Tweed Overdrive Special (continued)

[daveyajd]

Thanks for all the help everybody. I have gotten a fair bit done so here are some update pics. I will be placing an order with Doug in the next day or so then I will be on the homestretch. If you notice any possible issues, please let me know.


Aaron

[daveyajd]

Here are a couple more.


Aaron

[daveyajd]

Alright my final parts order is shipping to me as I type this. A couple questions about my tubes. I have some JJ 6L6s around here so that is what I will start with for power tubes, though I will probably try to acquire a set of 5881s down the road. I also have some JJ 12ax7s and an ecc81 PI tube I will use. The only tube I don't have is the 5879. I know tube depot has them and AES has them ( theirs state "short cut off" what does this mean?) Any other recommendations for where to source these? Also, I will start with the solid state rectifier and then try a gz34, 5y3, etc with different tube types. What have you guys found to be the best pre, PI, PT, rect combination?


I also came across a thread on here where Geezer mentions adding another 10uf or 25uf cap in parallel across V2-A cathode. I happen to have a 5uf 25v and a 25uf 50v lying around. Are those sufficient voltage ratings? It seems like they are considering voltage from there should be about 2 volts I just want to be sure.


One last question for the day. I have a .0047 and .0022 on my order to make the .0068 cap on the plate of V2 b. I need to run those in series to get the proper value, right? How have you all accomplished this? Put another turret on the board?


Thanks,
Aaron

[tubenit]

I have maybe 10 different 5879 tubes all bought off ebay.  I have not found a brand to be better than others.

Yes, the cathode caps you suggested are fine with the voltages you mentioned.

Parallel the caps to make the .0068.  However, I would build it first with .0047 & try it.  Then parallel safely the .002 with insulated alligator clipped wires and see what you like best.

With respect, Tubenit

[daveyajd]

So I have been searching for some step by step for powering this up when the time comes and I came upon this thread


http://el34world.com/Forum/index.php?topic=2376.0

where sluckey lays out a his procedure very well. Trouble is, I have not powered anything up so far. According to this list I will be jumping in after PHASE 3 I think. My PT is completely wired up. Primary, rect tube, heaters, grounds, etc. My OT is also wired to the tubes and all impedance taps are wired and soldered. I have not connected any of the filter caps yet. but I do have wires running from my tubes to my pots.

I do have a lightbulb limiter ready so I can put a fuse and lamp in and fire it up right? Then I can check voltages at the tube sockets with no tubes in at which point I will power down and move on to phase 4 and down the list. Can I also check my DC voltage across my relay diode at this point to determine my CLR for the OD LED?  (damn, that's a lot of abbreviations!) Am I also able to check my switching for the relay coil?

Any other thoughts to add?

Thanks,
Aaron


 

[Ed_Chambley]

Very nice looking build working here.  Lots of goodies in this design.

Consider making a Decade Box with Caps and Resistors.  It will make tweaking this baby much more pleasant. 

[sluckey]

Do all your relay checks and calculate your CLR for the LED at the same time you check your filament operation. Phase two. Your PT and mains wiring should have been already verified at this point. Don't use the lamp limiter while testing the relay. Voltages may be too low for proper relay and LED operation.

Be sure to put the amp back on the lamp limiter when you move forward for initial B+ testing.

[daveyajd]

Ok. Since I did not get a test on the PT right away I will be jumping into the testing process a little further down the list. I will plug it in with my limiter and look, listen and smell. Then I will have to measure my heater filaments at the tubes and my text tube pins 4 and 6, 2 and 8 at the same time. With the limiter on  how close to spec should my HV and heaters be?
Then I will power it back on with no limiter to check  for my CLR value. I am very excited to see this thing come to life and confident in my attention to detail thus far but I am still nervous.

Aaron

[sluckey]

Don't measure any voltages while plugged into the lamp limiter. They will be low.

[daveyajd]

Ok so I will use the limiter to protect my first power up to check the PT primary. Then I will power it up without and measure everything.

Aaron

[Tone Junkie]

Very nice looking build working here.  Lots of goodies in this design.

Consider making a Decade Box with Caps and Resistors.  It will make tweaking this baby much more pleasant.

The only bad thing about making your first decade box. Is then you end up like me with about 6 for every spot in the amp. (LOL) its an addiction I tell ya.
Bill
       

[daveyajd]

Alright! Powered up with no pop, fizzle, or smoke.  When I measure the voltages at the recto socket should I measure across pins or from pin to chassis ground? Heater voltage was right on 6.3. I measured the voltage from the diode at 4.68v. Can I even use the 5v LED mentioned above?


Aaron

[sluckey]

Can I even use the 5v LED mentioned above?

