Schematic to layout help

[dunner84]

A few years ago, I rescued a 1950s Masco ME 18 from a free bin at a recycling store. It was trashed, and in terrible shape, but I took it and restored it anyways. It turns out to be quite a nice harp amp, so I gave it to my father in law because he is a harp master.

I recently picked up the harmonica myself, and I really dig the tone of that amp, so I decided I should build myself one.

The originals are PTP rats nests, and I have no desire to build it that way. I have built several tube amps now including a few from scratch, but this is my first attempt at taking a schematic to a turret style layout. I would love some feedback on my first attempt. The digital schematic I have is very poor quality, so I apologize. Some of the component values are hard to make out; however, I have a very nice big paper copy filed away somewhere from my restoration of the original, so don't get too hung up on the values, as much as the overall layout of things going to where they are supposed to go. I am also a little unsure about how I did the input jacks, I did those from memory. Anyways, I appreciate your keen, knowledgeable eyes!!

[tubeswell]

still more connections to come I see.


Are you going to elevate the heater winding to the 6L6 cathodes?


You could run the 2 x 270k plate resistors straight to the 100k-12k supply resistor junction on the board (if the eyelet/turret alignment was nudged over a bit). If you have the filter caps on this board (instead of on another board), you could run the inverter supply node cap +ve pole to this junction as well (and have the -ve pole going straight to the ground return wire). Same with the pre-amp filter cap (going to the 2M7/330k/100k junction). Then you only have the reservoir cap-5k-screen node cap (which could go next to the 6L6 Rk||Ck). Then you wouldn't need other wires going to another filter cap board. YMMV


(Edited after Franco posted the hi def schematic)

[kagliostro]

Is this more readable ?



Franco

[dunner84]

Thanks for the input! Yes, I would be elevating the heaters as per the schematic. I did not include that in the layout. It was also brought to my attention that the second input, when not used, would bleed signal to ground. I thought about possibly replacing the 1/4 jack with a mono-rca jack.

[shooter]

I thought about possibly replacing

The folks here helped me and came up with this type input, works great.
fwiw

[dunner84]

That's exactly what I would want to do with the second input. Can it be used simultaneously with the other input?

[DummyLoad]

Can it be used simultaneously with the other input?

yes.

--pete

[DummyLoad]

suggestion: put some distance between the power switch/light and the controls. 


--pete

[DummyLoad]

see attached - edits in green of some of the obvious misses, but there may be more. hopefully others will catch what i missed. some of the edits, namely grounding, are just suggestions for quieter operation.


--pete

[dunner84]

I made an adjustment to the second input. I circled it on the schematic. Let me know what you think.  I will make an update to the layout tomorrow when I get home from work. I tried doing it in ms paint, and became incredibly frustrated

Thanks for all the help so far!

[kagliostro]

Using GIMP is a very quick job (a pair of minutes, including the time to download the files and start programs)



Franco

[dunner84]

Thank you! I am stuck at work for 24 hours, and the computers here are very limited, and we can't add software to them.. They can barely surf the internet with this old IE explorer nonsense...

[dunner84]

I had a chance to make some changes, and I also double checked/corrected the values against my nice clear paper copy of the schematic. If all looks good, I will be starting this build in a new thread very soon!
     

@ Dummyload, just wondering why you tied pin 1 of the preamp tubes to ground?

[tubeswell]

Looking better. Worth keeping the ground return points as close as possible to the ground return of the filter cap from whence the gain stage for that part of the circuit draws its power supply. (i.e move that 1M resistor ground leg closer to the PI filter cap ground by making a 'local star' etc. Read the attached article by Merlin Blencowe on grounding) . The ground returns for the pots should follow the same logic (i.e. don't have 2 separate ground return rails. Run the ground returns for the vol pot and tone controls to the ground buss for the pre-amp filter cap).


The reservoir and screen caps could go on the main board on the other side of the output tube Rk||Ck (next to the PI components).

[sluckey]

@ Dummyload, just wondering why you tied pin 1 of the preamp tubes to ground?

Pin 1 is used as a shield. The old metal tubes had the metal can connected to pin 1. I don't know if anything is connected to pin 1 in the glass tubes. If you have some look closely. If there is any metal in the tube base check for continuity between that metal and pin 1. Let us know what you find.

[DummyLoad]

the G (glass envelope) suffix tubes do not have a connection to pin1 - guess that it was assumed that you'd use a tube shield if needed with glass tube.


--pete