Tweed Overdrive Special & Carolina Overdrive Special

[bnwitt]

I really like the names you have on the face plate there perfect , I would only add two things on the back the effects in and out and the footswitch plug in for the channel switch. Bill

TJ, I haven't even started on the rear plate yet.  The one shown is from another amp.  I'll be sure to put the effects in/out on it.  Probably in place of the bias jacks since this amp is cathode biased.

[stingray_65]

Barry,

Superb job!  I like it.   Nicely done.

Any chance of fitting on a manual spdt switch to go with the relay?

With respect, Tubenit

I've been giving this some thought on how to have a panel mounted clean/od switch and a foot pedal too
Here's what I came up with

[Tone Junkie]

You guys make it easy for us newbies so much thought with so much detail and diagrams . Ive learned tons from you guys thanks for the good work . my soldering iron is a smokin so I better get back to work. Bill 

[Blind Lemon]

Good afternoon Gents:
Aint been around in a while, it's not surprising to see Tuber and the Geez are still a couple of the driving forces over here. Seems I'm building more than I hang out on forums any more, looks like I've been missing out.

I checked back looking for a flexible amp that would do country cleans and bluey OD and this thing looks perfect. I've read through the post and no one seems to think or feels it needs a traditional "full" tonestack. Chicken pickin Tele to rock Les Paul and this amp works, that great. I've got a chassis and transformers for a fixed biased 6550(or whatever) set-up. What do you guys think about this preamp driving that type of power amp? The amp would be used on big casino stages and outdoors mostly, in both a country band and a classic rock band.

BL

[tubenit]

I've got a chassis and transformers for a fixed biased 6550(or whatever) set-up. What do you guys think about this preamp driving that type of power amp?

Because the TOS has it's gain mostly in the pre & OD sections ........... I think it would work OK with a fairly clean power amp that was fixed bias.  The large 147uf cathode cap we use is to emulate more of a fixed bias tone.

IF you give it a shot let us know how it works for you?

With respect, Tubenit

[Tone Junkie]

Tubnit a question on the 10 watt 430 ohm resister you use on the output tubes would 400 ohm do the job properly or should I double up and make 430 out of 2 resisters. Bill
PS I also was going to use 6l6 tube,s should I change anything for this or will this be fine it just happens I have them laying around and cant afford 5881,s right at the moment.

[tubenit]

ToneJunkie,

Don't know the answer to that?  I use a 10w/360 ohm resistor but my plate voltages (348v) are less than Geezer's.

The 5881 tubes are only running at 38ma.  

My Carolina Overdrive Special (same amp essentially but with D-type tone stack) has higher voltages & I use a 360 ohm with that one also & have not had any problems. My COS has 6L6's not 5881's.

Calculate your ma after trying it. I would presume a 400 ohm will work but do the math.  Measure the voltage across the power tube cathodes and divide by 400 ohm.   For example:  If you measured 32v across the cathodes divided by 400 would be 80 divided by two tubes would be 40ma per tube.

With respect, Tubenit

[Tone Junkie]

Thanks Jeff you just tought me how to bias by voltage which I can relate to having mostly done variable bias amps.I will print this out and add to my wall of important knowledge, you have a couple things up there. Bill   

[Blind Lemon]

I'll do that and take some pics along the way.

BL

[tubenit]

I got the Tweed Overdrive Special Hoffman turret board finished.  Turned out nice!

I will admit I am NOT a strong detail person (or that patient) so the wires aren't nice and straight.   

However, this type of board seems very sturdy to me & was relatively easy to do. The parts that Hoffman sells fits the board just fine.

1)    I numbered the turrets so I could track easily what went where.
2)    I connected the appropriate turrets first.
3)    Then simply populated the board.


With respect, Tubenit

[Fresh_Start]

I will admit I am NOT a strong detail person (or that patient) so the wires aren't nice and straight.

Jeff - we've seen your cabinet work!    So what if you were in a bit of a hurry on this board.  You've got to be plenty patient to get your cabs to look as sweet as they do.  

As far as details go, you and Geezer figured this baby out through how many iterations???

