minimum degree of certainty/confidence and personal comfort level with the principles. If you have been 'soldering by numbers' up to this point but troubleshooting is probably beyond your comfort zone, you're probably best taking the amp to a qualified tech. There is no shame in this. If you ask for help but randomly try things after people are trying to help, you will lose support.

Allright, if you are up to the challenge, then start from the very beginning where the mains connection is made to the amp. Remove the plug from the wall. Take all the tubes out of the amp. Take clear macro shots of each section of the amp and post.

You should have an IEC entry module (modern build) or a 3 prong plug with black, white, and green wires terminating inside the chassis (classic TW purist build). Start there. Take the schematic for your amp and a highlighter pen and physically trace the wires going from the IEC or mains, to the Mains fuse and to the power switch. If in your mind, you run into a wall where your left brain struggles with spatial issues, continue to go over it again and again until you can be certain that power is getting to the on/off switch as intended. Your schematic should have some yellow ink on it by now.

Next, move to the power transformer. On a piece of paper, write down every wire on your PT; you should have something like one or two secondaries, a secondary center tap, a 6.3VAC filament supply (centertapped or non-centertapped) and possibly an (unused) 5VAC rectifier tube winding. Identify all of those wires on your paper. Now go through each wire, one at a time, and match where that wire terminates to where it is expected to terminate according to the schematic.

If at any time you feel that you cannot confidently verify and trust what your eyes and mind are telling you, more diligence is required

[xtian]

Paul Ruby's first-time power-up guide is very good:

http://www.paulrubyamps.com/info.html#FirstPowerUp

[shaunf]

Thanks for the responses.

Ok, here are the wiring diagrams for the transformers I am using:

[IMG2383]http://img.photobucket.com/albums/v206/ ... 5199EX.jpg[/img]

[IMG2383]http://img.photobucket.com/albums/v206/ ... S-9384.jpg[/img]

Here is a picture from when I was wiring up the transformers. The PT has wires coming out of of both bell housings. If you look at the grommet hole near the front of the amp, to the left of the switches, you'll see the heater wires and their CT, the 2 300V secondaries, and their CT. I clipped the 260V secondaries short and shrink wrapped. Both the CT's are routed down to a ground point just in front of the IEC connector.

Looking at the right hand side grommet hole, where the primaries come through. I clipped the 100v and 120v primaries short and shrink wrapped each. The 220V and 240V, I trimmed shorter, shrink wrapped individually, and then put a bigger piece of shrink over both just in case I needed them. I connected the CT and 230V primaries to the On switch.

[IMG1665]http://img.photobucket.com/albums/v206/ ... G_1588.jpg[/img]

[IMG1736]http://img.photobucket.com/albums/v206/ ... G_1650.jpg[/img]

[shaunf]

The Power switch. Before posting, I thought it might be the MOV that was faulty, so I removed it. I also desoldered the indicator light, so you can get a better view of the switch, and connections:

[IMG1740]http://img.photobucket.com/albums/v206/ ... G_1651.jpg[/img]

View of whole PS board
[IMG1980]http://img.photobucket.com/albums/v206/ ... G_1660.jpg[/img]

VVR and filter caps:
[IMG1607]http://img.photobucket.com/albums/v206/ ... G_1663.jpg[/img]

External bias pot, wired to turrets on PS board.
[IMG1556]http://img.photobucket.com/albums/v206/ ... G_1670.jpg[/img]

Power tubes:
[IMG1542]http://img.photobucket.com/albums/v206/ ... G_1668.jpg[/img]

[shaunf]

I've been through the PS section of the schematic. From the rectifier diodes, through the main filter caps, up until the Standby switch, I can find no fault in my connections. I'm assuming beyond the standby switch is irrelevant at this point since the problem exists with the standby switch open. The bias circuitry looks fine to me. My external bias pot is simply wired to the 3 turrets the legs of a trimmer pot would normally connect to. White wire connects to pot wiper, and to the turret closest to the 10uf caps, green connects to turret closest to the fuse holder, orange connects to 47k resistor.

