Plexi 6v6 Sluckey/Huss

[HommeMarrBuckley]

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[HommeMarrBuckley]

Ready to fire up


Here is the speaker jack and bias pot.
Speaker jack has green OT with NFB and Black OT to ground lug (I hope no squealing)
Bias Pot
White goes to 47k resistor and green goes to .022uf cap
Should I turn the bias pot all the way to the left or leave as is?


Alright,
So with speaker connected and hooked up to lamp limiter
should I power on with tubes or without?


If all goes well with no shorts
Plug in to wall, power on and check voltages
Again, recommend with or without tubes?
Just need to remember with voltages to switch over to milliamps/volts for pins 8 on power tubes, correct?
I don't mind checking voltages-it's just that when look at MM my probe hand is sometimes prone to move slightly

[sluckey]

Bias Pot
White goes to 47k resistor and green goes to .022uf cap
Should I turn the bias pot all the way to the left or leave as is?

You do have a jumper between the wiper and one of the outside legs right? If not, put one there now.


***DO NOT PROCEED TO THE NEXT PARAGRAPH UNTIL YOU HAVE SATISFACTORY RESULTS***
 
No tubes. Plug into lamp limiter. Be sure standby switch is in standby position. Turn on. If lamp glows brightly, turn off and find problem in AC mains circuit or PT wiring, filament string, or rectifier diodes. If lamp only glows dimly or not at all proceed...

Adjust bias pot for maximum negative DC volts on pin 5 of each power tube socket. Turn standby switch to operate position. Lamp may briefly glow brighter as the caps charge but should settle down to a dim glow. Check dc voltages at each of the filter caps. Check for dc voltage on pins 3 and 4 of each power tube. Voltages will be kinda low because of the lamp limiter. We just want to know that there is dc at each filter cap and on the power tubes. If all is OK so far, you no longer need the lamp limiter. Proceed...

Now turn off and plug straight into the wall. Standby switch to standby. Still no tubes. Turn amp on and recheck negative dc voltage on pin 5 of each power tube socket. You should have approx. -35vdc or more. Standby switch to operate. Recheck dc voltage at each filter cap and on pins 3 and 4 of each power tube. Voltages should be higher than expected because no tubes are plugged in. Also check for dc voltage on pins 1 and 6 of all little tubes. These should be high also. If all is OK so far, proceed...

Standby switch to standby. Check the ac filament voltage at each tube socket. BE CAREFUL AND DON'T SHORT BETWEEN PINS! For 6V6s measure across pins 2 and 7. For little tubes measure across pins 4/5 and 9. You should have 6.3VAC for each of these sockets. If all is correct, proceed...

Turn amp off and plug in all tubes. Connect a speaker. Set all knobs to ZERO! Turn on and look/smell for smoke, and listen for strange sounds and/or hum. Verify that all filaments are glowing. If you hear a loud squeal of howl, shut down and swap the OT primary plate leads between power tubes. Turn amp back on an verify that squeal/howl is gone. If all is OK so far, proceed...

Plug in a guitar and see it the amp makes music.

[HommeMarrBuckley]

That was a very clear and excellent reply Steve, unfortunately, I gave it a go and didn't make it past the limiter.
The limiter glowed bright.   I looked over everything and felt quite confident about my wiring but realize something is wrong.
I am hoping this PT isn't dead--I was told that all transformers were working.
My initial gut feeling is that it's the lamp because it didn't light up.
This is probably really dummy move.
I remember now the lamp had a (+) lug and the other didn't.  I think I got caught up with something and when I came back I forgot about it.
Im guessing the white (power cord) and black primary need to be soldered to that positive lug.  Mine isn't that way. 
I have a second one (not going to use it) that I can show what I mean--(the other lug has two holes)

[sluckey]

If you wire it the way I showed you it will work.

[HommeMarrBuckley]

It is.


Looked at it repeatedly, has to be lamp lugs or PT is DOA.

[sluckey]

Disconnect the PT wire from the power switch. What happens?

[HommeMarrBuckley]

Disconnect the PT wire from the power switch.

Should I disconnect the resistor from it (same connection), as well?
PS. I did change lamp lugs and nothing happened. (white)power with black PT to +lug and resistor to other.

