560V CT for jcm800 2204? what are your thoughts?

[Champ_49]

Hi All!

On to my next project. Another jcm800 2204 amp. 
I came across a classictone power transformer that has on their spec sheet the option of having 560V CT. Instead of the more common 690V. It has thw 690V option as well.should I try this transformer for a more "browner" sound?  Or would this just be wasting my time and money to work the build around this transformer To get the option.

Or I could just opt for the usual 690V CT PT.
Any thoughts would be of great help!

[kagliostro]

I came across a classictone power transformer that has on their spec sheet the option of having 560V CT. Instead of the more common 690V. It has thw 690V option as well

If I understand correctly and you can get a PT that has both 560v CT and 690v CT:

You can use the transformer's 690v CT winding and put a switch to swap to the 560v CT as an option

something like in this schematic (where the AC voltage is 275v and 190v)



this will give you the effect of a VVR with fixed voltage step

---

Some time ago Weber had a Kit named 6D30 with the same PT concept

https://taweber.powweb.com/store/6d30_schem.jpg

https://taweber.powweb.com/store/pt30sch.jpg

https://taweber.powweb.com/store/6d30_layout.jpg



K

[Champ_49]

thanks for the input!  Looks like I'll be going with a PT that has two CT options. 690V and 625V.  please tell me I'm not going nuts. I already built a 5f1, 5e3 a jcm800 and another jcm800.   This amp  building can be addictIve.

[shooter]

This amp  building can be addictIve.

As long as you haven't started selling your blood for parts, you're ok

[Champ_49]

I may have to resort to that if I keep this up. 

[Champ_49]

That is true.  And it's free as long as you have food on the table.

[Champ_49]

This is an amature question I'm sure.  But I can't figure out what the red/blue leads are on this power transformer (coming off the HV windings)
http://www.classictone.net/40-18054.pdf

Any ideas?

This is for a JCM800 2204 build so it's solid state rectification is all I know.

I am assuming I would choose either the red red or orange orange (depending on what I want for the HV).  Then ground the red/yellow (CT) wire.

For the high current heater winding, green green to the heaters, green/yellow (CT) to ground.

Now... I don't know what to do with that blue& red striped wire coming off the HV winding.  It says 50V bias for red/yellow and blue/red.  Not sure what this means.
For now I will assume that I should tie off the blue/red wire and not use it?? While the red/yellow CT goes to ground?

Any thoughts??

[shooter]

"FOR SOLID-STATE RECTIFIER, USE
ORN-RED/YEL-ORN LEADS. RED LEADS NOT USED.

RED/BLU-RED/YEL = 50V BIAS"

These note seem odd to me, without them I would probably use either both reds (7&12) for 690v or both orn (8&11) for 625v.  Then use red/blu and red/yell as the bias.

[Champ_49]

I was confused about this as well. 
But that is exactly what I was going to do here.  I will use the red red for the 690V.
Supposedly the tech at the dealer told me I can use the red red to the diodes as well. ..

Confused ...


am I right in saying that I tie off the red/blue while red/yellow goes to ground However? 

For a jcm800 I don't ever recall using wires from the PT for 50V bias  .

One thing I forgot to note was this.  The PT is designed for a jtm45. So maybe for a JTM 45 you'd want to do what it states which is to use the red red for tube rectification but orange orange for solid state since solid state design would have a higher plate voltage than a tube rectification circuit so the orange orange would compensate for that?? Does that make sense?  I'm assuming using the orange orange leads for a jcm800 build would yield a more evh brown sound??

[2deaf]

am I right in saying that I tie off the red/blue while red/yellow goes to ground However? 

For a jcm800 I don't ever recall using wires from the PT for 50V bias

Red/Yellow is the CT, so it always goes to ground.
Red/Blue can be used for the bias if you want, or it can be taped-off and the bias taken from one leg of the HT.  The tubes won't know or care how you got the bias.

[sluckey]

If your build will be following the JCM-800 2204 schematic...

Tape off the two red wires. Tape off the red/blue wire. Connect the red/yellow to ground at the first filter cap. Connect the two orange wires to the double pole STBY switch for your B+ rectifier. The bias circuit diode will be fed from one of the orange wires thru a 220K resistor.

If you find you want more B+, then disconnect the two orange wires and tape them. Then connect the two red wires to the STBY switch.

[Champ_49]

Thanks Sluckey and 2deaf.

So when you say you connect them directly to the standby switch do you mean something like this?
Via the two diodes and the power capacitor? 
Sorry I have to say reading a proper schematic is not my forte.  So I have to resort to a layman's layout.

[sluckey]

So when you say you connect them directly to the standby switch do you mean something like this?

No. That layout does not exactly follow the original circuit.

See the two red wires that connect to diodes on the board? Just color those two wires orange.

[Champ_49]

Thanks Sluckey. 

