Dandy
Addicted Member
Yes, but there should not be a ground loop problem. And think of the benefits of having your chassis grounded.
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Yes, but there should not be a ground loop problem. And think of the benefits of having your chassis grounded.
I built a preamp with tone controls in one of those thin SS chassis. I burned up several bits on my drill press. Not fun! One even welded to the SS chassis.
Tubby Tube
New Member
Are the AC mains red wires on the right twisted enough (homogeneously) ? I thought I would get cute and ordered some 20 gauge solid core wire with nice insulation and a cotton covering to give that old time look (tubedepot.com), but it does not twist so well with the wire from the power transformer. Anyway, now have to go to work for a week before I can work on it again. Excited to complete the project.....
Tubby Tube
New Member
Yes, it would be. There is an extra wire from the power transformer that is yellow with a green trace that I ASSUME is a center tap that needs to be grounded. For what winding, I’ve no idea. It comes off the primary side.
Being new to tubes, why are there two seperate 6.3 volt windings used?
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Dandy
Addicted Member
A bit of light reading for you: http://www.valvewizard.co.uk/heater.html
According to your schematic, one of the filament windings has a centre tap and the main secondary winding has a centre tap too, the yellow green wire which goes to ground.
The filament windings with the centre tap need to power the heaters of preamp tubes (to avoid hum) and the one without a centre tap the power tubes. See Old Charlie's instruction sheet for what to ground.
According to your schematic, one of the filament windings has a centre tap and the main secondary winding has a centre tap too, the yellow green wire which goes to ground.
The filament windings with the centre tap need to power the heaters of preamp tubes (to avoid hum) and the one without a centre tap the power tubes. See Old Charlie's instruction sheet for what to ground.
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So, some delays over the summer.
Old Charlie's instructions differ from the kit and other postings.
Some parts are different, had to guess as what capacitor values are intended to go where. I
Schematic varies, the 6N8P contains two of the same circuit apparently, and the items are reversed between OC's documentation and that available elsewhere and in the kit. Confusing but not really a big deal
The schematic shows a 1M resistor between pin 1 and 2 [or 4 and 5] of 6n8p which is not in OC's write up. anyone know the purpose?
Most other changes so far seem minor
I am trying to make an updated copy of OC's write up with better english, but it is really hard to edit that PDF, literally chinese characters layered under english
Almost done building , just checking to see if I am going to blow anything up
Old Charlie's instructions differ from the kit and other postings.
Some parts are different, had to guess as what capacitor values are intended to go where. I
Schematic varies, the 6N8P contains two of the same circuit apparently, and the items are reversed between OC's documentation and that available elsewhere and in the kit. Confusing but not really a big deal
The schematic shows a 1M resistor between pin 1 and 2 [or 4 and 5] of 6n8p which is not in OC's write up. anyone know the purpose?
Most other changes so far seem minor
I am trying to make an updated copy of OC's write up with better english, but it is really hard to edit that PDF, literally chinese characters layered under english
Almost done building , just checking to see if I am going to blow anything up
So
drum roll
It works
Apparently all we did wrong was wire the volume control backwards
so it is wired per OC's diagram, which required changing some resistor values from the kit and looking at the pictures and making some assumptions about capacitor values from the pictures
I have done some work on OC's PDF, but it is really difficult without paying for PDF editing software
drum roll
It works
Apparently all we did wrong was wire the volume control backwards
so it is wired per OC's diagram, which required changing some resistor values from the kit and looking at the pictures and making some assumptions about capacitor values from the pictures
I have done some work on OC's PDF, but it is really difficult without paying for PDF editing software
somewhat updated pdf of oc's original
https://www.keepandshare.com/doc29/108325/6p3p-6n8p-diy-update-pdf-4-8-meg?da=y
https://www.keepandshare.com/doc29/108325/6p3p-6n8p-diy-update-pdf-4-8-meg?da=y
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Tubby Tube
New Member
So, just getting around to putting some more effort into this. You skipped the 1.5 meg between the driver and output valves? I guess I will wire it as the schematic is shown and if it goes egg shaped, clip it out of there. As you noted, OC does not have the 1.5meg in the pictures...
So I am just getting around to finishing this project. Or re-starting it. At any rate, the schematic that came with the kit has the 1.5 meg between the driver and output valves. My plan is to build it as pictured, and if it goes egg shaped clip it out of there. Anyone know what the 1.5 meg resistor is for?
Tubby Tube
New Member
Welp. Fired it up, and the sound is very weak and slightly distorted both channels. Probably enough to drive a headphone. I wonder, the output tubes are 6l6g instead of the specified 6p3p. Could this be why? Also instead of the6n8p tubes for the driver, I got 6H8C. The voltages are all on the high side, expected given my 120 volt mains. The one voltage that is low is pin 6 of my driver tube, schematic shows 1.1v, it is about 270mv. Help me Obi Wan! 
My first tube amp.....
My first tube amp.....Tubby Tube
New Member
Buellor?
Tubby Tube
New Member
EDIT: Assembly error. Works great with the schematic as shown on the first page. Quiet too.
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Tubby Tube
New Member
A couple of tips for anyone doing this build. The volume pot goes on the side with the printed square outline. Put the wooden ends on before you build it!
Tubby Tube
New Member
Yes, post 13. Amp is running great!
