Tweed Overdrive Special & Carolina Overdrive Special

[tubenit]

DaGeezer and I have been trading ideas off forum trying to come up with an amp that will do both clean and OD well. With his trail blazing and help ........ this is what I have come up with. It sounded great with the band and cut thru the mix very nicely.

Basic idea is sort of a cathode biased D_mble but with a 5879 in the second gain stage of the OD. It doesn't sound like a Dumble to me but it does the blooming thing pretty good, IMO.  I'd been calling it a Wrecked D_mble because it has more crunch than a D_mble does, from my perspective.  

Thanks to DaGeezer for his help and inspiration! I wouldn't have come up with this on my own. I wasn't even thinking in this category til he got me started with his Maxim OD.
 

SCH file is here: http://www.el34world.com/Forum/index.php?topic=9636.0

Sound Clip is here:  http://www.el34world.com/Forum/index.php?topic=9637.0

With respect, Tubenit

EL34 EDIT:
To avoid confusion, all current schematics, layouts and materials list for this project can be found here
http://www.el34world.com/Forum/index.php?topic=9636.0

[Geezer]

Uh......don't let Tubenit mislead you! This is HIS design!  

Yes, I have been working on some pentode stuff, but this is in another league!

Looking @ the schematic, what you've basically done is build a sort-of mini SE trainwreck (3x gainstages into a pentode), then feed that into a bigger PP poweramp. Maybe someone has done that before, but I've never seen it.
It's kind'a along the same lines as the Guytron amps, but BETTER, as those are PP into PP, and yours is (sort of) SE into PP, yielding much better harmonics (I suspect).

The soundclip is fantastic.....I think this design is a real breakthrough for getting great tube overdrive at ANY volume. I suspect that you could feed the preamp into pretty much any clean poweramp & get similar results, since the tone is "happening" in the preamp tubes & pentode. I bet a simple pre-PI or post-PI MV would do the trick to control the output volume while allowing the preamp to do it's work.

Good job, my man!  

Geez'r

[Geezer]

Attached is my take on the COS....simplified with a single tone control in the "clean" section.

NOTE: given DaGeezer used a "tweed" tone stack ............ we're calling his design the Tweed Overdrive Special

To put it mildly, this amp ROCKS!  

The cleans are truely clean, or mildly overdriven if you crank up the gain a bit....goes from country clean to bluesy drive with a few simple adjustments of the gain & tone control.

The OD section is unbelievable....everything I have "heard" in the great amp clips I've heard on utube & such, but easily obtained without a bunch of tweaking of gain/drive & tonestacks....no "unobtainium" here!
I love the single OD tone control! Basically just get the distortion amount right with the gain & drive, then add or take away hi-end crispness with the tone control.

I played the amp with the band tonite (got lots of compliments) & then played for ~~ an hour after everyone else left.....I didn't want to stop. I went from chicken-pickin to blues to classic rock tones with a stomp on the channel select footswitch & by simply tweaking the guitar volume/tone controls.

The only thing I'm thinking is that I may want to reduce the mids "slightly" on the clean channel, as it seems a tad mid heavy when playing by yourself, but it sits very well into the band mix, so I'm not sure I want to do that. Maybe a cap selector switch for more or less mids(?). I'll have to experiment with that a bit......

Anyway, THANKS to Tubenit for the great design!

Geezer

[zendragon63]

Tubenit, guys--the COS OD section is a great innovation! Wired it up last night (though I ended up using a 6AV6 to drive the 5879 and a few different values). I can get this one to bloom into feedback now at a lower overall volume but it is still pretty articulate. Thanks for sharing your R&D. Regards.

dennis

[jojokeo]

I'd be interested in hearing about your findings. I finally got my mosfets from Mouser which were on backorder for while but I haven't had the time or willingness yet to redesign and make the changes yet.

Jeff, you've seen my schem but don't know if you still have it? If I put the VVR into it, would it be best to replace my vol control right before the pi? Or is it better to leave that and install it somewhere else?

[tubenit]

I don't know what is "best" but in both amps I did with VVR on the poweramp and LTPI, I did still keep the master volume prior to the LTPI.

