JCM800 2204 build questions

[sunshine]

I have just started this prokect. I am using this layout http://site.triodestore.com/JCM8002204V.2NEW.pdf" onclick="window.open(this.href);return false; .

Here is a link to my progress: http://s27.photobucket.com/albums/c200/ ... G_6122.jpg" onclick="window.open(this.href);return false; .

My first issue is that the layout shows a 9 pun voltage selector. I was sent a 7 pin selector. I used my ohm meter to try to tell which position used which pins. Did I do it correctly?

Next, the layout shows a black wire comming off the power switch labeled "A". "A" at the voltage selector is in red. I Ran a red wire from the center of the power selector to "A" on the power switch. Is that correct?

Also, I moved the ground from the AC power plug. I moved it from the cap mounting bolt to the star ground. Is that OK.

When studing the layout, I can't realy see what to do with the red and black wires from the choke. Looks like black goes to the board and to the 1/2 amp fuse. Is that correcr? Where does the red wire attach?

There is a white wire coming off the 1/2 amp fuse marked "OT CT". There is no white wire coming from the output transformer. What does this mean?

Plese make any other comments on my progress. I appreciate your time and look forward to any comments.

[TimK]

Being in the midst of a similar project myself, I think may be able to help a bit.

First off, I would like to state the importance of referencing a schematic as you build. Layouts can be confusing and are usually meant to be accompanied by a schematic. Here is a link for a 2204 build that has a voltage selector (scroll down for PDF schematic). Not sure if it is the same kind as yours but it might help.

Looking at the schematic, one side of the power switch does indeed go to the voltage selector via the 3A mains fuse and the other goes to the live side of the AC plug. Your layout has the AC live going first to the 3A mains fuse, on to the power switch and then to the voltage selector. I think this should be ok either way but first to the fuse then to the switch is the current safety standard for N. America I believe. Which is what you have already done I think.

One side of the choke should connect to the OT center tap (CT for short, check your output transformer diagram to see what colour the center tap is) and from there go to the 500mA HT fuse. The other side should go to where the power tube plates connect and then to a 10K 2W resistor that is strapped across a dual 50u filter cap. This is what the schematic and your layout both show.

I hope this helped. I would seriously suggest studying the schematic and following it through with your layout to become more familiar with the circuit. Best of luck with your build.

[sunshine]

Thanks so much for the recommendations. Your schematic is great and helpful. I am trying to identify the ct on the output transformer. Here is a link to the transformer I am using. http://www.magneticcomponents.net/40-18025_Stock.pdf

Is the white the CT?

I do see Center taps on the power transformer. It has two. http://www.magneticcomponents.net/40-18 ... _Stock.pdf.

Here are the specks to the choke: http://www.magneticcomponents.net/40-18032_Stock.pdf

So, Is it correct to attach the white from the OT and the red from the choke to the 500ma fuse? The schematic shows red and the layout shows black, so I should always fallow to the schematic.

[TimK]

Yes, the white wire coming from the middle of the OT primary side is the CT. It seems like you have the grommet with the OT primary wires coming through behind your bass pot (the red, white and blue wires). I don't know where your OT is on top of the chassis, but it might be better to locate this grommet and these three OT primary wires closer to the power tubes and the HT fuse, as this is where they connect to.

Your choke shouldn't care which way it is wired. I know the metro choke from the 50W kit used two black wires (just as your layout shows), so it doesn't matter as long as it is placed in the correct spot in the circuit. The OT CT and one choke wire connect to the same lug on the HT fuse. The other side of the choke goes to where the power tube plates connect to a 10k 2W resistor. Your layout and the schematic show this.

I would be very careful when trying to rely on wire colours from a layout. It can become very confusing because different transformers and chokes use different colours. This is why the schematic I linked you to has different colours labelled than you have on your components. Since your layout is from Triode Electronics, which is probably where you got your Magnetic Components stuff, the colours should be correct for you. However, case in point, the layout shows two black wires for the choke and your choke has a red and a blue wire. Even though it shouldn't matter which way the choke is wired, this still proves that layout colours are not to be trusted. Same story for the colours labelled on the schematic.

What I would suggest is drawing up your own schematic, taking care to label each component you have and which colour wires attach to what.

[sunshine]

I have just fired up the new build for the first time. If I touch v1 pin 1,2,3,6 or 7 I get a sound from the speaker. Here is a link to some photos of the input jacks. Have I built them wrong? Any trouble shooting advice is appreciated.

http://s27.photobucket.com/albums/c200/ ... 00%202204/

[toner]

Are you touching the pins with a meter probe when hearing the sound? It's normal to hear a pop or buzz when touching some of the pins.

The input jacks look okay. Does the amp sound okay?

[sunshine]

No, I get no sound from the amp with the guitar plugged in. Yes I was touching the pins with the meter probe.

[sunshine]

If I put another source as input like a cd player and turn up the pre amp and master all the way, I can hear the music. Sounds like one watt and a Little fuzzy.

[toner]

Check the resistor that connects to V3 pin 3 and 8. It should be 470 ohm (yellow-violet-brown), NOT 470k (yellow-violet-yellow).

[sunshine]

I have added more pictures. I have rechecked resistor values. The 470 was correct. I did find that the connection from the center to the right terminal of the bias pot was not installed. See picture 23. I have have biased the amp. The low channel now works but the high has no sound. From the low side all I get is very clean, no crunch even with the preamp dimed. I have a need for crunch. What do you suggest I look at.

PS: I put the cd player into the high input and I get a very low volume clean sound. With the guitar nothing.

[toner]

I looked closer at your input jacks. You have a short red wire between the low and high jacks that needs to be removed.

[sunshine]

I tried removing the red wire and this did not help. I took the board off, replaced all the wires and reinstalled. Here is a new set of pictures: http://photobucket.com/jcm800

I am getting a voltage of 8.5 on v1.6. It should be around 250. What steps should I use to diagnose the issue?

[toner]

What's the pot on the back between V1 and V2 for? Where does the yellow wire from it go to?

The short red wire on the inputs (pic below) needs to be removed if it's still there (old picture?).

Does V1 pin 1 have good DC voltage? If pin 1 has high voltage but pin 6 doesn't then the plate resistor that's marked below may be bad.

[sunshine]

Thanks again for looking at my project. I really appreciate it.

OK, I checked the resistance from H to v1.6 it is 100K. Anyway I replaced the two .022 caps and both 100k resisters. I pulled the board and replaced the wire under the board. Still the same 8.5v. If I measure the voltage at the back side of the 100k resister it is 285. At the front closest to v1.6 it is 8.5. What could cause this?

[sunshine]

The other voltages are
v1.1 259
v2.1 184
v2.6 319
v2.8 185
v3.1 252
v3.3 and 8 42.5
v3.6 255

You asked about the extra pot behind v1. That is the bias pot.
Layout http://site.triodestore.com/JCM8002204V.2NEW.pdf
https://docs.google.com/viewer?a=v&pid= ... nzYX&hl=en