First Time Member...Help with wiring up a Newmarket Transistor amplifier circuit

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9 Volt Licker
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Joined: 30 May 2023, 05:18

Post by 9 Volt Licker »

Hello future home to my serious nerdy mind :)

I'm pretty new to circuitry. I have built some kits and recently re-housed and modified a JHF1 Dunlop Fuzz Face. Works awesome. I'm a germanium transistor collector and have learned a bunch over the past year. I just bought a Newmarket Transistor amplifier circuit (pre-made) from the 60's. The Reverb ad said something about being a Deacy amp. It has a basic schematic diagram for the wiring but I've tried a bunch of different things an I can't get the thing to work. I figured I would ask if someone can help me understand what wires go where and where to solder them on the jacks and the only pot. I figure I'll mod it later but I just want to make sure it works first.

Pics are attached.
Q's
1 - Where does the input jack signal go to? The pot? Which lug? Which is in and which is out? Do I need to ground the pot? Do I need to ground the input jack?
2. Where does the pot wire/signal go in the circuit? Hole C?
3. Which hole is ground? Where should I solder the circuit ground wire? A jack?
4. Where do I solder the 9 volt red positive and black negative? Do I need to have an on/off switch?
5. I'm not attaching wires to a speaker like the outline shows. Where do those two wires go? The output jack? Do I need both wires?
6. Two holes look like they indicate 'lamp'. Does that mean I can add an LED through one of these holes?

I really appreciate any help anyone can give. I'm about to smack my head off a wall as I don't know what my neck steps should be after doing an ineffective troubleshooting.

Cheers
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mauman
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Post by mauman »

Welcome to the forum!
9 Volt Licker wrote: 30 May 2023, 05:52 Q's
1 - Where does the input jack signal go to?
Signal to lug C, ground to lug A.
The pot? Which lug?
If you want a volume control, wire it in before the signal hits the PCB. That's the "VOLUME CONTROL" schematic. 5k pot, C (reverse audio) taper, wire the incoming signal to pot lug 3, then volume pot lug 2 to PCB C, volume pot lug 1 to PCB A (which is also power ground.)

Which is in and which is out?
C & A are in, D & E are out.
Do I need to ground the pot?
Yes, lug 1 to ground.
Do I need to ground the input jack?
Yes, shield to pot lug 1 and PCB lug A.
2. Where does the pot wire/signal go in the circuit? Hole C?
Yes
3. Which hole is ground?
Lug A
Where should I solder the circuit ground wire? A jack?
Make the ground common to PCB lug A, volume pot lug 1, and the 9V negative terminal.
4. Where do I solder the 9 volt red positive and black negative?
9V negative to ground as above. 9V positive to PCB lug D.
Do I need to have an on/off switch?
Optional, if you do, wire it as shown between battery + and PCB lug D.
5. I'm not attaching wires to a speaker like the outline shows. Where do those two wires go? The output jack? Do I need both wires?
This is an amp, not a pedal, so PCB lugs D and E go to the terminals of a speaker. The schematic calls for 15 ohms, but 16 ohms would be fine. PCB lug D is also connected to +9V, but lug E is NOT connected to anything except the speaker (no ground.)
6. Two holes look like they indicate 'lamp'. Does that mean I can add an LED through one of these holes?
"Lamp" almost certainly meant "incandescent" at that time, so I'd start with a 9V or 12V incandescent bulb, once you get the rest of the circuit working. You can also use a meter to determine what's sitting on those two lugs (PCB B & F?). Probably voltage on one and ground on the other, but maybe not.

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soulsonic
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Post by soulsonic »

I'd like to add that it's wasn't accurate for them to call it a "Deacy" amp. The Deacy amp circuit uses two small transformers: one to drive the push-pull output transistors, and the other is the output transformer. You see this alot in old transistor radios.

If I had this, first thing I'd do is pull the heatsink off the two output transistors and see if they're NKT275s. If they are, you probably got some $$$. :lol:
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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