Too much B+ ??

[Toxophilite]

So on my now Ab763 lite (with tremelo build)
I 'm having some problem with my B+
I seem to have an excess of it
At the 1st filter cap I have 459-460
After the choke I have 454  (the choke is from a Hammond L100 Reverb/Power amp)
After the 1st 10K resistor I have about 453-454
After the 2nd K resistor I have 452-453

i'm using a 5Y3 for the testing

The first reading isn't too crazy but all the subsequent ones are way too high I think
What am missing/not understanding??

Here's a couple photos. THis is just the filtering system hooked up like it would be on little board, but between 2 terminal strips

[sluckey]

What am missing/not understanding??

You're missing the load. Right now there is no current being drawn from the supply so all voltages will be high. Don't worry about it. When you have the amp completely wired and tubes plugged in those voltages will drop considerably.

[Toxophilite]

Excellent, thank you so much

Does the power supply/filtering look half decently placed?

Onward!

[HotBluePlates]

You're missing the load. Right now there is no current being drawn from the supply so all voltages will be high.

Expanding on what Sluckey said...

Ohm's Law:
Voltage = Current * Resistance

You have resistance between different power supply nodes (the different filter caps separated by a choke or resistor). For there to be a drop in the voltage after each resistor, you must have current drawn through the resistor. For there to be current draw, you must have a tube in its socket (or a resistance from B+ to ground, which is not common in the majority of amps).

When you add the other circuit elements, and plug in some tubes, the voltages will drop and will descend along your B+ rail.

This is also a troubleshooting technique, as a tube that has a burned open cathode resistor (for example) will pass no current, and the voltage at both ends of the plate load resistor will be equal (no voltage drop across that resistor because no current through it).

[Toxophilite]

Excellent!
A little theory too!

[Toxophilite]

Weeeell
-I have the power supply/filtering built
-I have my preamp built
-The 6V6s are wired up EXCEPT for the bias. so currently have no -35 volts going to the 6V6s
The cathodes of the 6V6s are wired to ground
And The Phase inverter isn't done yet

I thought I'd check the voltages with a load..however I don't actually know if having the bias set makes a difference for 'load' on the power supply..likely it does

I got substancially lower voltages..Surprise!!
I may be learning a lesson in over-estimating the potential of ones PT etc.!!
Which is okay I can always switch back to a princeton or a 5F11 vibrolux with an extra gain stage
There's a lot similiar to all of these

here's the goods
prior to flipping the standby switch I have 460vdc at the firts filter cap

After it drops to:

  1st cap    -285
 post choke - 274
   2nd cap  - 242
   3rd cap -216

[eleventeen]

  Hey where'd those ~~175 volts go?

All kidding aside, in my experience that's rather a large difference between load and no-load, though...I must say.

maybe you should pull the 5Y3 and just for grins tack-solder a couple of 1N4007 diodes across the socket to see what you might get w/a SS rectifier. Probably +40-60 volts add'l.

[sluckey]

-The 6V6s are wired up EXCEPT for the bias. so currently have no -35 volts going to the 6V6s

I thought I'd check the voltages with a load..however I don't actually know if having the bias set makes a difference for 'load' on the power supply..likely it does

I got substancially lower voltages..Surprise!!

***DANGER***

DON'T PLUG THE 6V6s IN UNTIL YOU GET THE BIAS SUPPLY BUILT AND HAVE APPROX -35V ON PINS 5 OF EACH 6V6!

[Toxophilite]

Funny!
I tell you it's hard being ignorant!

So I hooked up the AA960 Princeton Bias steal(cause I don't have bias tap on my PT)
and sent -36 volts to the 6V6s..hmmm
big difference!
The other thing I did different is instead putting the 12au7a I had handy(initially) in the preamp section I put a proper tested 12ax7..which made a 20-40 vdc difference too)

Now after flipping the standby switch I get

455
453
424
392

Crazy electronics stuff!..there might as well be magic smoke or a ball of pure whit energy inside!

I still don't have the load of the phase inverter
I think I'll get to that tomorrow

[sluckey]

big difference!

