*"new" Tweed BluezMeister with 5879 OD

[tubenit]

I changed my 56T Plus into a Tweed BluezMeister with 5879 & CF OD.  The 56 T Plus was a really good sounding amp (& maybe my favorite for playing just rhythm), but the OD stage was subtle.  And the mid boost was noticeable but not a big shift in tone.

So, I rewired the first two preamp tubes into a different order.  

Very dramatic difference between clean and OD now!  This amp probably has the most sustain and overdriven tone of my 3 amps. I am thinking this is because the 6V6's may are being pushed as well as the preamp stages.  With the OD & mid boost engaged, I can almost sustain into feedback on any note.  The overdrive is not muddy sounding at all.  It has a very clear cranked, pushed overdrive tone.

The OD sounds very pushed and overdriven compared to my Tweed BluezMeister (original) and the D'Mars ODS.  The overdrive on those two amps have very smooth and nice sustain which is very clear sounding.   This TBM with 5879 has a FAT pushed overdrive tone that is quite different. It is not gritty but it sounds more cranked.

I have mentioned it before but I am convinced that the 5879 in an OD gain stage really benefits with a cathode follower with it. This is the first time I've tried a mosfet cathode follower with a 5879.  It has nice compression to it.

The amp sounds really huge for a small amp, IMO. I think it has some of that Bonamassa type cranked OD tone using a delay with it.

Anyhow, thought I'd share the schematic and layout.  I will try to record the OD sometime next wk or wkend IF I can get the OD to record OK.  

with respect, Tubenit.  

[TIMBO]

Sooooooooooo that's what you been up to,looks good.

[Slimtim]

Sweet.I wanna hear it.Why are the 6v6s and power section not in the layout?

[tubenit]

Why are the 6v6s and power section not in the layout?

It's just the way I have typically drawn them.  I'm really just drawing a layout board connected to pots, switches and tubes. 

On the SCH schematic that I attached, it does show the power section & B+ rail on the 2nd page. 

with respect, Tubenit

[SILVERGUN]

Well, I'm just gonna consider this a personal Christmas present 

I'll have to wait a couple weeks to unwrap it,,,that's all

Thanks,,,as always for ALL that you do!

[Jack_Hester]

Jeff -

Have you had a chance to make a sound clip of this latest build?  I always enjoy your playing, whenever you are able to make them. 

I can't get around to reading all the posts, but yours are among the first.  Fine business. 

Jack

[tubenit]

I drew up a Hoffman style board for the amp design.   

SCH versions is here:  http://www.el34world.com/Forum/index.php?topic=16449.0

CHECK for errors!

with respect, Tubenit

[Tone Junkie]

Looks like a good Christmas present to yourself I have found those are always what you want .
 
 Bill    

[Jack_Hester]

Here's a concept drawing that I made of Jeff's circuit, using a triode as the CF. And rather than his PI, I used the second triode in the tube as a Cathodyne PI. Saved adding another tube. The PI was taken from Merlin's book.

Forgive the unconventional schematic. I draw literally like it might be a P2P build, using actual tube internal layout taken from data sheets.

Look to my V4 for the CF and PI.  There are a couple other differences, but the CF and PI are the major ones.

Jack

03Jan14 - Note: See below for rev-C. 

[tubenit]

GREAT idea!!!   I like it.

I have a couple of questions (indicated in yellow):

1) looks like the 5879/CF is bootstrapped .............. correct?    (this may be a challenge switching from clean to OD because of the
    volume boost)

2) the 470k grid resistor and the 47k grid resistor to cathode .....................  did you mean to reverse those??  47k grid resistor
    and then 470k grid resistor to cathode?

EDIT:  per Merlin's article, you have drawn it correctly!  http://www.freewebs.com/valvewizard/cathodyne.html

I indicated in light green some component values that you might consider changing IF you want something of a tighter and more focused bass response.  Not necessarily better just another option in values to consider.  The 220p smoothing cap across the plate, I would use for added smoothness.  These changes do get the "clean" channel closer to Fendery clean tone, IMO.

With respect, Tubenit

[Jack_Hester]

Ok.  

To question 1 - Yes, bootstrapping is where I was headed with that mod.  As to the challenge, I just don't know as this is the first draft and no build to prove it out.

To question 2 - I applied Merlin's configuration for the Cathodyne PI:

http://www.valvewizard.co.uk/cathodyne.html .  

