NAD - 50w JMP clone
- Thread starter fitz
- Start date
OP
fitz
Ambassador of DIY
Got some changes to the board done tonight while it was out and easier to get to.
Here's a before pic of how it looked when it came to me in the old chassis.
Here's the stuff I changed to return some values to Marshall stock, and to add the EL34 / 6550 switching.
1. Changed the 150k to stock 220k and moved to a new turret (A) for connection to power before the standby switch.
2. Added a 270k resistor to new turret (B) - A/B will connect via switch for parallel 120k value for 6550 tube spec.
3. Changed the bias trim from 22k resistor & 50K pot to 47K resistor & 25k pot (trim pot mounted to rear chassis panel).
4. Swapped out the ugly 10k ceramic block resistor for same value - matches the 10k going to the cap above the board...
5. Added 470k resistors to new turret (B) that will be parallel to the 220K for a 150k value with switch connecting A/B for 6550 tube spec.
6 Changed the 100nF JCM800 cap spec to 22nF JMP spec.
7. Pulled the cap/resistor gain mod for a spec 10k.
Tomorrow I'll start on rewiring the tube sockets, power, pots & fuses.
If all goes well, I'll move on to reconnecting all the board leads and see if it bursts into flames...
Here's a before pic of how it looked when it came to me in the old chassis.
Here's the stuff I changed to return some values to Marshall stock, and to add the EL34 / 6550 switching.
1. Changed the 150k to stock 220k and moved to a new turret (A) for connection to power before the standby switch.
2. Added a 270k resistor to new turret (B) - A/B will connect via switch for parallel 120k value for 6550 tube spec.
3. Changed the bias trim from 22k resistor & 50K pot to 47K resistor & 25k pot (trim pot mounted to rear chassis panel).
4. Swapped out the ugly 10k ceramic block resistor for same value - matches the 10k going to the cap above the board...
5. Added 470k resistors to new turret (B) that will be parallel to the 220K for a 150k value with switch connecting A/B for 6550 tube spec.
6 Changed the 100nF JCM800 cap spec to 22nF JMP spec.
7. Pulled the cap/resistor gain mod for a spec 10k.
Tomorrow I'll start on rewiring the tube sockets, power, pots & fuses.
If all goes well, I'll move on to reconnecting all the board leads and see if it bursts into flames...
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