Steve Luckey AO-44 Pee Wee Build

[boxcarcut]

I've built Steve Luckey's AO-44 Pee Wee amp. I'm having some troubles with it and was wondering if anyone knew how I could reach him?
http://home.comcast.net/~seluckey/amps/PeeWee/peewee.htm

I would greatly appreciate it.

Thanks,
Tom

[HotBluePlates]

Why don't you post the trouble you're having here?

Sluckey is likely to find the thread sooner or later, but the rest of us might be able to help in the meantime.

[sluckey]

You can reach me right here.

[boxcarcut]

Hello Friends. First let me say this is my first attempt at a build. I know schematic fairly well and I'm comfortable with high voltages.

I built this AO-44 Pee Wee about a year ago and when I completed it, I didn't get any sound from it. Just a slight slight hum.

It's time to get this amp up and running (I'm building it for a friend for the holidays).

This is the schematic:
http://home.comcast.net/~seluckey/amps/PeeWee/PeeWee.pdf

These are my voltage readings:
AC Wall Voltage: 122vAC

Can Cap:
A: 314vDC
B: 302vDC
C: 290vDC
D: 288vDC

V1-A
1: 0
2: 2vDC
9: 216vDC

V1-B
3: 301vDC
6: 305vDC
8: 0

V2-A
9: 238vDC

V2-B
3: 301vDC
6: 308vDC
8: 0

12AX7
1: 189vDC
2: 0
6: 283vDC (this seems way off)

Here are some photos. (Please keep in mind this was my first build)
https://www.flickr.com/photos/34258368@N03/sets/72157648801344100/

I would appreciate some help. Thanks.

[Jack_Hester]

12AX7
1: 189vDC
2: 0
6: 283vDC (this seems way off)

Take a fresh set of DC voltage readings for all pins (1,2,3,6,7, & 8), except the heaters (4,5, & 9). 

Jack

[sluckey]

Tom, you omitted some important tube pin voltages. We need voltages for every plate, grid, and cathode for all tubes. And double check the filament wiring on the added 12AX7. My schematic shows it wired wrong. One side of the filament string should go to pin 9 and the other side of the filament string should go to pin 4/5 (tied together).

[boxcarcut]

Fresh voltages for 12AX7

1: 189vDC
2: 0
3: 1.3vDC
6: 284vDC
7: 0
8: 0

[sluckey]

Fresh voltages for 12AX7

1: 189vDC
2: 0
3: 1.3vDC
6: 284vDC
7: 0
8: 0

Pins 1, 2, and 3 are OK. Pins 6, and 8 are not. Those readings indicate the triode is not conducting. Pin 6 should be about 150 and pin 8 should be about 1.5v. A common cause for this would be a missing ground path for the cathode. Check resistance of pin 8 to chassis with an ohm meter. Should be 1.5K. Check directly on the socket pin.

[boxcarcut]

OK.

As Steve suggested I tied pin 4 and 5 together on the 12ax7. I now have a signal coming through!!!

12ax7 readings are now:

1. 184vDC
2. 0
3. 1.3vDC
4. -
5. -
6. 177vDC
7. 0
8. 1.3vDC
9. -

Now my only issue is the volume pot does nothing. Bass and Treble pots seem to be working fine.

[boxcarcut]

The left wiper on the volume pot wasn't grounded. All is good now.

Thank you all very much for the help.

I'm going to enjoy my new amp!

[HotBluePlates]

Sweet!

Easy to fix when you know where to look, huh?

[sluckey]

Let us know how it sounds.

EDIT... BTW, I fixed the schematic error on my website in case you want the updated file. You may have to hit refresh on your browser to load the current file.

[boxcarcut]

Very grateful for your help Steve.

It sounded super nice. I'll get myself I nice 12" this week for it.

-Tom

[boxcarcut]

I'm going to replace the 30/30/30/20 cap can. What would be proper values today?

[DummyLoad]

doug's 40/20/20/20. will require some machining, e.g. enlarge opening and drill two mounting holes - lowest cost. you'll need the 1.5" can cap clamp as well.

no machining for the cans below... but they are pricey.

this is the exact replacement:

https://www.tubesandmore.com/products/C-EC30-20X3-525

if it were mine... i'd hack in doug's 40/20/20/20, or the one below:

https://www.tubesandmore.com/products/C-EC4020X2-525

--pete

[sluckey]

doug's 40/20/20/20. will require some machining, e.g. enlarge opening and drill two mounting holes - lowest cost. you'll need the 1.5" can cap clamp as well.

That's what I'd do too. Probably should. However, amazingly, the original cans on both my AO-44s are working very well. Are you hearing any power supply hum? Is the can getting warm?

[boxcarcut]

I just thought I'd swap it out. Amp sounds super good. Low end is a bit muddy though. Hoping a new cap can will fix that.

[HotBluePlates]

Low end is a bit muddy though. Hoping a new cap can will fix that.

Not likely. You should directly change things that impact lows; filter caps are indirect at best.

1st choice of place to trim mud out of the bass would be preamp cathode bypass caps, but there aren't any in this amp. You would ordinarily reduce the value of cathode bypass caps. Try the other things below first, but you could always add a 1-2uF cathode bypass cap on one or more stages. That will trim bass by boosting the gain of higher frequencies; however, 1-2uF is not small enough to sound like "treble boosting." Overall signal level will change so this may not be an optimum first move for this circuit (unless you want more gain/signal level).