Look at the very bottom of the page and note that he has the grid stopper as a 470K and the grid leak as a 47K.  He gives an explanation for the grid stopper, but I may have missed his reasoning for the 47K value of grid leak.  Also, notice the diode in series with the 47K, that Merlin recommends for arc protection, found in the bottom of this page:

http://www.freewebs.com/valvewizard1/dccf.htm .

As to your other suggestions of component changes, I have saved you drawing to the same folder as I have the other TBM drawings.  This will be as far as I can go (drawings), for now.  

I really appreciate your looking my drawing over.  I've only proof-read it a couple times, but will do so again.  I tend to get component values and labels askew, when a schematic is this busy.  But, I think that it's reasonably complete.  

Take a look at my NFB.  Though I don't see it on your rendition, I brought mine back to the FX Return side cathode of my V2.  I did not include a means to switch it out.  I chose the value that you used.  I have another P-P that I used a 33K in the NFB, and brought it all the way back to the 2nd of three gain stages.  That one has a Cathodyne PI in it.  If and when I have that one open again, I may try your 27K, as it has a bit more gain than I want.  

Again, thanks for the comments and suggestions.  Have a good one.

Jack

Note:  You added your edit before I could post my response.  Glad you saw it.  Thanks again, for the comments.

[silverfox]

Tubnit-  "I think it has some of that Bonamassa type cranked OD tone using a delay with it."

I had heard of Joe in the past but really knew nothing about him. Somehow I ended up on this link: http://www.youtube.com/results?search_query=joe+bonamassa+just+got+paid+royal+albert+hall+2013&sm=1

I've played this video about 20 times since and try to hammer it out every other time I practise. Great guy, HUGE SOUND. Joe is also one of those really nice individuals in the music Arts. I won't say industry since his manager produces all their music outside of the mainstream.

Sounds like a winning design. Can't wait to hear it.

Silverfox.

2014- We made it!

[Jack_Hester]

Here is the complete drawing, with power supply.  Please check for errors.  And note, I placed a Hum Balance pot in place of the two 100R's that you have on your 6.3v filament winding.  This works very well in my Ampegs, fixed bias or cathode bias.  In the cathode biased models, they connect the wiper to the cathode junction of the power tubes, like you would if using the individual resistors.  Take a look.

Jack

03Jan14 - Note: See below for rev-C. 

[thelonious]

Thanks for sharing this, Jeff! I'm going to try this one out. Do you find that the mosfet works ok without a gate stopper resistor? I see a lot of people add a ~220R there.

[tubenit]

Take a look at my NFB.  Though I don't see it on your rendition, I brought mine back to the FX Return side cathode of my V2.  I did not include a means to switch it out.

I think that will work fine.  I would suggest the NFB switch.  I very seldom play mine with the NFB engaged. And there is a significant difference in sound between off/on with NFB.  It's a somewhat more aggressive/pushed tone without the NFB.

Do you find that the mosfet works ok without a gate stopper resistor? I see a lot of people add a ~220R there.

Just an error in the schematic drawing I posted.  There is a 220R/2w resistor there like on the D'Mars.

Restating something ............ there is a BIG difference in tone between the clean and OD. And the clean tone really is a nice warm clean sound.   I can not imagine anyone not being able to tell what is which with a "blind test".  Same thing with the mid boost.  You can easily hear the difference.  That makes those features very useful, IMO.

With respect, Tubenit

[Jack_Hester]

I think that will work fine.  I would suggest the NFB switch.  I very seldom play mine with the NFB engaged. And there is a significant difference in sound between off/on with NFB.  It's a somewhat more aggressive/pushed tone without the NFB.

Not sure how to approach this with my configuration.  Just a simple switch, to take it in and out?  Or, should there be more? 

Jack

[tubenit]

Regarding the NFB switch...............

Yes, a simple spdt.   It's in the original schematic at the top of the thread.

I am in the process of drawing up a layout board to go with your schematic. Will post probably tomorrow Thurs am.

With respect, Tubenit

[Jack_Hester]

Ok.  I saw how you have yours.  But, I meant to ask if I should include the paralleled capacitor and resistor, that you show on one leg of the switch.  Rather than just a NFB disconnect. 

Looking forward to the layout.  Thanks the the fine work.  Have a good one.

Jack

[tubenit]

Ok.  I saw how you have yours.  But, I meant to ask if I should include the paralleled capacitor and resistor, that you show on one leg of the switch.  Rather than just a NFB disconnect.  

