Elevated Heaters From A PT With No CT, WTF ?

  • Thread starter Thread starter Ben Waylin
  • Start date Start date
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The top connects to the 10k as normal and the circuit goes on from there.

Update your schematic using my drawing and we will confirm it’s correct or not
 
Post #12 but add the 220k like #15. You need the 220k to the new node AND the 100k to ground. And the 100k to ground is in parallel with the cap, just like #12. But then instead of connecting the 220k to point B, connect it to point A.
 
Here's a pic of my Superlead build. Look at the blue 100u+100u cap can on bottom right. One of the 100u (the top one) is for the PI and then there is a 330k to the other 100u with a 82k resistor in parallel to the ground lug. I did not use flameproof as @glpg80 suggests, I learned something in this thread and hope to fix that someday.

EDIT: Looks like I changed the 330k to 390k or maybe that pic is when I first built it. I remember settling on 58vdc when I ran it at 120vac power.

There is a black wire connected to the ground lug that is hard to see, it routes that ground to a better ground point.

20210613_105706.jpg
 
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SpiderWars said:
Bingo. Then measure and see what you get, you might have to adjust but that should be ballpark.
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Awesome ! Thanks my dudes !

So I learn something here... why tap off A rather than B ?

And by "adjust" you mean the value of the 220KΩ resistor, right ? Target would be +/- 45V
 
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PLX said:
Awesome ! Thanks my dudes !

So I learn something here... why tap off A rather than B ?

And by "adjust" you mean the value of the 220KΩ resistor, right ? Target would be +/- 45V
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30-60V per Merlin works fine. You have some play
That circuit as is should put you right around 40V
 
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T Wilcox said:
30-50V per Merlin works fine. You have some play
That circuit as is should put you right around 40V
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Excellent !

I'm going to lose about 32mA thru the two 100Ω resistors.. right ?

So it would be better to use the 200V tap instead of the 180V ?

qkIPfH1.jpg
 
PLX said:
Excellent !

I'm going to lose about 32mA thru the two 100Ω resistors.. right ?

So it would be better to use the 200V tap instead of the 180V ?

qkIPfH1.jpg
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Not quite following.. the 32mA is from the 6.3V with 2A on tap so whichever Ht sec you choose shouldnt matter but I'd probably use the 200 since the snork drawing shows 250V.
At 150mA per 12AX7 and that 32mA you are still using less than 500mA
 
T Wilcox said:
Not quite following.. the 32mA is from the 6.3V with 2A on tap so whichever Ht sec you choose shouldnt matter but I'd probably use the 200 since the snork drawing shows 250V.
At 150mA per 12AX7 and that 32mA you are still using less than 500mA
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Awesome !

Thanks guys !
 
T Wilcox said:
Not quite following.. the 32mA is from the 6.3V with 2A on tap so whichever Ht sec you choose shouldnt matter but I'd probably use the 200 since the snork drawing shows 250V.
At 150mA per 12AX7 and that 32mA you are still using less than 500mA
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Hey Todd, can you PM here yet ?

What's that 330pF Wima cap across the mid pot ? I can tell if it's the mid pot, but I think it is.

Does not show up on the schematic.
 
PLX said:
Hey Todd, can you PM here yet ?

What's that 330pF Wima cap across the mid pot ? I can tell if it's the mid pot, but I think it is.

Does not show up on the schematic.
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No , Im only at 36 messages here, 14 to go LOL
Im at work replying from my phone so cant see the layout to answer your question
 
Include the fuses in your schematic. I’m dead nuts serious about this when doing tricks like floating AC on DC from the same source with something like vacuum tubes especially with todays quality.
 
PLX said:
Hey Todd, can you PM here yet ?

What's that 330pF Wima cap across the mid pot ? I can tell if it's the mid pot, but I think it is.

Does not show up on the schematic.
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It looks like the cap across the mid pot is .0047uF and is a low pass that is shunting some signal to ground.
Post #14 of this thread (hope its okay to link threads from other forums) https://www.marshallforum.com/threads/bright-cap-jcm800-4104.93525/
shows the schem for the 4010 JCM800 combo which has same cap across mid pot. The assumption is it was to compensate the tone difference between an open back combo and the jcm800 head.
This thread: http://www.groomednoodlers.com/forum/viewtopic.php?f=20&t=2636 confirms that the original Snorkler was a modded 4010 combo so this was all Marshall
 
glpg80 said:
Include the fuses in your schematic. I’m dead nuts serious about this when doing tricks like floating AC on DC from the same source with something like vacuum tubes especially with todays quality.
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You're right, sorry.

I was so focused on working this out in my mind, I forgot to show the fusible links.
 
T Wilcox said:
It looks like the cap across the mid pot is .0047uF and is a low pass that is shunting some signal to ground.
Post #14 of this thread (hope its okay to link threads from other forums) https://www.marshallforum.com/threads/bright-cap-jcm800-4104.93525/
shows the schem for the 4010 JCM800 combo which has same cap across mid pot. The assumption is it was to compensate the tone difference between an open back combo and the jcm800 head.
This thread: http://www.groomednoodlers.com/forum/viewtopic.php?f=20&t=2636 confirms that the original Snorkler was a modded 4010 combo so this was all Marshall
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Ok, that's what I was assuming was going on there with that cap.

Thanks again !
 
PLX said:
You're right, sorry.

I was so focused on working this out in my mind, I forgot to show the fusible links.
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Yes we get ahead of ourselves and the reason I mentioned it again after the bold text prior was that if you don’t put it in the schematic, you’ll likely also forget it later on during assembly. Not trying to be an ass, just trying to make sure you’re building something safe.
 
glpg80 said:
Yes we get ahead of ourselves and the reason I mentioned it again after the bold text prior was that if you don’t put it in the schematic, you’ll likely also forget it later on during assembly. Not trying to be an ass, just trying to make sure you’re building something safe.
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I'm building in an old combo amp chassis. The mains wiring, mains fuse, pilot light are all already in place.

The existing mains fuse is 1A 125V.. should I use a lower rating there ?

On the secondary I'd need to add another fuse holder. I'm thinking a 500mA fast-acting for that one ?
 
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