Tweed Overdrive Special & Carolina Overdrive Special

[sluckey]

It's not critical. I'd use those 1000µFs in a heartbeat.

[nateflanigan]

Thanks, I didn't think it would be an issue.  Now if I could just find some available space in the chassis...

[Throstur]

I have been keepin an eye on this magnificent project since Tubenit and Geezer started it. I want to have a go at it and build one. I downloaded the schematics and layouts but can´t open the .sch files. Can you recommend a program that can? I have Microsoft Windows 7 Enterprise on my computer.

[sluckey]

http://www.expresspcb.com/ExpressPCBHtm/Download.htm

[Throstur]

I have been studying the SCH´s and the postings on this very interesting amp. Looks like a masterpiece. I will definitely order from Doug soon, what it takes to build one. What is the Wattage rating of this amp with 5881?

My "ordinary" english is OK but I still struggle with technical terms and especially abbreviated technical terms. Abbreviations are not used in my language that much.

What does PPIMV and VVR stand for and what is the basic difference?
 
Please don´t laugh much, but it took me awhile to figure out what IMHO meant, and that´s not a technical term 

[Willabe]

Throstur,

Don't feel bad, I was born and raised here in the states and I don't always understand what their talkin about.      

I'm 52 and I don't remember abbreviations being used very much, some things but not many, in every day conversation. I think it's more of a computer/internet driven thing. I think this internet thing kinda has it's own cluture, I'm not knocking it, but it's not quit the same as talking face to face with someone or on the phone. BTW (by the way ) it took me a couple of months to figure out what IMHO was too.   I don't know where your from, but you post/write better than I do, I'd never guess that your not from the US or any other english speaking nation. For What It's Worth IMHO you'll do fine.  

Anyway, Post Phase Inverter Master Volume and Variable Voltage (I should know this 3'rd letter, but...) Resistance? It's for lowering your Out Put/amps volume while keeping the "same sound" of an amp thats turned up. There's a thread going on for the last few days on it. Blues Bear, If I Recall Correctle, started it.

All the guys here are very nice, so if you don't understand something just ask, they'll be glad to help.

Here's the thread......          http://www.el34world.com/Forum/index.php?topic=10977.0


         Brad                

[Tone Junkie]

Well Brad here,s were Im at I just had to google it to find out what it meant.(LOL) IMHO Im behind the times. 

[Willabe]

Like I said ALL the guys here are very nice. I feel right at home.

BTW,    LOL?         


         Thanks,      Brad        

[67polara]

VVR is variable voltage regulator.

Tony

[Throstur]

Thanks guy´s, a good laugh is worth 30 minutes of jogging and a lot more easier  I have been hanging around this forum for many years on and off and have often be led through problems by bnwitt, prr, sluckey, tubenit, da geezer to name but few.

I´ll definitely go for the VVR then. There has be much talk about the overdrive and other nice features in this amp. I´m also very interested in how it works clean.

Has it around 40 Watts output?
Does it have good headroom?
Can the clean sound be compared to some amps we know, like Fender, Marshall, Vox e.t.c.

[Tone Junkie]

Throstur What i liked about the cleans on this was you cant compare them to any of those amps probably more like a dumble or train wreck clone it had blooming which those other amps dont really have in there cleans. depending on the setting of the first volume knob, then with the setting on your guitar volume itself. turn my guitar volume down to 3 and it has an almost jazzy sound turn it all the way up and you get a great blues clean with a little bite how much depends were you set your first volume knob. That said you could also dial in the cleans of those other amps also depending were you had everything sitting.
 But if you look at some of the other layouts use the one that parallels v1b with the unused triod you will have thats the one I built and wouldnt do it any other way. Bill

[Willabe]

VVR is variable voltage regulator.

Dhoo!    Thanks Tony, winter brain freeze.       :icon_pale:


              Brad      

[tubenit]

Has it around 40 Watts output?

I am using a 20 watt OT & 5881's.  My guesstimated wattage is 23watts measuring across speaker terminals. It can get loud which makes the VVR very helpful to me. I think this amp cuts thru a band mix really well, IMO.