With respect, Tubenit

[Geezer]

The Tweed Overdrive Special  got a workout "live" today W/ the band & it performed WAY above my expectations .... so "natural" sounding & so easy to dial in the desired clean & OD tones with the simplified tonestacks.

The added mids of the clean section (which I thought I wouldn't like) turned out perfect to help the guitar parts "sit" so perfectly in the mix between the piano, bass & acoustic guitar parts!

The amp was such a pleasure to play, it was truely "inspiring"......it's now officially my favorite amp.

Thanks again, T!

Geezer

[tubenit]

To put it mildly, this amp ROCKS!  

The cleans are truely clean, or mildly overdriven if you crank up the gain a bit....goes from country clean to bluesy drive with a few simple adjustments of the gain & tone control.

The OD section is unbelievable....everything I have "heard" in the great amp clips I've heard on utube & such, but easily obtained without a bunch of tweaking of gain/drive & tonestacks....no "unobtainium" here!

YES, ........ I AGREE!!!

This amp the Tweed Overdrive Special has waaaayyyy better harmonics and sustain and blooming then the cathode biased D-style HRM amp did.  The conversion was easily worth it.

Comparing the "Tweed Overdrive Special"  to the original COS which has a Dumble tone stack on the clean channel. My initial impressions are:

1) the 5E3 tone stack gives better cleans than the Dumblish tone stack and it is more articulate than the Dumblish tone stack

2) it seems like the VVR on the original does not eliminate the "blooming" effect like the PPMIV does at lower volumes. The
    VVR cranked down  to as low as 1/3rd  still seemed to allow the blooming to work great.  The PPMIV seems to eliminate
    some of the blooming  effect at lower volume but it works great at around "6" thru "10".   I will probably convert the amp
    to have VVR at some point.

3) The 5E3 tone stack on the clean channel and the hybrid 5E3 tone stack on the OD channel sure make dialing the tone in
    MUCH easier than the Dumblish tone stack and the HRM tone stack did. The original D-HRM was difficult to dial in.

4) the 5879 adds a dash of crunch and chime that the 12A_7 won't match in the OD

5) The clean and OD on the simplified match better tone wise than the D-HRM clean and OD which had a more midly clean.

6) The volume level of the clean and OD match better on the "Simplified".  My guess     is  the Dumblish tone stack had high insertion loss making the balance of tone from clean to OD more difficult to match.


I am currently using a 5751 for V1,  12AX7  in the V2a position, into the 5879 ........ into a 12AY7 LTPI. This seems to be working just great.  

DaGeezer thanks for the Tweed Overdrive Special design ............ it worked out perfectly.

With respect, Tubenit

[zendragon63]

Interesting observation on the tone stack. The gig last night was with a fellow guitar player whom I built a similar amp for earlier this year and the only difference was the tone stack--his was done with a James and my newest was the _umble stack. FWIW, the James stack noticeably more lower mids and a little lower overall stack loss. It depends on what floats yer tone boat. My boat apparently is the James.

4) the 5879 adds a dash of crunch and chime that the 12A_7 won't match in the OD  Amen.

Thanks again for the sharing. I will post a schem of what I end with as soon as the home computer is rehabilitated. Regards

dennis

[jojokeo]

T,
I don't think you need that bright switch on V1 do you since it effectively has this when the tone control is turn up and you're placing the 500p cap across lugs 1 & 2? That would leave you w/ 3 switches.
I like options 1, 3, & 4 but haven't heard or done the second. What does that sound like?

[tubenit]

The bright cap switch on the vol was a left over from the D-HRM build so I just left it there. I actually like it & surprisingly, I can hear a difference so I may just leave it. I think it would help between playing the Tele with strat type buckers vs. the Tele with traditional humbuckers.

The local NFB gives sort of a compressed sound that is a little cleaner in tone. Kind of hard to describe.

Thanks for the feedback.  I am leaning towards switches that make the clean channel more clean and the OD channel more OD.

With respect, Tubenit

[Geezer]

Ok, more experimentation........
As suggested, I tried paralleling the un-used 1/2 triode with different sections of the circuit.