Chip

[Tone Junkie]

Ok more dumb questions sorry      With your hundred ohm resister going to the cathode of the power tube Im figuring one side of the heater goes to one tubes cathode and the other side to the next one do I still ground my heater center tap. Sorry for the newbie question. Bill
PS. being that this is a rebuild i already have it grounded but didnt know if that caused problems to that type of bias circuit

[tubenit]

You do NOT use a heater wire ground IF you are using the 100ohm resistors (as an artificial ground) per Hoffman's Library of Info.

I did not ground those 100 ohm resistors to the power tubes shared cathode, but may try that at some point. I followed Hoffman's grounding scheme from his Library of Info and grounded the heaters that way.

With respect, Tubenit

[stingray_65]

Hey Geezer and Tubenit,

Why did you guys choose a cathode biased power section?

I have this PT that Magnetic Components says is a Super Reverb replacement, but the secondary voltages are higher than spec'd on the schematic.

The flea bay Sovetek 6L6WXT's are here and Thant tranny has a 53V bias tap.

So I'm thinking fixed bias might be in order here. the OT is rated between 50-60 watts and the Celestion I have is too.

What would be the pitfalls of going this rout?

Will the PPIMV need modified too?

[Fresh_Start]

Hey Geezer and Tubenit,

Why did you guys choose a cathode biased power section?

I have this PT that Magnetic Components says is a Super Reverb replacement, but the secondary voltages are higher than spec'd on the schematic.

The flea bay Sovetek 6L6WXT's are here and Thant tranny has a 53V bias tap.

So I'm thinking fixed bias might be in order here. the OT is rated between 50-60 watts and the Celestion I have is too.

What would be the pitfalls of going this rout?

Will the PPIMV need modified too?

Just to start Ray off:

How loud do you want this amp to be?  Sounds like you could use the entire poweramp including PI of a Super Reverb, adjust the dropping resistors on the power rail to get preamp voltages where Geezer & tubenit found sweet spots, and be good to go.

Just a couple of days ago there was a discussion of PPIMV circuits in a Plexi context.  The Trainwreck "type 2" is virtually identical to what the guys have used here, except that the volume pots are "grounded" on the bias tap instead of at chassis ground.  IOW you just insert the bias supply at the junction of the two 2.2 meg resistors instead of grounding that point.  Done.

That's going to be one clean, loud power amp.

Cheers,

Chip

[samato]

I'd love to hear one of the sound clips of this amp (especially the one with the band) but none of the links work for me.  Maybe because I'm using Firefox on a Mac?

[tubenit]

Why did you guys choose a cathode biased power section?

Because I like the sound of cathode biased amps alot. It is easy to do than fixed biased, IMO.

Because I don't need the extra volume at all. I need to preserve the hearing I have left.

And because I discovered with all 3 of my cathode biased amps, I can simply switch between 6V6 & 6L6 tubes with no problem.  I like being able to do that.  No re-biasing is needed.

with respect, Tubenit

[Geezer]

I'd love to hear one of the sound clips of this amp (especially the one with the band) but none of the links work for me.  Maybe because I'm using Firefox on a Mac?

Try this link>> http://www15.zippyshare.com/v/93652381/file.html

[stingray_65]

Just a couple of days ago there was a discussion of PPIMV circuits in a Plexi context.  The Trainwreck "type 2" is virtually identical to what the guys have used here, except that the volume pots are "grounded" on the bias tap instead of at chassis ground.  IOW you just insert the bias supply at the junction of the two 2.2 meg resistors instead of grounding that point.  Done.

Like this?

I've not built a fixed bias amp yet, and things seem to keep pushing me to on this build.

And where would I put the 1 ohm resistor to measure current draw?

Thanks Tubenit,

3 very valid points and I do agree on all 3. If this doesn't work for the best it should be easy for me to revert it back to cathode biased.

Ray

[samato]

I'd love to hear one of the sound clips of this amp (especially the one with the band) but none of the links work for me.  Maybe because I'm using Firefox on a Mac?

Try this link>> http://www15.zippyshare.com/v/93652381/file.html

That worked, thank you.  Nice sound, nice playing.

[Fresh_Start]

Stingray - I think you nailed it.  The 1 ohm current sensing resistors go between pin 8 of each power tube's cathode and ground.

I believe that it's important to use shielded wire going to and from the Master Volume pot since these grid leads carry relatively low signal levels but are in the poweramp end of the amp.  IOW the potential for lots of nasty interference in the neighborhood.

Chip

[tubenit]

I used different component values & PT than Geezer and am VERY happy with this amp.

