Why would my screens be higher than my plates?

[frischmann]

Hi Guys,
I have a tweaked D'lite with a choke and 6L6's.
I noticed my plates are at 416V and my Screens are at 426.

I seem to remember reading that the screens should never be higher than the plates.

I could use some help on where to look.

BTW,
The amp sounds sooo much better with a choke..

Thanks,
Paul

[JimiB]

Did you hook your center tap to the main filters (first ones after the recifiers) and the choke? Are your screens coming from the other side of the choke? Are you using screen resistors?

[frischmann]

Hi Jimi,
Thanks for responding.
I have the CT after the 22K dropping resistor. The screens come off of the other side. so the choke is installed where the resistor would have been.

I remember there was a mistake in the D'lite layout...I'll have to check that again..

I took all of my plate voltages while I was there

V1a-197
V1B-203

V2A-203
V2b-206

PIA-304
PIB-301

V4 Plate-416
screen 423

V5 same as above

Dropping string values (standard D'lite)
1k, 22k, 2k2

[Structo]

Yeah, I saw over at the BN forum you installed the choke.

You took out the choke simulator power resistor right?

The DC resistance of that Fender choke is probably way less than the resistor so it makes sense that the voltage will be raised on the screen node since that is what it feeds.

I think the choke is 100R right?

Try raising the 1K 3w to 2K2 on the string.

[frischmann]

Hey Structo,
I did take out the simulator (390ohm, 10watt) resistor.

The choke really makes the amp breath. It can just ebb into harmonics..
I'd like to get the plates up to match, I'm not sure where to look though.

[Structo]

#124 uses a 100R choke but then the first resistor after it is a 2K2.

That is the node for the screens.

You have a 1K there, try a 2K2 in it's place.

[frischmann]

Cool idea but isnt that the same resistor that feeds the PI plates (not looking at a layout) one leg of the 1K fees the choke the other side goes to the PI plase resistors....right?

Shouldn't I be able to get 425V on the plates of a 6l6 using the BN tremolux iron?

[frischmann]

BTW, using a 2.8H 90ohm choke.

[Structo]

I was just going by what the schematics show.

The only glaring difference is the resistor after the choke.

But your choke is 10 ohms less than the Dumble one so you will have to make adjustments for that.

What size are your screen resistors?
FET resistor?

Take a look.

[drz400]

Hi Guys,
I have a tweaked D'lite with a choke and 6L6's.
I noticed my plates are at 416V and my Screens are at 426.

I seem to remember reading that the screens should never be higher than the plates.

I could use some help on where to look.

BTW,
The amp sounds sooo much better with a choke..

Thanks,
Paul

Where is the bias set?
What happens when you apply a since wave?

[frischmann]

Thanks Structo,
I'll give it a try......I have got to get better at reading schematics.

[frischmann]

I checked the bias quickly,
It's at 415V @ 36ma and 38ma if I increase the range, it goes to about 410v at 38ma and 40ma.

I do not have a scope.....yet....

[JimiB]

looking at the dlite power supply schematic above give us the voltages of HT+A thru HT+E

[frischmann]

O.K. it looks like the supply measures like this
HTA-426V
HTB-426
HTC-420
HTD-329
HTE-322

[Structo]

That's kind of weird the choke wouldn't drop any voltage.

But I guess as an inductor it resists a change in current more than anything right?

Have you tried a 2k2 resistor where the 1k is yet?