Is that crossover normal on Sluckey layout Ab763?

[SourCream23]

Hey Guys! All you ok?

I have build a Ab763 based on Sluckey Ab763 layout (many thanks Sluckey!).
The layout is here http://sluckeyamps.com/tdr/tdr.pdf

The amp sounds great but I have that kind of distortion on output:

https://imgur.com/a/FFbAHQr
https://imgur.com/a/5oREw8S

Is that normal? I have put 5.6K instead 1.5K in grid stoppers in 6v6s but I have louder hum  and the amp distorts too early.

Any tip what I can do?

PS: the last coupling caps to power tubes are .047uf instead original 0.1uf in deluxe schematic. Any improvement on the sound using 0.047?

Thanks guys!

[pdf64]

The scope trace looks normal for pretty much any fixed bias AB1 amp to me.
How does it sound?
Why do you think it distorts early? eg what’s its power output into the intended value of dummy load resistor at the onset of clipping?

[Lectroid]

@SC23,

I'm curious if you put in the Master Volume sluckey put in the TDR?  I'm having what may be a related problem on my build of the TDR right now on another thread.  "AB763 DR Master Volume question"

   https://el34world.com/Forum/index.php?topic=29469.0

I changed out the caps for .047uF and I like the sound a lot.  I also have the stock 1.5K grid resistors on the 6V6s and no distortion.  Maybe something in the other thread can help.

[SourCream23]

The scope trace looks normal for pretty much any fixed bias AB1 amp to me.
How does it sound?
Why do you think it distorts early? eg what’s its power output into the intended value of dummy load resistor at the onset of clipping?

Hey pdf64! Thanks for the comments.

It sounds very good to me on cleans. Pristine sound, real deluxe reverb. My concern is about that crossover distortion. I really dont know if is sounds correct.

The bias is 24mA per tube, in my configuration about 70%. Cold bias do not solve the problem and hot bias makes it worse. The first thing that I checked was the bias. Second one was the grid stopper resistors. 5.6k gives me a lower output, maybe because my impression about the lower volume I said that distorts early. It adds a lot of HUM too. The crossover goes away with 5.6k but sounds very bad overall.

The amp with 1.5k grid resistor sounds very good and I have about 20W on total power.

[SourCream23]

@SC23,

I'm curious if you put in the Master Volume sluckey put in the TDR?  I'm having what may be a related problem on my build of the TDR right now on another thread.  "AB763 DR Master Volume question"

   https://el34world.com/Forum/index.php?topic=29469.0

I changed out the caps for .047uF and I like the sound a lot.  I also have the stock 1.5K grid resistors on the 6V6s and no distortion.  Maybe something in the other thread can help.

Hey Lectroid, how are you man?

The MV before the phase inverter did not work very well in my design. I just get a weird sound with pot in 0.
I get a weird distortion very treble along the notes. It seems the sound leakes in some way.

So, I decided remove the MV. Without MV the amp sounds very good.
Maybe I will try PPIMV with dual pots in future.
I have tried Type 3 train wreck too, does not work.

I will read your thread pretty soon.

[PRR]

That's a LOT less crossover distortion than most tube amps in HEAVY overdrive. Shut the hood and play it.

[Willabe]

Welcome SourCream23! 

That's a LOT less crossover distortion than most tube amps in HEAVY overdrive. Shut the hood and play it.

     

(Not laughing at our new member SourCream23.)

[sluckey]

It sounds very good to me on cleans. Pristine sound, real deluxe reverb. My concern is about that crossover distortion.

Looks like most all push/pull amps when overdriven. BTW, where is your scope probe connected?

The MV before the phase inverter did not work very well in my design. I just get a weird sound with pot in 0.

My amp has no sound at all when the MV is set to zero.

[pdf64]

… 5.6k gives me a lower output, maybe because my impression about the lower volume I said that distorts early. It adds a lot of HUM too. The crossover goes away with 5.6k but sounds very bad overall.

The amp with 1.5k grid resistor sounds very good and I have about 20W on total power.

It seems very unusual that 5k6 grid stoppers should have any adverse effect on hum, power output, or anything really.
And there may be a slightly reduced degree of bias shift when overdriven. Not that there looks to be much of that.

[SourCream23]

… 5.6k gives me a lower output, maybe because my impression about the lower volume I said that distorts early. It adds a lot of HUM too. The crossover goes away with 5.6k but sounds very bad overall.

The amp with 1.5k grid resistor sounds very good and I have about 20W on total power.

It seems very unusual that 5k6 grid stoppers should have any adverse effect on hum, power output, or anything really.
And there may be a slightly reduced degree of bias shift when overdriven. Not that there looks to be much of that.

Hey pdf64. I will do the test again. Maybe one resistor was too close the heater wiring.

It sounds very good to me on cleans. Pristine sound, real deluxe reverb. My concern is about that crossover distortion.

Looks like most all push/pull amps when overdriven. BTW, where is your scope probe connected?

The MV before the phase inverter did not work very well in my design. I just get a weird sound with pot in 0.

My amp has no sound at all when the MV is set to zero.

Hey Sluckey! Awesome see you here on my thread! Thanks!

The probe was in output jack.
I have tried many configurations to make the MV work but I did not have success. Pot 0 gives me sound.
I directly grounded the 0.1uf before the pot to test, but I still get sound at high volumes. My layout is exactly yours on tdr.pdf

Welcome SourCream23! 

That's a LOT less crossover distortion than most tube amps in HEAVY overdrive. Shut the hood and play it.

     

(Not laughing at our new member SourCream23.)

Hey Willabe! Many thanks man!

[SourCream23]

That's a LOT less crossover distortion than most tube amps in HEAVY overdrive. Shut the hood and play it.

Hey PRR! Glad to hear that! I really was doubt about that distortion. But I think that everything is ok.

I will try change the 1.5 to 2.2K. Lets see what happens.

The amp is sounding great!

[sluckey]

There are millions of satisfied Fender customers that have a 1.5K resistor on the output tube sockets. Most don't even know or could care less.

1.5K or 2.2K. I doubt you will tell the difference on any AB763 amp. If you do, then you qualify as a real cork sniffer. You'll likely have to upgrade that Kenwood scope if you continue down this path. 

[SourCream23]

Well, I just make it for fun. I dont have plans to spent more time on that amp. The result is awesome, and as I can see on thread, it seems that distortion is pretty common.