I do NOT like the PPIMV that I had in the amp and so I installed a Dana Hall VVR which I like real well. I could not turn the PPIMV below "6" and still get a good tone.  I can dial the VVR down to "3.5" and still get a great tone, IMO.

Just thought I'd share how I did it. In case, anyone else is interested in trying that.

I should mention that I installed two Dana Hall VVR's in two different amps in Sept '09. The amps have been used regularly and had NO issues with the VVR at all.

I should mention that there is a MORE dramatic contrast between clean and OD with the VVR then there was with the PPIMV.

With respect, Tubenit

[Geezer]

Another soundclip here>>

http://www.el34world.com/Forum/index.php?topic=10305.new#new

[mresistor]

Man oh man , that is a kickin' lil amp. Great sounds!  

love it!

[CircuitButcher]

Posted by: mresistor
Insert Quote
Man oh man , that is a kickin' lil amp. Great sounds! 

love it!

Roger that!

Hey Mr Geezer, what speaker/s were used in that recording?

Much difference between 6L6's and EL34's?

[Geezer]

Speaker is an Emi Private Jack in a 1x12 closed back, front ported cab.

The tubes are actually E34L's, which are "sorta" like a cross between the EL34 & 6L6 tone, and added more "punch" & clarity.
It could just be that all the 6L6/5881 variants I have are fairly well used & have lost their punch (past their prime), but I really like what the E34L's did for this amp.

I will post an updated (tweaked) schematic as soon as I have time to work it up.

[talsmag]

Hello,
This is my first post here.  I've been reading up on the TOS and it sounds like a killer amp.  I'm pretty stoked about building one.  My question is:  Does anyone know of a source for the 250K dual-gang pots?

thanks,
Gary

[stingray_65]

I purchased an Alpha for my TOS from Antique Electronics Supply: http://www.tubesandmore.com/

Part #  R-VA-8MM-2A

Between Doug's store here and AES you should be able to get everything you need.

I highly recommend to buy what you can here at Hoffmans first, especially the turret board.

I guarantee you won't be disappointed with Doug's service.

Ray

[talsmag]

Thanks Stingray,
I buy everything I can from Doug.  His service is top notch!

Gary

[Tone Junkie]

Geezer that sounded real nice wish I played that well, Have you ever got around to another schem. from where your at right know i think those el34L,s sound real nice. Bill

[talsmag]

This may be a dumb question, but I can't get my head wrapped around this master volume issue (not the PPIMV).  I understand that the master only affects the clean channel.  If that's the case, what's the difference between the master volume and the clean volume?  Is it there so you can crank up the clean volume and get some clean drive and then control the overall level with the master?

thanks,
Gary

[stingray_65]

This may be a dumb question, but I can't get my head wrapped around this master volume issue (not the PPIMV).  I understand that the master only affects the clean channel.  If that's the case, what's the difference between the master volume and the clean volume?  Is it there so you can crank up the clean volume and get some clean drive and then control the overall level with the master?

thanks,
Gary

Hi Gary,

Basically you've got it.

Just to be on the same page (the controls have had various names put on them as this keeps evolving)

on the clean channel there is in order of process,Volume, Tone, Fattness, Master Volume, PPIMV

On my build I labeled the first Volume as GAIN. this sets the overall signal that is seen from here out.

Tone is self explanatory

Fattness I labeled as Depth, this controls how much signal is inserted into  the second parallel gain stage

Master Volume I labeled mine as Clean Level.

OK
So when I set this amp up, I put the GAIN on 2 or 3
Tone and Fatness to taste
Clean Level around 5

Now the OD side.

I set the OD Drive to about 3
Tone to flavor
OD level around 2

NOW strum a few chords switching between OD and Clean channels.
set the Gains and Levels (master volume on clean side) so that there is no noticeable volume difference between channels.

from there, I can set the gain higher on the OD channel and use it like a lead boost pedal.

at least thats how I've set it up every time I let some one use it, LOL I'm not a musician.

In a nut shell the Master Volume as Tubenit labeled it and the OD level I use to balance the perceived volume of each channel. the PPIMV then is used for absolute volume levels for both channels simultaneously

Hope I haven't confused you more :)

Ray

[talsmag]

Thanks Ray,
Very nice explanation.  I get it now.

