tweed overdrive special, new build, questions.......

[micmac]

Hello,
I have read with interest the main post on the TOS. I find the variety of the tonal and gain possibilities to be just what I am looking for. So I figure on building one with some options added.
I thought to add remote/local switching of channel as well as effects loop, using the circuit mentioned elsewhere in this forum.

I do want to be able to run this at low power though and have been mulling over PPIV vs VVM. If I recall the comments of others here the PPIV is good at say 7-10, but starts to lose tone toward the bottom of it's range. Also that the VVM Is good all the way down without affecting the sound. Am I recalling that correctly?

My general tendency is not to go VVM because of added complexity, as well as active components which can fail (Geezer I think had this happen  IIRC???) I like simple so that steers me toward the PPIV.

I did see a PPIV used in the Matchless amps which use a single pot between the inverted and non inverted lines, not shunting the signal to ground but rather cancelling each other out. Has anyone here used this scheme or have any insight into this variation?

Thanks in advance for any help here!

Mike

[TIMBO]

Hey mate, The TOS is a great build, I have a pre and post master volume which will serve well. You can crank the preamp and listen at bedroom levels. I have done this to many amps.
Good luck with the build. 

[tubenit]

The TOS is a GREAT amp!   

Here is an old soundclip of the one I built: http://www.soundclick.com/player/single_player.cfm?songid=9488477&q=hi&newref=1

I've drawn up two schematics for you to consider based on your comments.  Both have an active FX involved.

One of them is simply the "original TOS" with active FX

The other one of them also adds a mosfet CF and what I consider to be an improved 5879 OD section. I think you would find this one to have a smoother overdrive then the original.  My D'Mars has a 5879 OD with a cathode follower and I like it a lot.

The SCH files have the B+ rail on the second page.  I recommend the PPIMV over the VVR. 

Either amp will turn out great for you.   Do you have amp building experience?  Will you be able to draw up a layout with the FX added?

With respect, Tubenit

[micmac]

oi Timbo...thanks for the "good luck" and reaffirming the PPIMV!

Hi Tubenit,
I have not built a tube amp before. I have worked in telecom engineering for a long time and while primarily mechanical, I have experience designing circuit boards and a lot of layout experience. I have worked (a little) with high voltage power supplies. Most of my instrument related stuff has been effects and the like.
I am confident in my soldering, assembly, fabrication skills. I have a decent understanding of noise and grounding. My lack of knowledge is with tubes in particular. I have read up on them and have a basic understanding of functionality. I am not nearly as up to speed as you guys when it comes to understanding the effects of changing biasing, and driving the tubes. SO I am smart enough to ask for the advise of those with more experience and perhaps have someone "looking over my shoulder".

To the particulars....I was liking the idea sticking to the original Schem. and of buying the stuffed turret board on this site. You have me thinking though! I do like the idea of the active FX loop. The tubes are not labeled on your schematic. I presume they are 12AX7's???

I could not see what you had for B+. The software I have for schematics is "KiCad" (a pretty nice open source package) so I am depending on JPG or GIF;s posted here to be able to read them........sorry.

I will look at saving my "so far" schematic to a viewable format and post it, hopefully shortly.

Are you familiar with or have any comments on the "matchless" scheme for PPIMV? I imagine that the TOS one may be a bit quieter at lower volumes since the signal path to pulled to ground.

regards...Mike

[tubenit]

Be sure you read up on amp building safety and draining high voltage electrolytic filter caps.

The tubes are not labeled.  You can use any of the 12AV7, 12AY7, 12AT7, 5751 or 12AX7.

I'd recommend 12AY7 (or 5751) in V1 (clean) and 5751 in the OD along with the 5879.  12AY7 in an active FX and 12AX7 in the LTPI.

Regarding the TOS original turret board. They're great and very quiet.  You can build a remote D'lator that plugs into the passive effects loop ............... OR build a turret board with FX added.  Your call.  Either is fine.

http://el34world.com/Forum/index.php?topic=10208.0

There is a photo, schematic and layout on post #5 on this thread for a remote active FX loop called the D'lator 
http://el34world.com/Forum/index.php?topic=10624.0

The program needed for the files is ExpressSCH and is a free download.  We have a library of 100's of editable files and layouts. 
http://www.expresspcb.com/expresssch/

As I understand it,  the Matchless is a form of a crossline master volume which I have used and is my least favorite and I think it sounds just awful.  I find the PPIMV much superior to it in tone, IMO.

