Tweed overdrive special - some guidance needed

[Fictitiousfreedom]

Hello fellow tube obsessed friends!

Ive been working on a Tweed Overdrive special for a few months. Its definitely the most involved build i have done so far. I mostly have done the common fender designs and a simplified SLO 100. Ive been trying to learn as much as possible during this build. Ive been reading Merlins book on designing guitar preamps as well as other important books on amps. The math is hard for me but ive been really trying.

I originally planned to do a dumble but found this design on the hoffman forum and it seemed a little more manageable. I created a layout from the schematic, ill attach both as well as pictures and my voltages.The amp works. The clean channel actually sounds very good. I have a few problems. The way the pots are labeled is confusing, as of now the fatness “Depth” Pot works on both channels, which i believe is how it is intended to work. The Clean channel Gain and Tone work on both channels which i do not believe is how they are supposed to operate. I really cant figure it out. I know the tones on my tweed deluxe interact but these tone pots fully affect the OD Channel. The clean channel is fine, it is only affected by the clean tone. Also the clean channel gain just sounds bad, on both channels. I have to keep it very low or i get a nasty clipping distortion that seems to distort the early transients of notes.

The OD Channel just sounds bad, its shrill and has no bottom end at all. Hopefully when i correct whatever my problems are that will change.

Lastly, The power transformer is getting pretty hot but only after running for over an hour or so. When using a 5y3 instead of the yellow jacket bridge rectifier it gets hot much faster. Also my 5881 Tung Sols are getting hotter than any tube i have ever seen. Like burn you hot. They are not red plating or arcing though. I have a set of sovtek 5881s and Psvanes as well. The sovteks seem to operate about the same as the Tung Sols. The Psvanes did redplate but that was the first time i fired it up and i have not tried them again. I have an old precision tube tester and all of my tubes show as perfect.

If anyone is willing to take the time to read this or go through all of my info i would be eternally grateful.I know this is a lot and the time and expertise some of you guys have is very valuable and not easily obtained so i really appreciate any help at all. Im hoping its something silly im missing.

Thanks, Camden

[Fictitiousfreedom]

Pics

[sluckey]

...as of now the fatness “Depth” Pot works on both channels, which i believe is how it is intended to work. The Clean channel Gain and Tone work on both channels which i do not believe is how they are supposed to operate. I really cant figure it out.

If you look at and understand the schematic you'll see that all those pots affect both channels. It's designed to operate that way.

[Fictitiousfreedom]

...as of now the fatness “Depth” Pot works on both channels, which i believe is how it is intended to work. The Clean channel Gain and Tone work on both channels which i do not believe is how they are supposed to operate. I really cant figure it out.

If you look at and understand the schematic you'll see that all those pots affect both channels. It's designed to operate that way.

I see. It just seemed strange to me that there would be so many level/gain knobs and ive never seen an amp where both channels tone controls affect one or both channels. Ill have to check when i get home but im pretty sure the od tone pot didn't affect the clean channel at all. Thanks again Sluckey. Now i just need to figure out how to make the OD sound good and also how to get my voltages right. Most of my voltages are fine, all of my nodes are about 20V higher than the schematic which from my reading shouldn’t really be a problem? The 5879s pins 7 and 8 are a good bit higher than the schematic. The real problem is that my V4 voltages are almost double the schematic on pins 1 and 6 and pins 3 and 8 are half of the schematic and that has got to be a major problem. The schematic lists them as follows….

Pin 1 - 168V
Pin 3 - 41.5
Pin 6 - 165V
Pin 8 - 41.5V

Mine are

Pin 1 - 246V
Pin 3 - 28V
Pin 6 - 230V
Pin 8 - 28V

Ive been reading what Merlins book says about phase inverters and LTPI to try and understand how to correct this but i need to study everything more before i can completely comprehend it and then be able to utilize what ive read.

[johnnyreece]

At first glance, your voltages are a little high. 5881 doesn't really want over 400 on the plates (you'll notice the schematic has them at 423-39 (cathode voltage)= 384V). I'm guessing the PT might get hotter with the 5Y3 because the SS plug doesn't use the 5V tap, and they 5Y3 does.

[sluckey]

Ill have to check when i get home but im pretty sure the od tone pot didn't affect the clean channel at all.

Just look at the schematic and you'll see that none of the OD controls (trim, drive, level, or tone affect the clean channel. This is by design.

