Amp build for a first time builder?

[yoyohomieg5432]

here are the pictures of the board up to this point. everything should be done/correct except for the components i'm missing.

today i did some more soldering with some of the potentiometers and i was able to get screws and attach the tube sockets. i can take a picture of what i have of the chassis tomorrow possibly.

[martin manning]

OK it's starting to look like an amp! Now that you have the tube sockets mounted, you can mount the PT and do the AC wiring on the primary and the filaments and HT wiring on the secondary. At that point you could power it up with all of the tubes in and check the filament circuits and voltages. Some people (including me) like to test things in stages rather than wire the whole thing up and hope that it's all good. If you go there, you'll have high voltage present on the rectifier socket, and you should tape-off the bias tap and filament center tap leads to prevent a short.

I've revised the build guide (some added text and a little reorganization) and layout document (made a bottom view of the board, and put more detail in the eyelet board wiring sketch). I also realized that I had the bias trimmer rotation reversed (the voltage becomes more negative with clockwise rotation), so I fixed that. These doc's are back on pg. 9: https://tubeamparchive.com/viewtopic.ph ... 321#226321

[xtian]

Nice docs, Martin! No grid resistors on power tubes?

[martin manning]

Thanks! This is still old-school in some ways, at least to start out. If it won't behave, those can be added later.

[yoyohomieg5432]

the mouser order came in today, I should be able to finish up the board now.

I'm going to be in Ohio visiting family for a few days so I won't be able to work on the amp for a little while.

[yoyohomieg5432]

just getting back home.. i completed the board. i'll post pics possibly tonight of everything i have so far.

what is the 47pF 500V capacitor for?

[martin manning]

I see I left that cap off of my board layout, but it's shown on the Fender drawing. Since it's across the output of the phase inverter, it is allowing high frequency content in the two phases to cancel, presumably to prevent oscillation.

[yoyohomieg5432]

i attached a picture of where i think the 47pF should go. I just wanted to confirm it before I solder it in.

[martin manning]

Yes, you've got it. You can see it on pg. 1, which has the old Fender layout, and also on the schematic, on pg. 3. Layout on pg. 9 (this thread) now updated.

[yoyohomieg5432]

i've got a few more questions

1) am i doing anything with the ground switch? on the layout it looks like its wired but i thought this wasn't needed anymore?

2) on your manual you talk about jumpers. what is this?

3) on the 5881 tubes, the 1 ohm resistors are going to the star grounds right? I haven't drilled any holes for these yet. should these all be secured with locking washers as well?

4) could you explain the star grounds? one side has a star shaped opening and the other side has 2 small holes. which side is screwed down and which side do i wire to? any idea on what size screws i need?

[yoyohomieg5432]

one more:

the power/standby switches i have came with 3 things: a washer, a nut, and another smaller nut that is circular instead of hexagonal with edges like a quarter. when i was installing the switches, if i stick the switch all the way through there is a lot of thread remaining. do i use the nut on the inside of the chassis to position the switch so that all of the thread isn't sticking out?\

from the bassman pics Martin emailed me it kind of looks like all 3 components are on the outside, but if i do that, as i said, a lot of the thread of the switch sticks out.

also, what side should the washer be on?

[martin manning]

i've got a few more questions

1) am i doing anything with the ground switch? on the layout it looks like its wired but i thought this wasn't needed anymore?
>>>The ground switch is only being used as a place to anchor the power cable hot (black) and neutral (white) wires and one of the power transformer primary leads. It's an SPDT switch, and you will just use the two "throw" terminals (and not the common "pole") so that the AC power leads will not short together in either switch position.

2) on your manual you talk about jumpers. what is this?
>>>"Jumper" is a general term for a wire connecting two points. It could be two eyelets on the board or two terminals on a pot or switch or socket.

3) on the 5881 tubes, the 1 ohm resistors are going to the star grounds right? I haven't drilled any holes for these yet. should these all be secured with locking washers as well?
>>>Those are properly called solder lugs, but they can be used to form a star ground (a common point where several ground connections are made). The ones I spec'ed are sized for a #6 screw. The ones near the tube sockets are placed on the socket mounting screws, and since they have a locking feature they will double as a lock washer there, and at the two other places where they are used (the B+1 ground and the earth ground for the power cable).
4) could you explain the star grounds? one side has a star shaped opening and the other side has 2 small holes. which side is screwed down and which side do i wire to? any idea on what size screws i need?
>>>Screw size is #6, the two small holes are for soldering wires to.

[yoyohomieg5432]

i'm working on adding more of the wires that will go from the pots to the board. i'm looking at the bassman pictures Martin sent me and i don't see any of that wiring. did they route all of those wires down the chassis so they aren't just kind of floating out on top of the board?

[martin manning]

one more:

the power/standby switches i have came with 3 things: a washer, a nut, and another smaller nut that is circular instead of hexagonal with edges like a quarter. when i was installing the switches, if i stick the switch all the way through there is a lot of thread remaining. do i use the nut on the inside of the chassis to position the switch so that all of the thread isn't sticking out?\

>>>Exactly.

from the bassman pics Martin emailed me it kind of looks like all 3 components are on the outside, but if i do that, as i said, a lot of the thread of the switch sticks out.

also, what side should the washer be on?

>>>I'd put the hex nut on the switch first, then the washer, put the switch through the chassis, and then put the finish nut (with the serrated edge) on the outside. Adjust the nuts so that there is only one or two threads showing past the finish nut on the outside, and then tighten the hex nut on the inside while holding the switch to keep it from rotating.

[martin manning]

i'm working on adding more of the wires that will go from the pots to the board. i'm looking at the bassman pictures Martin sent me and i don't see any of that wiring. did they route all of those wires down the chassis so they aren't just kind of floating out on top of the board?

Yes, they are run on/along the chassis surface.