#183 B+....

[mrdarwin]

Hi there!
Finished my #183 Dumble clone.
I need advices about some differences between tensions I read on some different schematic and inside my amp...
In my amp B+1 is 410v, before the choke, on the schem is 468v.
So B+2,3 can't be right!

I use hammond 290FEX 640V CT.
In standby mod: 638V AC and 285V DC after regulation
In operate mod: 410V-415V...

And when I'm trying to adjust PI trimmer, I can't get 5-6V higher on the test point near 4k7 resistor...(100k) always UNDER the other test point (110k)

any suggestions?
thanks

[Aaron]

I hope your not running EL34's. That transformer is rated at 5.5amps and 4 x EL34's will draw 6amps alone.

Aaron

[UltraHookedOnPhonix]

Hi there!
Finished my #183 Dumble clone.
I need advices about some differences between tensions I read on some different schematic and inside my amp...
In my amp B+1 is 410v, before the choke, on the schem is 468v.
So B+2,3 can't be right!

I use hammond 290FEX 640V CT.
In standby mod: 638V AC and 285V DC after regulation
In operate mod: 410V-415V...

And when I'm trying to adjust PI trimmer, I can't get 5-6V higher on the test point near 4k7 resistor...(100k) always UNDER the other test point (110k)

any suggestions?
thanks

Some twin PTs have 320V-0V-320V which will result in the voltages you posted. You need a 340V-0V-340V (680V CT) or a 345V-0V-345V (690V CT) power transformer which is what #183 had.

In France you have 230V/50Hz so if I were you, I'd take a look at the MOJO763EX:

http://www.mojotone.com/amp-parts/Trans ... sformer-EX

A pretty penny and yes has only 6A heaters but I take it #183 did too.

Or...

Tweek the PS string. The plates are going to sit a bit lower, but try lower the 3K resistor until the preamp voltages are where they "need" to be.

[mrdarwin]

aargh....
what xformer do you advise?
thanx

[ToneMerc]

Hi there!
Finished my #183 Dumble clone.
I need advices about some differences between tensions I read on some different schematic and inside my amp...
In my amp B+1 is 410v, before the choke, on the schem is 468v.
So B+2,3 can't be right!

I use hammond 290FEX 640V CT.
In standby mod: 638V AC and 285V DC after regulation
In operate mod: 410V-415V...

And when I'm trying to adjust PI trimmer, I can't get 5-6V higher on the test point near 4k7 resistor...(100k) always UNDER the other test point (110k)

any suggestions?
thanks

You need to use a power transformer that has a 230V primary, not a 240V primary.

You can decrease that 3K resistor to around 680-820R to increase your preamp voltages.

TM

[mrdarwin]

Thanks everybody for all infos.
In a first time, is it possible to switch el34s with 6l6s, even with a plexi OT?
I will decrease 3k resistor, and will order a mojotone PT. Any source in Europe?

[Guitarman18]

Hi mrdarwin,

Here you go;

http://www.allparts.uk.com/products/bla ... xport-taps


All the best,

Paul.

[mrdarwin]

Ok thanks!
But 6.3v@6A...
4xEL34 (1.5A)=6A... but 12AX7x3 heaters are 300mAx3=1A

Do I need 7A 6.3V, or 6A are enough? It looks like some #183 builders use this xformer...
What about 6l6 swaping?

[martin manning]

The Hammond data sheet indicates 6.5V at 5.5A, 7V no-load. Does it run hot? You could get some idea of how its doing with the increased filament current by measuring the voltage. If it is much below 6.5V then it may overheat. Changing to 6L6's will get you out of trouble, as they are 0.9A each, 4.5A total including the preamp tubes.

[mrdarwin]

Yes, the PT runs hot.
I tried with only two EL34s, (with 8ohms cab in the 4ohms OT) and get a nice creamy sound (dumble sound...). With for EL34s, the amp sounds crispy and tired...

I will run it with for 6L6s, and change the PT later (out of budget now...)

I assume it's ok regarding primaries of OT: 1700 for plexi, 2000 for Twin, not so far...

[martin manning]

I assume it's ok regarding primaries of OT: 1700 for plexi, 2000 for Twin, not so far...

Maybe not the best match, but you won't do any harm.

[mrdarwin]

I will try 6L6...
any #183 user/builder with 6A heater?

here is a pic:

[mrdarwin]

I sourced this PT:

720vCT 400mA with 60v bias tap
6.3vCT 7A

The HV secondary is it too much?

[strat100]

I have just used the Hammond 290fex in my 183 build and have also got a very hot transformer,nice to no that there is a proper transformer over this side of pond mind you it certainly costs us

[martin manning]

I sourced this PT:

720vCT 400mA with 60v bias tap
6.3vCT 7A

The HV secondary is it too much?

I think the secondary voltage is too high. I would look for a 100W Marshall transformer with lay-down mounting. There will be plenty of filament current available, but you will have to rework your rectifier into a FWB, and change a resistor in the bias circuit. This looks like a good option: http://www.classictone.net/40-18046.html The mounting centers are the same as the Fender 100W units. The chassis cut-out is close (see linked drawing), and the primary has both 230V and 240V options. I believe Triode Electronics will ship internationally.