Finally!
It's up and running.
My first mistake made last week was that I set the output tube bias at 2.5 mA (thinking the filament current is 2.5) instead of 50 to 60 for my 2A3 tubes. That's what blew the fuse when I turned up the volume a bit. All this hassle just from not reading throughly...
I still have one issue though. It's feeding my spare speakers which is around 86 db efficient but there is hum. Could it be from all these wires around it? Right now it looks just like Tubelab's "Checkout" process picture (no chassis, everything sitting on a piece of board).
It's up and running.
My first mistake made last week was that I set the output tube bias at 2.5 mA (thinking the filament current is 2.5) instead of 50 to 60 for my 2A3 tubes. That's what blew the fuse when I turned up the volume a bit. All this hassle just from not reading throughly...
I still have one issue though. It's feeding my spare speakers which is around 86 db efficient but there is hum. Could it be from all these wires around it? Right now it looks just like Tubelab's "Checkout" process picture (no chassis, everything sitting on a piece of board).
As a note, here are the measurements during last test run.
B+ = 376 vdc, B- = 232 vdc, input tube plate to ground = 178 vdc, 180 vdc, output tube bias current = 50.1 mA, 50.8 mA
Is it normal for B+ and B- resistors to get hot? Mine got hot to the point of deforming the plastic tips of test probe hooks.
B+ = 376 vdc, B- = 232 vdc, input tube plate to ground = 178 vdc, 180 vdc, output tube bias current = 50.1 mA, 50.8 mA
Is it normal for B+ and B- resistors to get hot? Mine got hot to the point of deforming the plastic tips of test probe hooks.
Hi, I'm using the hammond 272jx transformer.
B+ = 320v, input tube plate =176v output tube current 70ma
the resistors on mine are hot, but I can keep my finger on them for almost 10 seconds before I can't take the heat. I've seen that used as a general rule for electronics heat... not sure what it means, really.
Power transformer remains cool, the choke tx is pretty warm. Everything else other than the tubes stays cool
the choke is an easy upgrade. Remove R4 (double check this on the tubelab site!) and wire the choke in its place. (as long as you got the choke he recommends, which is the same resistance as r4)
I love mine! The highs might be a little muted, or maybe in my last amp the highs were exaggerated. I've got to do a little more testing w/ other amps to figure it out. This one definitely has more bass than my other amp! almost don't need the sub anymore!!
Other amp is a 6v6 PP
B+ = 320v, input tube plate =176v output tube current 70ma
the resistors on mine are hot, but I can keep my finger on them for almost 10 seconds before I can't take the heat. I've seen that used as a general rule for electronics heat... not sure what it means, really.
Power transformer remains cool, the choke tx is pretty warm. Everything else other than the tubes stays cool
the choke is an easy upgrade. Remove R4 (double check this on the tubelab site!) and wire the choke in its place. (as long as you got the choke he recommends, which is the same resistance as r4)
I love mine! The highs might be a little muted, or maybe in my last amp the highs were exaggerated. I've got to do a little more testing w/ other amps to figure it out. This one definitely has more bass than my other amp! almost don't need the sub anymore!!
Other amp is a 6v6 PP
OH That makes a difference. . 300b
I have no hum on mine at all. I'm actually quite surprised!
do the standards, like making sure the power is rotated 90 degrees from the output and choke tx's. Twist all of your interconnecting wires. My power wires aren't twisted or braided(but I don't think it would hurt), nor is the choke(I dont know for a fact, but twisting the choke wires together seems like a bad idea to me). The wires going to my external capacitor are twisted, and the wires going to the output tx's are twisted. The wires leading from my rca jacks to the amp are twisted. (I'll use shielded wire when I put it in its case) Try to set it up so that nothing is crossing over any of the power wires.
modifications I've made.... the 100uf power capacitor is a motor run cap. I added some 1uf poly/foil caps across the 4700uf caps on the input tubes. (not sure if it makes any difference or not, but had them on hand, so used them)
I think that's it... I did put all the tall components on the bottom side of the pcb, but that wouldn't make a difference w/ hum.
