Dumble - help needed urgently!

[martin manning]

Here are the seven points to check on the main power supply board.

[Mousey Dung]

Install both power supply boards and connect all of the primary and secondary leads from the power transformer, AC inlet, fuse, pilot light, and also the choke and standby switch. I believe this is about where you are now.

Correct!

After getting that far you can power it up with the limiter and check that all of the supply voltages are present and at reasonable levels.

Haven't powered up yet, but I have the limiter ready. By "present" do you mean to check if the green leads are giving 6.3V, yellow leads @ 5V, red leads @ 650V, red-blue lead @ 50V?
What are reasonable levels? As in +/- 3% ?

Check all of the high-voltage nodes (there are 6), the bias supply, and the relay supply.

You mentioned six high-voltage nodes? Not sure if I'm missing something, but I'd rather sound stupid than be dead. :-p What are the high-voltage nodes exactly?

[martin manning]

Well there are actually seven HV nodes (corrected myself above). Connect the green filament leads to the first power tube socket, and connect the pilot light. You'll have to extend the 6.3VAC filament voltage down the line of tubes later.

With the bulb limiter connected, the HV nodes (basically the positive end of each filter cap) will be a bit low, but they should all be at a similar level. The bias and relay supplies should be (guessing) something like -30VDC(?) and +4VDC(?).

If the limiter test looks good, i.e. the bulb flashes briefly when you turn the power switch on, and then dims, and brightens again before dimming when you turn the standby switch on, then you can take the limiter out. Then power it up on full voltage and measure the same points. The voltages will be high since no tubes drawing current, and for the same reason not much different down the string from the power tube plate supply to the first preamp node.

[drew]

You'll have to extend the 6.3VAC filament voltage down the line of tubes later.

This is something that is not shown on the layout diagram, by the way. And is a fiddly, time-consuming process.

[Mousey Dung]

Well there are actually seven HV nodes (corrected myself above).

Gotcha!

Connect the green filament leads to the first power tube socket, and connect the pilot light. You'll have to extend the 6.3VAC filament voltage down the line of tubes later.

By "first" power-tube socket, I take you mean V8, the one on the bottom left? And it should look something like the wiring in the image below?
http://brownnote.net/layouts/DLITE_DELUXEKIT_VER1.1.jpg

With the bulb limiter connected, the HV nodes (basically the positive end of each filter cap) will be a bit low, but they should all be at a similar level. The bias and relay supplies should be (guessing) something like -30VDC(?) and +4VDC(?).

Okay, another better-to-sound-stupid-than-be-dead question: From what I understand, to test DC voltages, you place one end of the multimeter to ground and the other to the node -- correct?

BTW, I REALLY, REALLY appreciate your help! Thanks so much!

[martin manning]

Yes, all correct above. Twisting the green filament leads together is a good idea.

BTW, I read where you asked about grounding the transformers. Ground the orange shield wire from the PT with the green/yellow and red/yellow CT grounds, and make a good electrical contact from the choke's mounting tabs to the chassis.

Bias and relay supply check points on the rectifier board are shown below. Be aware that the HV nodes will be around 400VDC.

[Mousey Dung]

Bias and relay supply check points on the rectifier board are shown below. Be aware that the HV nodes will be around 400VDC.

Okay, I used the a 60 W bulb in the limiter and it glowed faintly when I flipped on the power switch (with the standby remaining off).

I tested the DC voltages and got the following:
Relay: 7 V
B+ plate supply: 410V
Bias supply: -60V

How am I doing so far?

Next, I will connect the PS board without connecting it to the preamp, ensure that it is grounded, and then check the voltages at the 7 nodes.

[martin manning]

Looking good! If you had a short somewhere, the bulb would have been brightly lit. With power on and standby off you should also have ~3.5 VAC to ground from the filament pins on the first power tube, and your pilot light should be on.

Be careful of the plate node if the power supply board isn't connected to ground, and check the voltage on the large capacitors to make sure they are safe before going back to work.

[Teleguy61]

Once again Martin, you may ascend directly to heaven.
You are a saint.

[Mousey Dung]

QUESTION #8:

The chassis has numerous unutilized holes near the OT. Does this have any bearing on the hum factor? Is it important to have a sealed chassis near the transformers?

[martin manning]

The extra holes are not a big deal, don't worry about that.

When you get the power supply connected up, check voltages at the seven points and post them. The exact values aren't too important right now, it's more about having what looks like a reasonable voltage up around 400V at the reservoir (the 2x 100uF) and descending as you go towards the first filter, and about the same voltage at the two reverb supply nodes (which should be a bit less than the screen node).

While you have the power on, you can put your meter on the output transformer secondary from the 16-ohm tap to the common and see how much induced voltage is there. If its more than a few millivolts AC then you might have some audible hum. You could also connect a speaker and listen to it.

