Fender 5F8A Bias

[martin manning]

That all looks pretty good. You're only reducing the line voltage by 4%, meaning you'd get around 415V B+ without any reduction. Does that 15V make a noticeable difference in the amp's character?

[ViperDoc]

That all looks pretty good. You're only reducing the line voltage by 4%, meaning you'd get around 415V B+ without any reduction. Does that 15V make a noticeable difference in the amp's character?

Only one way to find out. I am still firmly entrenched on that pathway of building amps I've never heard in person before, so I'm going in with fresh ears and curious expectations. I've been burning this amp a bit today and played it through a Tone Tubby Amsterdam 90W Alnico and a Tone Tubby Ceramic 4040 40W in parallel, a recommendation by the maker. I know the numbers might be risky. Thom said the Tone Tubby 4040 is underrated on paper, so with a replacement guarantee, I'm going in full bore. It sounds really nice. The cranked rock tone from this amp is classic rock nirvana, OMG.

I've encountered some noise (super faint, high-speed ticking sound) that I hope is only a wireless internet conflict. It mostly goes away with humbuckers.

[ViperDoc]

Here are some gut shots of this build. I will re-run the master volume output under the board once I decide to stick with this PPIMV type. I don't like doghouses and I wanted to use the tweed chassis, so my available real estate is paying for it. The overdrive is very strident when cranked. Hopefully these photos might help to reveal (or eliminate) a potential solution. And please forgive the workbench shrapnel.

[Reeltarded]

If you are operating the amp with no shielding it will do bad stuff above the tree line.. 7-8 on the volumes and the RF fritter turns to hashing garglecillation

[ViperDoc]

If you are operating the amp with no shielding it will do bad stuff above the tree line.. 7-8 on the volumes and the RF fritter turns to hashing garglecillation

The only shielded leads are between the PI to PPIMV and from PPIMV to PT grids, all shield grounded to its own chassis lug on one end.

If adding, say use shielded wire on all tube grids?

[Reeltarded]

No.. tha amp needs to be sealed.. is it mounted with a shielded backplate?

[ViperDoc]

No.. tha amp needs to be sealed.. is it mounted with a shielded backplate?

No, it's on the bench. Quiet as a church mouse when not played.

[Reeltarded]

Yeah, but when you are plugged in with the volume up it collapses into blocking and oscillation.. ?

RF from all the tech we have these days.. dimmers and.. lite-brites and etch-a-sketch.

[Colossal]

For Martin and Doc,

Tung Sol 5881s may not appreciate high screen voltages, meaning over 400VDC or so. After a summer of abuse, one of mine failed in my Blonde Bassman. I would get the screens down. It should affect the sound for the better. Less harsh and smoother, warmer and more musical distortion. I have a pair of short bottle 6L6s in my Bassman for now, but prefer the 5881s (warmer and less clean). FWIW....

[ViperDoc]

For Martin and Doc,

Tung Sol 5881s may not appreciate high screen voltages, meaning over 400VDC or so. After a summer of abuse, one of mine failed in my Blonde Bassman. I would get the screens down. It should affect the sound for the better. Less harsh and smoother, warmer and more musical distortion. I have a pair of short bottle 6L6s in my Bassman for now, but prefer the 5881s (warmer and less clean). FWIW....

All recommendations welcome. I, in fact, just soldered an additional 470R 3W resistor in series with my screen supply to make each screen see 940R, it seemed to drop the screen voltage by 2 VDC and raise the gain a bit. My B+ is variac'd to about 397 and screens are 396 in normal configuration. I just took it off to compare and it sounds brighter with just the 470Rs on the screens.

Well, now I just bumped the AC line voltage to 115 to bring everything down; plates at 394, screens at 392. Sounds really good! Slightly cleaner.

EDIT: Now I just swapped out the Tone Tubby 4040/Amsterdam for a pair of Celestion Lead 80s. "I'm sorry, were you talking to me?" SOFAKINGLOUDANDROCKANDROLL.

[ViperDoc]

Here's an iPhone sound byte noodle, no polish for sure. Played through two Celestion Classic Lead 80s with a Nash HSS Strat with Lollar SC neck, then SC middle, then Low Wind Imperial HB in the bridge. First half volumes at 10 o'clock, then volumes at 1:20-2:00.

It plays clean. My impression of the distortion onset is harsher than I prefer. Sounds good, though. Gotta practice more!

5F8A Lead 80s.m4a

[Reeltarded]

That sounds in line with a good one. Throw a screamer on the front with no distortion, level up and tone moderate.. middle or tiny bit treble.

I like it.

Play only the bright side and turn that down with the guitar volume 100%. You are looking for just below breakup when you HAMMER it.. ok..

Tell me that isn't the best clean sound.. like, ever. It's great!

[ViperDoc]

Thanks, Reel, although I did realize I made a glaring error on the PI. I originally installed my 100K and 82K PI plate resistors in the wrong order, thereby unbalancing the PI! First thing this morning I swapped them into their correct positions and this amp now sounds so much smoother, what do you know! When I get a chance, I will post some comparative scope shots. You can see that one half was clipping harder than the other, and one seemed to clip softer and asymmetrically. We'll see! The audible rasp in the overdrive is about gone.

EDIT: New scope shots here: https://ampgarage.com/forum/viewtopic.p ... 04#p440204

EDIT: I WAS WRONG. I DID NOT MISTAKENLY PLACE THE 82K/100K ORIGINALLY. BUT NOW THAT I'VE SWAPPED IT, I LIKE IT A LOT BETTER. THE VOLTAGES ARE ACTUALLY BETTER BALANCED NOW. ??? I NOW SEE THE VIRTUES OF THE PHASE INVERTER BALANCE POT.

[ViperDoc]

I made a couple changes:

1) changed all preamp grid wires to shielded coax (Mogami 2314)
2) created an additional CRC filter off the PI node (thanks, Colossal) to supply V1 with its own 8 uF cap ( wondering if the cap itself should be shielded)

97296552-443A-40EC-84A2-FC40B3361039.jpeg

Still speaker tasting with this. Sounds nice and clean! And LOUD!

[ViperDoc]

So since I added the additional power supply cap, I've created some slight new noise. I'm going to rearrange the components a bit to get the new cap away from the input, and also separate the power supply dropping resistor. In playing this amp, it feels a lot more gainy than I think I'd like. I thought I'd play with separating the V1 common cathode. I recall if I was to maintain the same values, I would double the resistor values (turn a single 820R into two 1K5s) and halve the capacitor value (250 uF into two 125 uFs), although I think I might reduce those capacitor values to trim some bass a la the Tweedle Dee approach. Is there any predictable math on differing the separated V1cathode components to maximize even-order harmonics when jumping channels? Maybe since they're parallel, they ought to be the same?