I would think so, but put a 220Ω or 470Ω resistor in series with it just to be safe. I still don't trust that Radio Shack label for that LED. If it doesn't work then you can get a bagful of LEDs from eBay for about a dollar.

[daveyajd]

I went ahead and put a resistor in there to try it out. It worked fine. I didn't put anything as big as 220 or 470 though so maybe I'll up it a little before I solder it in. All my switching worked perfectly. I only had to move my red wire from the top switch lug to the bottom so it switched correctly. What about measuring the recto? Measure between pins 4 and 6 or from each to ground? I didn't measure that cause I wasn't sure. What about pins 2 and 8?

Aaron

[sluckey]

I went ahead and put a resistor in there to try it out. It worked fine. I didn't put anything as big as 220 or 470 though

Good. What value resistor? Now that you have a CLR installed, measure the voltage directly across the LED leads. What do you get?

Measure between pins 4 and 6 or from each to ground?

Do both. The AC voltage from each pin to ground will be half as much as the voltage between pins 4 and 6.

What about pins 2 and 8?

Measure that also. Should be 5VAC across the pins. Later on when you plug the recto tube in you will measure DC B+ voltage from pin 8 to ground.

[daveyajd]

The resistor on the LED measured about 110. The voltage across the LED now measures 3v.


Rectifier tube voltages:
-across pins 2 and 8 = 4.8 VAC
-from each pin to ground I don't get any reading


-across pins 4 and 6 = 118 VAC
-from each pin to ground =357 VAC


What's going on with my last set of voltage readings?


Aaron

[sluckey]

The voltage across the LED now measures 3v

Kinda what I thought would happen! RadioShack just labeled the voltage wrong on the package. Not the first time.

What's going on with my last set of voltage readings?

I don't know yet, but don't do anything else until you find out what's going on. There should be over 700VAC between pins 4 and 6. Some cheap meters cannot measure that high. Look at the specs for your meter. Which meter do you have?

[daveyajd]

I am using a Centech meter from Harbor Freight. Cheap I know, but it says it should measure up to 750 VAC.


Aaron

[daveyajd]

Ok. I think I see what may be happening. And it is because of the cheap meter. Voltage reads something like 117 but when I tap the display all of a sudden the top LED crystal in the display appears making it actually 717. But then the voltage starts climbing up in the 800 and beyond. I will have to round up a better meter and try again tonight.


Thanks,
Aaron

[daveyajd]

What is the best way to ground the input and effect sends jacks? They are all switch craft type and someone mentioned earlier that I don't need to run a ground wire from my speaker jack because it is already grounded at the chassis. Is it the same for these jacks or should I ground them at the bus bar?

Aaron

[tubenit]

I have quiet amps at idle.   I use Hoffman's grounding scheme and ground the input jack on to the buss wire.

Regarding the FX loop jacks.  I ground them to each other and not to the buss wire. .  IF it is an active FX loop & there is a potentiometer
on the back chassis where the jacks are, then I ground the potentiometer ground on to the FX loop jack's ground.

IF it is an active FX loop and there is an FX potentiometer on the front of the chassis such as an FX level pot, then I ground it on the buss wire.

With respect, Tubenit

[daveyajd]

Thank you. No pot for the FX so I will connect them and ground the input.


Rechecked my voltages and I was right. The meter display was failing. I got 724 VAC across the pins. Onto the next phase.


Aaron

[daveyajd]

I am so close! Here is something I just realized I might have done wrong. I arranged my pots a little different than they are on the layout so it's tough for me to easily draw a picture of what I did. Basically, I connected the grounds from lug to lug in the overdrive controls and then connected the last pot's lug to the bus. Same thing in the clean section and in that section I also connected the ground from the relay to a lug. I'm wondering if I have a problem because quite a few grounds go through the .0047 caps that ground the tone pots. That should affect them, right? Here is the layout and a picture to help visualize.


Aaron

[tubenit]

IF I am understanding how you everything wired to ground, I think it should be just fine.  Look at Hoffman's grounding scheme.  It works.
It's what I use and my amps are quiet at idle.

http://el34world.com/charts/grounds.htm

With respect, Tubenit

[daveyajd]

Ok. Thanks. I have been very good on my grounding. Everything has been done pretty much like Hoffman suggests. I guess my concern was that with each ground connected to the next pot and then ultimately running through that cap to the buss it is almost like I grounded every pot through a .0047 cap. Instead of just the tone pot. Clear as mud, huh? I may change it or I may not worry to much. I just have to finish populating the main board and then check and recheck the scheme and layout and I will be giving it a test run.

Aaron

[tubenit]

it is almost like I grounded every pot through a .0047 cap

IF I am understanding what you have done, ............ you simply have grounded a .0047 cap to a buss wire which is ground?

I don't understand the "through the cap" comment?