1st, I paralleled it with the triode just before the 5879 pentode in the OD section. It sounded pretty good, but it made the OD super compressed & lost all dynamics, so no good there.

Then I put it in parallel with the 2nd triode of the clean section. That fattened up the tone ALOT & gave it an almost pentode flavor. I can still get it spanking clean, but it is FAT & toneful. Also easier to get a great bluesy grind & the clean section balances with the OD section much better now. Another bonus is that it evened out the mid hump just a bit.

Of course, this also affects the OD section.....it has much more "range" of overdrive now, with better dynamics & punch (without added compression).

So, it's staying right there (paralleled w/ V1b).

Geezer

[Geezer]

Q1)
Did you change the plate and cathode resistor on that V1b when you paralleled it ........OR did you leave it the same?

Left the plate the same (shared by both triodes) but re-used the old cathode resistor/bypass cap leftover from the HRM (1.8k/1uf), so they share a plate resistor, but have separate bias resistors.

Q2)
Is the paralleled triode from the same tube or the left over triode on the V2 tube (tube in first gain stage of OD)?

The leftover triode in V2. The parallel triodes are in separate tubes......

G

[tubenit]

OK,  I did what DaGeezer did and paralleled the second gain stage of the clean. At least on my amp, that is quite a boost because I have it on a switch and can compare it.

Initially, I had a 5751 in V1 and paralleled a 12AX7 triode. It sounded better 12AX7 to 12AX7 triodes paralleled.

It makes the amp even more touch sensitive to play when engaged. I like it.

It's gotten messier with the conversion/rebuild but here is a gut shot of the chassis. It still is a quiet amp.

I'll update the schematic and layout in the SCH when I get a chance.

With respect, Tubenit

[Geezer]

that is quite a boost because I have it on a switch and can compare it.

Oh yes, it is a BIG boost in volume!

I may put a pot on the input of the paralleled triode input grid to control the amount of boost & make it a variable/footswitchable boost feature.......or not....I would probably just leave it on all the time anyway (it sounds so good when "engaged"). I'll have to think about it a bit........

[darkbluemurder]

Tubenit, Geezer,

Thanks for all your R&D work!

I have one chassis left over which should be large enough to house 4 noval and 5 octal sockets and 7 pots on the front. I also have a Hammond JX 372 and a TAD Blackface Bassman replacement OT so I could do one that can use either 4 6V6s or 2 5881, 6L6, KT66 whatever. I could then install a half power switch to switch from 4 6V6s to 2 6V6s and if that's not enough I can do the Carr 1/4 power switch (that would work with the duet of large tubes as well). The 5th octal socket could be for a GZ34 rectifier (the power tranny has a rectifier winding). However I could opt for SS rectification and use the 5V winding for the overdrive switching.

But that project will have to wait until the baby boy is a bit bigger (just six weeks old and does not need an amplifier to be heard).

Cheers Stephan

[tubenit]

I would probably just leave it on all the time anyway (it sounds so good when "engaged").

To be honest, I am somewhat anticipating leaving mine on almost all the time because it also sounds so good.

What surprised me is that while it does increase the gain somewhat, it does NOT lose any clarity in expression. It still articulates just as well as without the paralleled triode.

In other words, the tone is not as "clean" but it is as "clear". Hopefully that makes sense.  Some boosting mods seem to just muddy the tone but this doesn't to my ears at all. Instead it still articulates well and just increases the touch sensitivity in the playing.

Only disappointment so far with the paralleled is the 5751 triode paralleled with the 12AX7 triode didn't sound that great for some reason?  And I liked the 5751 in the V1 position really well.

With respect, Tubenit

[Tone Junkie]

From the looks of your sch. your using 275-0-275 with 150ma power tranformer so a hammand 270fx would be about right for this build which out put trannie are you using the one with 6600ohms for 35watts or 40watts. just checking what I can get. Thanks Bill

[tubenit]

I'm using a 20w 1620 OT.  The other original COS has a 1650 OT and larger PT.

