6G3 Capacitor Question

[dwinstonwood]

Thanks bmccowan!

I do enjoy projects more when I take my time. So much of this is new stuff that I like to finish a step and then look at for errors and then plan how and what to tackle next.

So, let me ask this. What gauge wire should I use for grounding? I haven't soldered up the ground wires to the chassis bolt yet because I wanted to get advice on that first.
Thanks.

[sluckey]

I like 20AWG for power grounds and 22AWG for preamp grounds. Anything bigger that that red/yellow PT wire is overkill.

[dwinstonwood]

Thanks sluckey! I'm thinking stranded, not solid, since it's less likely to break under stress.

I'll replace those wires tomorrow, solder up the two ground bolts (one near the PT for power and another near the Normal input jacks for preamp), and get the main board in and connected up.

Then, I can power up without tubes and find out what happens!

BTW, I have a black car, and all I know is that white stuff is hard to wash off.

[dwinstonwood]

OK, I'm trying to solve things myself instead of asking.

My 1 Ohm cathode resistors are 1/2 watt. Let's say I measured a voltage drop of .05V. Converting that to .05 amps times the voltage equals .0025 watts. So, 1/2 watt resistors are plenty big for this application, yes?

[shooter]

yes

[dwinstonwood]

Thanks shooter!

Here's my solution to installing the 1 Ohm resistors. Since pin 1 is not used - the JJ 6V6S's I bought don't even have a pin 1 - I used it to tie off the resistor.
Now, I can simply connect my test clip to the bare wire between pins 1 and 8 to take my readings.

[sluckey]

I hate soldering a wire to a dangling end of a resistor. I like resistors to be firmly supported on each end. I would have mounted the resistor ***BETWEEN*** pins 1 and 8. Like this...

[dwinstonwood]

I hate soldering a wire to a dangling end of a resistor. I like resistors to be firmly supported on each end. I would have mounted the resistor ***BETWEEN*** pins 1 and 8. Like this...

I like that!
I did notice that if the wire moves the the resistor moves, too. Over time it could get weak and snap off at pin 1.
Thanks!

[dwinstonwood]

Going back and doing this over is like building three amps.
The bright side is it's practice and the methods stick for future builds.

But, installing the main board and wiring it up is not something I want to do multiple times.

Is there anything wrong with my preamp wiring layout?

Thanks.

[shooter]

what ground does the wire I indicated "feed"?

[dwinstonwood]

shooter, Fender has it indicated as a grounded wire.

It looks like part of the NF circuit.

[shooter]

that's the PI main ground for the "long tail"
I typically ground the PI with the PA circuit, not the pre circuit

[dwinstonwood]

See, glad I asked!

Could I just run it into the doghouse hole and ground it at the negative end of the PA node one? It would be a much shorter wire that way.

[shooter]

short wires are good
I'd ground it with the cap I indicated

[dwinstonwood]

Oh...
I actually have that cap grounded with the 4th cap.

[sluckey]

Oh...
I actually have that cap grounded with the 4th cap.

And that's the way fender did it. I'd leave it just as your layout drawing shows.

[shooter]

I pointed it out not as a problem, but a potential one 

[dwinstonwood]

Thanks. It's just as easy to ground it here:

[shooter]

wire it per Fender, should be fine.  IF there is a noise hum issue with PI, it's easy to change

[dwinstonwood]

Thanks.
I found a photo of an original 6G3.
It's hard to tell, but it looks like the ground wire is attached to the underside of the board and is then soldered to the long brass sheet that other preamp grounds are attached to.
(see red arrow)

I'll start with the wiring in post #208 first.

[dwinstonwood]

I reached a saturation point.
Going outside to get air.

[dwinstonwood]

I just need to solder up the power cord.
I'll go over every connection tonight, and once more in the morning, and then I guess it's dim bulb time.

[bmccowan]

Looking pretty good. A question. It appears that you have a white wire running from the fuse to the switch. When dealing with the house current side of the amp I think it best to stick to norms. White is neutral. Hot should run from fuse to switch to PT. Neutral should go directly to the other PT lead. Good sketch of that in both Doug and Sluckey's pieces. If I'm seeing the photo wrong, sorry, eyes are old.

[dwinstonwood]

bmccowan, yes, you're right. I intend to wire it the way you're saying, I just used a spare piece of white wire I had. But, to avoid confusion I'll change it to a black wire!

