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

[Raoul Duke]

Ok - smoke test results:

I’m still upright and the house electrical system is still working, lol.

Current limiter with 40w bulb worked. Followed the start-up process and got both quick flashes with consistent “low glow”. No burning smells or odd sounds; in fact it was very quiet with just the very slightest electrical “buzz” when powered.

Line in to fuse/main/relay PT: 108 vac

Relay PT to PS board: 13 vac

12v out to relay coils, coils to rear panel switches: check (didn’t test foot switch end; still haven’t built it yet) relays “click” when switched and amp powered up/down

Main PT to rectifier board: 333 vac

Rectifier output to first reservoir cap on PS board: 465 vdc (second cap: 232 vdc)

Through “Standby” to choke and first B+ filter cap: 465 vdc
B+ filters: 1, 2, & 3: 462, 4 & 5: 458

Main PT bias tap to bias supply rectifier: 47 vac

Out to bias pot: -65 vdc

Couldn’t get any meaningful reading from Main PT to 1st power tube at either pin. Fluctuated between -.03 to.04 in the 20 vdc setting of my DMM. Same reading at the LED terminal strip leads to the LED (which did light pretty brightly). Not certain if the 40w bulb was limiting too much or if I need to re-flow those connections?

Ok guys, this is where I start to get lost, lol. Any advice is certainly appreciated!

[martin manning]

I'd call that a success.

I don't understand this, though:

Couldn’t get any meaningful reading from Main PT to 1st power tube at either pin. Fluctuated between -.03 to.04 in the 20 vdc setting of my DMM. Same reading at the LED terminal strip leads to the LED (which did light pretty brightly). Not certain if the 40w bulb was limiting too much or if I need to re-flow those connections?

If the panel LED is working then you have heater voltage. You should get ~3.2VAC to ground at pins 2 and 7 on that first power tube socket if you have the heater supply connected to it.
Do you have any of the OT leads connected at this point? [edit: from your last photo, it looks like you have all of the OT leads connected, and the screen voltage connected to the power tube sockets.]

[GAStan]

Fluctuated between -.03 to.04 in the 20 vdc setting of my DMM.

Did you try to read Volts AC?

[Raoul Duke]

Just tried a different DMM (Fluke 7-300) for the heaters and I’m getting 1.4 vac on each pin (2&7) at the first power tube with the limiter (40w bulb). Does this seem more correct?

[martin manning]

Measure across 2 and 7 and you should get ~6.3 VAC. You don't have a ground reference for the heater string yet since the 2x 100R are on the other socket.

[Raoul Duke]

Measuring across 2 and 7 gets me 7.2 vac. I’m assuming this is good because it’s at least 6.3 and it’s unloaded?

[martin manning]

Yes.

[Raoul Duke]

As Buddy Holly would say: “well alright”.

Thanks for the excellent test guidance Martin!
I have to thank Glenn as well for gently reminding me that I should have been reading AC, lol.

I guess I’ll start wiring in the main board tomorrow. Any tips or pointers an obvious novice like me would benefit from?

Thanks again guys! Couldn’t be doing this without you

[martin manning]

Next I would complete the assembly of the preamp board and drop it in. You'll have a bunch of wires hanging off of it which you will then be routing and soldering in place. You could finish the whole thing, or if you want just connect the PI socket, the loop jacks, the bias and power tube grid leads, and B+3 to the board. At that point you could fire up the power amp and test it.

[Raoul Duke]

Well, here’s the main board. Made it myself before I really understood the “flow” of things - so there’s an eyelet here and there that are a little out of whack. Also, the Aerovox mid cap was a sentimental choice because 30 years ago I lived down the block from the factory where these were made. Not sure if I should just throw the Sprague I have for it in or give it a whirl…

Also, regarding the tantalum “presence” cap at the top of the board - I’ve read a lot about the polarity question and seen the 124 pics where it was reversed by HAD himself. Any definitive suggestions on how it should be oriented in this circuit?

Let me know if anything looks grossly FUBAR’d, lol.

[ijedouglas]

Also, regarding the tantalum “presence” cap at the top of the board - I’ve read a lot about the polarity question and seen the 124 pics where it was reversed by HAD himself. Any definitive suggestions on how it should be oriented in this circuit?

Try it both ways and see which way you like it. I typically turn the presence on full and then try it both ways to see which I prefer.

[Raoul Duke]

Thanks Ian; makes sense to try it both ways.

Seems a lot of folks do it just that way. Not knowing the subtleties of electronics, I wonder why it can vary so much amp to amp…

[martin manning]

Tantalum electrolytics have very low tolerance for reverse voltage. At idle there is around a volt across the presence cap, so the negative should go to ground.

[Raoul Duke]

Got it, thanks as usual Martin. That’s where it is right now.

I imagine that connecting the PI first is merely wiring up that tube socket? I was inclined to do everything at once next; but after thinking about how much I learned from the previous exercise - I’m giving “wire the PI and test the complete power amp” serious consideration.

[martin manning]

I imagine that connecting the PI first is merely wiring up that tube socket?

The list I mentioned above: The PI socket, the loop jacks, the bias and power tube grid leads, plus NFB, presence pot, and PI ground, and finally B+3 to the board at the PI balance trimmer. The section of schematic shaded yellow, and the snip from the layout shown below. I think you have the green shaded part wired up already. BTW that yellow wire feeding the preamp signal to the loop jacks in the layout is the brown wire coming from the master volume wiper that is tied to the lone eyelet at the top right.