First D-style (102) build opinions solicited & build thread:

[martin manning]

I would move the white NFB wire to the other side of the blue plate lead to its left, to get it away from the green grid lead. That lead can be problematic. Other than that it looks ok. If you run heater voltage over to the other power tube and the PI some further testing can be done.

[Raoul Duke]

Thanks Tony, great advice for sure!

The details of lead dress and deliberately planning placement of every component or wire fascinate me. In my previous life, one of the assignments I enjoyed most was running a section that maintained weapons for a company-sized unit. The subtleties and details of making 300+ weapons systems work reliably and at peak performance were very similar to what you guys do with amps. The differences between “good enough” and an “extension of one’s physical-self” are small - but numerous and very important. This new hobby of mine seems to work the same way, lol.

I often compare your 102 and 124 layouts just to make sure I’m understanding things given my lack of formal/technical electronics knowledge. I also look through Rob Livesey’s sight for reference as well - just to see the practical application of the drawings. When I interpret something and see it verified in all three places; I know I’ve figured it out correctly.

The volume of knowledge you and Martin have documented in drawings and plans for all to use is really impressive. Other experts contribute regularly and they are appreciated as well - certainly by me and many others I’m sure. Really is a great “community” here at TAG thanks to the generous spirit of the many folks who share their knowledge with goobers like me, lol.

Anyhoo, enough of my rambling…

[Raoul Duke]

I would move the white NFB wire to the other side of the blue plate lead to its left, to get it away from the green grid lead. That lead can be problematic. Other than that it looks ok. If you run heater voltage over to the other power tube and the PI some further testing can be done.

Understood, thanks for looking at it. I was concerned that it (white wire) might be an outlying variable. The way I see it, I can either crank it hard left, then follow the OT leads to the impedance switch; or pick it up and “fly” it over. Of course there’s probably another way (or four) I haven’t figured out yet, lol.

Which sounds best Martin?

Also for clarification regarding the power amp testing - should I run the heaters across the power tubes to the PI?

[talbany]

The volume of knowledge you and Martin have documented in drawings and plans for all to use is really impressive. Other experts contribute regularly and they are appreciated as well - certainly by me and many others I’m sure. Really is a great “community” here at TAG thanks to the generous spirit of the many folks who share their knowledge with goobers like me, lol.

Correct it was a total group effort and was my honor to take part in helping others discover and build their own Dumble ODS Style amps.

Good Luck and enjoy that wonderful build you have there
Your Welcome!

Tony

[martin manning]

The way I see it, I can either crank it hard left, then follow the OT leads to the impedance switch; or pick it up and “fly” it over...

Referring to your third photo above, I would remove and reroute the blue wire going to PI pin 1 underneath the white NFB wire, and then shove the white wire over to the left, to the other side of the blue PI pin 1 wire, leaving 1/8" or so between them.

Start installing the heater wires in final position, from one socket to the next, but for now stop at the PI. You'll put in two sections of bridgework, 7/8"-1" above the solder lugs. By the end of the next testing phase, the power amp will be fully operational.

[Raoul Duke]

Thanks Martin - the subtlety gets me again, lol!
That small move you’ve suggested is exactly what I’m talking about. That 1/8” isn’t a huge difference; but enough to make it right. Will do and will get those heaters in. Looking forward to the testing part and more learning.

And thanks again Tony - I appreciate the kind words.

To all the folks here at TAG: may the new year be filled with health, happiness, and prosperity!

[Raoul Duke]

There, all ready for solder “next year”…

[ijedouglas]

There, all ready for solder “next year”…

Your lead dress looks nice and tidy but I would try and separate the grid, cathode and plate wires a little on the PI. HAD also tended to run the VxA cathode wire along the VxB plate wire. Take a look at the pic of #0183 and you'll see what I mean. I normally start out with something close to this and then use a chopstick and move the wires while listening.

183_front.JPG

183_side.jpg

#0124 PI

17.jpg

[martin manning]

There, all ready for solder “next year”… :D

Do you have a source of low-voltage AC, say an AC adapter or other small transformer? It would be nice to confirm the OT primary phase wrt the secondary.

[Raoul Duke]

Thank you both, I understand the importance of spacing and will try and make more wherever possible. I guess I took the layout pic too literally.

Yes I do Martin. I have a few including an old Radio Shack with switchable voltage. How would I go about doing this test?

Also - quick confirmation that for heaters: power tube pin 7 goes to 12ax7 pin 4/5, power tube pin 2 goes to 12ax7 pin 9?

Thanks again! This thing is starting to look somewhat complete. I’m pretty excited I got this far, lol.

[martin manning]

I don't think the power tube/preamp tube heater polarity makes any difference, but keep the like numbered pins on the same side of the heater string, i.e. 7 with 7 for the power tubes and 9's with 9's for all the preamp tubes.

For the phase test the amp is unplugged, with the filters drained.
Clip the OT CT (B+1) to ground. The cold side of the standby switch is a convenient place to attach a clip.
Plug your load resistor into the speaker jack. This will lift the speaker ground.
Apply some AC across the load resistor. You don't need much, 3-6 VAC is plenty.
Measure AC voltage from each plate lead (power tube pin 3's) to speaker hot. Pin 3's will have high voltage, so be careful.
You should see a higher voltage on the Brown plate lead (tube closest to the rectifiers) than on the blue lead, with the difference being 2x the applied AC voltage.

[Raoul Duke]

I sure will give it a shot. One quick question: what’s the safest way to get voltage to the load resistor? I have a couple of wall warts that I could sacrifice and graft some clips onto.

Got one in my hand right now - 12v, 7.5A output. Good candidate? I can probably root around and find something smaller if it makes more sense.

[martin manning]

Smaller is better to keep the voltage and current down. You could use that 12VAC, and put a 470 ohm resistor in series with it to get a nice low voltage across the load, and just a few volts showing up on the primaries.

[Raoul Duke]

I know I have something smaller around here; I’ll dig around a little. I know I have a few Electro-Harmonix 9v around - but I’m just about positive I know where a 4.5v is.

Are the clips the best way to hook it to the load resistor or should I strip the wires and solder them?

[martin manning]

Any way you can get AC on the OT secondary at the speaker jack is fine.