Next Build Coming Up - 183 50w

[martin manning]

I would check with headphones, DMM, or scope. Also, place the choke and see what effect that has. It’s likely that your positioning shown in the photo will be confirmed, but why not check?

[Raoul Duke]

Thanks Martin, I always appreciate your feedback - and agree that it’s easy enough to confirm before getting too far underway; so why wouldn’t I? Always trying to do the best build possible and this technique always gives back an improvement/lesson learned.

I’ll post results.

Thanks again!

[GAStan]

I would check with headphones, DMM, or scope. Also, place the choke and see what effect that has. It’s likely that your positioning shown in the photo will be confirmed, but why not check?

^^This is what I'd do.^^

[Raoul Duke]

Well, this is a first for me. I set up for the headphone test and placed the PT in such a way that it made sense for the internal layout as well as for drilling new holes. Next, I positioned the choke in its usual place for an ODS. Then I placed the OT where it “looked right” and fed the AC.

Next was the usual moving the OT around and finding the quietest spot - which wasn’t too far from where I started. Still a bit of hum; but noticeably quieter. Then on a whim before un-doing everything, I turned the choke 90 degrees and all hum disappeared. I turned it back - hum came back; turned 90 degrees and all quiet (literally silent). Moved it back and forth, side to side and the quietest spot is 90 degrees from its normal ODS placement. Nice.

I guess the choke is acting as a shield of sorts in that very specific spot (?) even though its coils are oriented parallel to the PT (though forward of its axis) with the OT perpendicular to both.

IMG_0348.jpeg

Like I said - this test always yields a result and a lesson. Now to complete the chassis prep.

Thinking of some long reinforcement plates inside the chassis under the PT for added strength, but not sure if I need it. Big washers might be just fine. Not really making Swiss cheese out of the chassis - as it is, I’ll only need to drill 2 holes per transformer as I can utilize existing mounting holes for the rest - and these chassis are designed to handle 100w iron. Yeah, I think I just talked myself into washers, lol.

The transformers won’t be mounted yet; just want to make sure everything is figured out for when the time comes.

[martin manning]

The lump of high-permeability steel that is the choke and its orientation can most certainly distort the magnetic field produced by the PT. I would go with it.

[Raoul Duke]

Finished the chassis prep today and started putting stuff on it. I forgot how many screws and nuts one of these takes, lol. Really trying to think through everything first and enjoy the process.

IMG_0349.jpeg

I pre-wired the volume and treble pots along with the 3 switches. Seems to have worked out ok - much easier than doing them in the chassis.

Onward.

[sluckey]

I pre-wired the volume and treble pots along with the 3 switches. Seems to have worked out ok - much easier than doing them in the chassis.

On several of my builds I temporarily installed the jacks, switches, and pots on the outside of the chassis. This is especially handy when the chassis has a lip over the pots like your chassis. When wiring was completed, I just flipped the wired assembly to the inside. Everything fits perfectly.

I like watching your projects progress.

[Raoul Duke]

Great tip, thanks Steve! I’ve done that with jacks - but never thought to do the whole control layout; which seems pretty obvious now that you mention it

And thanks for the compliment - my projects progress because of everything I’ve learned here from the generous and knowledgeable folks who are always there when I get stuck. Can’t thank you guys enough.

I try to give back anywhere I can but being technically “limited” it’s difficult. I try to use my build threads to help other beginners see that if you invest the time to learn and take your time - you can do it too.

[sluckey]

That positive attitude is exactly why I always follow your builds. Don't ever stop!

[Raoul Duke]

Thanks again! Twenty-eight years in the military in a team-oriented career field taught me 3 things that go hand-in-hand:

1. Embrace the suck and always stay positive because…
2. It could ALWAYS be SO much worse
3. Nobody does it alone - appreciate your teammates

It really is true - we can’t control most of what life throws at us; but we can control how we deal with it and realize it can always be much worse; and give credit and thanks whenever and wherever you can.
I’ve learned to unconsciously apply this philosophy to nearly everything and it works for me…

Anyhoo; enough sounding like a fortune cookie and on to the last couple days’ progress:

Trying to do the “outside in - layered approach” as seems to be the best practice for “D” style amps. The long wire runs along the back of the chassis are so much easier when you don’t have a bunch of stuff in the way, lol.

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Trying to really enjoy every little detail that goes into one of these as I progress. If there’s an amp build that proves the old “how do you eat an elephant?” adage - it’s a Dumble clone for sure.

[Raoul Duke]

I always feel like I’ve accomplished something once I’ve conquered the foot switch wiring on the back panel, lol.
I’m liking this 20AWG solid core - but it takes some extra effort to get it straight. Still perfecting my technique.

IMG_0350.jpeg

[dbharris]

Looking great Marc! Are you planning to use mostly metal film resistors for the preamp board?

-Dan

[Raoul Duke]

Thank you!
No, the pre board is a mix of MF and CF. I recently got a huge lot (cheap of course) of CC in the little drawer/cabinets at a flea market and have a couple of them on the tube sockets. I don’t really try to replicate exactly as HAD did it; I don’t have the patience or $$ to track down NOS parts, lol.

Got some more done today. Got into the relay “vortex” and drove on through, lol. Moving right along…

IMG_0529.jpeg

[Raoul Duke]

So I just realized that when I did the PAB relay wiring that following the layout and schematic is different than the board plans. I wired it as such:

Com1: bass pot wiper
NC1: J/R lug 5
Com2: J/R lug 2
NC2: treble CCW
Two 22m in the usual places as are the 12v supply and switch lead.

What will be different than wiring per the board plans?

[martin manning]

I think it will function correctly, PAB will be ON when the relay is energized.