I don't have time right now, but I might be able to draw up a layout with onboard FX if you wanted over the wkend? Of course, you would need to build your own board which is quite easy.

http://el34world.com/Forum/index.php?topic=15742.0
http://el34world.com/Forum/index.php?topic=9800.0

And Doug Hoffman has a turret drawing/board building program where you can design something from scratch.  You wouldn't really need that if you're using the original design. There are a number of reasonable ways to approach this.  We can offer some suggestions if you can narrow down what you're wanting to do.

Another option is to use the original TOS Hoffman style turret board and install an IronSound  solid state FX:
http://www.ironsounds.com/

However, I personally prefer the tube FX.

Anyhow, there is some info there for you to digest.  Lots of amp building experience on the forum here.  Sluckey is probably the best in trouble shooting and walking you thru solutions when something doesn't work.

Let us know if we can help.  And welcome to the forum!

With respect, Tubenit

[Willabe]

Be sure you read up on amp building safety and draining high voltage electrolytic filter caps.

Yes! 

[tubenit]

Micmac,

Please check out this thread where I show how to add FX to the original Tweed Overdrive Special Hoffman style layout board. 

http://el34world.com/Forum/index.php?topic=18927.0

IF you have any questions or need any help just let us know.

With respect, Tubenit

[micmac]

Lot's of good info! I'll have to digest it all a bit.

I think the end result is much cleaner and organized to add the FX directly to the turret board as described in your last post so I am inclined in that direction.

So far as safety....definitely! I have read up before and will read up again. Would be a crying shame to build a sweet amp to go with my custom guitar and not play it for having burnt off my fingers (or worse!!)

Thanks again for the enthusiastic support!

[micmac]

Well Ive been digesting the good info left for me.
Before I get to the back to the topic, I had put time and effort into doing the schematic in Kicad already as well as layout work in SOlidworks 3D CAD (in Solid works I can do the turret board as well as the chassis, fit checks, etc). So rather than start over and work the learning curve on the "default" software here I thought I would be better off with what I have at least for now. So I hope you all can bear with what I have and I hope the pdf's read OK here.

So have updated my schematic to include the active FX loop. Relays for both Channel and FX. As I think Tubenit mentioned in another post I have put the FX relay prior to the V4 so that when there are no FX plugged in but loop engaged it can be used as an additional gain stage.
1st question I have regarding the bias of the FX tube. In the schematic you show the bias as B+ (in the power supply there is only "B" for the screen). It would strike me that "B" would not be filtered as well as say "C" @ the PI. Conventional wisdom if I understand is that as you backtrack from the output, the more heavily filtered bias is used, so as to minimize hum/noise. So it seems that  I am missing something here? Is B+ something other than B, or should V4 be biased with "C" or something otherwise?

2nd question is regarding the NFB. I have selected an output transformer with 8/4/2 ohm taps. Would the NFB connect to the common of the switch? The original 022855 fender Xfmr is 2 ohm out only, so I am thinking that is the tap NFB should be connected to, given the 470 ohm value.

3rd (and last for now) regards the power Xfmr. The one selected has 305-0-305 as well as 355-0-355VAC secondaries. As I called it out I am using the lower V thinking to keep power/volume a little more managable. Are there any implications in one vs the other voltage?

Thanks for any help. If anything looks odd with the schematic please advise..........
best regards........

[tubenit]

B+ is not a "node" on the power rail.  It is simply a term meaning "the power rail".  If it were an effects pedal, we might use the term V+ meaning voltage.  B+ does not equal node B.

305-0-305 is fine.  With a 5Y3, you should have about 331volts and can use 6V6's.  with 5V4 you will have about 360v and can use 6V6 or 6L6/5881.  with GZ34, you will have about 390v and can use JJ 6V6 or 6L6/5881's.  with a solid state plug in rectifier, you will have 425+ volts and can use JJ 6V6's or 6L6/5881's.  You will have lots of options if you are using a tube rectifier?

