Tweedle Dee weak output

[fred.violleau]

Great cab as well!
How do you like the MV ?
I tried many different options, my initial MV implementation was like yours.
I eventually ended up with a LARMAR type II which was by far the best for me , totally transparent, with a great sound throughout the course of the pot.
I see that you left out the 470k resistor on the PI entrance, I am curious to hear the difference on your build

Any clip available ?

Fred.

[philbard]

Great cab as well!
How do you like the MV ?
I tried many different options, my initial MV implementation was like yours.
I eventually ended up with a LARMAR type II which was by far the best for me , totally transparent, with a great sound throughout the course of the pot.
I see that you left out the 470k resistor on the PI entrance, I am curious to hear the difference on your build

Any clip available ?

Fred.

Thanks! I do like the Master Volume, nice that it allows you to reach overdrive in the channels without blowing out the neighbor's windows. I'm new to this amp having never owned or built a Tweed before, so I picked and chose amongst the advice I found in the threads to get an initial build going assuming there will be mods, but basically went with the schematic in the files section attributed to Charlie and added the features that appealed. Component swaps and additions will probably come, right now I'm adding the switchable coupling cap feature you mentioned before as I mocked it up and liked it.

Will record something at some point...

Cheers,

[pompeiisneaks]

Hey Phil, congrats on your build!

Side note my coupling cap on V1A is .005 if instead of 0.02uf, and Marcus put this on a switch so he could have the 0.02 for single coils and the .005 for humbuckers.

Cheers!

Fred

Thanks Fred, I learned quite a bit from your build threads and also from the videos you put up. My build is a little heavy in the bass with buckers, sounds really good with single coils, so the switchable cap option might be a nice addition as I play with both types of pickups. The bigger bass does sound good at home volume levels but I suppose could be too much for a gig.

Still don't have a faceplate for it but wanted to wait until I was sure of the positions for the controls.
IMG_7535.jpg

Did I miss Fred's videos? I wanna see them!

~Phil

[philbard]

Hey Phil, congrats on your build!

Side note my coupling cap on V1A is .005 if instead of 0.02uf, and Marcus put this on a switch so he could have the 0.02 for single coils and the .005 for humbuckers.

Cheers!

Fred

Thanks Fred, I learned quite a bit from your build threads and also from the videos you put up. My build is a little heavy in the bass with buckers, sounds really good with single coils, so the switchable cap option might be a nice addition as I play with both types of pickups. The bigger bass does sound good at home volume levels but I suppose could be too much for a gig.

Still don't have a faceplate for it but wanted to wait until I was sure of the positions for the controls.
IMG_7535.jpg

Did I miss Fred's videos? I wanna see them!

~Phil

In this thread:
https://ampgarage.com/forum/viewtopic.p ... weedle+dee

[pompeiisneaks]

Oh yeah I did see that video Just getting senile hahah

~Phil

[philbard]

I eventually ended up with a LARMAR type II which was by far the best for me , totally transparent, with a great sound throughout the course of the pot.
I see that you left out the 470k resistor on the PI entrance, I am curious to hear the difference on your build
Fred.

Hey Fred,

Do you have a drawing of the LARMAR implementation? I found some on the net but wanted to be sure I wire it up correctly if I decide to try it. The 1M audio taper MV is not even enough, as you mention.

[Edit] I found Rob Rob's version. I have to study it a bit to see if it makes sense to add...

[philbard]

Great cab as well!
How do you like the MV ?
I tried many different options, my initial MV implementation was like yours.
I eventually ended up with a LARMAR type II which was by far the best for me , totally transparent, with a great sound throughout the course of the pot.

Fred.

I finally got the dual 250K pot and this morning installed a LARMAR II master volume control in the Tweedle Dee. Does indeed work quite well, pretty linear and blows away the other implementations of the MV I've tried. I really like the amp now.

One concern I have is how hot the 250R cathode resistor gets, I accidentally touched it after the amp had been on for 15 minutes and burned the skin on my finger. I know its been mentioned that Dumble used a stack with 2 100's and a 50. Assembled one but I notice its not held together very solidly by soldering the leads together, and also it won't be positively anchored to the board with just the leads going into eyelets. I suppose one way would be to tie the whole stack down with a wire running underneath the fiber board.

Anyone solve this? Also has anyone ever had the 250R fail under the excessive heat?

[bepone]

is that 27V on cathode resistor=?
this means you have power on it 3W and this is some heat

if is 27V then is too much for 6V6's , this means that currents summed are 100mA! and dissipation on the 1 6V6 is 50mA x anode voltage of 385V = 19.2W?! it is just double from normal! are tubes red plating?
maybe i misread something

[philbard]

is that 27V on cathode resistor=?
this means you have power on it 3W and this is some heat

if is 27V then is too much for 6V6's , this means that currents summed are 100mA! and dissipation on the 1 6V6 is 50mA x anode voltage of 385V = 19.2W?! it is just double from normal! are tubes red plating?
maybe i misread something

Just noticed that I installed 6L6GC's in the amp instead of 6V6's, no wonder. Bonehead mistake, I'll have to get the correct tubes.