[sluckey]

Disconnect the PT wire from the power switch. What happens?

[HommeMarrBuckley]

Here's a current pic now with PT disconnected from Power.
I believe all connections can be seen.
Going to put through lamp limiter.

[HommeMarrBuckley]

Turned on Power--nothing
No Glow on lamp limiter.

[sluckey]

With the PT wire still disconnected from the power switch, plug the amp straight into the wall and turn it on. The NE-51 indicator lamp should illuminate. Does it?

[HommeMarrBuckley]

No

[sluckey]

Measure the voltage across the lugs of the lamp socket.

[HommeMarrBuckley]

20-21 mv or
.003 V

[sluckey]

Is your meter set to measure AC Volts?

[HommeMarrBuckley]

now, yes
clips on secure,
right now about 26.1mV
did you want it powered on? because that's with it turned off

[sluckey]

Arrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrgggggggggggggggggggggggggggghhhhhhhhhhhhhhhhhhhhhhhhh!

[HommeMarrBuckley]

does that mean it should be turned on?
with or w/out limiter?

[Willabe]

Measure the voltage across the lugs of the lamp socket.

To measure a voltage the power has to be on.

[HommeMarrBuckley]

Powered on straight to wall about 50V AC
measured the resistor too and its close to 220k


so isn't that about half the voltage it should be receiving?-should the other free pt wire then be connecting to the other lamp lug?


Can I switch out and use a Fender style lamp?

[sluckey]

OK, I'm back and all rested. Sorry about losing my patience last night. Since we got nowhere last night let's just start over.

Forget about using that NE-2 lamp. Totally remove the lamp holder and resistor. Connect the power cord white wire to a PT black wire. Reconnect the other PT black wire to the power switch.

Now, install your Fender style lamp holder with a #47 bulb. Connect the two PT yellow wires to the lamp holder. These yellow wires only have 5VAC on them but that will operate a 6V bulb just fine. In fact, the bulb should last longer.

Now you are ready to begin testing with the lamp limiter again.

Let me ask about your PT. It came from a Hammond AO-43 amp, right? Did you ever apply 120 VAC to it and check for proper secondary voltages? If you did check it, was it OK. If you didn't check it, why do you think it is good?

[HommeMarrBuckley]

AWWWWWWWWWWWWWWWWWW  YEAAAAHHHHHHHHH!!!!!!!!!!!!
First of all,  Many Many Thanks Steve
I switched out the lamps and hooked up and lamp fired up-nice--you can see lamp glowing hooked up to lamp limiter---there was like no glow at all from the limiter when I switched it on. 

Then I went and played Operation (the board game) for real.  Man, takes my breath away--I joke now but I do take it serious, found myself wiping my brow several times.  Found myself at one point staring in to triple check the pin number before I probe, forgetting it was live right under my face, so quiet.

Here's the numbers
I did all steps (great tutorial-well written) Steve
but just will list values when it was fully operational
Filter Caps
preamp 443
tone     443
phase   443
plate    449
screen  449

Pins         Valve 4             Valve 5
3                 449                  448
4                 449                  448
5                 -54                   -55

Pins           Valve 1            Valve 2              Valve 3
1                 440                  441                    438
6                 439                  444                    439


Now, the only part that has me nervous a bit
My heaters all measured 7.36
Hopefully, this isn't a big deal.
I so bad want to put the tubes in and hook the speaker up
but I will wait to see if all is ok.  That might have to wait until tomorrow when I get home from work--won't put the soldering iron away just yet--fingers crossed about the OT wires.

By the way, I noticed with the solid state rectifier schematic there is a 5k 5 watt resistor between the choke and plate cap that I don't have--dunno if that could be playing a factor in anything.


Anyway, Im really happy, can't wait to see how it plays out.
Thanks again Steve!!
Im going to go drink a beer--Here's to you!!

[sluckey]

Great news!

The high filament voltage will come down when you put tubes in it. The high B+ voltages will come down with tubes installed as well.

I'm drinking a beer with you right now! Congrats...

[HommeMarrBuckley]

Ok, Plugged in and I got sound--no squealing---Great!