Double check the plate resistor values on the OD channel schematic. V2a is 180k not 100k.    (100k/plate & 1.5k/cathode, 120k/1.8k, 150k/2.2k, 180k/2.7k, 220k/3.3k and so on is the norm and there are lots of exceptions also.)

with respect, Tubenit

[tubenit]

A couple of things to note:

Regarding R28 which is the 82k resistor in the FX loop,  ..................  you may want to experiment with that value?  39k - 82k range

The 430 ohm 10w power tube resistor,  .................. you can use lower values if you want.  I've used everything from 250 ohm to 430 ohm with cathode biased 6V6 or 6L6/5881.   My Tweed BluezMeister with 6L6 uses 360 ohm.  My D'Mars with 5881's uses 270 ohm. The larger value seems to have a somewhat cleaner tone. The lower value seems to have a more pushed tone.

The PPIMV somewhat defeats the negative feedback in the amp. Not an issue, just an FYI on that.

And regarding the entrance to the OD section.  You can easily simplify this and find the one I am suggesting as possibly more useful & versatile  to you at the same time.  The "new and improved" one will work fine with Hoffman's TOS board & be easier to wire up.  Just solder the ground of the 120p cap to the back of the 100ka pot OR to the ground lug. The 100ka pot will allow more overdrive in the first gain stage of the OD. The 120p cap helps smooth the tone out in the OD given the 5879 is somewhat a chimey but excellent touch sensitive tube.

With respect, Tubenit

[micmac]

B+ is not a "node" on the power rail. ...........

noted....I have connected the FX bias to "D"

305-0-305 is fine.  With a 5Y3, you should have about 331volts and can use 6V6's.............................You will have lots of options if you are using a tube rectifier?

Great! I like options! Thanks for spelling out the variety. Lower power is of definite interest to me so i'll be sure to keep the various rectifiers noted and see about getting a selection to try........

V2a is 180k not 100k

corrected....thanks

Regarding R28 which is the 82k resistor in the FX loop,  ..................  you may want to experiment with that value?  39k - 82k range

I've noted the range on my schematic for reference once things get put together........

The 430 ohm 10w power tube resistor,  ...............The larger value seems to have a somewhat cleaner tone. The lower value seems to have a more pushed tone.

good to know what effect adjustments will have......

And regarding the entrance to the OD section..................The 100ka pot will allow more overdrive in the first gain stage of the OD. The 120p cap helps smooth the tone ...........

This works out very well for me! the simplification shifts the following components into a position better located for more direct connection to the tube sockets. I also like the idea of a broader range of drive adjustability.........Another thing may be to have a push=pull pot with switchable cap values (120pF and larger or smaller or none?????)

Am working on the mechanical layout now. The turret board is layed out with the simplified OD, and active FX. (I expect I'll have a "custom" Hoffman turret board made up via a DXF file). Even so things a bit tight with a 17" long chassis. The flow is nice as far as the controls, turret board and tubes go, but things are tight at the power supply end (am trying to maintain good separation of the pre-filtered AC from the rest of the circuit. I have looked for something a couple of inches longer but don't seem to be able to find anything (I did find a 20" @ watts, but the online checkout is flakey). If anyone has a line on longer chassis please advise.

As soon as I have the layout done I'll post some images and perhaps you guys can tell me if I am overly cautious (or not enough!!)

thanks and kind regards,
mike

[micmac]

Well it has been a busy week but have still managed to keep working out the details and layout. I reworked the relay circuit so that +5 runs out to the foot switch so that I can have an LED indicator there. It is in the schematic but not in the mechanical layout. I thought I would build it initially with just the local switch (for simplicities sake) and then upgrade it to the relay.

Since I plan to have a custom Hoffman turret board made I took the opportunity to tweak the original TOS turret board to include the Active FX loop, simplified OD front end that Tubenit suggested, and also did a couple of minor shifting of components in the interest of more direct wire runs.
Attached is the layout from the top view and another showing the front and back panels

I have ordered the transformers and inductor, as well as several other things. I am eager to order the Hoffman parts and the turret board but hoped I could have some extra eyes go over it before I do.

I think it is a pretty clean layout with direct runs, but I am new to this so any feedback is appreciated.

I will follow another post with the schematics, and another with a 3d images.

[micmac]

Here is the schematic.