My apology, I am not sure how you'd hook up that NFB.  I am inclined to think about leaving it out. IF you need something cleaner in tone, you can use LNFB around V1b like on Dumblish amps.

with respect, Tubenit

[terminalgs]

First, let me say that this is an interesting thread!

Which tube stage is driven to saturation when switched to OD? 

From just looking at the schematic,  It's hard to know since the trim pot before the pentode could very well be trimmed down quite low such than the difference in gain between the two switch positions ( as the signal exits the dpdt SW) is slight (10% 20%). If this is the case, maybe it's the 6v6s that are over driven?

Or if the trim pot delivers a decent signal to the pentode, is the signal that exits the pentode and hits the 500k level pot a clean sine wave ? Or squared off (I.e. saturated)?   If it's clean, is it the first 12au7 in the fx segment that is driven to saturation? 

[tubenit]

Which tube stage is driven to saturation when switched to OD?

As far as I know Jack Hester's  TBM 5879 OD is a draft and has not been built.

With mine which has an LTPI instead of concertina phase invertor,  I think most of the OD is from the 5879 since it has a very clean tone prior to switching the 5879 in. However, as one cranks the amp ........ I would expect the 6V6's to become more overdriven also.

On these type of high gain amps, you can't really crank every knob to "10".  It just doesn't sound right.  So on mine,  the clean volume is at 5,  treble 5, bass 7, mid 3,  OD trim 6,  OD volume 7,  FX send 5 & FX level 6-7.

I've never owned an oscilloscope, so that is the best answer I can give you.

With respect, Tubenit

[terminalgs]

Which tube stage is driven to saturation when switched to OD?

With mine which has an LTPI instead of concertina phase invertor,  I think most of the OD is from the 5879 since it has a very clean tone prior to switching the 5879 in. However, as one cranks the amp ........ I would expect the 6V6's to become more overdriven also.

On these type of high gain amps, you can't really crank every knob to "10".  It just doesn't sound right.  So on mine,  the clean volume is at 5,  treble 5, bass 7, mid 3,  OD trim 6,  OD volume 7,  FX send 5 & FX level 6-7.

You have a total of five gain controls (all the ones you've mentions except treble, bass,mid).  the FX send and FX level are both independent master volumes of sorts (esp. if nothing is plugged into the FX loop).  If you have 'FZ send' set to 5, the signal is being attenuated first 50%, and then about 60% with the 82k/100k "fixed" voltage divider (with nothing in the FX loop, that's 30% attenuation).  the 12au7 driving the 250k FX-level make-up pot, with pot set to 6, is probably a total gain of 4X or 5X ?  So, its possible all the OD crunch is in front of the 6V6s.

With clean-vol=5 and OD-trim=6,    it seems to be very possible that the pentode is not being driven to saturation, but rather the first 12au7 triode is.,  especially if the total sound produced by the amp with the OD-SW=off is clean (with those same clean-vol and FX-vols settings).

None of this is a bad thing,  especially if you are happy with the results (the only reason I bring it up is that I'm interested in understanding the circuit).

Personally, I don't like to build an amp that can't have all knobs set to 10 simultaneously, because,, well, if left unattended in the hands of another musician, they will all get turned to 10!   On the other 5879OD thread, I mentioned using the 2nd half of the dpdt to switch in a resistor on top a volume pot that comes later in the circuit.   For example, if you take the 100k FX-send pot that you set to '5', you could switch in a 100K resistor on top of that to produce the same 50% att. at max knob switch, thus giving you greater tune-ability on that pot, and the ability to crank it to 10.    Instead of the FX-send, you could do the same with your final master FX-level. 

[tubenit]

Personally, I don't like to build an amp that can't have all knobs set to 10

I have no doubt, some individuals like to roll all the knobs to "10". 


However, & just a personal preference .......... I have never played or owned any amp where I liked everything on "10".  I have found much more musically sweet tones with pots dialed more from 3 or 4 to 7 range typically.

With respect, Tubenit

[Jack_Hester]

I checked this thread a couple times today from work, but was unable to comment.  Shorthanded on help, and major busy starting up two of our generating units.

Anyway, that's a great layout drawing and schematic.  And, I have a question about your turret/tag board.

When you make a layout for one of your amps, do you have some standard for board size dimensions?  I buy blanks, sometimes fixed lengths from Doug, sometimes a large sheet from other sources, and cut them to fit whatever is needed.  On my little table saw with a tile blade.  Or, on a little Rockwell BladeRunner using a fine toothed metal cutting blade.  I have some tile blades for it, but they make a cut that is way too wide.  