Can you tell if the hum sounds like standard 60hz power noise? I'd guess the noise is coming from either the power, or getting introduced before the input tubes, and then getting amplified.
That's about all the advice I can offer, as Ive mentioned, this is my first amp, too. I know it's a good design. If nothing Ive mentioned helps, start checking any parts you've used that aren't new, or aren't what Tubelab recommended.
I've got a few synth projects on my bench that have been finished for months, but I haven't powered them on for the first time yet. Troubleshooting electronics projects is frustrating! I use a bunch of old opamps and transistors, etc from surplus stores in my synth, and so besides mistakes Ive made, I often have to hunt down bad components. Troubleshooting always takes longer than building the thing in the first place.
So, much sympathy, and good luck!
I have no hum on mine at all. I'm actually quite surprised!
do the standards, like making sure the power is rotated 90 degrees from the output and choke tx's. Twist all of your interconnecting wires. My power wires aren't twisted or braided(but I don't think it would hurt), nor is the choke(I dont know for a fact, but twisting the choke wires together seems like a bad idea to me). The wires going to my external capacitor are twisted, and the wires going to the output tx's are twisted. The wires leading from my rca jacks to the amp are twisted. (I'll use shielded wire when I put it in its case) Try to set it up so that nothing is crossing over any of the power wires.
modifications I've made.... the 100uf power capacitor is a motor run cap. I added some 1uf poly/foil caps across the 4700uf caps on the input tubes. (not sure if it makes any difference or not, but had them on hand, so used them)
I think that's it... I did put all the tall components on the bottom side of the pcb, but that wouldn't make a difference w/ hum.
Can you tell if the hum sounds like standard 60hz power noise? I'd guess the noise is coming from either the power, or getting introduced before the input tubes, and then getting amplified.
That's about all the advice I can offer, as Ive mentioned, this is my first amp, too. I know it's a good design. If nothing Ive mentioned helps, start checking any parts you've used that aren't new, or aren't what Tubelab recommended.
I've got a few synth projects on my bench that have been finished for months, but I haven't powered them on for the first time yet. Troubleshooting electronics projects is frustrating! I use a bunch of old opamps and transistors, etc from surplus stores in my synth, and so besides mistakes Ive made, I often have to hunt down bad components. Troubleshooting always takes longer than building the thing in the first place.
So, much sympathy, and good luck!
Hum
I connected it to my high efficiency main speakers. Yikes, loud 60Hz hum! I must have have mis connected the transformers or something else may have been damaged. Here's how it's wired.
PT: Hammond 272JX
Section 1 (600V CT @ 250mA DC) red-red to T1-4 & 5, red-yellow to T1-1
Section 2 (5V CT @ 4A) yellow-yellow to T1-2 & 3, black-yellow not connected
Section 3 (6.3V CT @ 8A) green-green to T1-7 & 8, yellow-green to T1-6
Primary (115V 60Hz 236VA) black-black to power supply.
OPT: Hammond 1627SEA
Secondary 8 Ohm yellow & black to speaker terminal, green & white not connected.
Primary 2500 Ohm - blue to T3-2 (left) & T2-2 (right), red to T3-1 (left) & T2-1 (right), yellow-blue not connected.
Any help will be appreciated. Thanks.
I connected it to my high efficiency main speakers. Yikes, loud 60Hz hum! I must have have mis connected the transformers or something else may have been damaged. Here's how it's wired.
PT: Hammond 272JX
Section 1 (600V CT @ 250mA DC) red-red to T1-4 & 5, red-yellow to T1-1
Section 2 (5V CT @ 4A) yellow-yellow to T1-2 & 3, black-yellow not connected
Section 3 (6.3V CT @ 8A) green-green to T1-7 & 8, yellow-green to T1-6
Primary (115V 60Hz 236VA) black-black to power supply.
OPT: Hammond 1627SEA
Secondary 8 Ohm yellow & black to speaker terminal, green & white not connected.