With respect, Tubenit

[Throstur]

Throstur What i liked about the cleans on this was you cant compare them to any of those amps probably more like a dumble or train wreck clone it had blooming which those other amps dont really have in there cleans. depending on the setting of the first volume knob, then with the setting on your guitar volume itself. turn my guitar volume down to 3 and it has an almost jazzy sound turn it all the way up and you get a great blues clean with a little bite how much depends were you set your first volume knob.

Sounds great Bill   I see that Tubenit uses 20W OT. I seem to remember that Da Geezer uses Super Reverb iron? Could be wrong though. What kind of PT/OT did you use Bill?

[Tone Junkie]

I used the weber clone of the super reverb Iron.  Same voltage as Geezers amp. all I had were some jj 6l6,s but they do the job. I keep thinking Im going to spring for some new 5881,s just hasnt happened yet.
Bill

[nateflanigan]

I wanted to give the fixed bias idea a try just for fun.  I built a little board and everything but once I got it hooked up I realized the bias pot I had around from a fender was only a 5k pot.  The bias circuit is just in the chassis, it's not wired to the amplifier circuitry itself.  At the wiper I'm measuring about -15v to -18v.  I'm guessing that's high since I have less available resistance than ray's schematic calls for.  What range of voltage do I want coming out of the bias circuit?

Thanks

Like this?

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

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

Thanks Tubenit,

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

Ray

 bias supply.GIF (14.73 KB, 455x472 - viewed 93 times.)

[nateflanigan]

Another question...
Can I pop a pair of kt88's into the TOS?  In trying to research this all of really been able to determine is that it depends on the amp.

[67polara]

I switch back and forth between 5881's and KT77's all the time I would think if you can handle the extra heater current it should work just fine.  I put a second transformer in just for the fil's on the output tubes.  The KT77's are much louder than the 5881's and I like the sound better.  I would think the 88's would sound nice also.

Tony

[nateflanigan]

Thanks, I'll do the heater current math and give it a shot.

[firemedic]

Just to interject real quick, my TOS is using the Tungsol KT66 -which has 0.9A filament current, less than a true 66. It compares favorably to the 5881, to my ears. But, I also changed the clean side to 5E3 component values, 12AY7 and all. Plus the paralleled triode 2nd stage which I agree is key.

[nateflanigan]

The heater current would add up to ~4.4a, my transformer is speced for 4 amps.  Probably ok to try it out and see if I like the sound, but if it's a keeper I'd add a separate filament trannie.

[nateflanigan]

two things...

First the bad, I tried setting up a fixed bias supply and messed something up.  The amp is converted back to the original cathode bias but theres some problems.  If I play quietly (like a comfortable living room volume) things are ok.  If I bring up either the clean master volume, the first input volume or the volume on my guitar I cross some kind of threshold and crackling starts.  Sounds a lot like scratchy pots (only I'm not adjusting pots) if I try to ignore it it slowly gets worse, then the power starts to fluctuate.  When I tried out the fixed bias, it was putting out about -70v, the power tubes lit up like light bulbs, the bias wouldn't adjust down, so I turned it off.  I've tried out a variety of tubes, the crackling happens either way.  What do you think I fried?

The good, despite the above issues I thought I'd try out the KT88's.  Played at low volumes I am loving them, they're really getting me closer to what I want from this amp.  Really big and articulate.  I cranked up the drive channel just to see what it sounded like, again huge, if you wanted to get this amp to do metal or modern heavy stuff this was lots of gain but still tight.

[adeptusmajor]

Hello,

This is my first post here, thank you for a great forum and project. I am building a TOS, the rest of my parts should be here today. This being my first tube/amp project, I have a couple of (stupid) questions that I haven't been able to find the answers to:

1. On the schematic, there is a "fake" center tap created with two 100 ohm resistors off of the heater wires, it says to connect their ground to the cathode of the power tubes. Do I connect the ground wire directly to pin 8 of the sockets or just to the same ground point that ties to the 10W resistor and 150uf cap coming off of the sockets?

2. All of the pots I have are audio taper, except for the 50k trim pot, which is linear taper. Is this correct?

3. There is .001 cap in parallel to the 180k resistor on the schematic (between D and V2 pin6) that is not shown on the layout. Was I correct in following the schematic?


That's all I've got right now, I'm sure I will come up with more dumb questions when I start wiring things up later. Thanks guys!!

[Geezer]

This being my first tube/amp project

Quite ambitious for a 1st project......