In looking at sluckey's layouts I see he wires his amps: line in > fuse > power switch > PT.
I've seen others put the fuse after the power switch, but I'll stick with his sequence.

Thanks! I'm almost at the end.

[bmccowan]

In looking at sluckey's layouts I see he wires his amps: line in > fuse > power switch > PT.
I've seen others put the fuse after the power switch, but I'll stick with his sequence.

Yup - that way you have fuse protection any time it's plugged in.
I'm hoping it fires right up with no issues. But if you have some - they should be easy to find as you have been methodical.

[dwinstonwood]

I'm hoping it fires right up with no issues. But if you have some - they should be easy to find as you have been methodical.

Ha! I was just in there soldering up the power cord and noticed that I attached the V1 plate wire to pin 9, not pin 1. Fixed it.
It would not have fired right up.

Here's the proper power cord wiring. Thanks again for calling that out.

[bmccowan]

noticed that I attached the V1 plate wire to pin 9, not pin 1

I have done things like that so often it's not funny. Just recently I confused pins 1 & 8 on a 6V6. That did not work out so well!

[sluckey]

Just recently I confused pins 1 & 9 on a 6V6. That did not work out so well!

 

[dwinstonwood]

pin 8?

[bmccowan]

Yup - typo I corrected - fat fingers and good wine!

[dwinstonwood]

Hoffman:

"Double check all your work:

Stop now and look at this post on my forum on how to double check all your work, this is very important
How to double check your work the easy way

Do not continue until you have double checked everything using my method above
Every time someone has an issue with the amp not working it is always because they skipped a step or did not double check their work thoroughly.

Hoffman law says this.
The amp would be working if it was wired properly and all the parts were installed and working correctly."

A voice is saying, "Aw, you can skip all that! You took your time and worked carefully."

Nope. I"m following the rules.

[dwinstonwood]

I've started measuring voltages.

With no tubes installed:

Pilot light glows.

40 watt dim bulb just barely glowing.

No smoke. No pops. No sparks.

Looking into chassis from the top (open side). Control panel facing away.

Right 6V6 tube socket grid - bias pot gives range of -61.4v to -45.8v
Left 6V6 tube socket grid - bias pot gives range of -61.5v to -45.8v

This is with a 470 Ohm bias resistor, 10K pot, and 27K safety resistor on the pot.

With no tubes - including no rectifier - no voltage on any of the six preamp tube plates and no voltage on the power tube plates or screen grids.

What should I do next?

[shooter]

next?

got filament volts were they belong?
IF so;
put rectifier only in and verify the PS makes VDC
IF so
probe the plate pins and make sure the DC is there;
IF so;
add preamp tubes, set your bias to max neg, measure vdc at plates and cathodes.
IF good-ish;
did you install 1 ohmers?
IF so, set up a meter to read across one, install PA tubes and get a quick read on the one ohmer's, do the math and evaluate

[dwinstonwood]

I'm also measuring 6.33V AC on pins 4 & 5 of the first 12AX7.

Unfortunately, my tubes haven't arrived yet! AES is not the fasted shipper.

Anyway, I suppose - with guidance - I can tweak the bias resistors to get the negative voltage range I need for the JJ 6V6S's.

Thanks.

[punkykatt]

you have the 1 ohmers install wrong. Put the ground wire on pin one.

[dwinstonwood]

you have the 1 ohmers install wrong. Put the ground wire on pin one.

Thank you punkykatt!!! Dang! I would have gotten different measurements and probably never figured out why.

Thank you!

[dwinstonwood]

Unfortunately, my tubes haven't arrived yet! AES is not the fasted shipper.

I take that back. They arrived today! Less than a week is pretty fast.

But, I found another big mistake in my work. I need to redo the heater wiring. I did it all wrong. It took me a long time to find photos of how to do it. I'm also out of solder, but that is supposed to also arrive today.

You either get frustrated and shelve it, or, you try to look at it as gaining experience. Perspective...

[bmccowan]

I just looked at your pics to see the heater wiring. You connect pins 4&5 but not 9 on the preamp tubes? You probably found the solution, but good heater wiring instructions here:
http://www.valvewizard.co.uk/heater.html

[dwinstonwood]

Yep! That's apparently series for a 12.6v secondary.