Oh and I have a question. Most of the cathode caps are in the single uF range. However the cathode cap on the FX return is 20uF which is around 10x what seems to be the norm. Could someone explain why that would be? Is it so big to avoid colouring the tone in the loop?

[micmac]

And here is the 3d

I still haven't done the initial filtering layout but there are some rough lines on the layout which hint toward what I had in mind for general routing.
Any comments are appreciated, especially regarding the turret board as I would like to get it and the rest of my parts on order.
Then hopefully I can get to the exiting part of actually  starting assembly!

thanks

[tubenit]

I think you've done a truly remarkable job with the drawings!   

A couple of observations:

1)  You have the PT & OT set up similar to how I see some of the Trainwreck amps.  I've never done that so I have no idea how well that works?
     Hopefully, you have had some experience with that?

2)  I think you may want to use relay switching from clean to OD?  IF so, look in ARCHIVES for lots of relay switching info.
     http://el34world.com/Forum/index.php?topic=14348.0

     IF you go that route and use relay switching,  Doug's boards and relay switching components are great and easy to wire up, IMO. You could
     work the layout a little to include the relay power supply (which I have on the side wall of the amp) & then all you need is a small space
     for the relay board.  IF you want to do this and need any further help or photos, let us know and we'll try to help out with it.  * see photo

     And you'll need to figure where to plug the foot switch in?

I am very much looking forward to your construction of this amp and hope you will post photos of the build!

With respect, Tubenit

[micmac]

thanks on the compliment on the drawings (It's my day job, so it's my thang...)

I am not familiar with Trainwrecks so could elaborate on the transformer comment please? As I layed it out I was forced to push them down to the end together since I only have access to the 17" long chassis (is yours longer..it looks so to my eye.) One thing I kept as "design criteria" was to keep the AC mains separate from the secondary, which in turn is separate from subsequent stages so as to minimize "crosstalk" and/or noise). I would have preferred more room but c'est la vie! It is fairly clear in my mind (not necessarily the clearest place though!!!)I will try to get some layout work done in that area so that my intent will be more clear.

I do intend to do relays for both FX and OD. The footswitch jack will be next to the input jack and the control wires (no audio here) will run up to the edge of the chassis and around the perimeter to the front panel. I didn't show the relay boards but they would likely have the front panes switch "on board" and be swapped out with the DPDT you see on my layout. The switching relays are shown on the rev 1 schematic pages (2ndpost back). I did refer to forum post for some conceptual inspiration. I did alter it so that instead of "DC return" being remote switched, the +5v is. This way I can have LED indicators out at the foot switch as well as on the panel. Wanted to keep the mechanical drawings clean and will update that later.....

How does the turret board strike you? (1st of the 3 recent posts). I think it is OK but as I learned a long time ago it is wisest for some other eyes to check your work!

I will post pix as things progress. I am not sure the lead time on the custom turret board but if all goes well I may be able to get things rolling mid to late next week????

[tubenit]

The Trainwreck amps are quite high gain from what I understand so if that PT & OT works on one end of the chassis for them, I would think it will probably be fine for you?  I'm just not experienced with that first hand. It seems a reasonable approach.

Trainwreck pics here:  http://ampgarage.com/forum/viewtopic.php?t=19

The layout looks reasonable to me and I don't see any concerns with it. I think you'll have a quiet amp using it. Double check your own work and if it looks good to you, go with it. I would think the main area you want to double or triple check is around the active FX.

I think the first TOS I did was in a 17.5"- 18.5" chassis but can't remember as I sold it to a friend who wanted it. I had the PT and OT on opposite ends of the chassis similar to Matchless or some HiWatt chassis layouts.  I only mention that simply to say there are numerous successful ways to approach these issues, IMO.

The chassis photo I posted is not a TOS,  it's my current D'Mars ODS with a 5879 overdrive section.

With respect, Tubenit

[sluckey]

I do intend to do relays for both FX and OD. The footswitch jack will be next to the input jack

The footswitch jack/wiring will be next to the most sensitive area of the amp. That 'may' invite popping sounds when energizing/de-energizing the relay. I would put it somewhere else.

[micmac]

tubenit...thanks for the additional clarification. I am going to try and get the turret board ordered today!

sluckey...Very good point. I was so hung up on the audio part I that I did not think of the switching pops. I will slide the switches farther away on the read panel. In addition perhaps adding a filter cap right at the relay/diode will help filter that a bit. Can't hurt anyway. Thanks for the heads up!