Primary 2500 Ohm - blue to T3-2 (left) & T2-2 (right), red to T3-1 (left) & T2-1 (right), yellow-blue not connected.
Any help will be appreciated. Thanks.
Here are a few things to try.
If the amp is still in the breadboard state see if moving or rotating the transformers makes any difference. Sometimes the 60 Hz magnetic field from the power transformer can get into the output transformers and cause hum. If the hum is audible as soon as the amp is switched on (before the tubes warm up) this is likely the case.
Try disconnecting the input wiring from the PC board. Run the amp with no input to see if you still get hum. If the hum goes away the problem is with the input wiring.
Make sure the metal case of the volume pot (if used) is grounded.
Does the hum level change with the volume pot setting?
If the amp is still in the breadboard state see if moving or rotating the transformers makes any difference. Sometimes the 60 Hz magnetic field from the power transformer can get into the output transformers and cause hum. If the hum is audible as soon as the amp is switched on (before the tubes warm up) this is likely the case.
Try disconnecting the input wiring from the PC board. Run the amp with no input to see if you still get hum. If the hum goes away the problem is with the input wiring.
Make sure the metal case of the volume pot (if used) is grounded.
Does the hum level change with the volume pot setting?
In order to find out what is causing the hum, try these experiments:
You stated that the hum was reduced when you added the choke. This implies that the hum is related to the B+ source. Try using a larger value for C4. My 2A3 amp uses a 22uF cap and a choke of unknown value. If you have another choke, try it, or try both in series. If any of this makes any difference the B+ source is the source of the hum.
There are 5 usual possibilities for hum.
The B+ source (the reasons for these tests).
The B- source. I never saw the B- source cause hum in a TubelabSE but a bad cap could cause it (C6 or C7).
Transformer interaction. You have already ruled this out.
Hum picked up by the input wiring. This will go away if the input wiring is disconnected.
The filament regulator could cause hum although I have never seen it happen either. Measure the voltage at the large pad marked F-4V near C1 (negative meter lead on ground). You should have about 3.5 to 4.5 volts. Measure the voltage at the filament pin on one of the output tubes ( the fat trace that runs along the back of the board on the top side). You should have 2.5 volts. If these voltages are OK the regulator is probably OK. I suppose a bad cap here (C1, C2 or C3) could cause hum.
You stated that the hum was reduced when you added the choke. This implies that the hum is related to the B+ source. Try using a larger value for C4. My 2A3 amp uses a 22uF cap and a choke of unknown value. If you have another choke, try it, or try both in series. If any of this makes any difference the B+ source is the source of the hum.
There are 5 usual possibilities for hum.
The B+ source (the reasons for these tests).
The B- source. I never saw the B- source cause hum in a TubelabSE but a bad cap could cause it (C6 or C7).
Transformer interaction. You have already ruled this out.
Hum picked up by the input wiring. This will go away if the input wiring is disconnected.
The filament regulator could cause hum although I have never seen it happen either. Measure the voltage at the large pad marked F-4V near C1 (negative meter lead on ground). You should have about 3.5 to 4.5 volts. Measure the voltage at the filament pin on one of the output tubes ( the fat trace that runs along the back of the board on the top side). You should have 2.5 volts. If these voltages are OK the regulator is probably OK. I suppose a bad cap here (C1, C2 or C3) could cause hum.
Hum was reduced by little when choke was put in. I just tried a spare 22uF for C4 and the hum is still there. It raised the bias current by about 10 mA though.tubelab.com said:
I'll try that tomorrow morning and report back.
I tried it the other day but still no change.
F-4U is 3.2V and filament voltage is 2.5 V before the cap change to 22uF.
I'll try replacing the caps mentioned and report back. By the way, should I check those caps with multimeter before pulling them out? Or is multimeter not a good device for it?
Here's a picture from this afternoon. B+ is 329, B- is 224, bias is 52.2 and 52.4. My output tubes are 2A3.
An externally hosted image should be here but it was not working when we last tested it.
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