My point is that yours seem to have some set size.  I just picked up a generic, pre-drilled board off of the bench that I've been threatening to use on something.  It is 10-1/4" x 3-1/8", 27 holes x 8 holes, at a 3/8" spacing.  

Your layout would be 28 holes by maybe 6 holes, if I were to use the same spacing.  I've never used one of these pre-drilled boards before, as I drill only what I need.  But, this one may be suitable for me to try out on this build, though I'm thinking that I may want to shave 2 holes width off, lengthwise.  Or, I may leave one set of holes empty down each side, and route wires through them.  

On some of my simpler builds, I've taken the schematic like I posted earlier (smaller build, of course), plot it to scale on a sheet of paper, tape the paper over the board, and center-punched it though the paper.  Drill the holes for turrets and mounting, and do the build just like it's drawn.  No schematic needed after that, as you can literally follow it on the board.  I've got a small AM radio transmitter that I plan to do this way, as it is ever so simple.  

But, back to your layout.  What would be your physical layout for what you've drawn?  Thanks for the fine work.  

Jack

[tubenit]

Jack,

I have used Doug's tagboard dimensions ............ but his turret board materials.  

In other words,  the turret layout and size of the board matches the tagboard.  I just use a hacksaw and cut the turret board material to a narrower width.  I actually like Doug's Hoffman style turret boards ................. however,  a paralleled turret board is easier to work with for an experimental build where one may be changing a lot of things around.

I had a small scrap leftover piece of the tagboard that I used to trace the size and the hole spacings.

This tag board has 2 rows of tags x 28 tags per row
The length and width are 300mm x 56mm or 11.875 x 2.25 inches

http://www.hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=BoardBuilding&ORDER_ID=968932707

Hope that helps.   with respect, Tubenit

The attached picture is mostly a paralleled turret board but with a few added turrets where needed.

[tubenit]

Yikes!  (in the previous drawing),  I discovered that I had drawn the bootstrapped 5879/CF incorrectly.  Hopefully, this is correct.

CHECK for errors!  If there is a discrepancy between the layout and the schematic, go with the schematic.

With respect,  Tubenit

[Jack_Hester]

Ok. On the turret board construction, the standard is really the application.  Most of the pre-fabricated boards that I've seen are 3-1/8" wide, by whatever length.  And, I buy those on occassion.  But mostly, I like to cut the width and length to the application. 

Another observation on the pre-drilled board.  The holes are large, so I'm thinking large turrets or eyelets.  I typically use smaller turrets, with an occassional large turret or eyelet.  But, for the sake of this experiment, I can use large.  Plenty of room for multiple components, if needed. 

Good catch on the drawing.  I'll save your update to my computer when I get home this evening.  Thanks for the continued fine work on these drawings.  Have a good one.

Jack

[tubenit]

IF you wanted to .......... you could just use Doug's tagboard for under $7.     

Only disadvantage is that they aren't as sturdy as his turret board material and turrets.

With respect, Tubenit

[Jack_Hester]

IF you wanted to .......... you could just use Doug's tagboard for under $7.     

Only disadvantage is that they aren't as sturdy as his turret board material and turrets.

I would, if I didn't already have materials on hand.  This pre-drilled board needs using, and I've got a large quantity of turrets and eyelets that will go in fairly quickly.  I'll hold off until everyont has had a chance to look the drawings over.  I plan to drop the NFB from my drawing, as per your comments on the lack of need.

I think that I have a generic aluminum chassis that I could use, though I don't have a cab.  If I can put my hands on a plate to cover the bottom of it, I'll just put rubber feet on it, and let it be one that can be passed around.  That way, I have a number of friends who would love to give it a tryout.  Especially a couple of guys over in Durham.  One of them would make some sound clips for me.

It's all pending on time, and a busy work schedule.  I'll post anything that I do, with pics.  Thanks for making this good stuff happen.  More to come.  Have a good one.

Jack

[Jack_Hester]

I have reconciled my drawing to reflect Jeff's changes, though I left one decoupling cap in the power supply to a value of 16uf (C27), as in the original drawing.  Jeff had changed it to a 26uf, and I'm thinking a typo.  Please confirm.

