JCM Mini Clone Issues

[Ten Over]

I did notice a missing 100k resistor that is normally wired across the v2 socket on the JCM 800 circuit. It normally connects across pins 1,6 and 7 but I'm not seeing it in your pics.

I see it. It is on a terminal strip.

 

[imgumby001]

They have separate wires going to R11.

Ok, copy that! Thank you gentlemen. I’ll be going over the voltages for the preamp tubes and phase inverter again. All heater voltages are good.

 

[imgumby001]

I see it. It is on a terminal strip.

Ok, yes. It was cramped in there so I mounted a little strip!!

 

[Ten Over]

Your pre-amp heaters should be around 3.15Vac to ground. Pin 2 on the power tubes should be around 3.15Vac to ground and pin 7 on the power tubes should be around 9.45Vac to ground.

 

[Ten Over]

I'm also interested in the DC voltage at the junction of R11 (470) and R21 (10k). The grid voltages for V3 (pins 2 and 7) will be nonsense, but I would like to see them, anyways.

 

[imgumby001]

Your preamp sockets appear to be wired correctly so I'm guessing that you may have gotten the order of the pins wrong when reporting the voltages. I did notice a missing 100k resistor that is normally wired across the v2 socket on the JCM 800 circuit. It normally connects across pins 1,6 and 7 but I'm not seeing it in your pics. Here is our member Rob's JCM 800 layout which shows the resistor across the v2 socket.

https://robrobinette.com/images/Guitar/Marshall/RR2104_Master_Volume_Micro/RR2104_Master_Volume_6V6_Layout.png

I just went over the voltages again, I’m getting what I’m getting. All the sockets are numbered, so I’m definitely not getting them wrong. The numbers are weird, make no mistake. If you consult the supplied voltages for the manufacture they are certainly off what is listed. I just can’t figure out why. All resistors check about where they should be. I just can’t explain why this amp is behaving so badly!!!

 

[imgumby001]

I'm also interested in the DC voltage at the junction of R11 (470) and R21 (10k). The grid voltages for V3 (pins 2 and 7) will be nonsense, but I would like to see them, anyways.

Ok. I’ll get on that right now!!

 

[imgumby001]

I'm also interested in the DC voltage at the junction of R11 (470) and R21 (10k). The grid voltages for V3 (pins 2 and 7) will be nonsense, but I would like to see them, anyways.

The junction of r11 & r22 is reading 36.09vdc

V4&5 pin 2 is 3.59vac and 3.6vac
Pin 7 is reading 10.68vac and 10.69

V3 pin 2 is reading 22.34vdc
And 7 is reading 20.8vdc

Hopefully that is what you needed. Thanks again!!

 

[dan40]

I just went over the voltages again, I’m getting what I’m getting. All the sockets are numbered, so I’m definitely not getting them wrong. The numbers are weird, make no mistake. If you consult the supplied voltages for the manufacture they are certainly off what is listed

Check those voltages on pins 4/5 and 9 again but make sure your meter is set to an AC voltage scale. Just want to make sure you are seeing the correct filament voltages.

 

[Ten Over]

I am looking at a picture of V1 right now. There is a blue wire running from a lug that is clearly marked "1" to a turret that is marked "V1-1" that also connects to R4 (100k) and C4 (.022uF). Do you see the same thing and if so, what is the voltage at that lug?

 

[imgumby001]

Check those voltages on pins 4/5 and 9 again but make sure your meter is set to an AC voltage scale. Just want to make sure you are seeing the correct filament voltages.

Heaters look good 3.6 vac for both legs.

 

[imgumby001]

I am looking at a picture of V1 right now. There is a blue wire running from a lug that is clearly marked "1" to a turret that is marked "V1-1" that also connects to R4 (100k) and C4 (.022uF). Do you see the same thing and if so, what is the voltage at that lug?

Yes, that’s absolutely correct. The reading is climbing continuously, but it’s around .7vdc currently.

 

[Ten Over]

Yes, that’s absolutely correct. The reading is climbing continuously, but it’s around .7vdc currently.

This is with the power on and the Standby switch in "play" mode?

 

[imgumby001]

This is with the power on and the Standby switch in "play" mode?

No, the standby is on. It’s is not in the play mode. Would you like me to redo all the numbers with the standby off?

 

[Ten Over]

No, the standby is on. It’s is not in the play mode. Would you like me to redo all the numbers with the standby off?

yes

 

[imgumby001]

yes

Copy. On it!

 

[imgumby001]

yes

Junction of r11 & r21 - 36.3vdc
V3
Pin2- 151.6vdc
7- 38.8vdc
V1
Pin1 turret v1-1- 226.2vdc

 

[Ten Over]

V1
Pin1 turret v1-1- 226.2vdc

Okay. Now proceeding in a clockwise fashion from that pin on V1 to the next pin, there is a shielded wire coming from the wiper of the Gain control. What is the DC voltage relative to ground on that pin with the power on and the Standby switch in play mode? Clockwise fashion is when viewing the socket from the solder lugs side.

 

[imgumby001]

Okay. Now proceeding in a clockwise fashion from that pin on V1 to the next pin, there is a shielded wire coming from the wiper of the Gain control. What is the DC voltage relative to ground on that pin with the power on and the Standby switch in play mode? Clockwise fashion is when viewing the socket from the solder lugs side.

V1
Pin2- 0.0vdc
In play mode

 

[Ten Over]

V1
Pin2- 0.0vdc
In play mode

Continuing in the same clockwise fashion with the power on and the Standby switch in play mode, the next pin has a blue wire that goes to R1 (10k). What is the DC voltage from that pin to ground?