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

[martin manning]

The 1R's are a very convenient way to measure the idle current when biasing. With 1R between cathode and ground, the voltage on the cathode in mV is equal the current in mA. With the test jacks connected to the cathodes, you can read the current and adjust the bias without removing the chassis from the head cab. Adds a few extra parts, but greatly simplifies biasing.

[Raoul Duke]

Should I be connecting pins 1 & 8 to ground with these?

Also - I’m getting tripped up by the foot switch. Here’s the connections on the chassis side looking at the DIN Jack from the rear with the square tab at 12 o’clock:

Pin 1 - PAB power in from power board
Pin 2 - PAB out to manual switch (with relay connected to center terminals)
Pin 3 - ground from 12v VR with connection to manual switches across bottom terminals
Pin 4 - OD out to manual switch (with relay connected to center terminals)
Pin 5 - OD power in from power board

Will the diagram on the original 102 layout work? Trying to wrap my head around this and I can’t see the trees…

[martin manning]

You're using pin 1 to support the grid resistors going to pin 5's so no. Just ground pin 8's using 1R's.

[Raoul Duke]

Understood, thanks Martin!

[martin manning]

I’m getting tripped up by the foot switch.
...
Will the diagram on the original 102 layout work? Trying to wrap my head around this and I can’t see the trees…

Yes. Connections are as follows:

A +12V power lead goes from the relay supply board regulator output to both relay coils, to the ends with the cathodes of the flyback protection diodes.
The other ends of the relay coils are connected to the center lugs of the pedal/manual switches on the rear panel. The relays are energized by grounding the coils directly using the pedal/manual switch, or, if the pedal/manual switch passes it on, by the footswitch. You'll note in the layout that only the OD pedal/manual switch grounds its relay in the manual position. That is because the Rock/Jazz switch is assumed to be an on-off-on type, which produces PAB by lifting the tone stack in the center position (essentially the same as the relay does). There is no harm in wiring both pedal/manual switches the same, even if your Rock/Jazz switch has a center off position.

Leads for footswitch LED power go from the relay supply board''s 1k current limiting resistors to footswitch jack pins 1 and 5
Pin 3 of the footswitch jack is connected to the relay supply ground.

[Raoul Duke]

Thank you for the explanation Martin; it helps me interpret the diagram and make sense out of the flow of things. Very much appreciated!

After reading many build threads, I opted for the MIDI cable with jacks on the amp and foot switch. Seemed like a better practical solution.

[Raoul Duke]

Ok, quick new guy question: should I have heaters wired up to the power tubes for this testing?

Haven’t made a lot of progress this past week due to seasonal chaos, but hoping to light this thing up for power testing this weekend.

[martin manning]

Keep the heater string as is, with the heater winding connected to one power tube, and the leads going to the pilot lamp. That’s all you need for now.
BTW, I would pull the power transformer heater leads out from under the brown plate lead and move them further away from the socket.

[Raoul Duke]

Understood, thanks Martin. These are the details that I appreciate learning.

I probably could have found some time to hurriedly run through this before now - but I’d prefer to take my time and move slowly. To be honest; I’m also slightly apprehensive. Retrospectively, I’ve learned and done much more than I would have thought possible a year ago thanks to all the help I get here at TAG - I guess this initial power-up and test is my QC Eval to determine whether I’ve internalized all the great lessons I’ve picked up from the direct coaching and “searchilizing”, lol.

Time to dig in and get it done.

[martin manning]

...I’m also slightly apprehensive.

Understandable. Take a few minutes to check the connections for the part of the circuit you are going to power up against the layout. You should be looking at a schematic as well, such as posted here: https://ampgarage.com/forum/viewtopic.p ... 69#p142469

Transformer primaries
- Line inlet through fuse and power switch to main and relay power transformers

Transformer secondaries
- Relay power trans to relay supply board, direct 12VDC output to relay coils, and relay coils to rear panel switches, 12 VDC outputs with 1k current limiters to footswitch jack pins
- Main power trans HV to main rectifiers, rectifier output to reservoir cap on main power board, through standby switch to choke and B+ filters
- Main power trans bias tap to bias supply rectifier
- Main power trans heater winding to first power tube socket, then to panel LED rectifier and panel LED

Stop there. You should have all leads on which voltages will appear secured. At this point you are testing the shaded portion in the schematic shown below. Use a really low-wattage bulb in your limiter initially if you like.

[Raoul Duke]

Hey, this is excellent information Martin! I truly appreciate it and will follow it to the letter. I’ve got my 40w bulb in the limiter ready to go.

We got some bad weather a couple of days ago here in the N.E. so I’ve been cutting downed trees and repairing fence line - which I finished today. Barring any last minute holiday madness - I’m hoping to run through this Friday or Saturday for sure. Fingers crossed, lol.

Thanks again; very much appreciated!

[martin manning]

I’m hoping to run through this Friday or Saturday for sure. Fingers crossed, lol.

Don't forget to drain the power supply caps when you shut it down. If you leave the standby switch on play the balance resistors on the reservoir will take care of that, but it will take a few minutes.

[Raoul Duke]

Understood, thanks Martin
I had about 30 minutes to spare for fun projects today, so I made the corrections you suggested re: heater wires and OT primaries. Then I wrote out a “dummies’” checklist incorporating your test process above (and ending with “drain the power supply caps”) so that once I do have the time - I don’t need to stare at the chassis, re-read the post, and scratch my ass for 27 minutes to remember what I was thinking of doing, lol.

IMG_0341.jpeg

To all the great folks here at TAG, I wish you and yours a peaceful and happy “next few days” in the interest of being as innocuous as possible, lol.

I appreciate the collaborative spirit, immense technical expertise, and personality/wit that I encounter here every time I pop in.
Thank you all!

[martin manning]

Thanks, same to you. Eagerly awaiting the results of the smoke test ;^)

[timrobertson100]

Looks good - and I hope you have a good break too.

I'm curious if it would be helpful to move the heater balance resistor to ground (right most resistor on that last photo), rather than to pin 8?