With respect, Tubenit

[tubenit]

Tubnit  what would a pair of 5881 like to see as the optimal impedence for the output transformer on this, then what would same question be for a quad of 6v6,s

I really don't know. But both amps have 8 ohm speakers and I hook up the 16 ohm wiring to them. And I like the way they sound & have had no issues.

I think DaGeezer used Fender replacement trannies such as Hoffman carries if I remember correctly.

Here is my updated schematic. I may change the paralleled resistor switch out for something different.

With respect, Tubenit

[Geezer]

Another slight tweak.........

I put a 250kA pot going to the paralleled triode.....the extra 250k load only decreased the volume/gain very slightly, but it really sweetened up the tone (taking just a slight "edge" off).
With the pot on the front panel (labeled "Fattness") I can go from stock to fat (or anywhere in between) with the twist of a knob.
I suspect it could be helpful when changing from single coils to buckers, but it does seem to be a useful addition.

Again, this amp is FULL of TONE! The cleans are sweet & full, & the OD can go from crunch to smooth with easy adjustments. It's a real winner!

I have found I don't even really need a Master Volume with this amp (I've been leaving it all the way up), as clean & OD masters work just finefor getting great tone @ lower volumes.

Geezer

[Geezer]

This amp is such a WINNER!

The tonal variations available are amazing, and all of them are the same at low volumes or cranked up loud. I just leave my PPIMV all the way up now, & use the clean & OD MV's to control the output & balance.

I have a switch to lift the ground lug of the "Fattness" control (250k gain pot for the parallel triode) & that kicks it up even further when I want.....makes the PAF bridge pup sound like a scream'n hot Tele!

[Geezer]

I used a Super Reverb PT & the OT is from a '60s HiFi, but I have run the preamp into 2xEL84's & there's not a significant difference in tone, as most of the tone in this design comes from the preamp.

So, any PT rated high enough to support the tubes you are running & any OT with a suitable primary for the type of output tubes you're using will work fine.

G

[punkykatt]

Im starting to build a thirst for this amp too. I still have my Bogen CHB-35A waiting for guitar tweeking. My first concern is, will the PT heater winding  of the Bogen handle the extra currant of replacing the 6C4  PI  (0.15A htr I) with 12AX7  PI (0.3A htr I) and adding the 5879 (0.15A htr I) Total increase of 0.3A? Total htr I of the existing Bogen with the power tubes is 2.35A, the increase would bring it to 2.65A.  Im guessing the htr winding can handle 3 amps????
I sure dont want to burn up the heater winding in that Bogen tranny. 

Am I right in guessing the htr winding can handle 3A?  Thanks Punky

[Geezer]

My experience with many Bogen amps is that their stuff had some room in the ratings...I'd guess that a small increase like that isn't going to do any damage, unless the load is already pushing the PT to overheat (which I seriously doubt)

BTW....sound clips are done & being processed....stay tuned!

Here is one of the sound clips:   http://www.el34world.com/Forum/index.php?topic=9726.0

Geezer

[Geezer]

Here's another version of the above linked clip, but this one demos just my amp & what it sounds like.

http://www.zshare.net/audio/786814058ef04507/

The guitar is an Ibanez Blazer strat (97) HSH config, with Dimarzio 59 PAF's in the neck & bridge (middle pup not used)

Here are the details, by section:

Opening = Clean/Neck & Bridge
Section 1 = Clean/Neck
Section 2 = Clean/Neck & Bridge
Section 3 = Clean/Bridge
Section 4 = OD/Neck
Section 5 = OD/Neck & Bridge
Section 6 = OD/Bridge
Section 7 = OD, "drive" tweaked up a bit/Neck
Fade out = OD, "drive" tweaked up a bit/Neck & Bridge

Geezer

[punkykatt]

"My experience with many Bogen amps is that their stuff had some room in the ratings."

Thanks for the input Geezer. I feel better about adding that extra tube.  Your amp sounds great and I love your playing style. Hot & spicy.     Punky

[Geezer]

When the amp was 1st built, node "F" supplied the 5879, but I'll have to recheck to see if I changed that when I rebuilt it.......I'll check & post asap (but may be a while, busy day)


On the MV, I have 2.2megs where Heinz has 470k (to keep as close to 220k as possible when the pot & resistors are parallel), as in the "LarMar" version.