[micmac]

Been running around a lot lately so have been absent (4 days away @ gtr making demo). Got most of the stuff ordered and in house. Doug turned around the special board really fast!
So I have the turret board all wired up, short the power tube cathode resistor, and power rail filter caps for "D" "E" and "F". The filters for "B" and "C" are mounted on the end of the turret board.
Also wired up a relay board on a vector board. Both are in the attached pic. They aren't mounted but just layed in the chassis to illustrate the intended location. Still have to drill out front and rear panel holes.
Anyway things are starting to happen! If anything jumps out as being fishy please point it out (I know it is a bit early for much but.......)

DOOOOH moment...reviewing my parts it seems I accidentally ordered linear instead of Log taper for the dual 250K PPIMV.

Also I stumbled into a bunch of old tubes! 12AY7's mostly but also AU's AV's, AT's, and 1 mullard AX. It is all old stuff (RCA GE Raytheon, and others. Also some 6v6's and rectifier tubes. Hopefully they are functional.

[micmac]

Hello All
Making progress on the assembly.
AC mains wired.
Power xfmr secondary wired. (unused secondary and bias tap sleeved and tucked away)
6.3VAC  in not hooked up yet (need to make up a board for relay reg.)
5.0VAC wired to rectifier socket (no tube)
The the relay regulator board will serve as 6.3V distribution as well. I plan to locate it just above and left of the reservoir cap. The secondary will connect there and feed the lamp, heater, and regulator.
I have done a Continuity check to make sure there are no shorts to ground. Everything seems connected as expected and the power and standby switches are functioning as expected. I am thinking this is a good time to plug it in and do a voltage check on the secondaries. If anything seems amiss please advise.
With the exception of signal lines to the power tube grids (awaiting the log taper pot) everything that runs front to back are wired as well.

questions.....
1) this schematic called for a pair of 100 ohm resisters creating a virtual ground on the 6.3V secondary. My XFMR has a center tap so I presume I do not need those. Am I correct?
2) One signal run is not a short jump. It is the yellow wire running from the left most pot to the relay board. In retrospect I am wondering if I should have used shielded cable there. Any thoughts?
3) any other thoughts or observations?

I think that is it for now.....

[tubenit]

You either use the PT center tap ............ OR create an artificial one but NOT both.   Some Hammond PT trannies have a built in center tap that one might not be aware of .............. so be sure what you have.

I would leave that unshielded.  I think it will be fine.

Nice progress!  Looking good.

with respect, Tubenit

[micmac]

The PT is classic tone 40-18094. It has the ctr tap on the 6.3V secondary so I'll be using that.
Got the 6.3v distribution / 5v regulator board together this evening.
Will post more pix of progress in a couple of days.
thanks!

[micmac]

Limited testing last night.
Used the Light bulb limiter and plugged it in (no tubes).
No smoke, fingers all intact!.
Voltages appeared as expected off the tranny. Hooked up 6.3 to the 5v reg/6.3 distribution board. Regulator works fine. 6.3 gets out to all the tube sockets.
I think tonight I will pop in the GZ34 and check voltage out on that. Will also populate the rest of the tubes to check the filaments are all lighting up and the 6.3V behaves under load.
Then it will be back off and get the turret board wired in.

So forward progress is being made....if slowly.

[tubenit]

Thanks for the update!  Looking forward to the success of your amp build!   

With respect, Tubenit

[daveyajd]

Congratulations on your build progress. It is looking very nice! My TOS build was my first amp build also. It turned out awesome thanks largely to the great people on this forum. Looking forward to the finished product.

Aaron

[micmac]

Thanks Aaron,
I have been following your build as well and the fact that the guys have been you along even though the main TOS design effort has past convinced me to "go for it". I am enjoying the tube discussion as I have some ideas floating around in that regard.
By the way I had been mulling over panel markings. I had always liked white on black But the easiest seems to be Black on metal (or something light) by using water slide decals. I have heard the decals can be made white with an ALPS printer???? Yours turned out mighty handsome! If I may ask how did you go about it?

