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My 1st tube amp build thread (and lots of questions)

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Nickbee

Member
Joined 2016
Hey Gang!

Figured i'd introduce myself and show the process of me building my 1st amp project. I hope this is a good way for anyone who is interested to follow along and for me to ask questions along the way.

I have a very basic understanding of electronics and have experience building all sorts of things. I also have OK woodworking skills, a decent table saw and an awesome router table.

I'll be building the "Chubby" Clementine. Since the PCB's are not longer being sold I'll be building up my own turret boards for the circuits. I'll be doing a ply box with aluminum top similar to how "Specimen Products" builds their chassis.

Info on this amp is here:
diytube.com • View topic - diy*tube clementine project (3/16/16 - back in stock!)

The main components I've gathered so far:
Power Transformer: AS-1T300
PS Caps: 4x M tube cap 100uF 550VDC
Pre tube:psvane CV-181-T II (6SN7 equivalent)
Power tubes: Psvane KT88-T II
Output Transformers: James JS-611HS
Khozmo 48 step 100K Attenuator

Here is the basic layout on the dinning room table:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


I'm working on the top panel and component layout now in illustrator. So more to come soon!
 
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Nickbee

Member
Joined 2016
Here are some initial mock ups on the top and bottom views.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


And now for some questions. I've read Bruce's article on grounding and shielding:
Grounding and Shielding for your DIY Audio Projects

Does my grounding scheme look viable?

I'm open to component layout suggestions. For now I've try to keep the grid resistors as close as possible and I'll be running the heater wires near the aluminum top.

I have most of my parts situated so the next step will be ordering the aluminum top from front panel express.
 
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DF96

R.I.P.
Joined 2007
myweb.tiscali.co.uk/g8hqp/
The PSU should have a bus ground. This should start with the secondary CT, then C7 -ve, then C8 -ve etc. This bus should then be connected to the main signal ground from the -ve of C9 or C10. It is vitally important that nothing is connected to ground between the CT and C7, as this connection carries charging pulses.

The audio star point should not be on the chassis, although it can have a connection to the chassis. Personally, I don't like star grounds. I prefer a bus ground, so ground can follow signal. This keeps loops small.
 
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Nickbee

Member
Joined 2016
DF96 said:
The PSU should have a bus ground. This should start with the secondary CT, then C7 -ve, then C8 -ve etc. This bus should then be connected to the main signal ground from the -ve of C9 or C10. It is vitally important that nothing is connected to ground between the CT and C7, as this connection carries charging pulses.

The audio star point should not be on the chassis, although it can have a connection to the chassis. Personally, I don't like star grounds. I prefer a bus ground, so ground can follow signal. This keeps loops small.
Click to expand...

Thanks for the comments DF96.

I've made some updates to the grounds.

- The power buss is now separated from the heater resistors
- The power buss wire is tapped off the -ve of C10 (see round yellow highlight)
- I added a small buss wire near inputs to tie all the ground wires together, this will then run to the chassis.

I completely forgot the draw in the shield wire from the transformer. Should that just go to the power buss?

Let me know how this looks and if you'd make any changes.

I need to add a few holes from wire management clamps and then I'm close to ordering the metal!

Thanks again!

An externally hosted image should be here but it was not working when we last tested it.
 
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Nickbee

Member
Joined 2016
Chris Hornbeck said:
It's unclear without a schematic whether or not the output transformers' secondaries are connected to ground. These must have a signal ground or safety earth ground.

All good fortune,
Chris
Click to expand...

the schematic can be found in this PDF. I don't want to post photos as I'm not sure of copyrights.

http://www.diytube.com/clementine/clementinemanual.pdf

The version I'm building (6V6) starts on page 7.

Because this schematic is from a PCB that is no longer available it's a little harder to follow as the schematic should terminals that were used. But I don't see the secondaries connected to ground anywhere. Maybe I'm missing it?

Thanks!
 
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Nickbee

Member
Joined 2016
kevinkr said:
One suggestion I would make would be to use a choke instead of resistor in the power supply, less voltage drop and less ripple.

Something like a 5H - 10H choke would work, might not hurt to simulate your proposed power supply in PSUD2. (free from duncan amps)
Click to expand...

There is a 1.5H coke in the power supply. It's that gray thing mounted to the left wall when looking from underneath. I guess I should label it :)

I will check out that app! Thanks!
 
