A little Valve Junior Renovation

[Southpaw Tele]

Okay, apparently the order for the eyelet board never went through. I went back to guitaramplifierpcbs.com and they had the Baby Will board back in stock. It's on the way. This may be a better option for a novice such as myself.

[Southpaw Tele]

Well, the version 2.3 of the Baby Will Lite IIb calls for an output transformer that is different from the one I purchased (that was originally for the 1.3 version). Getting frustrated! Grrrrrrr...

[JohnnyCrash]

Originally Posted by Southpaw Tele

Well, the version 2.3 of the Baby Will Lite IIb calls for an output transformer that is different from the one I purchased (that was originally for the 1.3 version). Getting frustrated! Grrrrrrr...

It'll probably still be fine.

They're obviously both output transformers spec'ed for two cathode biased EL84's, so I don't understand the issue.

Perhaps they like a certain OT better than the other, but it should work fine...

What OT do you have, and what do they now recommend? Do you have any specs for either OT?

[Southpaw Tele]

Hey Johnny,

Okay, the OT15PP from musical power supplies has the following specs:

15W to 22W PP guitar amplifer circuits using EL84 or 6V6 pair power tubes into 8000/7000 Ohm inputs with 4,8 & 16 Ohm Outputs

The 2.3 version calls for the OT20PP with these specs:


15W to 22W PP guitar amplifer circuits using EL84 or 6V6 pair power tubes into 8000/6600 Ohm inputs with 4,8 & 16 Ohm Outputs. It's basically an OT15PP with about 12% more iron. Use this if you are looking for a little more low-end response or want a true 6600Ohm impedance match.Circuits: Blues Jr, Marshall 18W, AC15, Princeton, Deluxe, Tweed Deluxe

I just need to figure out what's changed on the schematic?

[JohnnyCrash]

Originally Posted by Southpaw Tele

Hey Johnny,

Okay, the OT15PP from musical power supplies has the following specs:

15W to 22W PP guitar amplifer circuits using EL84 or 6V6 pair power tubes into 8000/7000 Ohm inputs with 4,8 & 16 Ohm Outputs

The 2.3 version calls for the OT20PP with these specs:


15W to 22W PP guitar amplifer circuits using EL84 or 6V6 pair power tubes into 8000/6600 Ohm inputs with 4,8 & 16 Ohm Outputs. It's basically an OT15PP with about 12% more iron. Use this if you are looking for a little more low-end response or want a true 6600Ohm impedance match.Circuits: Blues Jr, Marshall 18W, AC15, Princeton, Deluxe, Tweed Deluxe

I just need to figure out what's changed on the schematic?

Practically identical operating specs. EL84's will be around 8,000 ohms, so the impedances will be good with either OT.

It looks like one is a 15 watt rated OT and the other a 20 watt rated (the larger OT). As mentioned this means it won't break up quite as early and have a slightly better bass response. How much better for headroom and bass? I'd quess barely any (if any) noticeable difference in headroom, and a slightly noticeable difference in bass (mainly at higher volumes).

There is NO difference as far as the circuit is concerned. Just be sure to read the OT's wiring diagram and use the proper taps for either side (8k for the plates and whatever speaker impedance you plan on - better yet, put the secondary taps on a switch for more speaker/cab/impedance options).

All's well with what you've got. Solder safe.

[Southpaw Tele]

Thanks JC, I just got the pcb in the mail today and it's a nice 1/8" thick! I just need to order up all the caps, resistors, etc this weekend. I'll post as I go. Excited!

[Southpaw Tele]

Parts are on the way from Mouser and Antique Electronics Supply. I need to drill the chassis this next weekend. I'll snap some pics of me possibly screwing it up.

[rock_mumbles]

I just built a version 1.3 Baby Will for myself and am in the process of finishing up a version 2.3 for a friend. Either MPS OT will be fine, the "20" is fairly new so that's why it wasn't in the original BW specs.

I read where you said you want clean/loud with the Baby Will, they are loud, no problem there, I've trained my guitar player to use small wattage amps miked up, and his first response to the Baby Will was "wow it's loud!"