However, its like the sound/volume is holding back--I have an 8 ohm speaker hooked up correctly.
When I play a chord--its full but dies and fades oddly--almost like rolling volume down
I am hoping this sound/issue is related with biasing power tubes because bias pot is still all the way counter clockwise--(please let it be this)
Quick tutorial on biasing these 6v6 tubes properly?
(I have bias points and tiny flathead screwdriver)
I am not in a hurry--got home from work late but couldn't resist putting tubes in and giving it a go but willing to take time to do it properly.

This one sounds like it got some bite

[sluckey]

Read, understand, and do...

http://www.duncanamps.com/technical/lvbias.html

[HommeMarrBuckley]

LOL
I am actually on that very site and reading it.  But do you think this might be related to how sound dies when I play it?

For Pin 3 I need to set dmm to max dc voltage-understood.

When I measure pin 8 (bias point) I need to turn dmm to measure mV, correct?
But, should I remove red probe from dmm connection (VΩ) and re-connect red probe to dmm in mA connector (on dmm) when I do this measurement?

It seems I should take pin 3 voltage and turn bias to mA reading (that when multiplied) doesn't exceed 12 watts (because of 6v6 rating)

[sluckey]

Read the instructions for your meter. If you don't have any instructions, search for them with google.

[HommeMarrBuckley]

Alright, dejected.
measured 438 on pin 3
set dmm to mV and turned bias pot slightly to 2.8 mV which is low, correct
I dunno, something seemed amiss--left it at that, plugged guitar in and now no sound.
First thought is that I blew a fuse despite no smoke or sound, checked it and seems fine.
measured dc voltage at filter caps and points mentioned and it seems like I am getting accurate readings/voltages


Any help with why there is no sound?

[HommeMarrBuckley]

Upon further inspection, is this fuse toast? the strands look alittle off.

[Willabe]

Test it with your meter.

[HommeMarrBuckley]

Beeps for continuity.
Had to be when I checked the bias pot--I dunno set the meter to mV and put probes into bias points but remember some crackling (wasn't very loud) through speaker when slowly turned pot--reached 2.8 and stopped.
Lamp glows and tubes glow (read that doesn't necessarily mean they're good)
measured a couple points and a few filter caps and seemed like correct dc voltage.
Speaker has continuity and speaker and guitar cable.

Tomorrow, think I will remove tubes and redo Steve's reply 52
If readings are similar, I will swap 1st preamp tube with another and move on down the line if no sound continues, I dunno.

In terms of the speaker, it is a one 8ohm speaker.  I wired speaker (-) lug to ground of speaker jack and (+) lug of speaker to tip of speaker jack.

[drew]

^ You don't by any chance still have the amp plugged into the light bulb limiter, do you?

[HommeMarrBuckley]

No.

[EKDENTON]

Maybe double check your OT drawing If it is a multi-tap OT with windings for 4-8-16ohm speakers make sure that you have the correct wire on your speaker jack tip. Iv'e plugged an 8 ohm speaker in the 4 ohm jack by mistake and had very low volume.

[HommeMarrBuckley]

No multitap.
I am going to pull tubes and check voltages--figure if they're like before, then the circuit and hardware involved should be ok, I assume.  I was using JJ ECC83 S pre and JJ 6V6 S out tubes.  After that, I was reading that I should maybe and try to put a new 1st pre tube and sub on down the line.  But guess it could be a jack(s), speaker, cable, but they seem to be fine.

[HommeMarrBuckley]

Pulled tubes and inspected--no whitish stuff on inside--left them out.
Checked voltages and numbers are very similar to those in what I posted in #72 above.
When I checked the voltage in Pin 5 of the 1st output--it was tricky to get a reading on it but I did--5 on 2nd output was easier but they weren't as quick as other readings.  I am going to re-solder both of these lugs.  I dunno to tell how if a pin is too loose--it hasn't fallen out but it doesn't seem that sturdy either.