[Colossal]

I've been through the PS section of the schematic. From the rectifier diodes, through the main filter caps, up until the Standby switch, I can find no fault in my connections. I'm assuming beyond the standby switch is irrelevant at this point since the problem exists with the standby switch open. The bias circuitry looks fine to me. My external bias pot is simply wired to the 3 turrets the legs of a trimmer pot would normally connect to. White wire connects to pot wiper, and to the turret closest to the 10uf caps, green connects to turret closest to the fuse holder, orange connects to 47k resistor.

Well dude, you obviously have skills and know what's up (and your amp looks nice) so I hope you didn't take my previous email as derisive. Can you successfully "float" the amp at voltage with all of the tubes removed without the fuse popping? Also, can you measure 120VAC on your power switch, actual rectified DC voltage on your standby switch and heater voltage at 3.3-0-3.3 on the tube socket pins??

My instinct is that the VVR has no reservoir cap and is trying to source current directly from the rectifier.

[shaunf]

Hi Colossal,

If I know anything at all about amps, it's only from reading info on places like this. I have very little practical experience at all. This is my first scratch build of an amp. My only other experience comes from a bit of tinkering with my old Marshall.

I am grateful for your post and certainly didn't take offence to anything you said. I am a beginner, and here to learn from those more experienced than I am, and welcome any advice, criticism etc with an open mind. Even just your initial post gave me some structure as to how to begin to go about troubleshooting. When I looked at the schematic and traced my connections, it became clear that the problem had to be limited to a very isolated part of the amp.

As you have now indicated, it could be related to the VVR. Since removing it simply involves desoldering a couple of wires and reconnecting the standby switch to the primary filter cap, and resoldering the bias voltage wire, I have removed the VVR and retested, and the limiter bulb is glowing at a dull orange colour as expected.

Thanks very much for pointing me in the right direction. I'm going to carry on the startup process now, minus the VVR, and will have to try to pick up why it's causing this shorting problem with Hall Amplification on Monday.

[ampgeek]

That looks like a nice clean job!

What rotten luck that the center fuse tab lines up dead nuts perfect on the power board stand off screw!

Is it possible that there is contact between those two?

Good luck!
Dave O.

Edit: Just noticed that you have found an issue with the VVR. Hope that is all it is!

[shaunf]

That looks like a nice clean job!

What rotten luck that the center fuse tab lines up dead nuts perfect on the power board stand off screw!

Is it possible that there is contact between those two?

Good luck!
Dave O.

Thanks Dave. There is around a quarter inch of space between the fuse centre pin and the stand off screw so not much chance of touching. Still, I have put a piece of shrink wrap over the centre pin just to be safe.

[Colossal]

Hi Colossal,

If I know anything at all about amps, it's only from reading info on places like this. I have very little practical experience at all. This is my first scratch build of an amp. My only other experience comes from a bit of tinkering with my old Marshall.

I am grateful for your post and certainly didn't take offence to anything you said. I am a beginner, and here to learn from those more experienced than I am, and welcome any advice, criticism etc with an open mind. Even just your initial post gave me some structure as to how to begin to go about troubleshooting. When I looked at the schematic and traced my connections, it became clear that the problem had to be limited to a very isolated part of the amp.

As you have now indicated, it could be related to the VVR. Since removing it simply involves desoldering a couple of wires and reconnecting the standby switch to the primary filter cap, and resoldering the bias voltage wire, I have removed the VVR and retested, and the limiter bulb is glowing at a dull orange colour as expected.

Thanks very much for pointing me in the right direction. I'm going to carry on the startup process now, minus the VVR, and will have to try to pick up why it's causing this shorting problem with Hall Amplification on Monday.

Right on man. I consider myself a beginner as well and am grateful for all the guys that took (and continue to take) the time to endure my questions, many on this board and especially Mhuss in days of yore. One thing about amp failure is that you get a rich opportunity to truly immerse yourself in the why of the amp. The learning curve can be daunting but if you stay cool, troubleshoot in a controlled, linear manner, man, that's a good feeling when you can find the answer to your own problem.

I'm stoked that you can get a dull orange glow with the VVR out of the picture. To remedy this issue, the VVR must be electronically positioned just AFTER the first 80uF cap, but BEFORE the standby switch. The MOSFET needs a current source and at startup, inrush current is high to charge the caps up before the power supply reaches equilibrium. Just move the B+ IN on the VVR board to source that first reservoir cap. Take the B+ OUT on the VVR to Standby. The OT B+1 must also go to the standby switch of course. From there, the OT B+1 and everything else down the rail will see regulated voltage.