The big difference is that now you are not burning up your tubes, output transformer, and power transformer. Without the bias voltage on the tubes they were drawing crazy current which drug the B+ rail way down because your PT could not supply that kind of current. The 6V6s should have been glowing a pretty cherry color! Hope you didn't run it over a few seconds without the bias voltage.

[Toxophilite]

Ooops
As i said .'it's hard being ignorant!'
Truly!
Note to self; "Self!! Do not do that again!!"

Well it wasn't for more than, erp, more than a few seconds..
And I was using crappy old almost dead 6V6 and my old 5Y3, there was no bad smells or other unfortunate evidence.
The bias is hooked up now and I've had another good lesson..hopefully not a bad one
I'll proceed and see what falls out!

Thanks!

[Toxophilite]

Hello again
I've been working on the amp and have it all assembled. I've checked it over a couple times

Buuut It's not making any sound
The tube are lit up as is the pilot light
There's plenty of B+...probably too much actually. I still have about 230vdc on my preamp circuit and 400+ on the phase inverter
Checked the all the points where it;s delivered etc

I thought, okay maybe I cooked my transformers!
i tested the resistances and they seemed good(I looked online)
I thought I'd test the output transformer
I have another pushpull 6V6 transformer so I disconnected the OT leads off the 6V6s and hooked up the other transformer in the same way with some b+ , the speaker hooked up to the secondary and grounded it's shell to the chassis, just to make sure...no luck ,same results, no sound. I'm pretty sure the one I tested with was good

Checked over the schematic and layout again, moving slowly through the audio path and power supply
Everything seems good

So I checked the PT
right voltage at the heaters, right voltage at the primary
right voltage at the plates of the  rectifier, right voltages at the rectifier filiments

It seems like a short to ground of audio signal as it's sooo quiet
But I searched and searched , did conntinuity test etc and all seems well

Does excessive B+ throw things out with a result of no operation??

Any other idears??
 

[John]

First thing I'd check is the signal wires.Maybe there's one not soldered quite right? Also, check voltages on your grids, they should read 0 or at least less than a volt.

I had similar problem once, and was triple sure I had everything wired right, since I had checked 3 times. 4th time over I found my mistake, it was so obvious I couldn't believe it, think I had a wire hooked to the wrong end of a cap or something, I forget.

This is where a listening amp comes in mighty handy (search the forum). I haven't built one yet, but next time.....  ;)

[sluckey]

Probably a wiring error. We need to see your specific schematic since this is put together from more than one amp.

[Toxophilite]

Too true!
A wiring problem!
thanks for the moral support
A bad 6V6 cathode ground and a missed 100 ohm resistor to ground right before the negative feedback

It's running and sounds really pretty, not noisy(yay)..but it's quite quiet
I have it cranked all the way and it's just starting to crunch a tiny bit on the bottom
I wouldn't want to rehearse with a drummer, even a quiet drummer
Maybe a standup bass player..that sort of quiet,
Nice tone though, the EQ works well..I set it up alittle more like my super(1980 last of the silver faced mohicans)
I usually have the eq dialed down 333 pretty much.
Way quieter than the vibrolux..but I should try it through the JBL to compare
(I'm sure the vibrolux would be quiter with a fneder tone stack but the difference is pretty dramatic, I could use the vibrolux with a medium volume drummer,,,if i was playing a dirty sound)


I thought it might be a little louder.. could it be the small negative feedback resister?
It seems to have quite a curious little network of resistors and the .1 cap prior to the negative feedback
Is it all necessary?

Any ideas?

Also
 Now the B+ is a little low (at the first couple caps)and high(at the preamp)
I think the Phase inverter voltage is about right

399
394
336
315

Is there a way to bump this up a little at the power amp and take it down a little near the preamp end?

Resistors?
Sacrificing a goat?

[sluckey]

That AB763 Deluxe lite should be plenty loud enough for a small to medium club. Maybe try some good 6V6s. And use a GZ34 to increase the B+. Increase the size of the last resistor in the B+ string to decrease the voltage to the preamp.

