HRD > Bassman project! SUCCESS!!

[JSett]

POST VOLTAGES!

Also what means do you have for checking bias? Bias probe or something?

I have a Biasrite that I used. I'll post voltages in 2 secs

[JSett]

POST VOLTAGES!

V1

1: 179
2:
3: 1.21
4: 3.21
5: 3.21
6: 192.4
7:
8: 1.31

V2

1:
2:
3:
4: 3.21
5: 3.21
6: 187.9
7:
8: 1.31

V3

1:
2: 53.4
3: 84.3
4: 3.21
5: 3.21
6: 216.6
7: 84.3

V4

1: -40.6
2: 3.21
3: 414
4: 415
5: -40.6
6: 416
7: 3.21
8:

V5

1: -41.9
2: 3.21
3: 412
4: 412
5: -41.9
6: 414
7: 3.21
8:

[Dr Tony Balls]

V3

1:
2: 53.4
3: 84.3
4: 3.21
5: 3.21
6: 216.6
7: 84.3

Not sure if this is incomplete or the actual voltage, but if its accurate thats a problem. It should look more like:

1: ~220
2: ~50
3: ~100
4: fil
5: fil
6: ~220
7: ~50
8: ~100
9: fil

[JSett]

Not sure if this is incomplete or the actual voltage, but if its accurate thats a problem. It should look more like:

1: ~220
2: ~50
3: ~100
4: fil
5: fil
6: ~220
7: ~50
8: ~100
9: fil

Ill go double check, one sec

[JSett]

Obviously had a brain fart...

V3

1 218.7
2 53.7
3 84.9
4
5
6 218.7
7 53.7
8 84.9
9

My head is awash with numbers right now

I did notice that on your BF-50 layout of the one you made me, you have a 47k resistor from the 4ohm tap and then into the PI circuitry. On the schematic for this one its a (drastically different) 870R. I'm sure there's a reason for that, but worth noting?

[Dr Tony Balls]

And what are you reading with your bias rite? 6L6GC is a max dissipation of 30W, and you wanna run em some where between 50-70%. So with a plate voltage of ~414 you wanna see:

Hot - (70% * 30W)/414V = .051A
Medium - (60% * 30W)/414V = .044A. <-- what I shoot for
Cold - (50% * 30W)/414V = .036A

[JSett]

And what are you reading with your bias rite? 6L6GC is a max dissipation of 30W, and you wanna run em some where between 50-70%. So with a plate voltage of ~414 you wanna see:

Hot - (70% * 30W)/414V = .051A
Medium - (60% * 30W)/414V = .044A. <-- what I shoot for
Cold - (50% * 30W)/414V = .036A

I went with -48 on my Biasrite

I don't know if it's relevant but it's SUPER dirty even at low. With the master on full, bass 0 treble 10 and vol at about 2 or 3 its pretty overdriven! Almost like the BF-50 on about 7

[Scout]

Go to Rob Robinette’s amp page, lots of great building and troubleshooting pages there including amp start up after a rebuild.

[JSett]

I've stopped looking at it for now, it's making me furious

[JSett]

Someone suggesed the PI or Bias is wired incorrectly (which would explain why it's not particularly loud for it's design). Apart from the fact that Tony's plans show a different bias pot wiring to what you'd normally see in a Fender I can't see any issues with it at all.

The fact that it has the same issue with the tonestack lifted out of circuit confirms the issue likely isn't there, and would be further downstream, half confirms this.

I'm trying to cross-reference an OG AB165 schematic with Tonys but it's kinda tricky as I know there's a few differences because it's a conversion.


Somehow, somewhere, there is a ton of lows and low mids getting through and sapping power and screwing the sound with too much low end and early breakup - and pretty gritty breakup too. Fuck knows where though.

[Dr Tony Balls]

I'm trying to cross-reference an OG AB165 schematic with Tonys but it's kinda tricky as I know there's a few differences because it's a conversion.

Well I just did this and *GASP* I made a mistake! I dont think it'll be a game changer, but I could be wrong. I ha the value of the negative feedback resistor (R21) at 820Ω and on an AB165 that should be 47K! Make that change and see what happens.

Also the schematic for this conversion is pretty much the same as an AB165 in the places that it really matters. Differences are 1) power rail because we didnt add a choke, 2) bias supply is different because the transformer is different, and 3) added Type-2/LarMar master volume.

[Dr Tony Balls]

(delete)

[JSett]

I'm trying to cross-reference an OG AB165 schematic with Tonys but it's kinda tricky as I know there's a few differences because it's a conversion.

Well I just did this and *GASP* I made a mistake! I dont think it'll be a game changer, but I could be wrong. I ha the value of the negative feedback resistor (R21) at 820Ω and on an AB165 that should be 47K! Make that change and see what happens.

Also the schematic for this conversion is pretty much the same as an AB165 in the places that it really matters. Differences are 1) power rail because we didnt add a choke, 2) bias supply is different because the transformer is different, and 3) added Type-2/LarMar master volume.

Well well fucking well...

I've lost 2 days and gained a few dozen grey hairs over that resistor I actually considered changing that resistor but didn't want to mess something up further (as we got the 4ohm tap in the wrong place once and it made a horrible noise )

Guess what? It works! And it sounds pretty damn good

Maybe we should get a corrected layout/schematic changed in the earlier posts for anyone that stumbles across this thread in the future?

[Dr Tony Balls]

I'm trying to cross-reference an OG AB165 schematic with Tonys but it's kinda tricky as I know there's a few differences because it's a conversion.

Well I just did this and *GASP* I made a mistake! I dont think it'll be a game changer, but I could be wrong. I ha the value of the negative feedback resistor (R21) at 820Ω and on an AB165 that should be 47K! Make that change and see what happens.

Also the schematic for this conversion is pretty much the same as an AB165 in the places that it really matters. Differences are 1) power rail because we didnt add a choke, 2) bias supply is different because the transformer is different, and 3) added Type-2/LarMar master volume.

Well well fucking well...

I've lost 2 days and gained a few dozen grey hairs over that resistor I actually considered changing that resistor but didn't want to mess something up further (as we got the 4ohm tap in the wrong place once and it made a horrible noise )

Guess what? It works! And it sounds pretty damn good

Maybe we should get a corrected layout/schematic changed in the earlier posts for anyone that stumbles across this thread in the future?

Sorry.....guess I owe you a beer now?

[Dr Tony Balls]

Here's an updated schematic, ver 3.0:



Seems like too much negative feedback was just reducing distortion, highs, etc.