HLMP6000 bias question

[Natural Sound]

I'm in the final stages of preparing my Crack chassis plate to use a 6SN7 as the voltage amplifier. As you know the octal socket does not have the center tab used on the miniature socket for grounding the LED's. How critical is it to have the LED's close to the socket pins? Is it OK to install an additional terminal strip to mount the LED's and then use wire to go to the sockets? I happen to have some three pin center ground terminal strips in my parts bin that should do the job nicely. I ask because other Bottlehead kits I have built stress that the grid stopper resistors be mounted with the resistor body close to the tube socket pin. I was wondering if the HLMP6000 mounting was similar. For what its worth I plan on mounting the new terminal strip as close as possible to the socket. I'm thinking it should be fine.

[Paul Birkeland]

You can certainly use the extra terminal stip, that shouldn't be that big of a deal.  Just be sure not to use the 2nd center ground terminal on the terminal strip you add. 

There is another option you could try.  In the buildout, I call for ground to be run to the heater winding at the power transformer.  If you omit that wire, then add it from the star ground point to the octal socket (either heater pin will work for this), you could run the LED's from that tube socket terminal to each of the cathodes. 

I don't see any huge concerns with making that change in terms of noise, let me know how it goes. 

[Natural Sound]

Thanks Paul. Here are a couple of photos showing what I had in mind. I still need to drill a hole for the terminal block that terminates 1-5. I'll have to flip the TB around to achieve the proper spacing for the 10W resistors. Here is a photo of the 6SN7 cathode pins (A3 and A6) going to the added terminal strip. I'll run some bare solid wire from terminal 3 over and tie the two new pins together using the lower holes. I'll keep the heater ground option in mind if this doesn't work out for some reason.

BTW - After I took these photos I decided to flip the socket 180 degrees. The new terminal strip will be on the headphone jack side. That way pins A7 and A8 will be in a better position to accept the heater wiring.


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Looking into the future I'll probably add the speedball upgrade. The installation of the octal socket will interfere with the normal installation of the upgrade. You did warn me of this in another thread but I wanted to use the existing screw holes. Is there any reason why I couldn't mount the board that is closest to the transformer on the screw thats closest to the transformer? In other words, mount the PC board over the 6080 socket. Would this cause a heat issue because the board is not over the slots in the chassis plate? If you don't think this will work then I'll figure out another way to mount the boards. I want to plan as much as I can before I start painting.

BTW I don't have the speedball boards yet but have a good idea of how they install from the pictures on the website. This part of the modification might be a bit challenging.

[Jim R.]

I'm guessing that you'll probably have to rotate the large c4s board 90 degrees and drill a couple new holes for the stadoffs, but I'd do whatever it takes tokeep it under the vent holes.  Also, with an octal in front, you might have to install the c4s boards on edge so they clear the volume pot and headphone jack.

Nice experiment though, and I hope you'll let us know how it all turns out and sounds.

BTW, I'm building mine with a filament config switch so I can also use 6cg7/6fq7 for something close to that 6sn7 sound.

-- Jim

[Paul Birkeland]

I think you could get away with some 2" standoffs for the driver boards and probably be OK.

[Dyna Saur]

Another simple approach for connecting the HLMP6000s, is to use an insulated standoff (base threaded to match your socket mounting screws) and use it as the common (cathode) grounding point for the 2 LEDs. 

This can be mounted in conjunction with the existing terminal strip, and it would physically  "block" the center (chassis grounded) terminal, which may or not be used in the final circuit.   

Just a thought - I've used these insulated standoffs for years, nay, decades in my various designs and builds.

HTH

/ed B

[2wo]

I love those insulated standoffs. Often, I can point to point my whole circuit with the socket screws and maybe 1 or 2  more, on a transformer mounting screw or something