Is this confirmed? The Fat Sound website still is showing 12AX7 for all preamp tubes. Has the plate load for V2 changed?
azatplayer wrote:Oh and that cap by the power tubes cathode R/C is a .47uf OD. It has a wire coming from the led lamp to the front side of it. I was wondering if it had something to do with a fading circuit for the lamp?
Love your work Dave!
Ok, that makes sense and yeah, I read your posts on fading the LED. My mistake. Along that line, we need to revise where the LED is getting its DC from. In V1, it used to be a pair of diodes coming off the heater filament supply. I don't see that setup any longer in version 2. So I should revise that as well...let me know your thoughts on that and I'll add them to the scheme.
I don't see the 0.1 cap anywhere for the cathode on the power tubes...
Also here's an updated layout:
1-shorter signal/cathode runs for each tube
2-re-organized B+ supply with resistors
3-four solen on the chassis up front
4-two solens (smaller) on the board where they fit
5-forgot to spread out the pots...
Concerns:
1-location for OT/PT/choke
2-heaters running under the PS board vertically mounted on the right side
Is this confirmed? The Fat Sound website still is showing 12AX7 for all preamp tubes. Has the plate load for V2 changed?
Bump for confirmation on the 12AU7.
azatplayer wrote:Oh and that cap by the power tubes cathode R/C is a .47uf OD. It has a wire coming from the led lamp to the front side of it. I was wondering if it had something to do with a fading circuit for the lamp?
Love your work Dave!
Azatplayer, I can't find the other, more recent gut shot photos that show the close up of the orange drop. I need to update the schematic to show the revised LED circuit as the diodes are no longer on the edge of the board as in version 1.
It was a 12AT7 swap I believe to put more headroom on the amp. Here's the comment:
I just read the 76 page thread at TGP on this amp and people are getting theirs now. Someone brought one into a shop to get the "cleans a little more headroom" and they swapped the tubes to a 12at7 and it sounded better. I think the conversation continued to give this as the reason for the 12au7, Xits finally settled on. But that was many many posts ago.
Also, I put a voltage chart together for the rail and I think 300-0-300 is what I am going with. This puts 330 on the plates and 315 on the screens. Very similar to the vox night train. Anyone wants to learn the math here is the whole screenshot with values used:
Hey Colossal, heres a link to that pic http://www.fatsoundguitars.com/store/am ... guts-5.jpg
It well could be as you say, in parallel with the output cathode R/C, seen the hifi guys do that for some addes aparkle, and we have seen the original draft of this amp use that trick in V1's cathode too. Ive seen this value used elsewhere as well.
Could be that the wire from the led is using that as a ground?
As we've seen the divider dropped on the return from the volume, and also the grid leak dropped as well, thats adding SOOOO much greater signal, the amp would not be usable. WHich is the logic behind the 12AU7. Theres gotta be a gain drop somewhere to compensate for those circuit changes.
As we have only heard the original amp in the Greg V demos, and nothing of this much modified current amp, has me wondering if its as good.. HAS to be different.
azatplayer wrote:Hey Colossal, heres a link to that pic http://www.fatsoundguitars.com/store/am ... guts-5.jpg
It well could be as you say, in parallel with the output cathode R/C, seen the hifi guys do that for some addes aparkle, and we have seen the original draft of this amp use that trick in V1's cathode too. Ive seen this value used elsewhere as well.
Could be that the wire from the led is using that as a ground?
As we've seen the divider dropped on the return from the volume, and also the grid leak dropped as well, thats adding SOOOO much greater signal, the amp would not be usable. WHich is the logic behind the 12AU7. Theres gotta be a gain drop somewhere to compensate for those circuit changes.
As we have only heard the original amp in the Greg V demos, and nothing of this much modified current amp, has me wondering if its as good.. HAS to be different.
Azatplayer,
Thanks for the link to the photo. Ok, you are absolutely right, that orange drop is not connected in parallel with the output cathode resistor and bypass cap. You can see the unused turret there next to it. This location was used to power the LED on version 1. I suspect you are right about it playing a role in the LED. Your logic behind the 12AU7 in V2 makes good sense and with the divider gone, you are right, there's got to be some gain dumped somewhere otherwise things would likely get ugly. I've revise the schematic to reflect these changes. I'm trying to sort out however where that LED is getting its DC from as we don't see diodes anywhere tapping off AC (heater filament supply?).
Dave, theres another pic of the entire chassis, the wire leading from the .47 cap gos to the led hot side, its white and is covered loosely by a piece of white shrink. I think that there is enough room in the shrink for a diode. You can see the other leg of the led returning to ground thru a resistor too.
So, there would possibly be some AC at that entry to the .47cap on the socket side of the board. Would still have to be a heater supply i think.
I have been thinking about led's a lot lately. Thought about using a bicolour lamp for on/standby. Change colour when off of standby. Thought about using the cathode as a power source. Ive experimented with leds as cathode r/c's in preamps, pretty cool. And they fade out as current drains.
Im about to start Mats special 86, will be trying some led tricks out on that http://www.fatsoundguitars.com/store/am ... guts-7.jpg
I had a zoomed up look at that pic again. I think its a fair assumption the heaters are still connected on both of those turrets at the end. At least one anyways as thats all thats needed. Then they twist and head off to the output tube sockets. Dunno if it would fade much tho.
Hi Guys.
I was wondering if it's possble to speculate about the primary impedance of the output transfomer.
I'm building a 30w version ( 4xel84) thinking that a lar mar will be a fantastic solution as per volume requirements, I already made a chassis and a turrett circuit, but I still have to choose for the output transformer.
What do you think?
pls. any idea, suggestion or contribution will be welcome.
Thanks
Paolo
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