G

[Geezer]

Here is the latest schematic (accurate as of today) of the Tweed Overdrive Special.

I have made several slight changes since the last sound clips, such as lowering the clean channel plate resistors to get a bit more useful rotation (headroom) from the clean gain pot. It worked extremely well, & also improved the OD tone as well.

I also was feeling that the amp had a bit of a "choked" feel to it, so I removed the 220k/750p network from the clean section & that really helped....has a much more "open" feel to it now.

I will do an updated clip as soon as I get time..

Geezer

[Geezer]

Geezer, some questions:

1)  could the 250k pot for the paralleled triode be on the back panel?  Meaning
     that it's not adjusted very much & doesn't need to be on the front panel. YES

2)  I am wondering if we could have the two triodes that are paralleled share a
     cathode resistor of 1k and a cathode cap of 2.2uf and still have a similar
     tone? We could, but I have a 12AY7 as the V2 & it really is important to the OD tone on mine (the cleaner the signal going into the 5879 pentode, the better)....so, that means that the parallel triode is also a 12AY7.

3)  Please note that I have V2a paralleling V1-b for convenience on the layout.
     Is that OK with you? Yes

4)  Is the OD level pot really 1M or is it 250K?   I am using 250k and I don't
     turn it more then 3/4 of the way up. It is 1meg....comes in handy if you want to use the OD as a clean(er) boost instead of all out overdrive (turn the drive down & the level up to compensate). It does normally stay pretty low....could make it an "optional" choice, since it doesn't affect the Hoffman board layout(?)

5)  I wasn't sure how to accomplish the node F on the Hoffman style layout
     board?  Does this method look acceptable with the wire running under the
     board?  I figure the 1k/3w could be above the board.  Looks fine to me

With respect, Tubenit

Also, note that I have the OD tone wired different than you have it.....mine is the same as the clean tone control.

A few other things I saw:

*The connection from the clean gain pot to the 2nd triode is missing.

*V2, pin 8 cathode resistor should be 2.7k, not 1.5k

*the 250p snubber on the 1st OD stage triode is missing

*the screen resistor for the 5879 should come from point "F", not after the plate resistor

*5879 plate resistor should be 56k


Thanks for all you work on this!

Geezer

[Boots Deville]

Is the jury still out on the usefulness of the PPIMV in this amp, or have they reached a decision?

[tubenit]

I definitely need it (PPIMV) on my amp to get the tone and overdrive at the lower volume I want. However, I still am convinced the VVR is a better way to go which is what I have on the original Carolina Overdrive Special (vs. the Tweed Overdrive). But it's just my personal opinion and preference. IF I want singing sustain that holds notes almost til it feedsback, I need either the PPIMV or VVR to keep it at what is a reasonable volume for me.

With respect, Tubenit

[Geezer]

In my experience, it's not needed unless you want the amp at a whisper.
I can get basically the same tone & response from the PRE PI MV's that are already in the circuit. I'm sure a VVR would be best, but I'm a little shy of them myself, after I had one fry on me @ a gig a while back....the 1st time in 35 years of gigging that an amp failed on me @ a gig.

As soon as the boards are ready, I'm going to build an 2XEL84 version into a gutted VJr head and I will leave off the PPIMV (no room on the front panel)....the amp will be for a very talented kid @ my church that I've already converted over to be a tube-head!

[Fresh_Start]

Please forgive me for a basic question:  where are the filter caps in this layout?

One of the options Hoffman offers is placing the filter caps between the pots/ground bus and the circuit board.  Personally, I like the concept of having the preamp filter caps as close as possible to their respective circuits so that the current loops are minimized.   See "Method Two" 5th photo down HERE.  I've actually zipped-tied the filter caps on the edge of the board, but also committed the heresy of attaching the ground bus to the board instead of running it along the back of the pots (and using radial electrolytics), as you can see in this pic:



Ooops, hadn't got to the point of using zip ties in that build... but I got the idea from Doug!

Just a thought.