Now clean, OK a real 18W does not have much clean headroom, if you wire in the single triode/parallel triode inputs (or a switch) the single triode has more clean headroom, but the fullness of the parallel sounds really good. The 2.3 Baby Will does NOT follow the LiteIIb schematic as far as the shared plate resistor for V1. It uses a "split load" plate resistor (like on a Komet amp) the tube still sees the ~120K plate load but the output signal goes through a resistor on it's way through the amp circuit, this will give a bit more clean headroom than a stock LiteIIb.

So how to really make your 18W not an 18W, if you change the plate resistor on v1 you can make it so it doesn't overdrive so easy, that's what I did on mine. I changed the shared 120K plate resistor to 56K, the amp is no longer a "true" 18W, but the amp is now clean and loud running the parallel triodes (it just doesn't work in single mode with this low of a plate resistor). So to accomplish what I did with my amp on a Version 2.3 BW install the 56K resistor at R24 but for R8 use a jumper.

[JohnnyCrash]

Originally Posted by rock_mumbles

I just built a version 1.3 Baby Will for myself and am in the process of finishing up a version 2.3 for a friend. Either MPS OT will be fine, the "20" is fairly new so that's why it wasn't in the original BW specs.

I read where you said you want clean/loud with the Baby Will, they are loud, no problem there, I've trained my guitar player to use small wattage amps miked up, and his first response to the Baby Will was "wow it's loud!"

Now clean, OK a real 18W does not have much clean headroom, if you wire in the single triode/parallel triode inputs (or a switch) the single triode has more clean headroom, but the fullness of the parallel sounds really good. The 2.3 Baby Will does NOT follow the LiteIIb schematic as far as the shared plate resistor for V1. It uses a "split load" plate resistor (like on a Komet amp) the tube still sees the ~120K plate load but the output signal goes through a resistor on it's way through the amp circuit, this will give a bit more clean headroom than a stock LiteIIb.

So how to really make your 18W not an 18W, if you change the plate resistor on v1 you can make it so it doesn't overdrive so easy, that's what I did on mine. I changed the shared 120K plate resistor to 56K, the amp is no longer a "true" 18W, but the amp is now clean and loud running the parallel triodes (it just doesn't work in single mode with this low of a plate resistor). So to accomplish what I did with my amp on a Version 2.3 BW install the 56K resistor at R24 but for R8 use a jumper.

Great advice!

You also have some room to tweak how hard the PI hits the power tubes as well as how hot the EL84's are biased, but I'd start in the preamp like rock_mumbles just said.

[Southpaw Tele]

Sounds like good "sound" advice, thanks! Here's some pics of where I'm at, so far...



Still a ways to go on putting in all the resistors, caps, etc., but made some headway last night. This job is really paint by numbers, but fun, nonetheless.

[Southpaw Tele]

Okay, the PCB is all wired up. Next steps are to connect all the OT and PT leads.


Quick questions of the day: I have a homemade cab that I'll be using for this project (has a Lady Luck 12" in it).

1.) Should I vent it?

2.) I'm going to load the EVJ chassis so the faceplate is pointing at the ceiling. Transformers will obviously be pointed toward the speaker along with the tubes. Will vibration from the speaker damage tubes? I'll post pics when I have a chance. If tube damage is a problem, then I'll have to front load mount the chassis with the faceplace pointing at me.

[Southpaw Tele]

I should add that the cab is almost the same dimensions as the Epi extension cab. The speaker is center mounted on the baffle.

[JohnnyCrash]

Originally Posted by Southpaw Tele

Okay, the PCB is all wired up. Next steps are to connect all the OT and PT leads.


Quick questions of the day: I have a homemade cab that I'll be using for this project (has a Lady Luck 12" in it).

1.) Should I vent it?

2.) I'm going to load the EVJ chassis so the faceplate is pointing at the ceiling. Transformers will obviously be pointed toward the speaker along with the tubes. Will vibration from the speaker damage tubes? I'll post pics when I have a chance. If tube damage is a problem, then I'll have to front load mount the chassis with the faceplace pointing at me.

You may get different opinions on how much the heat will actually be a problem.

I'd vent the cab. It won't warp the tolex/cab, and the tubes may or may not die quicker, but I'd do it anyway. Excessive heat can also supposedly be a problem to transformers.

The next item is the tube rattle and ease of access to the tubes for changing. Tubes standing up usually have less audible rattle noise.

