Dropping string help

[danotron]

I'm building a Dlite...

I am using a Fender power transformer. It has a 355 volt secondary. I need a little help with the power supply dropping string, to get the correct voltages at the plates.

What voltage should I measure at each "node" of the dropping string?

Can I run my 6L6's at a higher voltage? Will this effect the tone? Does higher voltage mean louder power amp?

Should I use a modified version of the original droppping string?

I know I want about 190 to 200 volts at the first plate but what should the voltage drop across the plate resistor be?

[heisthl]

nodes A, B, C in your picture are good and well within the ball park, use a 22k for the next node D (approx. 320 v) and then a 2k2 with a 150k to ground for the last node E (approx 312). this will yeild about 200 on V1 (E) and 205 on V2 (D). Use an additional cap for the last node since your picture doesn't have it.

[dogears]

First of all, unless you are running ultralinear, I'd lower your screen caps to two 47uf in series.

Then, I'd raise the size of the dropping resistor to the PI to something in the 6.8K range. 2.7K is too small for 473V.

Try it and let us know what you get!

[danotron]

47uF?

Do you mean replace the 22uf/500v with two 47uF in series with 470K resistors accross them? I have see that a few time in the forum. What is the differance? IS it more stable?

Sorry for all the questions, just trying to understand it (the theory part)

[dogears]

Yes, but what you originally posted shows two 100uf caps on the screens.

47uF?

Do you mean replace the 22uf/500v with two 47uF in series with 470K resistors accross them? I have see that a few time in the forum. What is the differance? IS it more stable?

Sorry for all the questions, just trying to understand it (the theory part)

[danotron]

ok...so is this what I want?

[heisthl]

get rid of that 33k 10w resistor, everything else looks good

[danotron]

Great...thank you very much. ..I will give it a try...guess I'll have to order some parts....

[odourboy]

Great...thank you very much. ..I will give it a try...guess I'll have to order some parts....

Order some extra dropping resistors of varying values so you can tweak your dropping string once the amp is assembled.

[phsyconoodler]

One thing I noticed that may or may not be an issue.
You diagram shows a full wave bridge rectifier.If you are using a PT with a 335-0-335 secondary,then it will double the voltage to about 670v after the rectifier.
Are you using a typical fender PT for a super,bassman etc,or is this a 100 watt PT?

[heisthl]

he said "It has a 335v secondary" not a 335-0-335. This is probably from a new Fender which all seem to be using the full wave bridge style PS.
335 x 1.4 = 470

[danotron]

yes it is a newer fender transformer (from a super 60) and I am using a full wave bridge rectifier..does this change things?

470V sound about right....

[danotron]

I have my new power supply built and installed. Do these voltages sound correct?

A-482v
B-477v
C-437v
D-329v
E-322

These are he loaded voltages......

[odourboy]

Those look like a really good starting point to me. B+3, B+4 and B+5 are a touch higher than is typical for my builds, but I tend to aim for a lower plate voltages in the preamp than what may be typical.

Measure and report on the plate voltages (and cathodes while your at it) on your 12AX7s.

[danotron]

Checked all voltages again...the power supply voltages are a bit lower this time...

A-459v
B-454v
C-415v
D-313v
E-306

Plates:
CL1-196v
CL2-215v
OD1-192v
OD2-208v
PI1-313v
PI2-303v

Cathodes:
CL1-1.58v
CL2-1.65v
OD1-1.75v
OD2-1.53v
PI1-49.9v
PI2-303v

Are these good numbers?