[shaunf]

Right on man. I consider myself a beginner as well and am grateful for all the guys that took (and continue to take) the time to endure my questions, many on this board and especially Mhuss in days of yore. One thing about amp failure is that you get a rich opportunity to truly immerse yourself in the why of the amp. The learning curve can be daunting but if you stay cool, troubleshoot in a controlled, linear manner, man, that's a good feeling when you can find the answer to your own problem.

I'm stoked that you can get a dull orange glow with the VVR out of the picture. To remedy this issue, the VVR must be electronically positioned just AFTER the first 80uF cap, but BEFORE the standby switch. The MOSFET needs a current source and at startup, inrush current is high to charge the caps up before the power supply reaches equilibrium. Just move the B+ IN on the VVR board to source that first reservoir cap. Take the B+ OUT on the VVR to Standby. The OT B+1 must also go to the standby switch of course. From there, the OT B+1 and everything else down the rail will see regulated voltage.

I have to admit, walking away and going to have some dinner and a chat to the wife helped me not just chuck it in the bin! Man, I was bummed at first. But, of course you are totally right, and this little experience has already helped me understand this amp a little better, so for that I am grateful.

If I check the way my VVR was wired up, B+ IN was wired to the Standby Switch, and B+ OUT went to the cap. I thought this was a little wierd when I wired it up and it didn't quite make sense to me. Do you think it was the wrong way around? Here's the relevant page from the Installation Instructions:
[IMG768]http://img.photobucket.com/albums/v206/ ... titled.jpg[/img]

What do you reckon, did I misunderstand this diagram? I must admit, I just saw the Standby switchand just went from there, but now looking at it more closely now that you've opened my eyes, it would seem that the standby switch in the diagram is in a different circuit position to where it is in the Express. Is that right? and is that where I went wrong?

[Structo]

Sorry if I missed it but what amp is this?

I think I would be tempted to get it going at first without the VVR.

When you first powered up the amp with the light bulb limiter, did you do it without tubes first?

That is the best way because you are only running the power supply without a load.

If it passes that test then I will install the preamp tubes, then the power tubes.

Some amps cause the light bulb to glow more than others when the in-rush is over.

For first power up I use a 25w bulb then a 60w then a 100w.
If that all looks good then I plug straight into the wall.

Double check for wiring errors, particularly in the power supply.
Then check all grounds.

It will most likely be something simple that you either missed or made a mistake on.
The good thing is that most tube amps are forgiving if the short or bad load is not allowed to run very long.

I guess that is why some of us call it the smoke test.

Good luck!

[Colossal]

What do you reckon, did I misunderstand this diagram? I must admit, I just saw the Standby switchand just went from there, but now looking at it more closely now that you've opened my eyes, it would seem that the standby switch in the diagram is in a different circuit position to where it is in the Express. Is that right? and is that where I went wrong?

The standby switch is in the same location for the way Dana has drawn it in the installation document you posted as well as on the Express schematic. My guess, but I can't say for sure without studying your photos further is that you had either the VVR upstream of the 80uF cap (attempting to source current directly off the rectifier) or somehow otherwise incorrectly installed. In the way shown in Dana's document, the reservoir cap will fully charge upon powering the amp and then the cap will be immediately available to the VVR and the rest of the amp when the standby is thrown.

[shaunf]

What do you reckon, did I misunderstand this diagram? I must admit, I just saw the Standby switchand just went from there, but now looking at it more closely now that you've opened my eyes, it would seem that the standby switch in the diagram is in a different circuit position to where it is in the Express. Is that right? and is that where I went wrong?

The standby switch is in the same location for the way Dana has drawn it in the installation document you posted as well as on the Express schematic. My guess, but I can't say for sure without studying your photos further is that you had either the VVR upstream of the 80uF cap (attempting to source current directly off the rectifier) or somehow otherwise incorrectly installed. In the way shown in Dana's document, the reservoir cap will fully charge upon powering the amp and then the cap will be immediately available to the VVR and the rest of the amp when the standby is thrown.

If that's the case shouldn't the VVR B+ in and out be between the standby switch and the 25w resistor on the PS Board, instead of how it is between the multicap can and standby?