I also made a correction on my Mid pot location, to reflect the same circuit as Jeff's.  I added the cap around the 33K resistor (C17) above the 5879 tube, and the cap around the 68K (C20) above the PI.  

There are a few component value changes, to reflect his values, and I left my Hum Balance pot in place.  

I left the OD triode CF and the PI triode in the same tube (V4) as a 12DW7, making my CF the same as a 12AU7 and the PI the same as a 12AX7.  This one might be better as a 12AU7 tube, but I can experiment.

I left the active FX loop the same as Jeff's original, both triodes in one tube (V2).  But, can experiment here, as well, with different tubes.  

I will draw the layout as Jeff has drawn it, and add my component labels.  I have had to correct my labeling several times, as I reconciled to his.  So, I need to be sure that I have my layout just like his, drawn to fit this pre-drilled board.  I'll have that on the same drawing as the rest of what I've done.

I've got to go in at Midnight and work until 8am tomorrow.  Cold weather coverage at the plant.  Found that out just after noon.  It gets bone chilling cold down there on the water, and we're headed for the teens in temperature, tonight.  If all is quiet, and nothing freezes, we stay shut up out of the cold, until called.  Maybe I can make the layout drawing, then.  We'll see.  If not, tomorrow, after I'm home and have had a nap.

I'm posting my changes, up to this point.  And, will post the drawing with the layout (with component labels), when that one is finished.  Have a good one.

Jack

11Jan14 - Note: See below for rev-D. 

[tubenit]

Jeff had changed it to a 26uf, and I'm thinking a typo.  Please confirm

Actually, I did change it.  But as I said previously, some of the changes are just different and not necessarily better.  This can be viewed as one of those.  It simply tightened the bass response on that tube somewhat.  The original 16uf is just fine.

With respect, Tubenit

[Jack_Hester]

It's been a spell, but today (Sat) I was able to finish my layout.  Once again, modeling after Jeff's drawing, I set upon the task of making it reflect my tube lineup.  Because I have a different configuration than Jeff, I had to shift components in my layout.  And because making these type drawings are not easy for me, I really appreciate having his, to set the stage for mine.

Anyway, I tried to make mine follow convention as much as possible, though I tend to still draw literally as if I were building from a scaled drawing.  Here is that first draft, with my previous schematic.  I'm thinking that I will go back and do a schematic that, too, follows convention.  But for now, here's what I have.  

Again, Jeff is to have all the credit for the work.  

Note: When I do complete my new schematic, it will have a corrected component labeling (updated numbers).  Also, the pre-drilled board that I used to set the dimensions for this layout has holes that have 3/8" spacing.

More to come.  Have a good one.

Jack

12Jan14 - Note: See below for update to rev-D. 

[tubenit]

Jack,

THANKS for sharing your work and drawing.  It looks great!  And I think you're going to have an incredible build.

From my perspective, this is totally your amp design with the triode CF and the concertina phase invertor. Please feel free to rename the amp anything that suits you.

 

With respect, Tubenit

[Jack_Hester]

A fellow on another forum has offered me an empty Silvertone 1482 cab, that appears to be in very nice condition.  It has no chassis or speaker, but may serve as a likely candidate for this build.  That just came about this afternoon, so the timing was perfect.  I'm no woodworker, and this may enable a nice old cab to be pressed back into service with a new purpose. 

You'll notice that I put board dimensions on the drawing.  I didn't indicate the gap between boards, but I made it 1/4".  So, not knowing cabinet space available, I may or may not be able to use this type for the supply.  A canned cap may be in order, with the resistors mounted on the terminals.  We'll see. 

I may take my lead on a power supply from some that I see in older amps.  One that comes to mind is a Gibson GA-78, that has the power supply in the bottom of the cabinet, and a harness feeding the amp, which is mounted in the top.  As this Silvertone cabinet has the chassis to one side, the power supply could be mounted opposite of it.  Just an idea, as I don't know how much the speaker would crowd it. 

A question about the transformers that you use.  Do you have the spec sheets for them (PT, OT)?  Mostly, I need the footprint, to figure their placement.  I've got several nice ones, taken from trashed amps/radios, that I've marked with known information.  However, most are very large.  But, I like to re-use such when I can.  For the sake of the drawing, I like to put modern specs on it.  Others may take an interest, but only have access to new. 

Anyway, I'll plan to start on the schematic, tomorrow after Church.  I'll post that revision soon.  Have a good one.

Jack

[Jack_Hester]

I updated the drawing, and left it as the same revision.  The major change was to correct the component labeling to have sequential numbers.  

