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So I finished up my Deluxe today... did a visual double check of all my wiring and solder joints.... put in some tubes, and plugged her in with a speaker cab attached. I flipped the on/off switch..... pilot light goes on and everything looks good. B+ voltage is 391 which is dead on according to some voltages mentioned in another thread. I flipped the standby switch.... I get a hum coming from the speaker cabinet, but no sound from either channel after turning up both volumes.... then the smell of burning... the 5k resistor across the filter caps was sizzling. I thought maybe I had a bad resistor so I replaced it, checked out everything again just to be sure, and then tried firing it up again and the exact same resistor fried.

Any suggestions as to where to start looking for a problem? What could cause that?


Thanks,
Phil

That 5K is taking too much current.

Is it at least a 2 Watt, metal or ceramic power resistor??

Are the power tubes good?
Is the 2nd - 16uF filter cap good? Lift one end off & measure it.
Is the 5K accidentally connected to ground? Measure resistance

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I am using 2 watt carbon comp... and actually I used a 4.7 K instead of a 5 K because I didn't have any 5 K, but I have seen other Deluxe schematics that use a 4.7.

The power tubes are vintage tubes (I run vintage tubes in all my gear) but were run through a tester and tested ok. I realize that doesn't necessarily rule out there is a bad one... I could try running another set and see what happens.

I assume the filter caps are good because they are new (I got them from you back in the summer), but if I lift one end and measure, what should I be getting?

I will double check to make sure I don't have it grounded by accident....


And I appreciate the help...

You can try pulling them & see what happens. The caps should be good. pull a cap off at one end and measure it's resistance & see if it changes over 5-10 seconds (see below) or measure with a capacitance meter.

CAUTION: For this and any other testing of large capacitors and/or capacitors in power supply, power amplifier, or similar circuits, make sure the capacitor is fully discharged or else your multimeter may be damaged or destroyed!

A VOM or DMM without capacitance ranges can make certain types of tests.

For small caps (like 0.01 uf or less), about all you can really test is for shorts or leakage. (However, on an analog multimeter on the high ohms scale you may see a momentary deflection when you touch the probes to the capacitor or reverse them. A DMM may not provide any indication at all.) Any capacitor that measures a few ohms or less is bad. Most should test infinite even on the highest resistance range.

For electrolytics in the uF range or above, you should be able to see the cap charge when you use a high ohms scale with the proper polarity - the resistance will increase until it goes to (nearly) infinity. If the capacitor is shorted, then it will never charge. If it is open, the resistance will be infinite immediately and won't change. If the polarity of the probes is reversed, it will not charge properly either - determine the polarity of your meter and mark it - they are not all the same. Red is usually **negative** with (analog) VOMs but **positive** with most DMMs, for example.

If the resistance never goes very high, the capacitor is leaky.

The best way to really test a capacitor is to substitute a known good one. A VOM or DMM will not test the cap under normal operating conditions or at its full rated voltage. However, it is a quick way of finding major faults.

From geofex.com re-burning/hot components:

There's good news and bad news. The good news is that it's easy to find the problem, at least the thing that is burning. Just unplug the amp, open up the chassis and look for what's burned, charred, or overheated looking. That's what's causing the smoke/smell.

The bad news is that in almost all cases, the part that is burning is a power handling component. These are ALL expensive. Worse, in some cases, the part that is burning is not what is causing the problem, and you still have to find what else is faulty.

In some ways, having smoke coming out of the amplifier is kind of a deviant, hard-headed version of having a fuse blow - something is eating too much power, it's just that the fuse for some reason is not blowing. This is especially suspect if the fuse blew, and you didn't have another of the right rating, so you stuck in a higher current rated fuse.

Possible causes are:

Failing/shorted output tube - this can overheat the output transformer and/or power tranformer. More rarely, it can also overheat the choke, but usually the transformers go first.
Improperly biased output tube.
Failing bias supply on fixed bias amplifiers
Failing cathode resistor bypass capacitor on cathode biased amps.
Failing/shorted rectifier tube (or solid state diodes - they do fail, if rarely) can overload the power transformer as well as killing the power filter capacitors by letting AC through. A failing filter cap or shorted output tube can pull so much current that it overloads the rectifier tube, too.
Failing power filter capacitor. These can sometimes get hot enough to literally explode or burn, as well as just quietly overloading the power supply and popping rectifiers and power transformers.
Failing power transformer.
Failing power filter capacitor
Choke with a "soft" short between winding and core
Failing output transformer

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

On a side note, I am still trying to learn all the amp terms... is a Deluxe a fixed bias or cathode biased amp?

hmmmm..... where to start?!