1. On the schematic, there is a "fake" center tap created with two 100 ohm resistors off of the heater wires, it says to connect their ground to the cathode of the power tubes. Do I connect the ground wire directly to pin 8 of the sockets or just to the same ground point that ties to the 10W resistor and 150uf cap coming off of the sockets?

Directly to the cathode (pin 8)....you are "elevating" the heaters slightly for improved quietness (theoretically)

2. All of the pots I have are audio taper, except for the 50k trim pot, which is linear taper. Is this correct?

OD "drive" is also linear, but won't make too much difference.......

3. There is .001 cap in parallel to the 180k resistor on the schematic (between D and V2 pin6) that is not shown on the layout. Was I correct in following the schematic?

Yes, the .001 snubber needs to be there.

Good luck!

G

[adeptusmajor]

Thank you for the response

This being my first tube/amp project

Quite ambitious for a 1st project......

 :icon_biggrin:Not my first project, just my first "from scratch" tube build. I have built a ton of studio gear and have recapped and performed mods to a couple of tube amps, I'm just trying to learn as I go (so, again, I really appreciate everybody's willingness to share their expertise here). That being said, I have a problem...


I finished wiring everything up last night, powered on, light came on, heaters lit up. I took the amp off of bypass and pop goes the fuse immediately. First stupid mistake, when I screwed the cap can down one of the keps nuts caught the edge of the B+ wire going to the power tubes and grounded it. I felt really stupid for a couple of minutes and then proceeded to remedy the situation.

Second power up, lights came on, took the amp off of bypass, lights remained so I plugged in my fiddle and began to raise volume knobs. I got sound, it sounded kind of distorted and then pop goes another fuse. Time to inspect wiring again. Found nothing.

Feeling ballsy, I went for a third try, this time with the gtr plugged in from the getgo. Taking the amp off of bypass and playing immediately yielded a great sounding gtr tone. But now I noticed that within about 10-15 seconds the plates in the power tubes would begin to glow red so I quickly bypassed it. Same thing happens with two different pairs of 6L6's (RCA/Sylvania).

I used the BOM and schematic found here http://www.el34world.com/Forum/index.php?topic=9636.0
The only difference is that I added the relay switch circuit found in Hoffman's library page. Another strange issue is that when I throw the channel switch, the LED indicator comes on bright and then dims down about halfway within a second or two. I used a pretty large red LED that I clipped from some random board I had laying around, so I don't know any specs on it.

Measuring voltages coming from the filter caps gave me readings from 30-50V below what was listed on the schematic:
A = 380V
B = 374V
C = 304V
D = 262V
E = 186V
F = 185V

I will trace out the circuit again and do some more research when I get home from work later. I know I must be close, the amp sounds great for the few seconds that I have it on, and all of the controls seem to function properly. I just keep getting the red plates within 10-15 seconds. If any one could give me any pointers or advice I would really appreciate it.

Thanks guys.

[sluckey]

What voltages do you measure on pins 5 and 8 of the output tubes?

[tubenit]

And what size power tube cathode resistor do you have and the voltage across that cathode resistor also, please?

With respect, Tubenit

[adeptusmajor]

Voltage on pins 5 and 8 is 0 without tubes installed

With tubes, around 50mV on one and -50mV on the other. The reading never quite stabilized enough to be accurate before I had to hit the bypass due to plate lighting up.


The cathode resistor is 430R 10W as per the schematic, and measures a steady 0V with or without tubes.

[sluckey]

"plate lighting up" and "The cathode resistor is 430R 10W as per the schematic, and measures a steady 0V with or without tubes" are two inconsistant symptoms. Red plates means too much current is flowing through the plate. Plate current must flow through the cathode so there should be a healthy voltage dropped across the cathode resistor while the plates are glowing red. Unless something is really messed up in the wiring. Can you post some hi rez pictures of the output circuit?

[tubenit]

I'm wondering if the cathode resistor is actually grounded?  Any way you could check that out. Measure the "positive" end and then put the other probe on the chassis.

With respect, Tubenit

[adeptusmajor]

Wow

What a humbling experience...

I think I am in the clear now. I reread the response to my first post and realized I must have misunderstood the answer or just poorly worded my question regarding the heater resistors.