I found an error where I had a ground in the wrong place on the Tone Stack.  

I had to add a missing capacitor to the Volume pot, giving it the next highest number (C29)., rather than shifting them all.

I also added a missing resistor (R35) to the PI.  

Other than these changes, I believe that it can be considered ready for construction.  Please look it over and comment with errors found, or improvements.  Every time that I think that I'm done, I seem to find one more thing.  Hopefully, that's not the case now.

Jack

13Jan14 - Note: See below for rev-E. 

[Jack_Hester]

I'm thinking that this will be the last update, before a build.  I managed to put together something of a standard schematic.  It's still not entirely like most, but it's a start.

So with this revision, I have included the layout, the new schematic, my original format schematic, a Bill of Materials, and a complete sheet of the entire drawing.  I only drew the power supply once, as it's simple enough, as is.

I probably won't put a board together, or populate it, for a couple weeks.  My work schedule has me working before daylight until after dark each day, starting Thursday.  I had today off, and decided to stay in to head off a cold.  But, I'll try to make a start when the long hours are behind me.  Maybe I'll have the Silvertone cabinet in hand, to plan a chassis, and possibly a separate power supply.  

I'll post my progress, as it comes together.  Have a good one.

Jack

Note: C29 is now on the BOM and the new schematic (Vol pot R14).  Also, added the Hum Balance Pot to the Layout

[Jack_Hester]

Question for Tubenit.

Meant to ask it earlier, but do you use new tubes in your builds like this?  Or, old stock tubes?  Thanks.

Jack

[SILVERGUN]

Jack,
I've been reading along the whole time and really appreciate all of your work....

I'll be experimenting with this circuit in the upcoming weeks and trying a few of your ideas in conjuction with the original design.

Let me know if there is anything I can do for you as far as comparing notes.

Thank you for sharing all of your hard work....it looks great!  

[Jack_Hester]

Let me know if there is anything I can do for you as far as comparing notes.

Actually, I thought of making another quick sketch of a fixed bias power section, with independent adjustable bias to V5/V6.  But, decided to quiz Jeff as to why he chose the cathode bias on many of his designs.  Maybe all of them.  I hadn't got around to it, but now is as good of a time, as any.  I'm curious as to how the two compare, in voicing.  

Other than that, from your bread-boarding thread, I believe that you could answer a point (very soon) that he brought up about a possible volume jump.  That is, when switching to OD.  

When following my drawing(s), please comment on any discrepancies that you may find, so that I can correct and publish.  I think that I've look at it too many times.  Fresh eyes would be a big help.  

Other than that, post lots of pictures and sound-bites.  I'm very satisfied that Jeff's original circuit will perform as it should, as it's based on proven circuits.  The little bit that I deviated from his original is based entirely on an idea, and nothing to back it.  

Jack

[tubenit]

I use a mix of new and old tubes.  Usually NOS 5751's.  New 12AY7's.  Old 12AV7's.  New 12AX7's.  New power tubes. Usually new rectifier tubes unless 5Y3GT which will only be NOS or OS.

I like cathode bias tone. PRR stated some stuff about it on the forum yrs ago that convinced me more that's what I wanted.  I am not trying to go for more loudness and what I end up with using cathode bias is plenty loud for me.  Any of the quasi-pseudo pretend original designs I've come up with or worked on with Geezer have only been cathode biased.

Like on my D'Mars ODS,   I can use a 5Y3GT and 6K6 .......... or 5V4 and 6V6 ................. or GZ34 and 6L6 all with only switching tubes and not having to rebias anything using a 270ohm resistor & cathode biasing.  I like the convenience of that.

With respect, Tubenit

[Jack_Hester]

So, mostly new tubes.  I have an abundance of octals, of all sorts.  I'm fresh out of old stock 12AX7's, but that's because I used them as replacements for the newer stock (JJ's, Sovtek's, GrooveTube's, etc.) that I pull from old stuff, and replace with good, old stock.  So for once, I may use all new(er) stock on a build. 

And, I like your reasoning/examples for using cathode bias.  Makes good sense to me.  I'll leave the drawings as-is, on this build.  And, play with the fixed bias maybe next time. 

