Ok, I'm learning so go easy on me! I've assembled a PCL86 amp using a boost converter and buck converters for the heater and HT powered by a 20a laptop charger.
I'm just using a plastic box for the chassis to experiment and will build a proper chassis with a wooden enclosure once I'm happy with everything.
I've was initially following this schematic with PCL82
But then changed to this one
After building the first schematic, something was clearly wrong. On testing, the audio signal was coming through the speakers for a few seconds at the time I'm before bring interrupted by a short squeal/blip noise which would keep repeating.
I tested the voltage on HT tea and noticed that it was going from the correct voltage and rapidly dropping away when the blip sound was heard.
The LED on the boost converter unit was dimming in time with this
I decided to rebuild using the simpler PCL 86 schematic and found the same result.
A suspected that the boost converter may be faulty so ordered another one.
I replaced it but the problem is still there.
I've tested the voltage with the valve in circuit, the speaker connected but without an audio signal input and the voltage is stable.
As the problem persisted with the second, rebuilt circuit, and the boost converter is new, I'm not sure where to look to troubleshoot. The only thing that has stayed the same are the smoothing capacitors after the boost converter. I've checked these as per the schematic and it looks right.
The the heater supply coms via an LM317 step down converter. I bought a ready built module for this, I intend to build the slow start circuit at a later date. I have noticed that the heaters glow white hot for about a second on startup. I will definitely be incorporating this.
Here's a video of what I'm getting. I've only rebuilt one channel for now. You can see the speaker popping. It stops when I switch off the power supply.
Thanks!
I'm just using a plastic box for the chassis to experiment and will build a proper chassis with a wooden enclosure once I'm happy with everything.
I've was initially following this schematic with PCL82
But then changed to this one
After building the first schematic, something was clearly wrong. On testing, the audio signal was coming through the speakers for a few seconds at the time I'm before bring interrupted by a short squeal/blip noise which would keep repeating.
I tested the voltage on HT tea and noticed that it was going from the correct voltage and rapidly dropping away when the blip sound was heard.
The LED on the boost converter unit was dimming in time with this
I decided to rebuild using the simpler PCL 86 schematic and found the same result.
A suspected that the boost converter may be faulty so ordered another one.
I replaced it but the problem is still there.
I've tested the voltage with the valve in circuit, the speaker connected but without an audio signal input and the voltage is stable.
As the problem persisted with the second, rebuilt circuit, and the boost converter is new, I'm not sure where to look to troubleshoot. The only thing that has stayed the same are the smoothing capacitors after the boost converter. I've checked these as per the schematic and it looks right.
The the heater supply coms via an LM317 step down converter. I bought a ready built module for this, I intend to build the slow start circuit at a later date. I have noticed that the heaters glow white hot for about a second on startup. I will definitely be incorporating this.
Here's a video of what I'm getting. I've only rebuilt one channel for now. You can see the speaker popping. It stops when I switch off the power supply.
Thanks!
Just as in your other thread, I suspect the boost converter is getting overwhelmed by the load from the amplifier. I totally mistrust those cheap boost converter modules from E-pay.
Having said that, I have the expertise and resources to design my own DC-DC converters for this kind of application, and, no, I don't use a boost converter, but a proper push-pull converter of my own design.
As a test, you might want to exercise that boost converter with a resistive load to see how much load it will stand until it bows out of the game... You may need a bigger module than the one you have.
Having said that, I have the expertise and resources to design my own DC-DC converters for this kind of application, and, no, I don't use a boost converter, but a proper push-pull converter of my own design.
As a test, you might want to exercise that boost converter with a resistive load to see how much load it will stand until it bows out of the game... You may need a bigger module than the one you have.
Hi, again. I followed the video bellow. It works out fine for the builder. Reading in the comments, it's worked for others too.
I can understand your reservations in terms of reliability or longevity. But I think it should work. At least, it should work to start with.
The fact I've tried 2 BC's makes me suspect it could be something I've done wrong in the wiring.
I was hoping for some guidance on how to troubleshoot the problem, what to check.
Video bellow for reference.
Thanks 👍
I can understand your reservations in terms of reliability or longevity. But I think it should work. At least, it should work to start with.
The fact I've tried 2 BC's makes me suspect it could be something I've done wrong in the wiring.
I was hoping for some guidance on how to troubleshoot the problem, what to check.
Video bellow for reference.
Thanks 👍
Where are you in the UK? Anywhere near Lincolnshire? I'd be happy to have a look at it for you if you want to pop over.
If that's not possible check, recheck & check again your work. Have you connected to the correct valve pins? Have you got the right resistor values? This is an easy mistake to make for a beginner, a 100r/1k/10k/100k resistor can be easily confused, same for other values. Power it up and check your voltages to make sure your DC conditions are right, have you got bias, EG does the anode voltage drop on V1 and do you have a voltage on each (triode & pentode) cathode. Check your heaters are glowing. The other thing you can do is to put a 10r resistor inbetween your PSU and valve amp to check the current draw of the amp by monitoring the voltage across this resistor. This should be 0v at SW on then rising as the valves warm up.
