100 watt transformers?

[chuckb]

I' m in the process of building a Jcm 800 2204 style amp and have the chassis already laid out. I installed what I thought were 50 watt trannys but when checking the amp schematics that these came out of I found that the trannys are actually 100watt. I could probably use them for the 2203 marshall but the chassis doesn't have the room for the extra power tubes and cap cans. so my question is, "Is there a way to cut the power of these trannys for 100watt to 50watt so I can use them or will i just get the proper 50 watt trannys"? The trannys came out of a Gibson SG100 that used two 8417 power tubes, which can handle the 100 watts provided by these trannys.

Chuck.

[MWJB]

"Is there a way to cut the power of these trannys for 100watt to 50watt so I can use them or will i just get the proper 50 watt trannys"? Yes, use 2x25W power tubes. The PT can supply a 100W amp maximum...but will also work for 50W...25W...5W if you want. The PT doesn't dictate the power the amp must make, it just has to supply the correct B+ voltage (what is the B+ secondary rated at in terms of VAC?) & adequate current for B+ & heaters. Using a larger than spec'd PT is a great idea, better transient response, more consistent voltage supply...high end builders do this all the time.

[chuckb]

Hey MWJB, thanks for the response. i'm not to sure what the B+ secondary is rated at. I have a schematic of a similar amp only this amp uses' 4 x el34,it's the bass amp version. My trannys are the identical set that is on this schematic.

Chuck.

[west]

Is it possible to get 100W transformer by combining 2 50W transformers?

[MWJB]

[ATTACH=CONFIG]22617[/ATTACH] Hey MWJB, thanks for the response. i'm not to sure what the B+ secondary is rated at. I have a schematic of a similar amp only this amp uses' 4 x el34,it's the bass amp version. My trannys are the identical set that is on this schematic.

Chuck.

225VAC @ 500mA. Be sure to follow the SG100 rectifier & filter cap circuit, it's a voltage doubler 600vdc+ on the plates, screens run off 300vdc...not sure that it is the best option for what you want.

[MWJB]

Is it possible to get 100W transformer by combining 2 50W transformers?

Marshall & Danelectro have both used this principle with respect to output transformers....it seems a little impractical regarding power transformers though.

[chuckb]

so is there a way to get the correct voltages for that I need running two el34's?

[chuckb]

Hey mwjb, Here is the schematic showing the jcm800 and the plates carry a load of 468v, so by using these trannys I will get 132v more than i need on the plates ? If this is correct is there any way to lower the plate load?

Chuck.

[MWJB]

so is there a way to get the correct voltages for that I need running two el34's?

The PT will support 2xEL34 at 600vdc+ wired as per the SG100, with the voltage doubler. However the '81 2204 schem shows 365vdc on the EL34 plates. You could stick a full wave bridge rectifier on the SG100 PT B+ secondaries, this will give you a shade over 300vdc on the EL34 plates...nearer to 365v than 600v. If you do decide to go this route, then you can just graft the Fender bassman 5F6A bias circuit onto the SG100 bias winding, rather than use the SG100 voltage doubler.

Most folks seem to run JCM800 2204 builds at more like 440-470vdc these days though...no obvious/easy way to get that from the SG100 PT.

[chuckb]

Thanks for the info. I guess I'll just scrap the idea of using these trannys for the JCM800 build and purchase the proper ones for this amp. I may find that i can use these trannys (SG100) down the road for another build where they're more compatiable or just sell them. Any idea of the quality of Ceritone trannys?

Chuck.

[big_teee]

Thanks for the info. I guess I'll just scrap the idea of using these trannys for the JCM800 build and purchase the proper ones for this amp. I may find that i can use these trannys (SG100) down the road for another build where they're more compatiable or just sell them. Any idea of the quality of Ceritone trannys?

Chuck.

I used the Classictone JCM800 Bundle in my Amp a few years ago.
http://store.triodestore.com/marshall50wbundle.html
They're hard to beat for the price.

[MWJB]

[ATTACH=CONFIG]22620[/ATTACH]
Hey mwjb, Here is the schematic showing the jcm800 and the plates carry a load of 468v, so by using these trannys I will get 132v more than i need on the plates ? If this is correct is there any way to lower the plate load?

Chuck.

That's more "a" schematic than "the" schematic ;-) Not saying there is anything wrong with it, just that there can be a pretty broad interpretation of what a JCM800 2204 actually is.

There's always a way to do something, the question really is, "is it practical" to do it? You'd need something that can take 10W+ without burning up...like a large W 1.2K resistor after the rectifier, but this will probably have a large & negative effect on tone. It makes more sense to go 600vdc, 300vdc, or new PT.

[big_teee]

What makes a JCM800 2204 different from the regular JCM800 is the Cascaded Preamp.
I used the Classictone Iron and mine is 345-0-345.
My AC is high, it is 125-127V.
My 2204 Runs on 492V.
If I ever build another one, I'll use Iron something like this.
Lots of flexibility for different tubes.
http://www.classictone.net/40-18095.pdf

[chuckb]

Ya, new trannys it is then. thanks guys for your input.

chuck.

[big_teee]

Ya, new trannys it is then. thanks guys for your input.

chuck.

One more thing, on the 2204.
It is very prone to hum.
Make sure you use the 5 hy choke, and not the 3 hy.
It is easy to get the wrong set, on marshall iron.
Good Luck,