Princeton Chassis Progress pics 12-4-2013 - back to it

[Bob-I]

Bob,

Looks like you have the 220/150k plate resistors on V2 the wrong way round?

Crafty

Wow, good catch. That wouldn't a sounded too good

[Structo]

Yeah, I made that same mistake on my 100w ODS.
Martin saw it and I quickly corrected it.

Sounded like ass before and sounded like heaven after I fixed it.

[Bob-I]

Yeah, I made that same mistake on my 100w ODS.
Martin saw it and I quickly corrected it.

Sounded like ass before and sounded like heaven after I fixed it.

My problem is I'm colorblind so I wouldn't have caught that until I measured voltages.

[amplifiednation]

Bob,

I would personally use 100uF on plates, and 16-20uF on the screens of those 6V6 tubes. I like how that feels and sounds.

jelle

Bob this is what I did on my 6v build. My intention was to series the 100/100 can for 50v... until I realized that isn't possible. It's 500v so I just went with 100uf

[groovtubin]

This is what I like to think of as a honeymoon fit, real tight.

I'm still trying to find a way to fit a loop in here too. I'm thinking an ironsounds loop mounted in a cap pan under the chassis.

In reality I don't think that will work, just not enough real estate. I'm actually not a big fan of the way a dumbleator colors the tone, I like the way my amps sound. Maybe I'll put the ironsounds loop into an external chassis.

Probably shoulda gutted n rebuilt like you did Bob, dang i must be nuts! lol!

Only mine isn't a gut job, I bought the chassis and fabricated the boards.

I've tried modding like that, it really makes more since to gut and start over.

i hear ya Bob, dang thing did sound phenominal, despite working for practically free! lol! Did a 70`s circuit! INSANE on 6V6`s!

[Bob-I]

i hear ya Bob, dang thing did sound phenominal, despite working for practically free! lol! Did a 70`s circuit! INSANE on 6V6`s![/quote]

Gotta love those 6Vs cranked up.

[Bob-I]

Bob, have you considered the Zero Loss FX Loop from Metro Amp?

http://metroamp.com/store/index.php?mai ... cts_id=499

Tom, I read a bunch about this loop on the metro forum. It appears this was designed around the Marshall cathode follower tone stack. Comments around other amps are that it's not a great fit, but in some cases it may work on a plate driven tone stack. Since the Dumble loop is driven by the stage following the tone stack, or the OD stages I'm not sure this will be right.

[Structo]

Thanks for the info Bob.

In fact, I did use an Ironsounds loop in my D'lite when I built it.
Seemed to work fine.

I just decided to built a Dumbleator and prefer that to the SS loop.

[mlp-mx6]

Is that the Weber chassis, the Allen (stainless steel) chassis, or from some other source? Thanks.

[Bob-I]

Is that the Weber chassis, the Allen (stainless steel) chassis, or from some other source? Thanks.

It's an Allen chassis.

[Bob-I]

Slight delay. I ordered the wrong relays, they don't fit the boards. Otherwise it's pretty much done.

I wired the PT secondaries to a DPDT switch. I expect 330V from the low setting, 400 from the high.

I'm concerned about the bias. I built a full wave - bias from the secondaries, calculated ~30-45 at the low power setting and ~43-57 at the high power setting. I may need a larger pot over the 10K I have in there now.

330V at low power - bias range -30-54 seems about right
400V at high power - bias range -43-57 seem cold

Thoughts?

[Smitty]

-30 to -54 seems right for 400v

-20 to -44 for 330v may work

if you're concerned you may go too low then -25 to -49

my guess is between 27 and 33 at 330v, unless you like it cold.

you can bias pretty hot at 330v and not encounter the same problems you do at 400v with 6v6s.

you can bias the darn things into class A at 330 if you ran the screens 100v lower. someone say OC3?

[martin manning]

Assuming high = 400 Va-k and 395 Vg2, low = 330 Va-k and 325 Vg2, and 70% Pa max for the idle point, I get Vg1 = -38V for high, and -28V for low. (GE '55 6V6GT data sheet)

[Bob-I]

Assuming high = 400 Va-k and 395 Vg2, low = 330 Va-k and 325 Vg2, and 70% Pa max for the idle point, I get Vg1 = -38V for high, and -28V for low. (GE '55 6V6GT data sheet)

Thx, I never thought to check the data sheets

I need to change the tail resistor. Right now I have 270K to a 10K pot to a 33K tail. By dropping to a 22K tail I can get the range I need for those voltage, 28K for low, 25K for high.

[dreric]

Bob,

How's the build coming together?

Did you go with 50/50 or 100/100 on the cap can?

What schematic / values did you use to design the circuit?

Eric