[Toxophilite]

I have a strong Sylvania GZ34 in the amp and a equally strong pair of RCA 6V6s

My problem could've been the little 10" alnico 50s Rola(English Pre Clestion) in my little test cab.
I swapped it in there recently and forgot.
When I tried it with the JBL D130 it was vastly louder..many many times louder.
I couldn't really try it out as I have a surly building caretaker nextdoor (it is after 10 after all..)but I'll give it shot tomorrow day and report back
I'm getting about
403 at the first filter cap
400 at the next
340
and 318

I have a few questions if I may

I'm not overly attached to rectifier sag as I generally like a nice clean tone with nice bottom end
I have other tube rectified amps if I want that sound for recording
The super reverb I've been gigging with for the last 20 years is solid state rectified and it's a lovely sounding clean amp. I use pedals for distortion as it just won't distort nicely and it's impossibly loud much past 4.

Could I get a bit more voltage at the first few positions by making a little diode bridge and having the amp solid state rectified?
There's lots of instructions on line, I could even make a plug in unit. I have lot's of old octal tubes and even some neat octal plugs with insulated metal caps.

- Is there any big difficulty with that option?
Beside likely having to drop the B+ at the preamp or just before the Phase inverter

- Also I was originally planning on putting in a tremelo, I have the 12AX7 socket wired with heater and ready to go.
Will the addition of this extra load drop the preamp B+ removing the need to increase the last dropping resistor?

- I have seperate preamp question for Sluckey if I may, regarding grounding.
I noticed you lead the 12AX7 Cathide bypass caps and resitors to a seperate ground (C)

Right now the 12ax& cathode is grounded to the same ground as the preamp (I just figured out your grounding scheme ABCD etc)
But for the 12AX7 cathodes the layout is numbered, it says 'Ground 1'
But the schematic has the letters and no specific letter ground for the cathodes..I could've missed it though.

-Do you mean the 'A' grounding point?

I get a lot of noise form my preamp ground when I touch a probe to it.
-I'm suspecting the problem is the cathode ground..Yes?

I have all my filter caps in a row grounding to a little bar run across the back of the terminal strip they're attached to .It's then attached to where the centertaps ground.

-Would I be better off running seperate wires from the negative side of the caps to a grounding point at a small distance?


okay that was a three part question

Out of curiousity what function does the 220K resistor to ground in paralell with the first filter cap/caps have?

Thanks all for your patience and much appreciated assitance!

[sluckey]

Could I get a bit more voltage at the first few positions by making a little diode bridge and having the amp solid state rectified? Is there any big difficulty with that option?

You cannot use a diode bridge but a conventional diode rectifier will give you more B+. Not difficult at all.

Will the addition of this extra load drop the preamp B+ removing the need to increase the last dropping resistor?

Not enough to make a significant difference. However, I would not connect the tremolo circuit to the B+ node that feeds the preamp.

I get a lot of noise form my preamp ground when I touch a probe to it.
-I'm suspecting the problem is the cathode ground..Yes?

You should not get any noise when probing any ground. Check that.

About my grounds... The purpose of my layout drawing is to provide a board drilling template AND to show how to interconnect the board to the other components. It's not a complete layout drawing. You must refer to the schematic for connections not related directly to the board. And since you are doing a true point to point wiring, you'll have to adapt. Best to follow a schematic.

Out of curiousity what function does the 220K resistor to ground in paralell with the first filter cap/caps have?

It's called a bleeder resistor. It helps drain the charge on the filter caps when you turn the amp off. It has no purpose when the amp is on.

[Toxophilite]

Thanks Sluckey(yet again!)
You and all the other contributors have been invaluable in this build.
It's been quite a pleasure adding to my limited understanding of the building process and how the amps work. Cool stuff.
I transfered back to my original thread  because I thought I was straying back into general build/ trouble shooting questions. If you want you can see my current progress there.
I'm quite pleased with my stubby little plug in SS rectifier

I also might've solved my distortion problem and will likely know tomorrow when I can test the amp at volume.
If so then maybe I'll get to work on the tremelo circuit.
Thanks again