With respect, Tubenit

[daveyajd]

I look at it like this:

Lug 3 on the tone pot connects to the ground with a .0047 cap. (Not a wire)
Lug 3 on any other pot connects directly with a wire.
So it seems like what I have done is the equivalent of using a .0047 cap on every pot (because they all use that cap to get to the buss) instead of just a wire on as it would show in the schem. Not to worried about it but it was something I wondered about.

Aaron

[sluckey]

So it seems like what I have done is the equivalent of using a .0047 cap on every pot (because they all use that cap to get to the buss) instead of just a wire on as it would show in the schem. Not to worried about it but it was something I wondered about.

If they all must get to ground thru that cap then it ain't gonna work. Just run a wire from each pot lug that should be grounded DIRECTLY to the buss. Otherwise, why even use a buss? Don't daisy chain your ground wires.

[tubenit]

OK, I finally understood what you are saying.   You threw me off saying you followed Hoffman's grounding scheme. (which you haven't actually followed)

Follow Sluckey's excellent advice.

With respect, Tubenit

[daveyajd]

Just tracing my schematic against my build and I noticed these two resistors from the power tubes to the cathode cap and resistor. Have these really gotten overlooked on the layout? Seems they would have been caught by someone and corrected. They were on the BOM so I have them, just not sure how/if I need to install these.


Aaron

[Glennjeff]

Those two 1 Ohm resistors are so you can measure the bias of each individual output valve, IIRC they are a new addition to the circuit diagram and may have been overlooked on the layout. (Tubenit emphasises that one should use the circuit diagram and not the layout as the accurate reference.)

They are traditionally soldered directly onto the cathode pin (pin 8) of the tube socket, soldered together at the opposite ends and then wired to the cathode bias resistor/cap junction.

The circuit will work fine without them but you will only be able to measure the average bias of the tube pair, which is fine if you buy matched tubes.

I'm getting anxious with anticipation for switch on, plug in and strum 

[daveyajd]

I'm getting anxious with anticipation for switch on, plug in and strum 

Man, me too!    


Thanks for the info. I will just go ahead without those for right now. I also noticed that the layout I used (flipped version) also used a 150k plate resistor for the 5879. The scheme called for a 56k so I switched that over. How would a 150k affect that tube. More gain?


Should be completing it very soon.


Aaron

[Glennjeff]

Higher plate resistance = more gain, less headroom before hard clipping I believe 

My 5879 has 82k plate R.

Tweak to taste in the future.

[tubenit]

I also noticed that the layout I used (flipped version) also used a 150k plate resistor for the 5879.

I am not seeing that?  I looked at 3 layouts for the TOS in the SCH library.  All of them including the flipped layout show 56K for the plate resistor for the 5879?

http://el34world.com/Forum/index.php?topic=9636.0

With respect, Tubenit

[daveyajd]

This is the version I have always had. Granted this is probably the original download from a couple years ago.


Aaron

[daveyajd]

SUCCESS!!! 


Well, mostly. I did have a nasty squeal on first attempt, switched the OT leads and solved that. I do have a few things to look into so I'll list them here and see what you guys think.


My OD and Clean channels are reversed. When the switch is down(clean) I actually get the OD signal and when the switch is up the LED lights up and I get the cleans. What is the simplest move to make to turn these around?


My PPIMV works very well but from about the 2 o'clock position to just before all the way up it has a weird and vey present noise. Below that the amp is very quiet. All the way up and there is still just a little something there.


Lastly are my voltages. I have posted my readings and they are all pretty close. Take a look at my PI numbers though. Not sure why those seem so off.


The only component differences I have from the schematic are my cathode cap and resistor values. (100uf and 360R) and the cap connected to V2 pin 6 is .0047 instead of the .0068.


Thanks for all your help. I will be getting some recordings as soon as I can.


Aaron

[sluckey]

What is the simplest move to make to turn these around?

Rotate the switch 180º.

[tubenit]

V4-6   LTPI plate is just 60V??     In contrast  V4-1 is 211v?

I would expect close to 200v plus or minus on V4-6.  Maybe that is part of the problem with the PPIMV?

I currently would not be concerned about the .0047 instead of the .0068.  And the power tubes 360R and 100uf is fine also for now. You can tweak those later.

With respect, Tubenit

[daveyajd]

Rotate the switch 180º.

Ha! yes that would make the switch positioning correct but then the LED would light in the down/clean position.




I am going to investigate this PI voltage thing.


Aaron

[sluckey]

Ha! yes that would make the switch positioning correct but then the LED would light in the down/clean position.

Picky, picky! Are you saying you want the LED to light up when in overdrive mode? If so, you'll need to reverse the NO (normally open) and NC (normally closed) contact connections on your relay board.