Jack

[SILVERGUN]

OK guys, I got it up and running...after a "few" hours of straightening out a couple mistakes on my new board, and the setup of this circuit  

This is how mine is set up currently:
SS rectifier with 335 VDC on the plates of 2 NOS GE 6V6GT's, cathode biased, with a 270ohm resistor and 100uf bypass cap, approx. 30mA bias current,,,, into a Deluxe Reverb OT,,,, using a 12BZ7 as the bootstrapped cathode follower, and LTPI... 50/40/20/20/20 filtering

-I just ordered some 6K6GT's and i'll report back when those are in,,,,,but for now, I can't get it past 2-3 without disturbing the neighbors   (I shoulda seen that coming)

Here's some brief, first impression notes:
- The clean IS very Fender'ish and reminds me very much of the AB763 DR I was just playing with....I'd love to add reverb to it, because without it, it's a little dry for my taste (and playing ability)
- The mid boost control is useful and seems to make the tone rounder overall......
- The clean can get very "pushed" by cranking the effects send and return,,,, and this affects the OD channel as well, which I like...it will take a little time and knob tweaking to find the sweet spot, and balance the drive of each channel.
- I did find that I could balance the volume of the 2 channels by the setting of the OD volume control...

- Switching in the OD channel adds a strong, fat, gritty "cranked" quality, that reminds me a lot of a good Billy Gibbons lead tone, at lower "drive" settings, but gets bigger, wider, and much meaner at higher gain settings,,with a ton of sustain, and harmonic blooming.........I wasn't able to really crank it yet, but I'm looking forward to the next chance I'll get.....
It might have to go back to the shop for play testing and recording.
- I (of course) wanted to see how much oomph I could get out of it, so I tried replacing the 12AU7 in the effects loop with a 12AX7, and it just wanted to sing all day....
- Only problem is, I have an inherent noise issue with running it flat out on the breadboard like this, so I'll have to work on getting it more quiet,,,and figuring out what I can and cannot get away with, gain wise.

I'll try to get an actual schematic together as soon as I settle on a couple things...

I'm really excited to get a slight delay in the loop and really get it singing  

[Jack_Hester]

Looking forward to seeing your schematic of the finished amp.  Great job on such a fast turn-around. 

Jack

[SILVERGUN]

Great job on such a fast turn-around. 

This is how it was possible

[tubenit]

Silvergun,

VERY cool stuff you're doing there and THANKS so much for sharing it!

With respect, Tubenit

[SILVERGUN]

VERY cool stuff you're doing there and THANKS so much for sharing it!

Thank you sir,,,,call me inspired....

I took the board back to work today so that I could crank it and give a report....here it is:
- The amp is voiced very nicely, and although I am a tweaker at heart, I was not inclined to change or even question ANY of the coupling cap values.......good, more time for play-testing
- This is a complex amp, and although it is hard to get a bad sound out of it,,,, one way is to crank everything to 10..
the controls are very interactive, and with them all on 10 you lose any real separation of the 2 "channels" (not to mention that there is just too much gain here to have control just maxxed out)
- There IS A TON OF GAIN (OD) here, and you can make the clean stages a drive channel just by turning up the preamp gain control past 6 (1st volume), and turning the effects send up to 6 or higher,,,and adding the mid boost...at that point the clean channel has a comparable amount of gain to a stock Trainwreck express,,, cranked ......yes, I just said that
- The problem with that is that when you add the 5879 stage, you wont hear the personality of the pentode come through because it's just gain on top of gain and it crushes itself,,,,,,so you have to set the amp up the way tubenit describes "his settings", so that you can appreciate the contrast of the 2 channels (even though it's not actually 2 channels,,,you are just swithching in and adding the 5879 to the equation)
-In my attempt to get the first 2 stages a little cleaner, I ended up with a 5751 there and thought that was a perfect tube for that location....it got rid of some front end noise, and it will stay for now
- I started poking around with the scope to figure out where the most OD was coming from and saw that you could see it in a few different locations just by changing the effects send/return levels in conjunction with the input volume or the pot feeding the grid of the 5879.......so what I'm trying to say is:
-If this was my gigging amp, I would spend a month getting the settings just right and then remove all of the control knobs except for the volume going into the PI (the "master")
- The character of the 5879 is the special feature of the OD in this amp and care needs to be taken in how you use it....it adds a fatness and feel of depth and dimension that makes it stand apart from a standard 12AX7 gain stage....too much gain going in will result in that character being overshadowed.....I'm wondering if we can extract any more character from it by changing component values (my lack of preamp pentode experience stopped me from trying that)
-There was one other item worth noting....the PI itself is responsible for a lot of gain and clipping and it seemed like no matter what signal I fed into it, it was coming out squared off.....I had a 12AX7 in there, and wished I had a 12AU7 handy because I would love to try it in that spot....I think that the PI gain could be lowered because the input sensitivity of the 6V6s is pretty high........

