Tonebox

[Sonny ReVerb]

Greetings!

This is my first post in ages. First amp build in many years due to divorce, living in an apartment, yada, yada... I've built a P1 eXtreme, 18W, and a scavenger amp made out of the parts from an old tube film projector. Finally back in a house and looking forward to melting some solder.

Steve Luckey gave me some Visio assistance and he asked that I post my efforts here. (Thanks, Steve.)

This amp is a mix of ideas that I hope will produce some pleasing sounds. Two channel - first channel 1960 brownface (6G4,6G5,6G7) preamp, second channel typical blackface with added mid and raw controls; reverb and trem on both channels; cathodyne PI; and cathode biased power amp (5881/6L6) with bias vary trem (Silvertone 1482). Essentially Carr Rambler based (I haven't been in one, but it's supposed to be a blackface Princeton Reverb preamp with a 5E5 Pro power amp) with a second brownface channel added.

 The dropping string is just a guess at this point. There is one triode unused, though I may try a 12au7 for the PI and leave half of that unused. I put some grid stoppers on the PI and power tubes a la Valve Wizard. Most of the parts are on the way, but it may be a bit til my garage is ready for the build. Classic Tone iron; Vibrolux Reverb PT, choke, and reverb trans, but I also got the tweed style OT. Plan is to put it in a 1x12 combo cab for club/jam use.

Any tips, ideas, or critiques are welcome.

Chris

[sluckey]

Looks good. I wonder if mixing resistors will be needed for the two preamps?

[Sonny ReVerb]

Good question. I considered mixing resistors. I ended up basing it on the 'one wire reverb on both channels mod' which reportedly works ok without mixing resistors. I also looked at Bruce's tweed mixer version (connecting the V1b/V2b plates prior to the coupling caps), but since the brownface channel has a lower B+ I didn't think that would work out. I'd like to try a jumper to connect both channels, so mixing resistors may be necessary.

UberVerb: http://el34world.com/Forum/index.php?topic=15253.msg147010#msg147010

[Sonny ReVerb]

Any other opinions or experience about mixing resistors/no mixing resistors?

[sluckey]

Just try it both ways. You may want to plan your layout with the mix resistors in case you do find you need them.

[Sonny ReVerb]

Board layout.

Notes: I'm planning on using a JJ 40/20/20/20uF cap can for filtering. Brownface channel will have the tone stack on the pots. A few of the other components are off board in typical Fender style.

[Sonny ReVerb]

Also, I stuck some extra turrets in for options; NFB, if desired; possible use of channel mixing resistors; and split plate load resistors in case there is too much gain in the brownface channel.

[Sonny ReVerb]

This might be helpful. The >> or << symbol means go in to the second connection point.

[sluckey]

FYI, your links to flickr simply link to an image file. I thought you were gonna provide the actual Visio file?

[kagliostro]

+ 1 (What Steve Say)

Franco

[Sonny ReVerb]

The Visio file is several MB. I used to use Image Shack for photo hosting, but they're not free anymore. They allowed direct links which I prefer in posts, because they're easier to read without downloading a file. I thought the Flikr thing would work as a substitute.

[kagliostro]

Free hosting


Image = http://imgur.com/ (don't require to be registered for the Upload - they didn't cancel files after a certain time)


File = https://www.mediafire.com/ (requires to be registered for the Upload but it is free and they didn't cancel files after a certain time)


Franco

[Sonny ReVerb]

Thanks, I'll give those a try. I saved the board to a separate file. See if this works.

[kagliostro]

All fine, perfect 


Franco

[Sonny ReVerb]

Finally, a bit of progress. My table saw and drill press are back in the garage and I've got all the parts for the build. I bought a VR chassis from Marsh. Most of the fab work was done, but I wanted to add a couple of pots, etc. I built a jig for my drill press so I could work on the angled face. I can't say modifying a steel chassis is my favorite way to spend an afternoon, though. I also drilled the board and mounted the turrets.

[Sonny ReVerb]

More progress.

[Sonny ReVerb]

I predict a smoke test in the near future...

[sluckey]

Hopefully no smoke. But it's so neat that if it does smoke you'll be able to quickly spot the problem.

[Sonny ReVerb]

Thanks. Unfortunately, it'll have to wait a couple weeks (work calls). I hate when you get to the end of a build and you have to pay $7 shipping for $2 worth of parts. :(  At least I got some work done on the cab - speaker mounted, chassis bolt holes drilled, and tilt back legs mounted. I usually build my own cabs, but this time I bought one from Mojo. They did a fine job on it, I have to say.

[Sonny ReVerb]

No smoke! Successful power up. The speed pot works backwards. Should be an easy fix.

Any brown face 6G5/6G7 tone stack experience out there? I wired it up with reference to the Fender schematics, but the Bass pot seems to work backwards?

http://monster.partyhat.co/article/amplifier-tone-stacks/

This page shows the stack but the graphic doesn't match the schematic - there's no connection from Treble 3 to Bass 1?

[Sonny ReVerb]

I believe that amplifier-tone-stacks page is in error. The Bass pot should be reversed - lug 3 on top and lug 1 on the bottom.

'How to Hot Rod Your Fender Amp...' shows what I think is the correct wiring on page 139:

https://books.google.com/books?id=SN55k8YBCi0C&pg=PA139

[HotBluePlates]

I believe that amplifier-tone-stacks page is in error. The Bass pot should be reversed - lug 3 on top and lug 1 on the bottom.