Gary

[nateflanigan]

What are people using for the OD switching?  There's a few mentions of relays through out the thread, as best as I can tell a regular DPDT switch would work.  Are there any kits anyone can recommend for a drop in relay board? 

Thanks

[Geezer]

Are there any kits anyone can recommend for a drop in relay board?

I use the Weber relay boards (low power version).

http://taweber.powweb.com/store/chansword.htm

[duke of earl]

Wow that is the kind os sonic beauty I have dreamed of owning. That is some really fabulous fretboard work I must say!

[nateflanigan]

Thanks Geezer!  I also found one on the london power site, it's like 4x as much though.

[stingray_65]

What are people using for the OD switching?  There's a few mentions of relays through out the thread, as best as I can tell a regular DPDT switch would work.  Are there any kits anyone can recommend for a drop in relay board? 

Thanks

REALLY??

C'mon Nate! if you can build the power supply for a tube amp, a switching relay will be a walk in the park!

I build mine on a proto board from radio shack, relay can be bought from Doug if you like dependable relays and fast shipping.

LOTS of builders here would walk you thru it.

The TOS I built had MANY firsts for me, a switching channel was one of them, most likely the easiest part of the build.

Ray

[nateflanigan]

Ha!  Nothing like a swift kick in the pants to get the old gears spinning.  A quick google search got me sorted on how relays work, I don't know why it never made sense to me.  

Stinray, have you tested that diagram you have further up the page for using a panel switch and footswitch?  I'm worried about shorting the control voltage to ground, or is it too low to pop circuit breakers?

[stingray_65]

Nate,
I implemented that schematic exactly.

You aren't shorting the control voltage to ground, That is a coil, one side to + the other to ground. You're simply switching the ground side of the coil.

Ray

[talsmag]

Hello everyone,
I'm in the middle of my TOS build and have a question about where to use sheilded cable.  Is it necessary to use it on all the runs from the pots to the board or is that overkill?

thanks,
Gary

[tubenit]

I tend to only use it on long runs & not short ones from the board to pots.

This photo is NOT a very good example because it's not clear. The "thicker" black wires are the shielded.  I used quite a bit black wiring to ground to a buss bar so it's a little confusing, IMO. The thick black wires on the socket side of the tagboard are B+ wiring that has shrink tubing around it (probably overkill).

http://s28.photobucket.com/albums/c216/tubenit/?action=view&current=completedchassiswiring.jpg

With respect, Tubenit

[theundeadelvis]

Anybody know if this is the kind of dual-gang pot needed for this build? http://www.mojotone.com/guitar-parts/Guitar-Potentiometers/Fender-CTS-250K-Dual-Stacked-Potentiometer-TBX-Tone-Control

Thanks!

[Geezer]

This is what I used>>

http://www.mouser.com/ProductDetail/Alpha-Taiwan/RV24BF-10-15R1-A250K/?qs=R1h7DEsyLZi9EhQqk47wow%3d%3d

http://www.mouser.com/catalog/specsheets/TW-700160.pdf

[theundeadelvis]

Thanks Geezer! I've spent all morning trying to find a single distributor that would have 3 parts I need, to save on shipping, but since I've had no luck, it looks like I'll be placing a couple orders anyhow.

[nateflanigan]

I'm still a little foggy on the relay wiring, what's on the schematic is clear but how exactly to wire the AC to the solenoid isn't.  I'll be using the LED/bezel combo that Doug sells and attempting to do the switching al'a Ray's diagram.  I think I tie one leg of the 6.3v supply to one of the solenoid pins but ahhhhhhn what about the other one?  Or do I have it completely wrong.  Here's what I have so far...

[sluckey]

Is that Doug's 5 volt DC relay? If so, you gotta build a power supply for it. See this...
http://www.el34world.com/projects/relay_switch.htm

[nateflanigan]

Wow, that is something else.  Couldn't be more clear now, thanks!

[67polara]

I used a 6vdc wall wart for the power supply I just took the case off wired it to the power switch and done!  Bought mine at the .99 store LOL.  I also used a Linrose Superbrite LED PN 3990a5 with a 220 ohm resister in series  wired right across the relay coil terminals and now have an OD indicator light you can see across the room.

Tony

[nateflanigan]

How critical is the filtering in that circuit?
http://www.el34world.com/projects/relay_switch.htm

I've got a bunch of 1000uf 10v caps around i'd like to use.

Thanks!