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DF96

R.I.P.
Joined 2007
myweb.tiscali.co.uk/g8hqp/
Nickbee said:
But I don't see the secondaries connected to ground anywhere. Maybe I'm missing it?
Click to expand...
The circuit diagram shows no secondary grounding, so the PCB might not do this. It should do this for reasons of safety. An audio OPT has sections of secondary and primary interleaved so that coupling is tight. There will be layers of insulation between them, but this can never be fully trusted. Therefore the secondary should be grounded.

The 1.5H choke is almost certainly too small. The PSU will resonate just in or just below the audio frequency range - PSUD2 will show this as ringing after a change in load current. This could make for 'lively' sound, but it won't be hi-fi. There is a strange school of thought among some SET designers which causes them to deliberately build bad power supplies and then prefer the resultant poor sound.
 
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Nickbee

Member
Joined 2016
M3Roc said:
Would it be possible to build this in two mono configurations without the volume pot to be used with a preamp? What kinda output power are you expecting per channel?
Click to expand...

I think because of the simple circuit this would make good monoblocks. Although you would have to use 2 6SN7s which means each monoblock would only be using half of the 6SN7. I'm too much of a novice to know if that's ok or if there would be a better tube suited for this purpose.

I think this design should yield about 5-6W per channel from what I've read.
 
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Nickbee

Member
Joined 2016
DF96 said:
The circuit diagram shows no secondary grounding, so the PCB might not do this. It should do this for reasons of safety. An audio OPT has sections of secondary and primary interleaved so that coupling is tight. There will be layers of insulation between them, but this can never be fully trusted. Therefore the secondary should be grounded.
Click to expand...

Thanks! So with my chassis layout what would be my best bet for grounding the secondary? Should I connect them with a buss near the OPT and run a single wire to the input ground?

DF96 said:
The 1.5H choke is almost certainly too small. The PSU will resonate just in or just below the audio frequency range - PSUD2 will show this as ringing after a change in load current. This could make for 'lively' sound, but it won't be hi-fi. There is a strange school of thought among some SET designers which causes them to deliberately build bad power supplies and then prefer the resultant poor sound.
Click to expand...

I'm not married to the 1.5H choke as it was not a huge investment. The question is what size would be better suited and would it mean changing any of the other PS components? Obviously the 4 100uF M tube caps were a bit of an investment :)

I've also decided to redraw the schematic as one cohesive drawing and create a BOM since enough has changed from the original PCB version of this amp. Since life is busy right now if might take me a little while. But I'll have more free time during the holiday week.
 
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Sheldon

Member
Joined 2003
Nickbee said:
I think because of the simple circuit this would make good monoblocks. Although you would have to use 2 6SN7s which means each monoblock would only be using half of the 6SN7. I'm too much of a novice to know if that's ok or if there would be a better tube suited for this purpose.
Click to expand...

It's ok to use only one section of the dual triode. Or use the electrically equivalent 6J5, which contains a single section.

Sheldon
 
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DF96

R.I.P.
Joined 2007
myweb.tiscali.co.uk/g8hqp/
How you ground the secondaries doesn't matter too much, as long as they are grounded so an OPT insulation breakdown will blow a fuse instead of killing someone.

I would go for a 5-10H choke - but play with PSUD2 first. You need to ensure that any PSU ringing is below 20Hz, and the further below the better - provided that a lower frequency does not lead to weaker damping.
 
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Nickbee

Member
Joined 2016
ok here's an update. I started redrawing the schematic with the parts I'll be using. I have not laid out a schematic since high school so I'm a little rusty.

Anyway, here's the power sections it stands now:

An externally hosted image should be here but it was not working when we last tested it.


I looked at the power supply software and it's way over my head. I also looked at the Hammond 5H and 10H chokes and figured I could put the 5H under the chassis. The 10H would require mounting up top and rearranging the furniture. So for now the 5H is spec-ed. If someone has the time and could look at my power circuit in the software that would be great. If not my other option is to just build it this way and take some measurements when it's up and kicking.

I added grounds to the speaker outs. Next I'll work on getting the rest of the circuit laid out in a new cohesive schematic.

Here is the updated component layout:
An externally hosted image should be here but it was not working when we last tested it.
 
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