'How to Hot Rod Your Fender Amp...' shows what I think is the correct wiring on page 139

Or use the original Fender layout.  It's easier to interpret because it looks just like the pots when viewed from the inside of the chassis with the lugs on top.

[Sonny ReVerb]

Thanks, I used a VTB pot layout, but that would have been a help. I've got it sorted out now.

[HotBluePlates]

Looking great!  I hope you're enjoying the new amp!

[Sonny ReVerb]

Thanks, I am. This thing is killer. The volume of the Brown channel ramps up much faster than the Black, obviously due to the linear versus audio taper pots. Reverb and tremolo work fine and on both channels. This is the first amp I've done with reverb, first combo, and first one using a choke. Voltages worked out pretty close to what I was shooting for. See what you think. (Cab by Mojo.) I might try to do a video or mp3 to demonstrate the tones.

[Sonny ReVerb]

Final schematic

[ToneJunkie]

Sweet Build! 

[Ritchie200]

Wow!  That looks really nice!  Now you need to post some sound clips.

Jim

[Sonny ReVerb]

Thank you, gents. I'm really enjoying the amp. It can get way loud. I thought it wouldn't be as loud with the cathode biased 5881's, but it seems every bit as loud as my VR. Should be an excellent gig amp. I'm a little surprised how much the FMV tone stack attenuates the signal. I've read about that, but it's interesting to hear it in practice. When you raise the Raw control and lift the tone stack, it has a big effect. Nice to have that available.

One issue, though. I've tried the amp with several different guitars. With higher gain pickups (humbuckers) there is a weird, unpleasant, 'brappy' distortion on the note attack when the amp volume is cranked up. I've tried it through both inputs, but not much change. Any ideas? I've got a large (470k) grid stopper on the cathodyne. Do I need to go bigger? I may leave it alone because I play mostly single coils.

I'll try to get some sound clips together soon.

[Sonny ReVerb]

First attempt at sound files. Be kind! Not sure if they capture the overall effect. Close mic'ed with an SM57.

https://soundcloud.com/user-208278224/tonebox-black-strat-clean

https://soundcloud.com/user-208278224/tonebox-black-strat-dirt

https://soundcloud.com/user-208278224/tonebox-brown-strat-clean

https://soundcloud.com/user-208278224/tonebox-brown-strat-dirt

https://soundcloud.com/user-208278224/tonebox-black-strat-trem

https://soundcloud.com/user-208278224/tonebox-black-p90-clean

https://soundcloud.com/user-208278224/tonebox-brown-hb-dirt

[Sonny ReVerb]

Had a strange issue when I powered up the amp the other day. No sound at all. After checking a couple things I found that one power tube was cold and the other was slightly red plating. I powered off the amp and broke out my tube tester. Both tubes tested good with no shorts or other issues. I swapped the position of the two tubes, powered up, and the amp worked normally.

Has anyone experienced anything like this?

[shooter]

Has anyone experienced anything like this

I fixed an ampeg that did something similar, turned out to be a flaky coupling cap to the pwr tube grid, was passing big DC, (sometimes!),  probably not your case

[tubenit]

Thanks for sharing the pictures, layout, schematic and tone sound clips!   I always think it contributes in a very positive way to the forum when someone does a somewhat innovative build and shares at that level!

I really like the vibrato on the amp.  Best vibrato I've ever heard was on a Dano Centurian with 6Au6.

With respect, Tubenit

[Sonny ReVerb]

Thanks, shooter. It seemed like the filament wasn't getting power, but I'm not sure what caused it.

Thanks, tubenit. Most of my tube amp knowledge has come from these forums and guys like you.

I'm pretty pleased with how the vibrato turned out. I wasn't sure how strong it would be since the power tubes are cathode biased.

[Sonny ReVerb]

I took the amp to the local Blues jam last Wednesday. I really enjoyed hearing the amp played in a band setting. With the Black channel volume at seven or so, we had to push the raw control up to seven to get sufficient stage volume. Definitely not as loud as a fixed bias amp. Also, it wasn't as bright as my friends Tweed Bassman, but the tone was pretty tasty. Overall, a success. Might have to try 6L6's...

[tubenit]

Thanks for the update and the tone review in a band mix!  Glad you're liking the tone.  I would think that amp would be very loud already?

Maybe the 6L6's would be a little bit louder but I wouldn't think too much louder? 

You could consider trying a Dumble tone stack with a PreAmp boost and a midboost switch?  That will definitely get you some more volume.  And that is something you can use relays to be foot switchable or use mini-t0ggle switches.  Just an idea.  You could do that on one of the channels and see if you like it?

With respect, Tubenit

[Sonny ReVerb]

Well, it happened again - powered on and one power tube was cold. It was on the same side as last time, so I ruled out the tube. Pulled the chassis and found a bad solder joint. The heater wire looked like it was connected properly, but when I probed that particular wire it slid right out of the solder. I re-flowed the solder and all is working normally.

Happy Holidays, all! May you have a warm tube amp to keep you company!

[sluckey]

Well, it happened again

That's a good argument for making a good mechanical connection prior to applying solder.

[Sonny ReVerb]

True. That's exactly what I thought when I found the bad joint.

[Zarrir]

Awesome build!  These Visio layouts are killers.