Well I sure hope its not a failing transformer, after all they are new Heybours! I will try pulling the power tubes out of my Bassman and the rectifier out of my Champ (cause I know they are good for sure) and try those tubes and see if its a tube... I think that might be the simplest thing to start with and will rule out the tubes..... does that sound reasonable or should I approach this a different way?

Assuming all the wiring is correct.

Start here:

Is the cathode bias resistor/capacitor pair in good shape?

Pull the tubes & quickly see if it gets hot. If it does, change them. If not,
Measure resistance at intersection of 5K & 22K to ground. If low, there may be a prob with the cap.

I'm pretty sure it's not a transformer! Deluxe is cathode biased.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen... I should be able to find some time to take a look at the amp this weekend and try out what you suggested and will get back to you soon!

Ok I'm just a complete bonehead.... Turns out I had 1 wire connected wrong!!! I didn't see it the first few times I looked through the wiring. The wire that goes from the 5K resistor to pin 4 of the power tube... I actually had that wire going to pin 5 instead - so if I read the schematic right I was actually grounding it out and thats why I was having the problem. What a moron eh?

So once I got that straightened out, I fired it up and checked the voltages, which I will list below. V1 voltage is high, but I am running a 12AX7 in V1 because I don't have a 12AY7 yet so I assume thats why the voltage at that tube is off. Here are the voltages:

B+ 350 VDC (should be 391)

V1
Pin 1 - 266 (should be 129)
Pin 3 - 4.0 (should be 2.0)
Pin 6 - 268 (should be 123)
Pin 8 - 4.0 (should be 2.0)

V2
Pin 1 - 176 (should be 129)
Pin 3 - 1.0 (should be 1.1)
Pin 6 - 212 (should be 175)
Pin 8 - 51 (should be 70.5)

V3
Pin 3 - 342 (should be 380)
Pin 4 - 316 (should be 338)
Pin 8 - 20 (should be 22)

V4
Pin 3 - 341 (should be 382)
Pin 4 - 319 (should be 339)
Pin 8 - 20 (should be 22)


I went through every single connection in the rest of the amp and everything is as it should be. The second channel works, and the first channel is dead. Channel 2 sounds good, but it doesn't appear to have the volume it should, and it stays clean up to full volume. I'm thinking I have a bad solder joint somewhere, so my next step is going to be to go through the whole amp and re-solder each joint.

The voltages are quite a way off so you should check the components leading to them. v1 especially should not be that different despite it being a 12AX7.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Ok, so I finally got a chance to do some work on my Deluxe.... I went through and tried to resolder most of the joints in the amp... some of the voltages have improved, some got worse.... the B+ and power tubes are pretty close, but the preamp tubes are a mile out (they actually got worse!!!! ) I suppose its possible that I may still have a cold joint somewhere, not sure. Here are the voltages now:


B+ 390 VDC (1 volt off, I think that is ok )

V1 (all the voltages on this tube got a ton higher!!!)
Pin 1 - 300 (should be 129)
Pin 3 - 5 (should be 2.0)
Pin 6 - 301 (should be 123)
Pin 8 - 5 (should be 2.0)

V2 (this one got worse too)
Pin 1 - 208 (should be 129)
Pin 3 - 1.4 (should be 1.1)
Pin 6 - 242 (should be 175)
Pin 8 - 58 (should be 70.5)

V3
Pin 3 - 381 (should be 380)
Pin 4 - 353 (should be 338)
Pin 8 - 23 (should be 22)

V4
Pin 3 - 375 (should be 382)
Pin 4 - 353 (should be 339)
Pin 8 - 23 (should be 22)


I am getting way too much voltage to the preamp tubes and not sure why.... oh, and not sure if its related, but the first channel is also dead. ??? Once again any suggestions are MUCH appreciated!

Are you 100% sure the jumpers on the board are correct?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Also make sure your ground connections from the cathode resistors on V1 & V2 go to ground.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps