Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Buck112 on November 20, 2018, 10:52:24 pm
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Hey all, first time poster, here.
I am about to start piecing together a Ricktone Tremodrive circuit and was hoping someone may have answers for some admittedly novice questions, so here goes.
1: The power for the circuit comes from 2 120v to 12v PTs for the 12v heaters, and then back to 120 and the voltage doubler to the plates. Both PTs I am using are center tapped. Should I ground the center taps together, separately, or not at all (soldered together to an unused lug)? I have seen all kinds of contradictory info online about this topic, and have no clue (and in Rick's wiring diagram one center tap is grounded and the other PT has no center tap).
2: It seems to my inexperienced eyes that if you followed the grounding scheme in the wiring diagram, you would be creating unwanted ground loops, or at least be doing some redundant soldering; it appears to me that a lug of each terminal strip is used as a sort of star ground, but both of these lugs are tied together and sent back to the power sections ground, AND each lug where the ground come together (in a star) is already grounded to the chasis via the screw connecting the strip to the chasis. Am I wrong, is the diagram wrong? Educate me, please!
3: One last unrelated item. I an adding 2 additional 120v neon bulbs for overdrive and tremolo engaged indicators. They will be wired in parallel with the power indicator. Amplified Parts says you need a resistor in series when using one of these bulbs. I get that, my question is, will one resistor before the power indicator take care of the following two bulbs? Seems to me it should, but i would rather not risk anything.
This will be my first scratch build, as well as my first time building a high voltage circuit, any additional information or experience anyone may have with this circuit would be very much appreciated! Thanks for reading, be well, cheers!
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1. It's only necessary to ground one of the 12V center taps. Makes no difference which one.
2. The ground lugs of those terminal strips are hard wired together to ensure a good ground connection. They don't rely on a mechanical connection which may loosen and provide a poor connection. That was common practice back in the day. Don't worry about it. Look at this pic of an example of a high quality amp with the ground lugs connected together...
http://sluckeyamps.com/hammond_2/big_guts.jpg
3. You need a resistor for each neon bulb. Two bulbs need two resistors. However, if you are using 120v rated neons that are in a chassis mount indicator assembly similar to the one shown on your drawing, it's likely that a resistor is included inside the assembly.