Jack

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Hey Jack, would the lower power tube operation be related to the subnotes? Because the goal is a 1 to 2 watt amp, not 5. The guy I'm building it for is out for that low watt full throttle amping. He's already got a Cornford Harlequin , that's 5 to 6 watt. And a little too loud for that purpose. OTOH, I want to supply him a great sounding little tone monster...it already looks awesome!!!TriodeLuvr wrote: ↑Mon 06/21/21 9:25 amUse the 390 ohm by itself first. Then measure the DC voltage across the resistor and from one of the anodes to ground. Those two measurements will allow you to calculate the anode to cathode voltage and current flow. I would use 5W as a good upper limit (the sections together are rated for 5.5W).
Jack
You’re running the tube at 3.7W, which is 67% of the maximum allowable dissipation (5.5W). If you want to be sure it’s class A1, and that there’s minimal chance for crossover distortion when it’s driven hard, change the cathode resistor to 240 ohms. That should put the operating point almost exactly where Brimar and GE data sheets suggest, even if B+ sags a little when you draw the additional current.Bieworm wrote: ↑Mon 06/21/21 11:20 pmIn that context my amp now is biased at 34% dissipation. Isn't it better practice to have at least 60 to 70%?
Is it then possible there is crossover distortion at act, causing the weird subtones?
Maybe this is a good idea: put a 220 Ohm resistor in series wit a 220 Ohm 4W pot and adjust the bias by ear?
https://www.gotron.be/componenten/passi ... o-lin.html
BTW, the 100k anode resistors on V1 are identical and read 99k. I think I should do some tube rolling to rule out the difference doesn't start there
The hardest thing is the low wattage.. it so contra intuitive on many areas. The fact that the volume knob is maxed out when doing tweaks and such.. how often do we do that with an 18 watt? The 18 watt behaves different too when dimed, and I forget to compare the situations for both amps in state of maxed out. Very confusing...JMPGuitars wrote: ↑Tue 06/22/21 6:11 amIt's definitely an improvement, but there's still lacking articulation. Between about 1:30 to 2:30, and 3:30 to the end sound the best. Any time there's a lot of distortion, notes are getting lost.
I'd go with the hotter bias / slightly higher B+ and see what that sounds like. Try adding the .047µF film cap in parallel to the preamp filter cap and see if it affects the unwanted stuff.
Thanks,
Josh
Do you mean the preamp filter caps? They are coupled on the same B+3 node as the plate resistors of V1a+bgeoff 1965 wrote: ↑Tue 06/22/21 9:02 amwhat about the filtering between V1a and V1b anodes Jack,could that account for the difference?
That wouldn't be a factor, because the two anodes are connected together. Even if they weren't, it wouldn't explain this. DC current flowing into either section through the cathode resistor must equal the current flowing out of that section through the respective anode resistor. There's no other path for the current to take, unless it's also flowing through the grid circuit due to a gassy tube. If that was the case, both sections would show the same fundamental imbalance because they're in the same envelope - cathode current would be higher than anode current. Cathode current equals the sum of all the other currents out of the tube.geoff 1965 wrote: ↑Tue 06/22/21 9:02 amwhat about the filtering between V1a and V1b anodes Jack,could that account for the difference?
That's all good news! The schematic I was working from shows the V1 cathode resistors both at 1.5K. Seems like you're about done, and I think your client will be very pleased. Just need to let Josh critique the sound!Bieworm wrote: ↑Tue 06/22/21 2:27 pmDid some experimenting.. higher B+ wasn't any nicer, on the contrary... on various bias settings. Now I landed on 264R (390//820R) and I'm pretty satisfied.
The discrepancy on V1 anodes and cathodes is due to the different cathode resistors. V1a is 2k2 and V1b is 1k5. I tested by lowering the cathode resistor on V1a and the voltages on that half both dropped substantially. So that's off the table...
I'll post a clip ASAP, but the power went down in the area...just while I was soldering the speaker to the cable ☹
Maybe I will keep the soundclip for myself and spare me the critiqueTriodeLuvr wrote: ↑Tue 06/22/21 2:50 pmThat's all good news! The schematic I was working from shows the V1 cathode resistors both at 1.5K. Seems like you're about done, and I think your client will be very pleased. Just need to let Josh critique the sound!Bieworm wrote: ↑Tue 06/22/21 2:27 pmDid some experimenting.. higher B+ wasn't any nicer, on the contrary... on various bias settings. Now I landed on 264R (390//820R) and I'm pretty satisfied.
The discrepancy on V1 anodes and cathodes is due to the different cathode resistors. V1a is 2k2 and V1b is 1k5. I tested by lowering the cathode resistor on V1a and the voltages on that half both dropped substantially. So that's off the table...
I'll post a clip ASAP, but the power went down in the area...just while I was soldering the speaker to the cable ☹
Jack