18 watt liverpool pcb build

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JoshBernstein
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18 watt liverpool pcb build

Post by JoshBernstein »

Hey all,
I've been building an 18 watt liverpool based off RJ's pcb design. Its for a friend who is also a member of the amp garage, he's building the cabinet for it and i believe that he will post some of his progress in this thread as well. The build went together fairly easily, and it is up and running. There is a hum that i need to kill though, and i suspect it is just lead dress, so I'll chopstick around. Said hum is affected by all controls including volume, so i know its in the early preamp. I suspect there may be some minor oscillation i need to kill too as it ticks faintly when cranked. But the drive sounds gorgeous and the cleans are pristine. A very well put together parts package from RJ.
Nick, who i built this for, lives in europe so i had to use a dual primary pt to get it running here, and ill convert it to run on the voltage over there before i mail it. I still have to put in the pilot lamp, but ill do that when it's ready to be converted to uk voltage. Pt leads were left long as they need to be reconfigured for euro voltage.

The pt is a heyboer, ot is made by edcor, tung sol preamp tubes and nos russian power tubes. Ill upload some sound clips soon as well.

Any advice on the him would be more than welcome

More detailed pics and clips to come.
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Last edited by JoshBernstein on Sun Jul 02, 2017 3:38 pm, edited 2 times in total.
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

Parts when they first arrived:
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RJ Guitars
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Re: 18 watt liverpool pcb build

Post by RJ Guitars »

Josh, What you've described is generally going to have something to do with a bad ground. So I've followed the ground paths and I see something that needs a 2nd look... there is a wire that doesn't appear to be soldered. let us know if that is the problem or at least part of it.
Thanks,
rj
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RJ Guitars
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Re: 18 watt liverpool pcb build

Post by RJ Guitars »

Also I'm hopeful that you got the replacement resistor I sent for the Output tubes cathode bias circuit. That little chassis mount unit is OK for a test but it will require a good solid mount to the chassis in order to meet it's power rating. That probably isn't causing you any grief at this point but you'll want to replace it before all is said and done. thanks, rj
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RockinRocket
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Re: 18 watt liverpool pcb build

Post by RockinRocket »

Id try different tubes to reduce the hum first. I found that in most cases its new production tubes having issues.
A ANOS Mullard brought my amp to zero hum vs JJ 803 long plate hum I was getting before.
They don't make them like they used to as the saying goes.
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

RJ Guitars wrote: Tue Jul 11, 2017 7:15 pm Josh, What you've described is generally going to have something to do with a bad ground. So I've followed the ground paths and I see something that needs a 2nd look... there is a wire that doesn't appear to be soldered. let us know if that is the problem or at least part of it.
Thanks,
rj
I actually did notice that wire after my initial fireup and soldered it. I agree that it seems like a ground issue but that wire doesnt seem to be the culprit. Ive also replaced the resistor with the new one you sent, ill upload an updated photo in a few minutes. Thank you for your help!
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sonicmojo
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Re: 18 watt liverpool pcb build

Post by sonicmojo »

RockinRocket wrote: Tue Jul 11, 2017 10:03 pm Id try different tubes to reduce the hum first. I found that in most cases its new production tubes having issues.
A ANOS Mullard brought my amp to zero hum vs JJ 803 long plate hum I was getting before.
They don't make them like they used to as the saying goes.
+1, especially V1 on the higher gain builds. I've found JJ803 to produce hum in that spot on high gain amps also but usually when a smaller cathode bypass cap is used which is not the case in a Liverpool.
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Mark
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Re: 18 watt liverpool pcb build

Post by Mark »

Isn't the power transformer a little big for this amp?

What is the rail voltage on this amp?
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

Hi all, here are some updated pics of the amp. Hum is cured, just a lead dress issue, and the amp sounds great. Something im a but worried about is theres dc on the presence pot, about 64 volts. What is this from? Is it normal?
As for the pt, it is large, but it was supplied to my by rj specifically for this build. I used the 260 volt tap and am getting 363 volts off the first filter cap.
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romberg
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Re: 18 watt liverpool pcb build

Post by romberg »

JoshBernstein wrote: Thu Jul 13, 2017 12:37 am Something im a but worried about is theres dc on the presence pot, about 64 volts. What is this from? Is it normal?
The presence pot is taped into the resistors on the phase inverter cathodes. The PI is probably drawing a couple of mA current. This current across the tail resistors will produce a DC voltage (which biases the PI). So, the presence pot will have this DC voltage as well.

However 64 volts seems high to me. Are you sure it is not 6.4V? The schematic I'm looking at has the presence pot connected to the top of a 4k7 resistor. The 4k7 connects to ground. 2mA through 4k7 would be around 9.4V.

Mike
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

Its definitely 65, sometimes even jumps above 70. When i touch the meter leads to it it even arcs to the probe sometimes. Ill check my work around that area and see where ive gone wrong.
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romberg
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Re: 18 watt liverpool pcb build

Post by romberg »

Looking at this schematic:

http://ampgarage.com/forum/download/file.php?id=6861

and your pictures I can't seem to find R14 (from the linked schematic above). R14 should take the DC bias current of the PI to ground. If it is not there and all of the PI current is flowing through your presence pot (which it kinda looks like it might be from your pics), then 2mA of current would give you about 50V on that pot. Which is close to what you are seeing. Is R14 suppose to be mounted on the pot? There don't seem to be enough resistors on the board to account for the five I see on the above schematic.

Mike
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

romberg wrote: Fri Jul 14, 2017 12:00 am Looking at this schematic:

http://ampgarage.com/forum/download/file.php?id=6861

and your pictures I can't seem to find R14 (from the linked schematic above). R14 should take the DC bias current of the PI to ground. If it is not there and all of the PI current is flowing through your presence pot (which it kinda looks like it might be from your pics), then 2mA of current would give you about 50V on that pot. Which is close to what you are seeing. Is R14 suppose to be mounted on the pot? There don't seem to be enough resistors on the board to account for the five I see on the above schematic.
Mike
This is a moddified version of the liverpool, and only uses 2 output tubes. It was built off the schematic and layout that rj provided for me. Im not sure if he'd want these documents shared, but there is no r14 equivalent in his schematic. Is it something that should be added? The presence pot in this case is only 5k
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sluckey
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Re: 18 watt liverpool pcb build

Post by sluckey »

but there is no r14 equivalent in his schematic. Is it something that should be added?
Not necessarily. But your presence pot would be about 5K if your circuit doesn't use that 4.7K resistor. And it would be wired a bit differently. Look at some early Marshall schematics to see what I'm talking about.

Meanwhile, check resistance from pin 8 (probe directly on the socket pin) of the PI tube to chassis. What have you?
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JoshBernstein
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Re: 18 watt liverpool pcb build

Post by JoshBernstein »

sluckey wrote: Fri Jul 14, 2017 4:35 pm
but there is no r14 equivalent in his schematic. Is it something that should be added?
Not necessarily. But your presence pot would be about 5K if your circuit doesn't use that 4.7K resistor. And it would be wired a bit differently. Look at some early Marshall schematics to see what I'm talking about.

Meanwhile, check resistance from pin 8 (probe directly on the socket pin) of the PI tube to chassis. What have you?

As i typed that last response i realised i used a 25k pot by mistake. I have the correct one sitting right here. Ill pop that in and see what ive got.
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