Lastly your convertors may not like the initial high current draw of the heaters and or not like a no load situation till the valves warm up. To eliminate them try and knock up a linear power supply and power the amp with that.
Good luck, Andy.
If that's not possible check, recheck & check again your work. Have you connected to the correct valve pins? Have you got the right resistor values? This is an easy mistake to make for a beginner, a 100r/1k/10k/100k resistor can be easily confused, same for other values. Power it up and check your voltages to make sure your DC conditions are right, have you got bias, EG does the anode voltage drop on V1 and do you have a voltage on each (triode & pentode) cathode. Check your heaters are glowing. The other thing you can do is to put a 10r resistor inbetween your PSU and valve amp to check the current draw of the amp by monitoring the voltage across this resistor. This should be 0v at SW on then rising as the valves warm up.
Lastly your convertors may not like the initial high current draw of the heaters and or not like a no load situation till the valves warm up. To eliminate them try and knock up a linear power supply and power the amp with that.
Good luck, Andy.
Nice one, Andy. I'm nowhere near Lincolnshire unfortunately. Plenty of info there to be getting on with. I'll go over everything again and check it all over. All part of the fun! Good to get some pointers though.
The boost converter is definitely getting overloaded as it tries to supply the amplifier, so maybe there is a mistake in the biasing of the amplifier, or there is a wiring mistake that overloads the B+ generated by the boost converter.
To be brutallly honest, the overall lash-up looks kinda messy, with opportunities for wrong wiring.
Another thing to check is the voltage feed from the laptop adapter to the amplifier, to make sure it is not being overloaded. The rep rate of your problem seems to indicate that the laptop adapter is going into auto-restart protection mode in response to an overload. I find it somewhat difficult to believe that you have actually have a 20A laptop adapter - most of them clock in at around 80-100W max load, some considerably less. You may want to put a multimeter is series with the feed from the adapter to find out the actual current draw from the adapter, and compare that to the nameplate rating.
To be brutallly honest, the overall lash-up looks kinda messy, with opportunities for wrong wiring.
Another thing to check is the voltage feed from the laptop adapter to the amplifier, to make sure it is not being overloaded. The rep rate of your problem seems to indicate that the laptop adapter is going into auto-restart protection mode in response to an overload. I find it somewhat difficult to believe that you have actually have a 20A laptop adapter - most of them clock in at around 80-100W max load, some considerably less. You may want to put a multimeter is series with the feed from the adapter to find out the actual current draw from the adapter, and compare that to the nameplate rating.
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Did you remember to put dropper resistors in series with the tube filaments? The std laptop adapter usually puts out 19V - what is it in your case?
Solid state amps, and particularly tube amps, if not assembed into a metal enclosure, are going to be prone to hum and interferences.
Tube amps, with their high (and sensitive) impedences are better housed in metal boxes, aluminum, etc.
Tube amps, with their high (and sensitive) impedences are better housed in metal boxes, aluminum, etc.
That's not the issue here - the amplifier is cycling on and off - that seems to point to the adapter powering the amplifier operating in auto-restart in response to an overload. This is common behavior for a well-protected SMPS presented with an overload.
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I had another look at the amp today. Unfortunately I only got 10 minutes but I switched it on and checked the voltage at the DC Jack. Weirdly, the DC voltage now seems to be staying stable, I'm getting a constant 20v from the PSU and 230 on the boost converter output. All I'm currently gettn from the speaker is static. As soon as I cut the supple to the PSU, I hear the audio crystal clear from the speaker.
I wil go over the other pointers suggested when I get some more spare time.
Thank for the input.
I wil go over the other pointers suggested when I get some more spare time.
Thank for the input.
Hmmmm. I find it kinda wierd that you're only getting music when you cut the power. You might want to check the orientation of the bypass cap for the output stage cathode resistor. If it's the wrong way, you may be getting too much bias current though your output transformers. If you find that the cap is in backwards, toss it and put in a new one, as it will likely be toast due to the reverse bias.
Also, you report that your filaments are flashing white at turn-on. You may want to up the output voltage on your filament regulators and put in a dropper resistor to soak up the voltage difference. That way, there will at least be some well-defined resistance in series with the filaments and hopefully less current surge at turn-on.
Also, you report that your filaments are flashing white at turn-on. You may want to up the output voltage on your filament regulators and put in a dropper resistor to soak up the voltage difference. That way, there will at least be some well-defined resistance in series with the filaments and hopefully less current surge at turn-on.
Regrettably I didn't get any spare time to delve any deeper tonight and the amp is in my shed away from the house. But, I will look at the bypass cap tomorrow. Thanks again for the help.
I took a few pics of the circuit. Excuse the untidiness. This is just for testing purposes, I have some 1mm shrink wrap tubing for the cap and res legs which has arrived since I soldered this. Nothing is shorted, there are gaps between everything!
https://ibb.co/kK7SSJ7
https://ibb.co/jG5gS2g
https://ibb.co/mXvk1K2
https://ibb.co/kK7SSJ7
https://ibb.co/jG5gS2g
https://ibb.co/mXvk1K2
One of the other things I noticed in the schematic is that there are no grid stoppers on either the input triode or output pentode. A 1k resistor applied at the control grid of each tube 1/2 might help - the hashy stuff you are getting when the amp is powered up might be parasitic oscillation.