[HommeMarrBuckley]

Before I started with tubes,
This is my bias supply.
I dunno but with bias points--should those 1 ohm resistors just be connecting with pin 8 And Then from pin 8 connect to cap?
I have that the bias point connects to pin 8 And to Cap
Ran out of space on my board but tried to mimic Steve's layout using bias points

Here's the mm
When I am measuring the bias resistors--black probe connects to com,
What should my red probe connect to VΩ or mA,
and then what setting mV or mA/A
From what I read milliamps is nearly identical to millivolts
Dont mean to annoy anyone

[Willabe]

When I am measuring the bias resistors--black probe connects to com,
What should my red probe connect to VΩ or mA,
and then what setting mV or mA/A
From what I read milliamps is nearly identical to millivolts

With a 1 ohm bias R between the power tubes K (cathode) and ground the DCmV will convert directly to DCmA's. So to make the test measurement easy we test for DCmV's.

So set your meter for mV and plug the red meter probe into VΩ.

(Your not annoying anyone.  )

[HommeMarrBuckley]

Brad
You're my technical tool guy, probably wouldn't have built my limiter if you wouldn't have stressed it
I'll blast "Shadow Play" just for you later!
Thanks

[Willabe]

     RORY!!!!!!!!     

[HommeMarrBuckley]

B---You sure bring some good luck.
I won't be posting any more troubles----cuuzzzzzzzzzzzzz....
This baby is pumping!!!!!!!!!
You could probably tell but, for whatever reason, I was nervous to put the tubes in, well after Brad helping me understand my dmm, I thought I would put the tubes in and try it out, and wouldn't you know--put 'em in---and no sound--dejected yet again.  Felt miserable.
So, I decided to just measure across the bias resistors with my guitar plugged in.  The reading was less than 1mV so I decided to adjust the bias pot a little.  Then I strummed my guitar which was lying by the floor--nothing.  Turned it a little bit more probably till 2mV or so, leaned down and strummed---what? I could hear something--at first I thought is was the strings echoing off the wall but it was above me and the speaker was on the table---adjusted the pot more and the volume started to rise and I started smiling.  The tubes just weren't getting any current.  I immediately realized you need to be hella slow with adjusting the pot too because it jumped to 24 mA fast and I quickly backed it down.  Here's my breakdown.
Pin 3
450V  20.5mA (.0205) = static dissipation wattage of 9.225, then
Pin 3
430V 20.5mA (.0205) = static dissipation idling wattage of 8.815 which I was cool with (no pun intended)
I may try to bump it a little but still will keep it well under 12


The funniest thing (now it is) is I shut it off and removed the dmm and turned it back on to give it a go with my guitar.
Well, I powered on and set normal to about 2 and cranked master----No Sound Again!!!!
What the $*%&!!!!!!!!!!!!!!! Started sweating like a maniac and realized I was looking at the controls backwards. HA!
SO, I only turned the presence and bright pots---Such a relief!  Backward controls and reverse pots---Ill get it eventually.
But yeah it can get loud---I went through some riffs but it was getting late.  I will have fun with it this weekend.  There is no hum at all.  (I know everyone has their system but I am a firm believer in grounding each section with their respected filter cap and then grounded at one point at input.  Im a believer because it works for me.)  Anyway, I am pretty exhausted and beat mentally--but nothing like solving a dilemma--such a great feeling!  I will be able to sleep good tonight without all those questions running through my head like last night. 
Thanks to Brad and other members for their help/support when I hit a wall, but most importantly supreme thanks to Steve for bearing with me through all of it--I would have never made this thing without you--you're a good man.  Lastly, thanks to Matt for offering this forum--it has given me the opportunity to enjoy something I really love.
Cheers All!

[Willabe]

Sluckey did all the heavy lifting.

Very glad you got her figured out and up and singing! 


 

[sluckey]

I see a big problem with your bias test point wiring! You have two red wires on each red test point. One red wire goes to pin 8 of a power tube. That's good. The other red wire appears to go to the positive side of the bias caps. THAT'S BAD!

Remove the red wire that goes to the bias cap. Do that for each red test point. There should now be ONLY ONE wire on each test point and it should connect directly to pin 8 of a 6V6. The black test point should connect to chassis ground, preferably at the same point the PT center tap connects to chassis ground.

Now, connect a wire from the positive lead of the bias cap to chassis ground. Look at my layout. This is clearly shown.