[Fictitiousfreedom]

At first glance, your voltages are a little high. 5881 doesn't really want over 400 on the plates (you'll notice the schematic has them at 423-39 (cathode voltage)= 384V). I'm guessing the PT might get hotter with the 5Y3 because the SS plug doesn't use the 5V tap, and they 5Y3 does.

That makes since. I gotta figure out why my voltages are so high. Is the small difference in my B+ voltages from the schematic listed voltages enough to make the power tube plates high or is it something else? I can not find anything different from the schematic so either a component is fried or i need a lot of adjustments to component values. Hopefully i don’t need to lower my B+ because from my research it is a little tough to correct. Unless the problem with the plate voltage and the PI being too high is something someone with more experience can easily spot than i have a whole lot of research and calculations to do, which i plan to do anyway i just hope i can figure it out.

The amp is honestly the quietest amp ive ever owned. There is absolutely no hum at all.

Ill have to check when i get home but im pretty sure the od tone pot didn't affect the clean channel at all.

Just look at the schematic and you'll see that none of the OD controls (trim, drive, level, or tone affect the clean channel. This is by design.

I see. I was somewhat baffled by the schematic in that regard. I assumed i just didnt understand how everything was implemented and what techniques were used, i guess thats the problem with not fully understanding the theory before jumping in. Thank you.

[bepone]

remove all the wiring and place exactly like dumble did, this is making huge difference

[bepone]

use of too much metal film resistors is not good way in guitar amp...

[Fictitiousfreedom]

remove all the wiring and place exactly like dumble did, this is making huge difference

Thanks, ill get right on that right after i spend a months salary on Nos carbon comp resisters lol

‍🫡

Anyone else got any advice? I know its a shit ton of work even just looking over everything so i really appreciate anyone willing to help me. Im going to continue reading as much as possible but it takes a lot of time and ive already neglected most other things in my life so any help would be much appreciated by my loved ones lol

[sluckey]

remove all the wiring and place exactly like dumble did, this is making huge difference

This is not a Dumble amp. Look here...

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

[johnnyreece]

Just checking; are you measuring the voltages with the right conditions? As in, is the MV supposed to be at a certain level when you measure? Sometimes voltages are to be measured with everything on 0. Does adjusting the MV change your measurement?

[bepone]

remove all the wiring and place exactly like dumble did, this is making huge difference

Thanks, ill get right on that right after i spend a months salary on Nos carbon comp resisters lol

‍🫡

you can use cheap carbon film, koa speer also, but i was reffering to wires only, lead dress, this is free

[bepone]

remove all the wiring and place exactly like dumble did, this is making huge difference

This is not a Dumble amp. Look here...

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

ok , didnt see , but at the end it is Dumble derivation

[Fictitiousfreedom]

remove all the wiring and place exactly like dumble did, this is making huge difference

Thanks, ill get right on that right after i spend a months salary on Nos carbon comp resisters lol

‍🫡

you can use cheap carbon film, koa speer also, but i was reffering to wires only, lead dress, this is free

Im sorry man, i honestly thought you were joking. Could lead dress cause higher plate voltage or my problem with the PI? I thought my lead dress was pretty good because i have such a quiet amp. i tried to follow the short chapter at the end of merlins book on lead dress but it isnt a very thorough chapter. Id like to read his others for more info. I am open to anything that helps. Ive only used metal film in everything ive made but i definitely need to grab some carbons.

Just checking; are you measuring the voltages with the right conditions? As in, is the MV supposed to be at a certain level when you measure? Sometimes voltages are to be measured with everything on 0. Does adjusting the MV change your measurement?

I measured again and did get a drop in voltage with the MV change.
All the way up i get 422v and down im at 444v, its late and i may have mixed that up.
Thanks for your help! It actually triggered a thought process that helped me more than all the reading ive been doing.
This is different kind of amp. Sluckey hit the nail on the head immediately.
The MV is the wrong taper. I replaced it trying to troubleshoot a really dumb mistake earlier…….. my pots wired backwards. All of them.
So the master volume is pretty horrible under half way. I was trying to keep the volume down and not understanding at all how the pots operated i had it setup poorly. I now have a good grasp on how to set everything and i love the concept and the tonal options it provides.

I just need to understand my PI voltages and also if my power tubes plates are too high.

Thanks for the help guys. I really do appreciate it!