pullshocks wrote: ↑Sun Apr 18, 2021 2:31 am
What volume setting on the amp during your test? I have not turned up past 2
The Ampbooks paraphase calculator indicates a pot setting 4k ohms would be balanced. How does that line up with what you saw with the signal generator?
I think it was between 2-4 during that test
I will set it to 4K and see what I get . That would be at 40% rotation and I was getting a good balance between low noise floor and good tone there
Have you played around any more with the trim pot? I tried setting mine by matching the voltage on my multimeter measured at the grids to the power tubes. They matched voltages at 3.9K. Sounds good, but I haven't had a chance to turn up much since the change. It seems a hair louder at this spot. It was a bit off from where I had set it by ear.
pullshocks wrote: ↑Fri Apr 16, 2021 2:52 pm
I find the switch very subtle. Look forward to trying this.
Thanks for posting.
Yep, I've found the switch to be *incredibly* subtle.
I finally grabbed a few minutes this morning to update the layout I made with all of the changes from this thread...
Attached are the new layout and a version where I marked the areas that changed.
Will update the original location of the layout as well - let me know if I'm missing something still...
I plan to try and implement these changes and see where I end up.
Hey BobL, another thing to consider...
I built the amp based off your schematic (thank you again it's awesome), but I split the power supply ground differently than your schematic. I split the power-amp ground bus from the pre-amp ground bus. The power tubes and their filter caps are grounded at the power supply ground point and the pre-amp and the 2 pre-amp filter caps are grounded through the pre-amp ground bus to a point near the input jack. I've understood this split ground scheme to be best practice and quieter (maybe others have more perspective?). Out of curiosity, I switched the ground scheme to match the schematic as posted, and it introduced a loud buzz that was preset at any volume setting.
The same thing happened when I ground the balance pot to the power-amp filter caps. It was much quieter grounded to the pre-amp.
The link below has a similar grounding scheme as I've tried to describe.
Gotcha... so nodes C and D ground off to the pre buss on the right... that makes sense.
I should have parts today, and I'm looking forward to trying to get everything shoehorned in here and brought in line with the latest understanding of the circuit... hoping to have it ready to play with the band on Wednesday and see how it does.
pullshocks wrote: ↑Sun Apr 18, 2021 2:31 am
What volume setting on the amp during your test? I have not turned up past 2
The Ampbooks paraphase calculator indicates a pot setting 4k ohms would be balanced. How does that line up with what you saw with the signal generator?
I think it was between 2-4 during that test
I will set it to 4K and see what I get . That would be at 40% rotation and I was getting a good balance between low noise floor and good tone there
Have you played around any more with the trim pot? I tried setting mine by matching the voltage on my multimeter measured at the grids to the power tubes. They matched voltages at 3.9K. Sounds good, but I haven't had a chance to turn up much since the change. It seems a hair louder at this spot. It was a bit off from where I had set it by ear.
Mike
Yes, and what I had it set at "4k2" was fine until I turned the volume past 4 and I started getting that splatty distortion. I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but... Just for fun I played it last night for over an hour with the Pi pot set full clockwise where I had it and it is one of the best tones I've ever gotten. It was very lovely and full of harmonics. In the end if it isn't hurting anything then the sound is what matters to me not whether the meter says it's balanced. Neither the OT or PT are getting warm let alone hot and the tubes are not red plating.
I think the splatty sound is blocking distortion based on the symptoms but I've never quite dealt with that before so I welcome any suggestions.
It would make since that as I increase the PI pot the signal increase is causing grid conduction on the 6v6's but I'm not sure I fully understand the concept yet.
This Aiken article describes my symptoms to a T https://www.aikenamps.com/index.php/wha ... distortion
If I can get the tone I got last night AND cure the blocking distortion or whatever it is then I'd be one happy camper
T Wilcox wrote: ↑Tue Apr 20, 2021 6:15 pm
I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but...
I thought earlier we decided that the OT in your diagram was 6k6 when it should be 8K?
T Wilcox wrote: ↑Tue Apr 20, 2021 6:15 pm
Yes, and what I had it set at "4k2" was fine until I turned the volume past 4 and I started getting that splatty distortion. I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but... Just for fun I played it last night for over an hour with the Pi pot set full clockwise where I had it and it is one of the best tones I've ever gotten. It was very lovely and full of harmonics. In the end if it isn't hurting anything then the sound is what matters to me not whether the meter says it's balanced. Neither the OT or PT are getting warm let alone hot and the tubes are not red plating.
I think the splatty sound is blocking distortion based on the symptoms but I've never quite dealt with that before so I welcome any suggestions.
It would make since that as I increase the PI pot the signal increase is causing grid conduction on the 6v6's but I'm not sure I fully understand the concept yet.
This Aiken article describes my symptoms to a T https://www.aikenamps.com/index.php/wha ... distortion
If I can get the tone I got last night AND cure the blocking distortion or whatever it is then I'd be one happy camper
I accidentally started out with a 470k instead of a 470 ohm resistor on my PI cathode. I had a terrible splatty sound when I turned up (but also little volume). Again, hard to see clearly, but maybe check that PI cathode resistor? Looks like yellow, purple,black in the pic you posted? That could do it.
