Dropping string help

[glasman]

The voltages are not too bad, but for my tastes I prefer the CL plates at the 182 to 185 range. If it were mine I would probably raise the 6.8 to 7.5K or so. That should make the top end a little sweeter sounding. and drop both the OD, CL and PI voltages down just a tad.

Gary

[dogears]

Try a few different tubes in V1 and V2 to keep the voltages down, especially on V1B. You could go to a 24K drop to V2 to shave a few volts.....

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?

[RJ Guitars]

So I have a question that kinda goes the opposite direction from Danotrons's. If I have a Power transformer that is just under the 325-0-325, can I reduce those dropping string resistors to bring my voltages up?

I have a Hammond 272JX - which is rated at 300-0-300. No we all know that a Hammond will actually make more than the rating so I figure this thing will come in somewhere between 312 to 318 volts... so I'll start pretty close to the magic 325 to begin with.

Any thoughts??

rj

[Bob-I]

So I have a question that kinda goes the opposite direction from Danotrons's. If I have a Power transformer that is just under the 325-0-325, can I reduce those dropping string resistors to bring my voltages up?

I have a Hammond 272JX - which is rated at 300-0-300. No we all know that a Hammond will actually make more than the rating so I figure this thing will come in somewhere between 312 to 318 volts... so I'll start pretty close to the magic 325 to begin with.

Any thoughts??

rj

That's not really Rocket Surgery. Once it's up and running, measure the voltage drop across the resistors, calculate the current draw, then recalculate based on the amount of voltage you want to drop. The current draw won't change much.

I built an amp with a 272HX and it sounds GREAT. Except that a bad tube blew the OT, it's my favorite gigging amp (maybe until I take the Brandon chassis amp out )

[Fischerman]

RJ,
I built my 50W HRM using a 272JX PT. As you said...those series of PT are rated for a 115vac primary so all your secondaries will be high when using the typical 120vac-or-greater wall voltage. My heaters ran at just over 7vac so I had to reduce that too.

My B+ in that amp is ~435v (I'm using JJ KT77). That amp also has a built-in D'lator but it's supply taps off of the screen node and doesn't affect the other voltages much at all. The preamp supply voltages are 410v-335v-300v using a 3K-15K-10K string with a 150K FET simulator resistor at the last node. Preamp plates (using 220K/150K on both V1 and V2) are 192v-196v-210v-215v. Not saying these are the best values/numbers...just giving them to you for info (I actually think it might have sounded better at slightly lower voltages but I never got back to this amp...building other amps sidetracked the tweaking).

EDIT: That amp has a BM PI...that will affect all the preamp voltages because it runs more current than the 'regular' Fender-value PI.

[RJ Guitars]

Thank you guys for the help, you've confirmed my own inclinations to some extent. That is, the dropping string should be all about getting a specific voltage at a certain point. Occasionally I run into the notion that you have to use very specific values of resistors in the dropping string and never vary the values/ratio or the mojo goes away. I can't follow the technical reason behind that thought but there are still a few things I've yet to learn...

I had not thought about the heater voltage being a bit high, I suppose I could also pad that slightly if I really wanted it to be right on 6.3. Otherwise I assume the only down side might be that the tubes life goes a little short.

Thanks again,

rj