Chip

[Boots Deville]

Question.  In Geezer's latest schematic he has added a .001uF cap bypassing V2A's plate resistor.  There is also a 250pF cap from plate to cathode on that same triode.

Quoting Merlin's book, Fig. 2.23, page 54, he shows both these two arrangements, plus a third where the cap runs from plate to ground, and states "All three circuit variations give identical attenuation characteristics".

So my question is, do we need both the .001uF across Ra and the 250pF from plate to cathode, or would just one suffice?  What was the design decision here?

-John

[Geezer]

where are the filter caps in this layout?

Wherever you want them to be........either build cap farm/board, or use multi-section cans, or mount them directly onto the turret board (which I actually like to do).

Question.  In Geezer's latest schematic he has added a .001uF cap bypassing V2A's plate resistor.  There is also a 250pF cap from plate to cathode on that same triode.
So my question is, do we need both the .001uF across Ra and the 250pF from plate to cathode, or would just one suffice?  What was the design decision here?

The 250pF cap from plate to cathode is from the original Dumble OD design (certain non-HRM models), and once I got the amp up & running, I felt I needed a bit more of the hi-end hash removed, so I tried a .001 across the plate. It acomplished what I intended, so I simply left both caps in place. I guess I now have an effective .001250 cap(?)

I know there have been comments about these "smoothing" caps being bandaides, or fixes for inferior designs, but I care not about that.....I'm interested in the resulting tone, & if I found (thru real world experience & experimentation) that I could solder an 1887 Indian Head penny across the plate load to get the tone I was looking for, I'd do it, regardless what the cork-sniffers said.  

[Tone Junkie]

A question on v2b were you see the 68k going into #7 pin back up and look on the board it looks like its going to the wiper on a 50k pot by the way its drawn. Bear with me im a newbie is that what it is . if so should it be on the back or am I just not understanding what Im looking at . Im waiting for some parts to start building the turret board. Thanks Bill

[Geezer]

Hey Bill, good question.

That is pot is termed a "trim" pot, trimming the signal (to taste) entering the OD.
Dumble (& most other clone builders) put that pot inside the amp as a "set & forget" type thing.
I have mine on the front panel, labeled as the OD "gain" pot, along with the OD "drive" & OD "Level"....I like to be able to tweak it, but that's just my preference. I can get many more good tone variations from my amp by being able to adjust all the pots "on the fly".
The choice is yours where you wish to mount it...inside, on the back panel, or on the front.

G

[phsyconoodler]

I put mine on the back panel.I don't like too many controls on the front of an amp.But that's just me. YMMV.

[Geezer]

When I build this circuit into the JVr carcass, I will put everything I can onto the back panel (due to limited space on the front)....will probably have just:

 Input - Clean Gain - Tone - OD Drive - OD Level - OD Tone

OD Trim & PPIMV will go on the back.

I think I'll just wire the Fattness (parallel triode level) at a set amount via an internal voltage divider(?). It sounds best to me when the level of parallel boost is slightly below the full effect (tuned down ~~ a 1/4 turn from full up).

G

[Geezer]

I'll try the preamp into my 6BM8 power amp this evening & let you know how it sounds.....I've been wanting to do that anyway, as I haven't tried it since completeing all the re-builds, tweaks & upgrades

I've run it into 2xEL84's & it is stellar! A bit less mids & alot more chime. That's what will be in the VJr rebuild.

G

[Geezer]

OK, the 6BM8's have almost zero headroom, at least with any substantial volume. It's like "Overdrive" on the clean channel, & "MORE Overdrive" with the OD engaged. It may be that tweaking the PI could yield more headroom. I may try that (maybe raising the plate voltages to the PI, if possible)

This preamp definately likes a clean poweramp.

NOTE: Work is being done to try to come up with a more suitable PI for 6BM8/ECL82 type tubes>>

http://www.el34world.com/Forum/index.php?topic=9751.0

[Geezer]

Just tried the T-ODS into my HoSo56 poweramp & it sounds great, so there's enough grunt in 2xEL84's for it to work, but the 6BM8s just ain't got what it takes, at least not with the PI I have pushing them at this time.