Man, I feel like I've made every possible mistake building this amp. I also wired up my pots backwards initially
T Wilcox wrote: ↑Tue Apr 20, 2021 6:15 pm
I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but...
I thought earlier we decided that the OT in your diagram was 6k6 when it should be 8K?
Craig
FWIW, I'm using the OT from a Blues JR, 6k9 primary and it sounds great. No splatty overdrive.
T Wilcox wrote: ↑Tue Apr 20, 2021 6:15 pm
I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but...
I thought earlier we decided that the OT in your diagram was 6k6 when it should be 8K?
Craig
haha yeah thats what I meant 8k not 6k6. Im at work so going from my memory, thanks for the correction
Its an OT for a 5E3
I also dont think this is my problem but wouldn't hurt to have a much lighter OT if it sounds as good. Will see
that TW OT I used is huge compared to a 5E3 Ot
Last edited by T Wilcox on Tue Apr 20, 2021 8:58 pm, edited 2 times in total.
T Wilcox wrote: ↑Tue Apr 20, 2021 6:15 pm
Yes, and what I had it set at "4k2" was fine until I turned the volume past 4 and I started getting that splatty distortion. I have ordered a 6k6 primary transformer for a 5E3 from mojotone that should be here thursday to rule that out but... Just for fun I played it last night for over an hour with the Pi pot set full clockwise where I had it and it is one of the best tones I've ever gotten. It was very lovely and full of harmonics. In the end if it isn't hurting anything then the sound is what matters to me not whether the meter says it's balanced. Neither the OT or PT are getting warm let alone hot and the tubes are not red plating.
I think the splatty sound is blocking distortion based on the symptoms but I've never quite dealt with that before so I welcome any suggestions.
It would make since that as I increase the PI pot the signal increase is causing grid conduction on the 6v6's but I'm not sure I fully understand the concept yet.
This Aiken article describes my symptoms to a T https://www.aikenamps.com/index.php/wha ... distortion
If I can get the tone I got last night AND cure the blocking distortion or whatever it is then I'd be one happy camper
I accidentally started out with a 470k instead of a 470 ohm resistor on my PI cathode. I had a terrible splatty sound when I turned up (but also little volume). Again, hard to see clearly, but maybe check that PI cathode resistor? Looks like yellow, purple,black in the pic you posted? That could do it.
Man, I feel like I've made every possible mistake building this amp. I also wired up my pots backwards initially
Mike
Ill check that tonight! thanks
Speaking of every mistake possible. I found that I had the 4700uF for the 6vdc reverse polarity. Noticed it was a little bulgy on the top lol
This was after the videos I posted but replacing the cap didnt change anything tonally
I am very happy to say I found my problem....and embarrassed
Well it wasn't the resistor, that was actually 470 ohm as it should be. But I did another check on all components and found a 2k2 where it should have been 1k0 for the reverb cathode. Still not much change
Then I checked my spec sheet for the OT again to verify I landed the 8 ohm tap correctly, I did.
Then I noticed I had the brown primary landed on HT and the red CT landed at the plate of the 6v6 DOH!!!
Swapped them and voila a fully functional amp that is twice as loud as it was before fixing that
What a bonehead mistake but once I found it, it was easy to correct. Hey I told you guys I like learning things the hard way, didn't I?
Glad you found that! Now... do you know how to test your OT for impedance? I don't mean to be a jerk, I am making sure you know that the OT is connected correctly for the speaker load you have on it. 8 ohm, right?
"Education is what you're left with after you have forgotten what you have learned" - Enzo
T Wilcox wrote: ↑Wed Apr 21, 2021 3:50 am
. But I did another check on all components and found a 2k2 where it should have been 1k0 for the reverb cathode.
The reverb return cathode resistor was discussed earlier, the photo shows red red red 2.2 K
Hrm... well, made the following changes to mine tonight:
Added a 4th node, and switched to 22/47/22/22 with 4.7K between nodes B and C and C and D.
Sent node D to the preamp.
Sent grounds for nodes C and D to the same ground as the preamp.
Swapped V2 pins 2/7.
Replaced the 1K resistor on the reverb return grid with 2.2K.
Swapped the A/B switch to the middle lug.
Seems to be humming just as much as it ever did. It's late, so haven't really had a chance to play it or mess with the reverb. Flipping the voicing switch introduces a pretty good pop going from A to B, and does seem to change the tone more. PI balance pot seems to have a different impact on the nature of the hum now... introduces a hiss vs changing the tone of the hum, but I can get rid of the hiss at certain settings. Hum seems here to stay.
Made so many changes, it ain't particularly pretty in there at this point, but pretty confident it is all wired as per my layout.
T Wilcox wrote: ↑Wed Apr 21, 2021 3:50 am
. But I did another check on all components and found a 2k2 where it should have been 1k0 for the reverb cathode.
The reverb return cathode resistor was discussed earlier, the photo shows red red red 2.2 K
Then that's why I had that there, I've slept since then lol
I'll put it back
dorrisant wrote: ↑Wed Apr 21, 2021 3:58 am
Glad you found that! Now... do you know how to test your OT for impedance? I don't mean to be a jerk, I am making sure you know that the OT is connected correctly for the speaker load you have on it. 8 ohm, right?
Never had to test an OT for impedance
Not sure I do now since I have the spec sheet right in front of me!?
Care to enlighten me?