I guess that's it for now.....I'll try an AU7 in the PI tomorrow and see what I see....I'll let you know...

Hope that wasn't too much rambling, but I wanted to get that typed out while it was fresh in my head because I didn't write any notes tonight......it was just a knob turner night...these are all just opinions , and first impressions that I will try to confirm with MORE testing.

The amp sounds great!  

[tubenit]

Wow!  I find your report very interesting and very helpful information.  And I think we're arriving at some similar conclusions.

I have had to discipline myself to "think about" these amps in a different framework.  As you said, the clean channel above 6 with mid boost has quite a bit of gain.  However, a 12AY7 in V1 & at around 4 to 4.5 has a pretty clean tone to my ears. 

Overly simplified,  I typically use 4 to 7 range on any of the pots that are connected to the gain.  Then you've got to experiment to see what the best tonal pot settings are from my experience.

Sort of an odd way to think about amps IF one is prone to rolling all the dials to "10", .............. HOWEVER,  the 4-7 ranges allow one to dial in some very sweet musical and useful tones.  Cranking everything to 10 loses musical sweetness and just adds a thicker layer of mud to the tone, IMO.

I am typically using a 12AY7 in V1 on these type amps but have also used 12AV7 and 5751's on occasion.

I have tried a 12AT7, 5751 (nice) and a 12AX7 in the LTPI position.  I liked all of them in that position.  

So far, I like 12AV7 or 12AY7 best in the FX, but have also had reasonable results with a 12Au7 and 12AT7.

Given the variety of 12A_7's and pot controls and rectifier tube choices, ........... you can really get quite a variety of tones out of one of these amps, IMO.  

With respect, Tubenit

[SILVERGUN]

Given the variety of 12A_7's and pot controls and rectifier tube choices, ........... you can really get quite a variety of tones out of one of these amps, IMO.

I was thinking about this some more last night, and realized that I should have made a few disclaimers BEFORE posting my comments above...
Firstly, I should've posted an accurate schematic for what I've done because it is a slight deviation of your design,,,and any of the opinions I stated above are based off of my modified take on your design....so I apologize for any misleading info. that others may take away from this....
I know that YOU know what I mean, but I probably should've given a more accurate account of how the amp sounded before I started modifying it for more gain.....

So here's some thoughts:
- All of my statements were a result of having a 12AX7 in the effects loop, which I think is probably not "the right" tube for that spot,,,,but in my eternal search for more gain, I had immediately replaced the AU7, and never looked back........with that higher gain tube in that spot it turns the effects loop into a big gain stage which makes the send/return controls more like additional gain controls than their intended purpose of loop "balancing"

The amp sounded great as designed, I just have a tendency to immediately start modifying things towards my personal taste (maybe not the best idea for a well thought out design like this....I could've at least given it 24 hours   )...

When I get a little bit of time, I'm gonna "roll-back" the amp to stock, and try to get a sound clip done for anyone who is interested,,,,,before I go any further with my own tweaks.....
Then,, I'm thinking that maybe I should just start a new thread of this modified version, so as not to muddy the waters for guys who will just want to build strictly off of T's design....
I also don't want to confuse Jack with my "hot-rod" tendencies....I'm sure that it can be difficult to keep up with all of my random thoughts about which tubes in which positions, and which controls set where.....I'll try to do a better job of being more specific

[Jack_Hester]

I also don't want to confuse Jack with my "hot-rod" tendencies....I'm sure that it can be difficult to keep up with all of my random thoughts about which tubes in which positions, and which controls set where.....I'll try to do a better job of being more specific

I am.  Confused, that is.  But, not in a bad way, as I'm really enjoying your commentary.  I do hope that you document your build as-is with a schematic, before moving too far from it.  Gives me a better picture to carry, as I go back over your descriptions. 

Otherwise, continue on with your trials. 

[Jack_Hester]

On the rev-E drawing that I have posted, the Trim is in the wrong place on V3, on my conventional schematic.  It should be moved to the Control Grid, and not the Cathode.  It is correct on the layout and my original schematic.  I made the correction on my drawing, but have not plotted.  Will post, when I plot it again.

Jack