Run the relay supply and relay supply ground wires from the rectifier board around to the footswitch jack if you haven't done that yet, and put them in the corner of the chassis where the back meets the bottom. In the drawing the ground wire is not shown correctly; it should connect to the center lug of the PAB switch, with the other black wires.

The next step in my mind is building out the HV power supply to the power tube sockets, which would include connecting the output transformer primary leads (might as well connect the secondary to the impedance switch too, but don't solder the 4-ohm tap yet) and the screen supply leads. There is always the chance that the OT primary wires will have to be reversed, but the colors (blue and brown) shown on the OT spec sheet and in the layout drawing look correct to me. Leave enough length so that you could swap them if necessary. Complete the bias circuit (test jacks, 1-ohm current sense resistors, bias trimmers, and power tube cathode grounds) on the back panel.

At this point you should power it up again with the bulb limiter and measure the plate and screen voltages on power tube pins 3 and 4, and the bias voltage on the wipers of the bias trim pots. Check the range of bias voltage by sweeping the trimmers, and put them at their most negative setting.

I would get all of the interconnections on the panel mounted components done next including the resistors and caps that are mounted on the pots, switches, and jacks, but don't solder the lugs where a wire from the main board is connected until you are wiring in the main board.

[martin manning]

Note the addition to the picture above showing the power supply board and the seven test points. Be sure that the ground wire from the screen filter does not connect to the eyelet shared by the 22k 3W and the 22uF 450V.

[Bob Simpson]

I paid Moss for some parts in Jan 2011, was told 5-6 excuses why or they are being shipping out....still waiting almost 4 years later.

TM

I didn't mean you, TM.
I knew you knew...

Response intended for OP.

Bob

[Mousey Dung]

Run the relay supply and relay supply ground wires from the rectifier board around to the footswitch jack if you haven't done that yet, and put them in the corner of the chassis where the back meets the bottom. In the drawing the ground wire is not shown correctly; it should connect to the center lug of the PAB switch, with the other black wires.

Wow, great you spotted that. Makes perfect sense!

The first board I connected was the rectifier board, so the leads going to the footswitch are already connected.

Right or wrong of me, I actually started the assembly by making four main building blocks, essentially comprising the chassis and three boards. I connected all the leads on the chassis controls as much as I could, just short of connecting them to the boards. I did the same for the boards -- connected them as much as I could, just short of splicing them to each other and the chassis.

I also proceeded from the assumption that there were good reasons for the layout, that wires were meant to run in exactly the same way as depicted, meaning if a wire went around the corner of a component or section, or hugged the corner of the chassis, I would do the same. Consequently, I didn't take any liberties with simplifying what appeared to be a redundant and excessive grounding-wire scheme.

The next step in my mind is building out the HV power supply to the power tube sockets, which would include connecting the output transformer primary leads (might as well connect the secondary to the impedance switch too, but don't solder the 4-ohm tap yet) and the screen supply leads.

I had already connected the OT primaries and secondaries, on being advised yesterday to fully mount the boards, etc. So when I ran the first bulb-limiter test, it was already connected. Hope that wasn't a bad thing. I will go desolder the 4-Ohm connection now.

There is always the chance that the OT primary wires will have to be reversed, but the colors (blue and brown) shown on the OT spec sheet and in the layout drawing look correct to me.
Leave enough length so that you could swap them if necessary.

I hadn't anticipated this and cut the blue and brown wires to length. Hopefully, no reversing will be required.

Complete the bias circuit (test jacks, 1-ohm current sense resistors, bias trimmers, and power tube cathode grounds) on the back panel.

This was one of the first things I completed, along with the chassis "block" approach.

At this point you should power it up again with the bulb limiter and measure the plate and screen voltages on power tube pins 3 and 4, and the bias voltage on the wipers of the bias trim pots.

Will do, report on results coming up...

Check the range of bias voltage by sweeping the trimmers, and put them at their most negative setting.

Will do and report results.

I would get all of the interconnections on the panel mounted components done next including the resistors and caps that are mounted on the pots, switches, and jacks, but don't solder the lugs where a wire from the main board is connected until you are wiring in the main board.

Due to the advice from yesterday re. mounting everything before running the bulb-limiter test, I've already connected most of the leads connecting to the main board. The main-board leads corresponding to the bottom right of the layout diagram, which mostly run to the V1 to V4 section, are not soldered in yet. Is it okay to let what I've soldered remain for now?

[Mousey Dung]

Note the addition to the picture above showing the power supply board and the seven test points. Be sure that the ground wire from the screen filter does not connect to the eyelet shared by the 22k 3W and the 22uF 450V.

That's a good catch, a mistake I could easily have made. Glad to say I didn't. Maybe there's some hope for me after all.