I had connected the resistors directly to ground, and then also connected pin 8 of the power tubes directly to ground. Common sense should have told me sooner that I was bypassing the cathode resistor and caps.

I removed the ground wire, no more red plates, and now I get 40V across the cathode resistor. And the amp sounds very nice, too. Hopefully I'll get a chance tomorrow to really open this thing up and see what it can do.

So now I'm wondering if I should have connected the 100 ohm resistors from the heater wires to pin 8 instead of to ground?

Anyway, I have to say thank you one more time for all of the fast, helpful responses. And also a big thanks for those of you who put this great project together, and to Doug Hoffman for his excellent service.



(On a side note, last week I just finished wiring a new theatre system at a college down here, and out of well over a thousand connections made, testing revealed only two faults - pins 1 and 2 reversed on a couple of mic jacks. I had been gloating a little, but now this whole amp experience so far has helped knock me down a couple of notches, which I obviously deserved.)

[tubenit]

So now I'm wondering if I should have connected the 100 ohm resistors from the heater wires to pin 8 instead of to ground?

Either should work fine. You can try both and see what is quieter. I just connect my 100 ohm resistors to ground.

I am willing to bet all of us have made comparable or goofier mistakes at some point. Just part of the process.

With respect, Tubenit

[rzenc]

Hi,

don't mean to hijack the thread...I'm planning a TOS build with 4x6AQ5/6005W and would like to include VVR as well, however I have never done it and was wondering if NTE2973 will withstand current consumption for a quad of 4x6AQ5/6005W. I will follow tubenit directions about vvr'ing power plates, G2 and P.I. Also, I searched mouser for NTE2973 and got a message saying: "Not recommended for new desings"..Does it mean NTE will discontinue this part? Are you aware of a suitable replacement/upgrade for it?

With Respect.
Best Regards.
Rzenc

[theundeadelvis]

Should the 250k drive pot be audio taper also? Thanks!

[jojokeo]

...wondering if NTE2973 will withstand current consumption for a quad of 4x6AQ5/6005W.

searched mouser for NTE2973 and got a message saying: "Not recommended for new desings"..Does it mean NTE will discontinue this part?

It should easily handle the current comsumption - it's rated for 14A continuous, and No, ignore the message.

Should the 250k drive pot be audio taper also? Thanks!

No, use a linear taper pot since it's a votage divider

[theundeadelvis]

Thanks!

[darkbluemurder]

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

Thanks

REALLY??

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

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

LOTS of builders here would walk you thru it.

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

Ray

That's what I thought as well but I fried a power transformer by trying to get the control voltage from the heaters (center tapped) using a bridge rectifier (grounded). I am yet to successfully implement channel switching into an amp - after six successful complete single channel builds. I would really appreciate more info on this.

My TOS build is getting closer - I already started to drill the chassis. But it will only become a TOS if I get the channel switching down. BTW I will use a Hammond 372JX transformer which has a 5V-0-5V secondary winding. How would I go about using this with a 5V relay - just use one 5V and the 0 tap or both 5V taps? And do I connect the 0V to ground?

Thanks and kind regards,
Stephan

[tubenit]

IF you do a search on the AmpGarage forum for "relay switching" ............ you will find ALOT of information.

http://ampgarage.com/forum/search.php

And in Hoffman's Library of Information, there is 5 pages of schematics, layouts and info:

http://www.el34world.com/projects/relay_switch.htm

With respect, Tubenit

[darkbluemurder]

Thanks, T. The Hoffman library is very instructive.

Cheers Stephan

[sluckey]

How would I go about using this with a 5V relay - just use one 5V and the 0 tap or both 5V taps? And do I connect the 0V to ground?

If you will not be using that 5 VAC winding for anything else, I'd use it for the relay supply. BTW, that PT is not 5v-0-5v. It's 5VAC with CT, which is to say, 2.5v-0-2.5v. Wire it like the circuit in the pic. Don't use the center tap. It's OK to connect the negative ground side to chassis. The 7vdc output will drop some when you connect the relay coil. If it doesn't drop enough to suit you, put a resistor in the positive line.