I just got it fixed. I'm measuring 6.35V AC down the line.

OK, so I have the tubes. I guess the next thing to do is to install the rectifier and check for plate and screen voltages? This is the part where I get apprehensive. I'll be charging the filter caps.

I'm going to take a breather and eat. I just spent an hour twiddling with those tiny socket pins to get the heater wiring right. I want to approach this with a calm and alert state of mind.

[dwinstonwood]

I had some free time to take more measurements.

With ONLY the rectifier in:

Right 6V6S Plate Pin 3 = 325.1VDC
Right 6V6S Screen Pin 4 = 324.8VDC

Left 6V6S Plate Pin 3 = 325.2VDC
Left 6V6S Screen Pin 4 = 324.7VDC

Should I measure all of the 12AX7 plates, too, at this point - with no tubes installed?

Also, since I have the cap pan screwed on and the caps are under the chassis, anyway, I've been draining the filter caps at the point in the image. Is that a good, reliable place to drain them? I'm being ultra safety conscious!

Thanks.

[shooter]

the reason I poke the no tube plates is to "catch" a wiring error befor it puts 300vdc on the grid, instead of the plate.
your drain hole is good, what are you using?

[dwinstonwood]

Thanks!

I made a discharge tool. I might could have used a smaller resistor, it takes about 3 minutes to drain the caps down to zero. Plus, I might add a clip instead of the probe, but I don't want to forget it's connected! The probe is sort of idiot-proof in that regard. Plus, it makes me stand there and watch the meter.

OK, I measured all six of the 12AX7 socket plate pins:

V1 - pin 1 = 315.0VDC
pin 6 = 315.4VDC

V2 - pin 1 = 319.1VDC
pin 6 = 318.8VDC

V3 - pin 1 = 322.2VDC
pin 6 = 321.7VDC

Just to consolidate numbers. Here are the grid negative voltage ranges. I have the pot set to maximum negative voltage.

Right 6V6 tube socket grid - bias pot gives range of -61.4v to -45.8v
Left 6V6 tube socket grid - bias pot gives range of -61.5v to -45.8v

[shooter]

one like I used in my career days 

[dwinstonwood]

  I like the C-clamp ground. It shouldn't accidentally come loose! How many volts were you dealing with?

[sluckey]

Just to consolidate numbers. Here are the grid negative voltage ranges. I have the pot set to maximum negative voltage.

Right 6V6 tube socket grid - bias pot gives range of -61.4v to -45.8v
Left 6V6 tube socket grid - bias pot gives range of -61.5v to -45.8v

Too high for 6V6s. Shoot for a range of about -20 to -40. Change that 470Ω bias range resistor on the bias board to 1K and see if that gets you there. If not, experiment with that resistor value to give those 6V6s what they need. Fender claimed -26v on the original but since your B+ is gonna be lower your bias voltage will probably be lower too.

[dwinstonwood]

Thank you sluckey!

I bought a range of resistors from 470, 1K, 4.7K, 8.2K, to 10K. I'll get the bias pot to cover that -40-ish to -20-ish range next.
I might wire up some clip leads so I don't have to solder in resistors between each test (thinking out loud).

But, so far, no shorts, smoke or sparks!

[66Strat]

Those B+ voltages look low. Were the voltage readings taken with the current limiter light bulb in circuit? What are the AC secondary voltage readings, and how do they compare to the transformer's published specifications?

[shooter]

reply #68 has 270-0-275, tube rec?, if so I'd think 325vdc would be close, loaded 290?

[dwinstonwood]

Those B+ voltages look low. Were the voltage readings taken with the current limiter light bulb in circuit? What are the AC secondary voltage readings, and how do they compare to the transformer's published specifications?

Thanks.

Yes, the dim bulb tester was being used. Now that I know there are no shorts I can measure again without that in series.

But, I did intentionally go with a PT with lower secondary voltages than the AB763 Deluxe Reverb PT that Hammond suggests for this amp.

I'll post voltages without the dim bulb.

[dwinstonwood]

Thanks for reminding me about the dim bulb tester 66Strat.

No power tubes: Plate on the right 6V6 socket now measures 417VDC, and the left socket is 418VDC.

With tubes installed I might actually be near my target voltage of 375, or somewhere near the schematic voltage of 365. I don't know how much the 6V6S's will drop the voltage to be honest.