While not a normal 2nd step, look at the 0.047uF and 0.1uF caps in the tone circuit. If you change those to 0.022uF for each, the amp sound won't change much but the impression of mud will be reduced.

And you could reduce the value of any of the coupling caps. No recommended values, you'll just have to try incrementally reducing wherever you like and hearing the impact.

[sluckey]

I originally had 22µF cathode bypass caps on the preamp triodes. I removed them specifically to decrease the muddy bass. Did you put bypass caps in yours?

Some other things to try in addition to HBP's suggestions... Reduce the 100µF bypass cap on the output tubes. Removing that 10K/.001µF across the plates of the output tubes may lower the bass response a little. You could just unsolder one end of either of those components to test.

This amp has a huge OT (relatively speaking) and that probably contributes a lot to the bass response.

Your speaker choice can have a big impact on the bass response of this amp. I like the sound thru a little 8" Rola that I scavenged from a small Hammond Leslie unit.

[DCgtrguy]

boxcarcut, do you have any sound clips? I have a Hammond E-100 amp, 1/2 of which is an AO-44. I would need a chassis and a PT to be able to build the Pee Wee Fender amp. Steve Luckey or anyone, thoughts on where to get a chassis and PT?

[sluckey]

Steve Luckey or anyone, thoughts on where to get a chassis and PT?

I'll sell you an unmolested AO-44 (no tubes) for $45 plus about $12 for USPS flat rate shipping if it fits a medium box. The unmodified AO-44 in the first 3 pics on my website is the actual unit.

     http://home.comcast.net/~seluckey/amps/PeeWee/peewee.htm
 
EDIT... The AO-44 is no longer available.

[boxcarcut]

I have a few questions about this project.

The pee-wee schematic shows an LED being used off the heaters. What type of LED should I use and with what bezel?

Would using a #45 bulb off the heater winding be too much for this PT (since it already has a 12ax7 added to the circuit).

Any links to LED's for this project would be helpful.

Thanks

[sluckey]

Here's one. Scroll down to the Led lamp Assembly...

     http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Lamps&ORDER_ID=!ORDERID!

Or go to Radio Shack.

[boxcarcut]

Steve,

Could I run a #45 bulb off the 6.3v heater supply and not ruin the PT?

[sluckey]

You could but why? #45 is rated 3.2V @ .35A.

Better choice... #47 is rated 6.3V @ .15A.

I choose to use a LED partly because I was concerned about the extra current draw using an incandescent lamp, but mostly because of the convenience inside that tiny chassis.

Even better... LED with 4.7K resistor, heck, the PT won't even know it's there. Look at the pic of how mine is installed. Very convenient and takes up very little room.

     http://home.comcast.net/~seluckey/amps/PeeWee/A_big_bottom.jpg

My second choice would be a 120V neon lamp that can be wired to the PT primary circuit.

[PRR]

Incandescents fail in a few years. (Yes, they are the traditional Fender glow.)

Neons "fail" (flicker endlessly) in a few decades.

All evidence shows that an LED run well below rated current (20mA for most small jobs) will out-live the user.

As an ex-maintainer, I much prefer to do the LED; then I'll never have to deal with it again.

You "can" solder an LED and its resistors to the lugs of a standard Fender #47 holder, so it looks stock on the outside. This may be "creative wiring", meaning bent leads, flying joints, and careful check for ANY way the 6VAC could get shorted to chassis or itself (that would be bad). If you are obsessive about neat wiring you'll probably prefer to bust-off the socket and hang a bit of tag-board on the socket bracket to support resistor and LED.

[DummyLoad]

http://www.pinballlife.com/index.php?p=product&id=1174

LED replacement for #47  lamps.

--pete

[boxcarcut]

What's ideal plate current for 6GW8's.

B+ 304V
Cathode V-Drop 9.4V

Plate Voltage 295V

These amps use a 130R cathode resistor.

Using the "transformer shunt" method, I got 22mA and 34mA respectively. Seems high for a 9 watt tube.

Any thoughts would be appreciated. Trying to dial this amp in.

[PRR]

I don't see a problem that needs fixing.

One tube is at 10.3W, but the "9W" is a Design Center spec. They expect individual tubes to run more or less. This variation is well within the fudge factor.

The un-balance looks bad, but I don't know that it makes any real difference. THD will be up and Power at specific THD will be down. But hardly-any. And guitarists are not adverse to THD. And if it comes up a half-Watt shy of book-power output, you could have picked a bigger tube to cover unexpected variations.

You could swap-swap-swap 6GW8s hoping to find a better match. But they don't grow on trees.

You could change from one 130r cathode resistor to two 270r, one per cathode. The unbalance would be less. Now you may "need" hefty cathode capS to maintain proper push-pull action. And I doubt the benefit would be obvious.

Swap tubes. Does the 35mA stay with the socket or move with the tube? If it is about the socket, there's a leaky grid cap.

[boxcarcut]

I now have the amp completed. Any tips on reducing 60 cycle hum on this amp? I have replaced the filter cap can.

Could the 60 cycle hum be from all the components and wiring so close together? Or maybe isn't properly grounded?

Looking for some ideas.

Thanks guys!

[HotBluePlates]

I now have the amp completed. Any tips on reducing 60 cycle hum on this amp? I have replaced the filter cap can.

Could the 60 cycle hum be from all the components and wiring so close together? Or maybe isn't properly grounded? ...

Look at your wiring and compare to Sluckey's or the original. I have an original AO-44, and it still has the original cap can. There's no hum in mine, so...