[tubenit]

Swapping out the transformer was a breeze, probably the easiest "mod" that can be done to an amp, just pop it in and solder a few wires - nothing to it. Well, the result was simply spectacular! Gone were the nasal, thin sounding BAAAD over-driven sound that I remembered. With the new OPT, I can easily dial in a number of great sounding "patches" - from clean cleans to growling Marshall-y overdrive. Immediately, the amp moved from the bottom of the heap to the very top, just like that.

Excellent!  That's good to know. Thanks for sharing it.

With respect, Tubenit

[Ross]

Hi folks,
What dimension chassis would be appropriate for the TOS? I am interested in putting it in a combo cabinet. What similar sized Big Name chassis/cab would be perfect?
Regards.

[tubenit]

I used a 20" x 8" x 2.5" blank chassis.  It worked fine and would work just fine for a combo amp also. There was quite a bit of room.

The blank was supposedly for a Marshall or Bassman head.   There are obviously other options that would work as well. You could look at the Fender Super Reverb style chassis if you want to go more that route.  You'll need to make you own front panel plate of course.

with respect, Tubenit

[tubenit]

Occasionally, you can find blank "amp chassis" on ebay. This is an example, not sure about the thickness of the aluminum though?

http://www.ebay.com/itm/Tube-Amp-Chassis-19x8x2-12-gauge-/171015101106?pt=LH_DefaultDomain_0&hash=item27d14b5ab2

With respect, Tubenit

[moonbird]

The title says 12 gauge I think? Right? 

[Ross]

Thanks for the cab specs, Tubenit. It's the thought of that odd millimeter here or there that would complicate it's fit in the cab or is not as big a deal as I imagine?
1.  Super Reverb is the cab size to go for, or is a generic 12" speaker type sufficient?
2.  Is there room for ears or should the side folds be bent inwards?
 The thickness of the aluminum would be 2mm, at least in these parts.
 A little personal background: With the help of an engineer friend and after a year or so of reading up, I put together a 50 W plexi type and a chimp er champ but the enclosures left something to be desired. This project I want to look its best. From all the raves about the design it would be a darn shame not to.
I also had an experience similar to Jazzbo8's:
A guy spun me the trannies but with "hifi" in mind. After taking them out and putting in some old iron ("Levant"?!) the 50 watter sounded much better.
BTW: An ancient pair of Telefunken EL34 also sounded better than the (caveat emptor!) TubeStore.com "matched" set.

[tubenit]

I have always built my own cabs ............ so matching the cab and chassis is probably something you'll have to figure out on your own  OR
use something that is already a match like Super Reverb chassis and SR cab. My chassis has the ears out.

The TOS is a "tweaker's  amp" which means that you may or may not like the "original" design of it?  Be prepared to build it & then tweak things like coupling caps, tone stacks, cathode values .............  to get it to suit your style of playing, speaker, guitar .....etc

With respect, Tubenit

[Ross]

Does this sound right? The 3 H choke at 120 hertz offers 2.25 kOhms impedance. To swap the choke with a resistor would one use 2.2 Kohms?
Assuming a current of 160 mA this makes 60 watts on the resistor. What is the safety factor here? ie: what power capacity should it have?

Re the cab discussion: after shipping, customs, etc. the box would cost almost as much as the rest of the amp!

[sluckey]

Does this sound right? The 3 H choke at 120 hertz offers 2.25 kOhms impedance. To swap the choke with a resistor would one use 2.2 Kohms? Assuming a current of 160 mA this makes 60 watts on the resistor. What is the safety factor here? ie: what power capacity should it have?

Usually when replacing a choke with a resistor you would chose the resistor value to be equal to the dc resistance (DCR) of the choke. For example, a 3H choke 'may' have a DCR of 150Ω, so use a 150Ω resistor. And if the current will be 160mA the resistor will dissipate 3.84 watts. Double that wattage for a safety factor (7.68 watts) and get the next common resistor wattage. In this example I would use a 150Ω/10W resistor.

But, if you're talking specifically about replacing the 3H choke in the TOS amp, there won't be anywhere near 160mA flowing thru that choke because the output tube plate current does not flow thru the choke. There's more likely only about 10mA flowing thru the choke so the replacement resistor could be lower wattage.

[Ross]

10mA- of course! Not the first time I've made that mistake. I don't get the theory behind the choke's DCR. Copper resistance yes, but as to the function of the inductor I thought that it would show the 3 H at double the mains AC: X = 2piFL.