[daveyajd]

WOW! Un-f'ing believable! Just spent the last hour+ lost in playing this thing.


I popped a different ECC81 in the PI. Seems to have evened things out. Voltages are around 177v on 1 and 6 now. I will post a new voltage table in a bit. As well as a completed chassis pic.


So to switch the NO and NC would I do something like this?


Aaron

[daveyajd]

Alright I'm going to say it again. This amp is a lot of fun to play! Right now I am playing it just as the open chassis playing through a cab with 2 vintage Jensen 12" and this thing is very quiet. And flexible.


This was my first build ever so I am going to consider this a huge success. I genuinely want to thank everyone who visits this forum and took the time to answer any of my questions and help to keep me on the right track. Now that it's done let the tweaking begin.


A few notes on fixes I had to do after power up:
- Had to swap the OT leads
- A new PI to trouble shoot odd voltages. ( I posted a table with my current readings)
- Flip the wires coming back to the board from the trim pot. (Knob on 10 was full OD)
- Still need to figure out how to get the LED light working as it should.


That's it.


One more anomaly I had was a weird squawk/squeal when OD was engaged and I turned the PPIMV past the 3 o'clock position. Not sure about that. It happened but I can't really reproduce it.
My 4 year old was hanging around and she said "Your amp is beautiful daddy but that sound is not nice."


Here are a few pictures of the final chassis build and I will have some sound files up soon.


Aaron

[Glennjeff]

Hi daveyajd,

Great eh! 

Some of those squeals and noisies when the PPMIV is turned up high may indicate an instability.
Make note of them and any other strange behaviours, they cam usually be addressed fairly easily.
Sound clips of any strange noises would also be helpful.

Some sound clips of the amps tone would be great too.

All the best.
Glenn

[sluckey]

So to switch the NO and NC would I do something like this?

Yes. Since you have a double pole relay swap NO and NC for both poles.

[tubenit]

Congratulations on a successful amp build!  It was a complex amp and it looks like you did a great job with it.  I would love to hear soundclips. 

Glad you got the LTPI plate voltages corrected.  That may have resolved the PPIMV issue since you said you have not been able to reproduce it?

With respect, Tubenit

[daveyajd]

So I'm not sure what happened but my amp has fallen apart sonically. Everything was working great and I was playing it everyday and loving the sound. But of course I could not leave well enough alone and had to mess with it just to see.    So I decided to adjust the power tube cathode cap and resistor. I was putting a 47uf cap parallel to the 100uf and increasing the resistor from 360 to 428 by putting a 68ohm in series with it. When I fired it back up there was hum and hiss on the OD channel especially when the PPIMV was anywhere but all the way up and the Lean was all the way down. Clean channel seemed to still be fine. Also the relay switching now seems to make an audible pop that it never made before.


So I changed the cathode back to its original values and still have this ungodly squeal and squawk in pretty much the whole range of PPIMV.


Here is a sound clip recorded with my phone. The background noises are my daughter playing around but you will hear a hiss (now on the clean channel) and then a switch to OD and the crazy noise.


https://soundcloud.com/daveyajd/weird-sounds

[tubenit]

When you increased the cathode resistance, you probably put more voltage on the plates.  I am wondering if you damaged a power tube?

Do you have another set of tubes to try?   

Also keep in mind, sometimes we bump or move something other then what we are working on ......................... & when that happens, we think the problem is related to the area we are modifying and it may be related to something else.  Go back and measure voltages on your tubes.  Does everything look OK to you?

With resepect, Tubenit

[daveyajd]

I was afraid I might have damaged the tubes. Like the amateur I am I accidentally did my desoldering of the old components with the tubes still in. Dumb ass! I do not have another set of matched tubes to try out but I have a couple of randoms I could try. The voltages are all still measuring the same. I am bumming right now until I get this figured out.

Aaron

[tubenit]

Do you have a pair of 6V6's that you can try?   Or some 6L6's that are close to matched?   If so, maybe use those if the plate voltages are not too high?

With respect, Tubenit

[Glennjeff]

Hi daveyajd.

Can't seem to get to your sound clip, sound cloud says it's "not there" or "private".

Desoldering with valves in is not likely to have been a problem, it is often standard factory procedure to solder up sockets with valves in place so the socket pins seat correctly. Nor is the small increase in cathode resistor likely to have been a real budgie killer. If you put the second capacitor in with wrong polarity it could have been a problem.


Just for giggles, TEMPORARILY put a 630 volt coupling capacitor between pins 3 of the output tubes. (Pin 3 of one output tube to pin 3 of the other output tube), Any value from 0.001uF to 0.01 should do for the sake of diagnosis.) Does this cause any change ?

The obvious question is "Why did you feel the need to alter cathode bias component values ?".
You must have had a reason.

All the best
Glenn.