Sorry.  I wasn't sure what you meant. So the layout is in fact not the original circuit?
I think this was the only layout iVe seen from different sites. Is there another original layout out there that I missed?

Edit: ok. I see what you mean. This is not in fact the origin layout. Would you still say this layout would work ok? Yes. The orIginal  had a different kind of switch I can see as well. I think this layout uses the plexi style switch?

[sluckey]

I wasn't referring to any particular layout when I described how to connect the PT. I was looking only at the original schematic. Mojo has a layout that more nearly matches the original schematic. It's here...

http://www.mojotone.com/Amp%20Kit%20Schematics%20and%20Wiring%20Diagrams/British%20Kits/JCM800%20WD%20-%2003042013.pdf?ck=RDmK7s0CAq9M3n-b&vid=RDmK7s0CArZM3hgo&cktime=131789&gc=clear

Ceriatone also has a layout but it looks more like the Triode layout. Any layout will work, but you'll have to adapt your PT to it. And as you see, there may be small differences between newer layouts and the original schematics. I've never seen a Marshall original layout such as Fender produced. I suggest picking one layout and stick to it. If you are buying a kit, use the layout provided with the kit. If you are scratch building your own layout, I suggest using the original schematic.

Hopefully you now understand how to connect your PT and understand the two voltage options (red v. orange).

[Champ_49]

Thanks Sluckey.  I am sticking with the triode layout for this one. I had ready built a jcm800 2204  using a triode layoit.  I wanted to try another one but with a different PT with voltage option and OT and just because this thing is addictive.  The only thing is the PT I am using is a lot different than the PT in the last one I built in terms if the wires and such.

So I will stick with the triode layout.  The only thing confusing was that the PT has a note saying the red red is for tube rectification and the orange orange for solid state rectification

I have my fingers crossed bit I am assuming I can use red red for higher voltage or orange orange for a bit lower voltage.  So I'll probably try both voltage options to see how it sounds. 

[2deaf]

I don't know if it's a big deal or not, but the 40-18054 is a laydown model that requires a big hole in the chassis.  40-18095 is an upright model and it has 560V in addition to 690V and 625V.   

[Willabe]

Do you actually have orange/red-yellow/orange wires? Or just orange-orange? (The notes say orange-red/yellow-orange wires, the picture shows orange-orange wires?)

The notes say; RED/BLU-RED/YEL = 50V BIAS. I think that should say red/blue = 50v bias. The red/yellow is the CT. 

The only thing confusing was that the PT has a note saying the red red is for tube rectification and the orange orange for solid state rectification

I have my fingers crossed bit I am assuming I can use red red for higher voltage or orange orange for a bit lower voltage.  So I'll probably try both voltage options to see how it sounds.

A tube rectifier will have a larger voltage drop than SS rectifier. But you can use either pair of B+ leads for either type of rectifier as long as you don't get a ridiculously hi B+dcv.

On the PT spec sheet, the bottom left gives the B+ output dcv's for a given pair of B+ leads with a given rectifier. (I don''t think a 5Y3 will have enough current for a pair of EL34's in grid bias?)



                  Brad   

[shooter]

Tape off the red/blue wire

Could you still use that wire to connect the bias diode to as a generic question, not specifically for this build?

thx

[sluckey]

Do you actually have orange/red-yellow/orange wires? Or just orange-orange? (The notes say orange-red/yellow-orange wires, the picture shows orange-orange wires?)

The pic shows two reds, two oranges, red/yellow, and red/blue. The red/yellow is the centertap and will be connected to ground regardless of whether you use the two reds or the two oranges.

The notes say; RED/BLU-RED/YEL = 50V BIAS. I think that should say red/blue = 50v bias. The red/yellow is the CT. 

The 50v on that red/blue wire has to be referenced to something. In this case it's referenced to the red/yellow center tap. If you were to measure voltage between the red/blue and the red/yellow, you would expect 50v. If you measured the voltage  between the red/blue and any other wire on that secondary winding you would expect some other voltage.

I thought the picture and labeling were pretty straightforward. Maybe this would have been easier to understand. Probably not.   

[sluckey]

Could you still use that wire to connect the bias diode to as a generic question, not specifically for this build?

Sure. But the series resistor would not be 220K. It would be a much smaller value, more likely 470Ω to 1KΩ.

[Willabe]

I thought the picture and labeling were pretty straightforward. Maybe this would have been easier to understand. Probably not.   

No, that's clearer.

That must be a typo in the notes for the PT secondary wire colors. But a rose by any other name (or color) is still a rose.


                Brad   

[2deaf]

Do you actually have orange/red-yellow/orange wires?

I don't see this on the diagram.

The notes say orange-red/yellow-orange wires,

A slash means both colors are on the same piece of wire.  A dash means  "to".  So it means 312.5V (Orange) to 0V (Red/Yellow) to 312.5V (Orange) or 312.5V-0V-312.5V.

[Willabe]

Doh!   

My mistake.