2nd Gen Build Started (that didn’t take long…)

[martin manning]

No just stand it up on three legs.

[Raoul Duke]

Exactly what I did. The board looks great and everything fit pretty well based on your drawing.
Real tight over there with the transformer though. I may have to drill new holes for the board slightly higher. An 1/8” might as well be a foot in that corner, lol.

1000uf caps don’t seem to come in small sizes and I’m thinking of shortening the power transformer studs. The regulator barely clears it and I’d need to install the PT first,make the lower wire connections next, then try and fish the screws and nuts to mount the board. Is that typical of 2nd gens in that area of the chassis?

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[martin manning]

Looks very tight indeed. Lower voltage caps will be smaller. 12.5 mm D by 30 mm L at 25V seems to be a common size. Laying the reg down flat might be a better option.

[Raoul Duke]

Understood.
Can I get away with 25v there? Not needing 50v definitely gives more options.

[martin manning]

For sure. I don't think you could get more than 20V on the first two (10V each), and the third one is at 12V, of course.

[Raoul Duke]

Got a little done over the past couple of days.
I’ll revisit the small boards in a couple of days when the new, smaller caps come in for the relay board. Actually, every one of the small boards is waiting for something.

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Got the woodwork on the head cab done - just need to decide on a suede/grill color combo…

[ijedouglas]

Got a little done over the past couple of days.
I’ll revisit the small boards in a couple of days when the new, smaller caps come in for the relay board. Actually, every one of the small boards is waiting for something.
IMG_0181.jpeg
IMG_0180.jpeg
Got the woodwork on the head cab done - just need to decide on a suede/grill color combo…

Looks great!

Something I've found that makes life a lot easier is to wire in as much of your tubes wires as possible before doing any resistors. Screen, plates, grid and cathode wires can all be connected after the socket is installed and will be easier without having to feed them under resistors etc.

[Raoul Duke]

Great tip Ian, thanks!

Compared to my first build - this is making a lot more sense to me; but any tips from the expert builders like yourself are always appreciated!

I was reading an old thread where Colossal talked about the psychology involved with seeing your first build through to a satisfactory completion and how it conditions your response to the next build. I think he used a basketball analogy? Anyhoo, I can now relate to that

Really enjoying this new hobby!

[Raoul Duke]

Martin,
“Ground the primary CT, which in this case (OT sitting on the bench) means connecting it to the secondary common.
Apply low voltage AC across the secondary.
Measure voltage from each plate lead to the secondary hot lead.”

I’m thinking that the ground from the low voltage goes to the CT/secondary common and I’m “back feeding” the voltage through one of the secondary taps? Then measuring one probe on a plate lead, one probe to the ground connection?

Thought I understood, but now that I’m getting to it I’m scratching my head…

[martin manning]

Connecting the CT to secondary common just establishes the ground reference for the primary. One side is then in phase with the secondary, and the other side is out of phase. The voltage measurement tells you which is which.

[Raoul Duke]

I understand the principle but am unsure of the actual “hook-up” of the test. Is my previous post close?

I just don’t want to fry anything (including myself, lol).

In other words, am I connecting the wall wart power directly to one of the taps with the center ground to the ground reference, then measuring as stated in my post?

Thanks again and apologies if this is like explaining basic stuff to a 5 year old, lol. Just trying to get it right and understand what I’m doing.

[martin manning]

I’m thinking that the ground from the low voltage goes to the CT/secondary common and I’m “back feeding” the voltage through one of the secondary taps? Then measuring one probe on a plate lead, one probe to the ground connection?

Almost... The connections are right, but the voltage measurement is from each plate lead to secondary hot, not ground. Exactly the same as you did on your 102. If you use the highest impedance secondary tap you will minimize the secondary current and the voltage that appears on the primary. I can't recall what voltage your wall wart was, but you can run the low voltage AC through your load resistor (put it in series with the OT secondary) to further limit the current.

[Raoul Duke]

Thanks Martin!
I’ve got a 9v wall wart that I’ve adapted a center ground insert for, so that’s what I’m going to use.

This OPT has 4, 8, and 16; so I’ll feed voltage to the 16 and measure between the 8 and each plate lead separately.

Always appreciate the guidance! Thank you!

[martin manning]

I’ve got a 9v wall wart that I’ve adapted a center ground insert for, so that’s what I’m going to use.

This a 9VAC wall wart, right?

[Raoul Duke]

Yes.