Tubenit and/or others.....Also a question regarding the cathode bypass cap on the return stage of the FX loop (I added this to the original TOS). It was shown as 20uF on the schematic which strikes me as much bigger (approx 10x) than I had seen anywhere else in that application. I generally see bypass caps in the 2.2uF down to .01uF. Could anyone comment on what effect a big cap has. And also a voltage reading at that point would be useful so as to determine the rating.
That cap is missing at the moment so I would like to get something in there. I did not see 20uF available when I ordered parts. I have some 10uF in house. I could parallel 2 of those but if one works just as well it would be "cleaner" to use just one.

Yesterday I finished wiring the f-B panels. Got the turret board in and wired most all of the stuff on the "socket side". Eyes started bugging out on me so it was time to knock off for the day (that's when mistakes happen!!!)

Thanks in advance for the help.

[tubenit]

Regarding the cathode cap on the return stage of the FX ..............................

It's totally a "season to taste" type thing.  I've done 2.2uf, 5uf, 10uf, 25uf and 47uf on that return stage cathode cap.

I have a 47uf on my D'Mars and a 5uf on my Tweed BluezMeister.

DaGeezer and I co-labored on this original design.  Both of us have commented that the TOS is definitely a "tweaker's amp" where trying different caps and resistors may be useful to you depending on your style of playing, guitar, speaker ................ etc......

Once you get it up and running, just post your results and what (if anything) you want different and I think I can give you some reasonable ideas to try. 

With respect, Tubenit

[daveyajd]

All of the design work for my front and back plates was done in Inkscape. Though it seems the program you used for your layout would work just as well. (I did chassis layouts in Inkscape as well.) After I had my template done I found a very helpful trophy shop. They had a few choices of anodized metal combinations. (ie black/silver, black/blue, gold/red) Kind of similar to how pick guards are made with multiple colored layers. They loaded my template file which was black writing on white background. Then all of the black writing was laser etched into the metal revealing the color underneath. On mine it happens to be silver. Then they cut it out using a large press shear. I was very happy with the way it turned out and it was quite affordable.

Aaron

[micmac]

Regarding the cathode cap on the return stage of the FX ..............................
It's totally a "season to taste" type thing.  I've done 2.2uf, 5uf, 10uf, 25uf and 47uf on that return stage cathode cap.

OK so I'll try the 10uF to start and go from there.....

Aaaron....thanks for the info. I hadn't thought of a trophy shop. I can "save as" a number of different formats with Solid Works so I expect one of them would work. I'll have to do some looking locally to see what's out there.

Here's a couple of more pix. I had some "mini" banana jacks kicking around so I mounted some on the rear panel to provide easy bias check points. Conveniently located near the PT's so they served to mount the 1 ohm resisters as well. I thought that worked out pretty "clean" and straightforward.

Getting close........

[daveyajd]

I can "save as" a number of different formats with Solid Works so I expect one of them would work.

That seemed to be the trickiest part if I remember right. I tried all kind of vector file types, dxf......I think what worked the best for me in the end was either a simple pdf or png file extension

That is looking great. You will have one fine amp here very soon.
Aaron

[tubenit]

That is an impressively well done well thought out build!  THANKS for sharing the photos.

Looking forward to your tone review!   

With respect, Tubenit

[micmac]

Hello All
Have been terribly busy with other things, so a bit slow on testing. Did get to some tonight.

Fired it up with tubes installed, 8ohm resistive load.
No snaps crackles or pops! No smoke! No electrocutions!

I put together a table of voltages (see attached pdf) measured throughout. Plates, Grids, and cathodes on all tubes. Also Supply voltages at each filter cap.
Put a formula to calculate current. I put actual measured resistance instead of "1 ohm" figuring on a more accurate result but the meter was a little flakey at low R values. I have a better meter elsewhere so will have to enter better numbers.

OH...and as I mentioned earlier the PT secondary I used was the 305-0-305 so supply voltages may be smaller than you all are used to seeing.
As usual any observations are welcome.........

[micmac]

ooops.... in the pdf I think I inverted a couple of stage descriptions.

"FAT" and "1st OD" should be swapped (Vplate is shared)

[tubenit]

Your dropping resistors are   choke   node B   10k   node C 10k    node D  22k    node E  1k   node F

I would change the 22k between nodes D & E to 10k or maybe smaller.  I think your node E and node F voltages would benefit from being higher.

with respect, Tubenit