Tube rattle can usually be tamed with tube socket retainers, but it looks like your sockets are all on-board. You might be able to drill two small holes on either side of the socket holes on the chassis and mount spring retainers.

In the end, I wouldn't worry about how you plan on setting the amp/cab up on both counts (heat vents and tube rattle)... if it rattles, you can improvise tube retainers pretty easily.

[Southpaw Tele]

I do have the tube retainers that were included on the Baby Will's BOM, so that should help. I cut a vent hole out near the baffle, just to play it safe. If worse comes to worst, I can always build another cab so I can front load the chassis. Back to work today, but should finish up the PT work tonight. I'm still waiting on tolex and I need to post some pics.

[Southpaw Tele]

Oh and a quick PS...last night, while trying to solder the OT to the speaker out pcb, I may have lifted the metal on the pcb. Unfortunately, I did it to the 16 ohm jack, which is what I'll be using in the combo. I ran a wire from the damaged spot to the next logical solder point on the little pcb. I'll post pics later tonight in case this makes no sense.

[Southpaw Tele]

Well, it's all put together and time to test and quite frankly, I'm afraid to turn it on.

[Southpaw Tele]

The amp works! But...there's some hum after about 1 or 2 (out of 10) on the volume. I also get some squealing noises from both the volume and the tone pot at near maximum settings.

Is this a heater wire routing problem or crappy soldering technique? Or something else entirely?

[JohnnyCrash]

Originally Posted by Southpaw Tele

The amp works! But...there's some hum after about 1 or 2 (out of 10) on the volume. I also get some squealing noises from both the volume and the tone pot at near maximum settings.

Is this a heater wire routing problem or crappy soldering technique? Or something else entirely?

First - get some photos for us.

The squealing:
1. Is it only when the Volume and Tone are cranked?

If its all the time - reverse the OT's plate leads to either EL84 tube.

2. If its only when the Vol/Tone are cranked - its likely lead dress.

Make sure the wires going to and from the pots are as short as possible and if they cross other wires, try to make them cross at 90 degree angles from the other wire.

In fact, clean up ALL wiring, not just the preamp section. Make them short and away from each other (or at 90 degrees if/where possible).

Also, after shortening all of the lead-dress, use shielded wire from the input jacks. If that doesn't cut it, add shielded wire to and from the grids, also maybe between plates-to-pots if its still squealing.

Check all grounds at the Vol/Tone. Hell, check each and every solder while you're at it.

Hum:
Make sure heater wires are twisted.

Also check your grounding. Make sure the pots are grounded. Check to see if you're grounding scheme is good (higher current parts of the circuit should be on a different ground lug than lower current spots) - keep the PT grounds seperate from preamp grounds, etc.

Where is your OT grounded? At the output/speaker jack, or somewhere else?

Finally, verify every solder, resistor/capacitor value, and check your voltages.

Photos will help us troubleshoot... but they're also nice to look at - its like we get to feel like we built something. Vicarious living is fun

[JohnnyCrash]

PS were planning on any mods to the Lite circuit?

If you want more headroom, a wider (and more even) frequency response (lower lows, higher highs, and more balanced from low to high) - I'd suggest a negative feedback loop. I'd suggest a 47k resistor from the output jack/OT's output tap (16 ohm if it has one) to the unused phase inverter input (the grounded 0.1uF cap on V2 - leave it grounded and have the 47k run from the OT tap to ground at the grounded end of the 0.1uF PI coupling cap).

The headroom bump isn't too much - the overall max volume will be the same, but it helps the Volume pot stay cleaner through more of its range.

Other than that, you could mod tone (cathode bypass on V1 could go lower to increase gain at upper-midranges), or even add a "Clean/Dirty" switch to cascade V1 or not (a DPDT switch and a 470k/500pF resistor/cap combo).

[Southpaw Tele]

Muchos gracias Johnny, as always. The squeal is just near max volume and treble on the pots. I need to switch up the grounding scheme...everything is going to one post attached to the chassis. I'll retwist the heater wires and make sure to right angle them.

I'll snap some pics when we get home tomorrow and post them on this thread. Not the neatest build to look at, but it's my first and after tackling the hum issues, I'm sure my next will be neater work.