G

[Geezer]

Observations of the amp in a live setting (Dance cover band I play in) thru a 1x12 closed back cab, ported, w/ an Eminence Legend 1258.

The amp sounds better live than I hoped, especially the overdrive!

The "Fattness" control basically serves as follows;
*Country/Clean Rock/Motown stuff = Fattness pot all the way OFF.....this gives a nice mid dip that is very Blackface-like. Makes my PAF HB equipped strat sound like a Tele (a Good Thing).
*Blues/Classic rock = Fattness pot turned up ~~3/4 gives a nice mid boost that helps cut thru the mix. Nice growl when digging into the strings.

The Overdrive is quite unbelievable.....the tone I've had in my head all these years (& have spent countless hundreds of $ on OD pedals searching for it) is MINE!
We do a pretty good version of "China Grove" & the OD nails that tone, both in the opening chord progression and in the solo. Pinch harmonics just scream.
Basically any OD tone you want is there (except Metal, of course) & easily obtainable with simple adjustments that are easy to replicate/remember. Reponds perfectly to the guitar volume & tone, too.

It's really hard to describe just how much I enjoy playing this amp!  

I'll try to get more soundclips up this weekend.

Geezer

[Geezer]

I have not grounded 2 & 6 on of the 5879 tubes in any 3 of my amps. Seems to work just fine without that. I'll try grounding them and see if there is any difference. They're just "open" pins on mine.

Then don't worry about it....it had been said before that it probably wasn't needed, but I had done so on my builds. You have proved it is not needed!  

Thanks for all your work! As soon as they are available from Doug, I'm placing an order for at least 2 (for now)...one for the VJr rebuild & one for a 4x16GK6 (16v EL84-type) version I'm going to do.

G

[tubenit]

How well, in your opinion does this type of control suite this amp, as i have heard its not that great. But in saying that a single tone control is great for the overdrive.

Remember that the Tweed Overdrive Special came after the Carolina Overdrive Special with the main distinguishing difference being the Tweed had a simpler tone control between V1a & V1b. The COS has a typical D_mble typology in it's tone stack.  I have both the COS and TOS amps.

The Tweed Overdrive is MUCH easier to dial in a tone that you want. Having said that, the COS can give more of a mid-scooped tone & the PAB with mid-boost offers some variance of tone and overdrive. I played both amps yesterday comparing them & decided each had enough strengths of their own NOT to convert the COS tone stack into the Tweed.

I would say the TOS is a little more touch sensitive to play and the COS has a smoother overdrive.

As a side note, the PAB on the COS boosts the overdrive as much as switching in the paralleled second triode on the TOS

IsoTone, thanks for cleaning up the schematic!  It looks alot better.

With respect, Tubenit

[Geezer]

IMO, the basic topology has been established by Tubenit (that it works & fantastically so), so add whatever tonestack you want to the front end (clean pre).
I have considered trying some of the other single & two controls styles myself, as I sometimes find myself wanting to be able to bring the mids down just a "touch".
Any fairly low loss stack should be just fine.

[Geezer]

Do you think that using a Bogen CH-35 as a base for this amp would sound ok? I have one that I converted to 6L6's laying around which I would like to gut and  try. What do you think about using those tranny's?

I think it would work fine......what you need is a good, fairly clean poweramp section, which the Bogen has.

[tubenit]

Doug posted this picture someplace else but I thought I'd post it here to give you guys an idea on what a Hoffman turret board might look like for the Tweed Overdrive Special.

With respect, Tubenit

[Boots Deville]

I have a question about the pot labeled "Master" on the layout, not the PPIMV, but the located above the DPDT OD switch on the schematic.

If I'm reading the schematic correctly, it looks like when that switch is in the OD position, the wiper is disconnected and that pot becomes simply a 1M resistor to ground,  Therefore it would have no effect on signal level.  Is that correct? 

I plan to build one of these, and in drawing up my own version of the layout for it, if that pot only effects the clean "channel", then I will locate it next to the clean tone control and label it something different.  I would just like to get clarification from you guys who are actually playing thru the amp, that my perception of how that control functions is correct.

John