When you have made this correction recheck your bias adjustment.

[HommeMarrBuckley]

Yes, I wasn't sure and didnt know.
My grounds are ground.
I ran out of space for my board but tried to copy yours.
On your layout, the 1 ohm resistors are connected between the bias caps and pin 8 of power tubes.
Since my 1 ohm resistors aren't on the board, I thought I should mimic that on bias point by having a wire to the cap and wire to pin 8.  My reasoning might not make sense, but i was trying to copy how it looked physically to the eye not realising that the bias pot enables the connection to the output tubes and I was probably providing it twice in a sense.
So I should just keep the 1ohm resistors only connection to pin 8.  Gotcha.

[sluckey]

On your layout, the 1 ohm resistors are connected between the bias caps and pin 8 of power tubes.

You are overlooking the fact that the turrets where the top of the 1Ω resistors are connected to the bottom of the bias caps are all connected to ground. IOW, the positive side of the caps are connected to ground. And the top side of my 1Ω resistors are also connected to ground.

So, you need to think of it in terms that one end of the 1Ω resistors connect to pin 8 of the tubes and the other end of those 1Ω resistors connect to ground. That's not the case with the way you have yours wired. When you fix that, the bias pot should be much easier to adjust correctly.

[HommeMarrBuckley]

Alright, disconnected the extra wires on the red bias points.  Actually, wasn't as bad as I thought it would be.
I disconnected one and had to be careful because it involved underboard wire connection with resistor.  I don't mind working with this fiberboard but once you get it set and screwed in, it's difficult to take back out and examine, if your connections are tight and really need to look, you're going to have to desolder some wires to free the board up which opens the potential for wiring issues when you go back to re-solder. Fortunately, I didn't have to do all that.   With the second bias point removal, I just disconnected it from the red bias point and then used that as a ground (it was originally connected underboard to the (+) bias caps but I only had one ground for bias--I realized that upon inspection-the black bias point was the only ground)
Might be hard to follow but now there is a ground from black bias point and ground from (+) bias caps that meet up with other output grounds (striped red 2ndary, striped green filament and plate and screen ground) and they are the last point (opposite input) on ground bus.
So, now out with it man!


Pin 3 Valve 4
438V
MA .0212 which equals 9.28 static dissipation wattage


Pin 3 Valve 4
418V
MA .0212 which equals 8.86 static dissipation idling wattage


Any other voltages you think I should check, Steve? (if so, if you could, just let me know if it's ac, dc etc so I don't short with my mm)

[HommeMarrBuckley]

Um yeah, this thing rocks. 
I don't even know if I would use my Muff Pi or Soul Food pedal with this.  Definitely giving me rock tones that I like--haven't even tried cleans.
First thing that always comes to me is that from day after day playing electric unplugged, messing around with garageband or little practice amp and then I plug into a quality amp like this, is the clarity and range---it's awesome but you need to be on point. You hit a chord or note wrong and it's there--nowhere to hide.
I really pushed it and gave the neighbors something to think about.
Will check out the different settings.  Right off the bat, noticed that the Presence is way different than that on my Bassman.  It has like a bellowy, almost like reverbish effect when you jack it.  But definitely significant.
Really enjoying myself. 
For sure, a cool, amp. 
I have a second Hammond AO43 chassis w/transformers (scored both on ebay for $100) so beyond happy with little amount of money needed to fulfill this.
Unless Steve or someone has technical question, this is pretty much it.  Ill post when I finished the cab, just have to tung oil it and put on the hardware (handle, feet, etc.)

[sluckey]

Good job. Glad it all worked out.

[HommeMarrBuckley]

Here's the finished product.
Considering filming how it sounds with my phone.  Have played it more and more and still figuring out tones--I have a strat with 7 setting pup selection that I installed but overwhelms my brain because I am always checking it out how things sound with it--neck or bridge or neck middle or bridge middle or all three  I even haven't had an urge to put any pedals with it which to me is a good sign.  Good earthy grit and can pack a punch.
I goofed alittle on the back of head with finishing washers but the thing has got it's little quirks all over the place. 
The tung oil will probably take on a darker tone with time.  Curious to run it through different speaker combos.