I also noticed that you aren't applying any global feedback. Once you get things working so you actually get music when the power is on, some feedback applied from the output to the cathode of the input tube could help increase the damping factor and tighten up the bass, otherwise it might be a touch flabby, given that you are running pure pentode mode at the output.... If you have access to a scope, you might want to take a look at the output vs. the input with an attenuated input signal to get a sense of the overall gain of the circuit, as you are currently running totally open loop, and may be severely overdriving the input with your music source.
I also noticed that you aren't applying any global feedback. Once you get things working so you actually get music when the power is on, some feedback applied from the output to the cathode of the input tube could help increase the damping factor and tighten up the bass, otherwise it might be a touch flabby, given that you are running pure pentode mode at the output.... If you have access to a scope, you might want to take a look at the output vs. the input with an attenuated input signal to get a sense of the overall gain of the circuit, as you are currently running totally open loop, and may be severely overdriving the input with your music source.
Good thinking, as you say it sounds like a stage is biased into cutoff at full power but as the HT/B+ voltage drops it might briefly be biased correctly. Some readings of DC conditions should be indicative. Some good close up pics of your circuit would help us here, we might spot something you've missed.
RE FB on this amp, I've built two or three small SE amps including a PCL82 amp and found that there was big discernible improvement with FB applied.
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There's a lot of great info here and I'm doing a lot of reading up and trying to digest it all! I'm learning but I learn by being hands on and trial and error. I like to just get stuck in. I'm getting my head around the theory slowly but surely. These pics show what's going on around the socket pins.
Again, please ignore the messiness. Everything you see will be rebuilt and rewired properly once I know I'm capable of building a working amp. I will insulate all the legs properly with shrink tubing and will be getting some better double tags trip to make the layout easier.
These are the pics:
https://ibb.co/kK7SSJ7
https://ibb.co/jG5gS2g
https://ibb.co/mXvk1K2
"You might want to check the orientation of the bypass cap for the output stage cathode resistor."
So, we are looking at the 100uf 63v which is connected between pin 7 on the socket and the ground tag, in series with the 180R. I understand that electrolytic capacitors need to be wired with correct polarity, I've got the negative sides connected to ground which I presume was correct?
Again, please ignore the messiness. Everything you see will be rebuilt and rewired properly once I know I'm capable of building a working amp. I will insulate all the legs properly with shrink tubing and will be getting some better double tags trip to make the layout easier.
These are the pics:
https://ibb.co/kK7SSJ7
https://ibb.co/jG5gS2g
https://ibb.co/mXvk1K2
"You might want to check the orientation of the bypass cap for the output stage cathode resistor."
So, we are looking at the 100uf 63v which is connected between pin 7 on the socket and the ground tag, in series with the 180R. I understand that electrolytic capacitors need to be wired with correct polarity, I've got the negative sides connected to ground which I presume was correct?
That looks ok, your right, the negative of the cap goes to ground. Take a DC voltage reading at each pin and post the results. It should be something like pin -
1) 0v
2) 2v ish
3) HT less a bit
4) & 5) 13v
6) HT less a bit
7) 8 to 10v ish
8) 0v
9) HT less a bit, say 100v ish
All those numbers are off the top of my head but should be about right. Pin 3) Pentode g2 should be a tad lower than the anode at pin 6) .Don't worry about the mess, I've built amps that way and they've worked fine.
1) 0v
2) 2v ish
3) HT less a bit
4) & 5) 13v
6) HT less a bit
7) 8 to 10v ish
8) 0v
9) HT less a bit, say 100v ish
All those numbers are off the top of my head but should be about right. Pin 3) Pentode g2 should be a tad lower than the anode at pin 6) .Don't worry about the mess, I've built amps that way and they've worked fine.
Right here goes...
HT 228v
1 0v
2 0v
3 226
4 and 5....... 13v when measured pin 4 to pin5, I've got the live from the LM317 to pin 4 and the Negative to pin 5. When I measure between pin either pin 4 or 5 and the Boost converter Neutral, or the ground tag It shows voltage on on each of the pins. around 130v, which Immediately starts to drop down for as long as I hold it on them.
6 228v
7 0v??
8 0v
9 207
I have had the boost converter output set to 230, I see this is almost certainly a mistake. My rational here was the "Va" and "Vs" quoted in the specs for the valve. I thought that this was the the necessary HT voltage. I'm rethinking that now 😆.
HT 228v
1 0v
2 0v
3 226
4 and 5....... 13v when measured pin 4 to pin5, I've got the live from the LM317 to pin 4 and the Negative to pin 5. When I measure between pin either pin 4 or 5 and the Boost converter Neutral, or the ground tag It shows voltage on on each of the pins. around 130v, which Immediately starts to drop down for as long as I hold it on them.
6 228v
7 0v??
8 0v
9 207
I have had the boost converter output set to 230, I see this is almost certainly a mistake. My rational here was the "Va" and "Vs" quoted in the specs for the valve. I thought that this was the the necessary HT voltage. I'm rethinking that now 😆.