High Voltage Hijinks

I received my package!

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Updated PCB with less risk of arcing on some connections and more space between power tubes.

The chassis from JLC is great. I did it with Fusion 3D and everything is on point. It feels very solid (2mm Alu) and the powder coating is great. I just have to grind a few spots as they don’t support masking yet and I need some grounding points.

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I will do the headshell myself and solder it all together asap. Still waiting for the replacement for the power transformer end bells and the vynil faceplate…
 
I just finished rebuilding my Simms Watts. Original PCB replaced with sheet metal, made my own ugly layout with improvisation and with bad circuit positioning which I noticed too late. I’m bit ashamed showing it as it’s a mess between strip and p2p layout. Everything looked ok when comparing to schematic and beeping gnd connections with DMM.

So tomorrow is time for assembling a light bulb limiter and looking how I might have succeeded or failed. If able to fire it up, gonna add heat resistant silicone for wire and component support. Also some zip ties are needed!

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Oh and it’s star gnd now apart first two preamp stages which are connected to bus leading to the one true ground spot.

Edit. Just noticed one resistor lead unclipped from the picture. Good catch!
 
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JohnnyCreepy said:
I just finished rebuilding my Simms Watts. Original PCB replaced with sheet metal, made my own ugly layout with improvisation and with bad circuit positioning which I noticed too late. I’m bit ashamed showing it as it’s a mess between strip and p2p layout. Everything looked ok when comparing to schematic and beeping gnd connections with DMM.

So tomorrow is time for assembling a light bulb limiter and looking how I might have succeeded or failed. If able to fire it up, gonna add heat resistant silicone for wire and component support. Also some zip ties are needed!

View attachment 108019

Oh and it’s star gnd now apart first two preamp stages which are connected to bus leading to the one true ground spot.

Edit. Just noticed one resistor lead unclipped from the picture. Good catch!
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God job! And Godspeed if you have to troubleshoot it ;)
 
Okay, test through 100W light bulb limiter and without tubes, bulb went bright for a second and went quickly dim. Removed limiter and went powering without tubes. No fuses blew, good. Then voltage readings and all good, but all were naturally high without any load. Filaments had 6.7vac and so on. But there’s always but, butt.

With tubes I went. Bias pot maxed (-59 VDC), GNFB off and DMM connected to the first filter cap (~500VDC) and in few seconds increasing hum started from speaker. Quickly turned off. All pots were at min. Gave another go, but now GNFB on and same problem occured. Again didn’t have guts nor time to check output tubes 10ohm resistor readings about current draw.

Suspects:
-10ohm resistors are bad
-I’ve got bad GND connection somewhere
-bias isn’t cold enough
-output tube grids are picking oscillation

Gonna look into troubleshooting tomorrow… Guess it’s no god luck nor good speed? But neverthless mankind is unkind men, long live troublesheet. :D
 
Is it a hum or more a squeal? Might be worth trying to swap OPT wires.

Otherwise your wiring could easily be made way tidier really. It seems all the wires in and out of the PT are not twisted, and you have lone cables (I suppose signal cables) laying at 45° on top of heater wire etc.

Did you balance your heaters to ground too?
 
If the global NF wasn’t hooked up while it was first happening it won’t be the OT primary wires. I like to hook up the GNF last after everything else is working.

Is the OT itself toast?
 
Asdrael said:
Is it a hum or more a squeal? Might be worth trying to swap OPT wires.

Otherwise your wiring could easily be made way tidier really. It seems all the wires in and out of the PT are not twisted, and you have lone cables (I suppose signal cables) laying at 45° on top of heater wire etc.

Did you balance your heaters to ground too?
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Sounds like tube bias runaway like tubes draw too much current. OPT wire shouldn’t matter if NFB isn’t connected. Dunno if PT side wiring shouldn’t matter that much ’cos there’s distance to signal wires. Output grids are my suspect as I made mistake with connecting grid resistors to bus shared between each pairs via pin 6. Gonna fix that and add some shielded wiring. Heaters are balanced from HTR center tap, but connector was crimped instead soldering.
Hal Harvey said:
Is the OT itself toast?
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OT was fine last time I was playing twi weeks ago. Without tubes there was normal pops from speaker when taking tube pin readings.

Don’t have any energy to look into amp today, better to get into it on holidays.
 
No solution yet, but a breakthrough on where to look. Removed pre tubes and no screech/current sound. PI back in and all good. Biased el34 from 3% to 43% and it was considering max dis.limit as 22w instead 25w. Okay, then tried V2 back in, ringing sound back in running over current sounding hummie. V2 out and V1+other tubes in, no problem.

So now main suspect is V2 circuit, it is preamp triode halves with a gain pot between. Maybe that pot, bright cap (new 500p silver mica) or some other part around V2 is just bad. Ysterday changed bypass cap from V2b to PI input with no luck. 500p cap is first in order when I get back to the bat cave.
 
Finally started my build.

I was sitting on everything except the replacement end bells for the PT so I thought... let's dodge the familly in law and hide in the workshop.

(I also have to tolex the headshell but the woodworking is done on it).

Sadly forgot to take pictures of the "clean" PCBs with the components and without the wiring, but at least you know where I am now. Populating the board was really easy, I like my libraries in Fusion now.

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But look at that mess around the tone stack... I switched the order on the front plate compared to the PCB so yeah. Those shielded triple cables are hell. Very rigid. Don't think I will use them again in such a small form factor. I have a few switches off board (channel switch, bright switch for the clean and "shape" for the OD) so all is tidy now. If you are really patient you can take everything off without desoldering anything, just have to unscrew the pots and the switches, and unplug the Fastons.

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Electronic wide, I am obviously missing the transformers, and the LEDs. I also have to do the FX loop switched jacks thingie.

Bonus shots: front and back! The vynil arrived ;)

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Bought some stuff for the grid that will go to the laser cutter... Let's hope it turns out as good as it is in my mind ;)
 
Clean layout & build :D
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Almost all wires try to cross somewhere near 90 degree angle, fixed some cold solder joints, removed unnecessary shielded wiring, replaced with normal and added heater CT lift. I got almost all hum away, but not all. I’d say it belongs to the design because of V1b tonestack and second gain pot routing between V2a+b.

Added some heat resistant silicone for wire and component support. Gonna call it done.

Next please…
 
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JohnnyCreepy said:
Clean layout & build :D
View attachment 108761

Almost all wires try to cross somewhere near 90 degree angle, fixed some old solders, removed unnecessary shielded wiring with normal and added heater CT lift. I got almost all hum away, but I’d say it belongs to the design because of V1b tonestack and second gain pot routing between V2a+b.

Added some heat resistant silicone for wire and component support. Gonna call it done.

Next please…
Click to expand...

Awesome!!!!

I need to get back on the wagon, I have not picked my soldering iron up much lately.
 
JohnnyCreepy said:
Clean layout & build :D
View attachment 108761

Almost all wires try to cross somewhere near 90 degree angle, fixed some cold solder joints, removed unnecessary shielded wiring, replaced with normal and added heater CT lift. I got almost all hum away, but not all. I’d say it belongs to the design because of V1b tonestack and second gain pot routing between V2a+b.

Added some heat resistant silicone for wire and component support. Gonna call it done.

Next please…
Click to expand...
Looking good! One last and overlooked source of hum are the small ground loops you might have been the ground of the pot and the actual pot itself when it’s on a bare chassis. But if you are happy with it leave as is!
 
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