[philbard]

is that 27V on cathode resistor=?
this means you have power on it 3W and this is some heat

if is 27V then is too much for 6V6's , this means that currents summed are 100mA! and dissipation on the 1 6V6 is 50mA x anode voltage of 385V = 19.2W?! it is just double from normal! are tubes red plating?
maybe i misread something

Had some 6V6's from a Deluxe Reverb, put them in and now the cathode resistor voltage is 21.3v, much better. Thanks for spotting that.... Will see if the resistor stays cooler.

[bepone]

ok with this voltage you are on 100-110% means you are running your amp in class A, not class AB, which is good tone-wise. but not for the life od the output tubes! maybe you can reduce little bit currents , adding 50 Ohms in series with cathode resistor, so total would be 250Ohms+50=300 Ohms which will bias lower your amp.

situation now:

voltage on each 6V6 is : Vak=375-21=354V
through the cathode resistor 4 currents are passing, V3-a, V3-g2, V4-a, V4-g2 and their total sum is
cathode voltage/resistor value = 21,3/250=0.0852 A = 85mA

this divided by 2 , thru each 6V6 passing half= 42,5mA

this multiplied with the voltage 354V= 0.0425*354=15W

means, over the max dissipation of the 6V6.. if we assume g2 current is cca 4-5mA, then anode current is around 37mA, Padiss =13.5-14W, still is over normal biasing range of 65-70% of max dissipation /6V6 has anode dissipation od 12W, JJ claims 14W

tonewise you are close/or you are in/ class A so your amp dimmed will not go in farting blocking distortion, or will but effect will be reduced, which is good, but from dissipation aspect , 6V6 is working on 110%, and their life will be shortened due to excessive heat.

current can be dropped in two ways, reducing voltage on g2 grid , Vg2 , inserting resistor of 500-1000ohms 5W in Ub+ line going to g2,
or incresing cathode resistor for cca 30-50 Ohms doesnt matter the value, just to choke little bit anode current.

[ChopSauce]

ok with this voltage you are on 100-110% ...

So am I - roughly. Isn't that a wanted feature?

[philbard]

ok with this voltage you are on 100-110% means you are running your amp in class A, not class AB, which is good tone-wise. but not for the life od the output tubes! maybe you can reduce little bit currents , adding 50 Ohms in series with cathode resistor, so total would be 250Ohms+50=300 Ohms which will bias lower your amp.

situation now:

voltage on each 6V6 is : Vak=375-21=354V
through the cathode resistor 4 currents are passing, V3-a, V3-g2, V4-a, V4-g2 and their total sum is
cathode voltage/resistor value = 21,3/250=0.0852 A = 85mA

this divided by 2 , thru each 6V6 passing half= 42,5mA

this multiplied with the voltage 354V= 0.0425*354=15W

means, over the max dissipation of the 6V6.. if we assume g2 current is cca 4-5mA, then anode current is around 37mA, Padiss =13.5-14W, still is over normal biasing range of 65-70% of max dissipation /6V6 has anode dissipation od 12W, JJ claims 14W

tonewise you are close/or you are in/ class A so your amp dimmed will not go in farting blocking distortion, or will but effect will be reduced, which is good, but from dissipation aspect , 6V6 is working on 110%, and their life will be shortened due to excessive heat.

current can be dropped in two ways, reducing voltage on g2 grid , Vg2 , inserting resistor of 500-1000ohms 5W in Ub+ line going to g2,
or incresing cathode resistor for cca 30-50 Ohms doesnt matter the value, just to choke little bit anode current.

I did some new voltage readings this morning, with the 6V6's installed, here is the chart.

Tweedle Dee Voltages 8_28.png

I also measured the power tubes with a bias meter, they are drawing 40 ma, so with the 371v-21v=350v, that indicates 14w dissipation if my math is correct. That appears to be right at the top end for JJ 6V6's, so I would agree it is running them pretty hot. I have a 50ohm wire wound resistor here, I'll put it in series with the 250 ohm and see where I go from there.

Thanks!

[philbard]

ok with this voltage you are on 100-110% ...

So am I - roughly. Isn't that a wanted feature?

My amp does sound good. It also gets pretty hot, but Fred also mentioned that his does too. Yours?

[bepone]

ok with this voltage you are on 100-110% ...

So am I - roughly. Isn't that a wanted feature?

not really also for single ended designs with one valve in class A, it is common rule of thumb to keep them lower, at 80% for extended lifetime .. for classic PP designs with fixed bias are at 60-65%..here is automatic bias so can be higher, but not 110%..you will have more heat in the vunerable tubes and shortened life, sooner cracklings or noise , depending of the quality of 6V6's.
one can say , why, they can be abused! ok im fine with that for me is the same, but is not recommendation or how needs to be set.