Gut and refurb old ss combo

[Greg_L]

Ah, instead of nodes placed in relatively close proximity to the point they're feeding you've made them remote, centralized and reduced the length of B+ wire snaking about sending appropriately stepped power from a centralized point. Transformer to Quadzilla to point of use via neatly braided cables that reduce EMI & other issues as they go AND an Earth bus to bring it all home neatly as well.
Tidy mind!

Ha yes, pretty much. Gold star for you.

My original intent was to have each node's filter cap on the turret board with it's respective part of the circuit, but that would have made the board too crowded and too long. It's a common way to do it when building from scratch, and in the future I will probably do it that way if given the option, but my board space is a little limited on this one. Had I planned for it a little more I could have gotten a bigger board with more turret space and probably made it work. But the way I ended up is the way Fender did it for decades so it's fine.

[Greg_L]

I never plan on getting inside an amp but it's still very interesting.

So far, for me, this power node/filter cap stage stuff was the hardest stuff to wrap my head around. The way it's drawn on a schematic makes sense - just follow the line. The way it's actually implemented in amps is kind of crazy. I've yet to find one that's very intuitive. Marshalls are especially bad about just having gigantic filter caps at random spots with long wires running everywhere. I've spent literal hours with a schematic in one hand and an open amp on a table in front of me trying to trace out what's going where. But it works. You can't argue with decades of kick ass amps kicking ass.

[Tadpui]

I just got my shipment of retube kits for all 3 of my amps, and I'm thinking about going ahead and swapping in the new tubes in all 3, and using the existing tubes as spares. But the JCM is the only one that I actually know how to bias (well...I did blow a fuse last time I tried...so maybe I don't even know how to bias that one!). I'm not even sure if my Mesa or Fender amps have bias pots to adjust it.

Where do you go to figure all of this stuff out? My Google attempts basically just lead me to sources that I don't trust much (Gear Page, Marshall forums, Les Paul forums). Is there a good reference source for bias settings for various amps? Or do I just go to the manufacturer and hope they reply?

[Greg_L]

I just got my shipment of retube kits for all 3 of my amps, and I'm thinking about going ahead and swapping in the new tubes in all 3, and using the existing tubes as spares. But the JCM is the only one that I actually know how to bias (well...I did blow a fuse last time I tried...so maybe I don't even know how to bias that one!). I'm not even sure if my Mesa or Fender amps have bias pots to adjust it.

Where do you go to figure all of this stuff out? My Google attempts basically just lead me to sources that I don't trust much (Gear Page, Marshall forums, Les Paul forums). Is there a good reference source for bias settings for various amps? Or do I just go to the manufacturer and hope they reply?

Use a tube bias calculator....like this:
https://robrobinette.com/Tube_Bias_Calculator.htm

You'll need a bias probe and a multimeter and the confidence to measure stuff inside a live amp. You'll want to know your plate voltage, enter your tube type and plate voltage into the calculator site, and look at the figures for AB fixed bias settings. Aim for the 60% figure and call it good.

Your Mesa may not be adjustable. The Fender and Marshall most definitely are.

[Tadpui]

Use a tube bias calculator....like this:
https://robrobinette.com/Tube_Bias_Calculator.htm

You'll need a bias probe and a multimeter and the confidence to measure stuff inside a live amp. You'll want to know your plate voltage, enter your tube type and plate voltage into the calculator site, and look at the figures for AB fixed bias settings. Aim for the 60% figure and call it good.

Your Mesa may not be adjustable. The Fender and Marshall most definitely are.

Awesome, thanks! I'll start a new thread when I get down to brass tacks. I don't want to hijack your awesome build thread and sidetrack it with my amateur fuse-blowing antics

[Greg_L]

Awesome, thanks! I'll start a new thread when I get down to brass tacks. I don't want to hijack your awesome build thread and sidetrack it with my amateur fuse-blowing antics

[JD01]

Thats probably more appropriate.

It's a lot of unnecessary info if you never plan to get inside an amp.

The idea of it really appeals cos I like the science of the electronics... I just couldn't manage the soldering.

Have you ever thought about making pedals?

[Greg_L]

Have you ever thought about making pedals?

No. Not even a little. I do not like pedals.

But I have thought about preamps. Like real tube mic pres, not the fake stuff that's advertised as tube pres.

[Greg_L]

Easter progress....

Assembled the turret board. Fucking Orange Drops. So big. I underestimated the gigantic honking bulbous fuckedness of Orange Drop caps when designing my all-inclusive compact board layout. What a tedious pain in the ass this was. The over-spec 1-watt resistors are a little big too, but they aren't really a problem. This is usually my favorite part of a build, but not this one. It's finally done though and done cleanly. I was very careful and methodical and triple-checked everything. Hopefully it works out.



Bass channel and tone stack


Normal channel and tone stack


This little bit here shows part of what I was talking about in the rectifier/filter cap post. This is not usually included on the main circuit board in Fender amps, but I fit it onto mine. This string of diodes on the far end of the board is the diode bridge rectifier. High voltage AC will come in from the power transformer at the top, and it will leave as high voltage DC at the bottom. From there it will go to the first set of filter caps - the reservoir caps - and also pass along to the standby switch, the OT center tap, and choke, as per the schematic. The extra turrets at the very end of the board will be used for those connections. Also in the pic is the bias circuit, which is also not usually included on the main board. The bias pot is already mounted on the chassis.


So now I'm in the home stretch. Still a lot to do, but now I can install the board into the chassis and get started connecting wires to things.

[Lt. Bob]

Your Mesa may not be adjustable.

I don't think they are ..... Mesa wants to sell you tubes that they pick to fit the bias of their amps.

For me that's great since in 58 years I've never checked a bias in anything except the gRamp which you wanted me to dbl-check after shipping.

[WhiskeyJack]

this entire thread has melted my tired brain. I think maybe i'll try and reread it when i am more functionable.

But it looks pretty cool..

Also i may have asked this once before but other than looking neat and tidy is there some sort of function to twisting up all the wires?

[Greg_L]

Also i may have asked this once before but other than looking neat and tidy is there some sort of function to twisting up all the wires?

Twisting AC wires, like the heater filament wires, does have benefit. There's an electrical field around those wires, and AC goes back and forth, so twisting them together creates a sort of natural canceling effect on the electrical fog surrounding those wires. It's subtle, and sometimes does nothing, but twisting certain wires together is worth doing even if for no other reason than making it easier to deal with a bundle of wires. Wires floating and flopping and snaking around is not good. Sometimes long runs of wire are unavoidable. You want some "cable management" in an amp like you would behind a desk filled with a ton of audio gear. You want everything routed cleanly and efficiently and securely. Twisting wires together is a simple way to keep them secure...the right wires. You can't just twist any wires together.

[Greg_L]

I don't think they are ..... Mesa wants to sell you tubes that they pick to fit the bias of their amps.

For me that's great since in 58 years I've never checked a bias in anything except the gRamp which you wanted me to dbl-check after shipping.

I think Mesa gets away with it by biasing their amps cold. They know our wall voltage across the U.S. falls within a certain range. They know what their plate voltages will be. They know how much wiggle room there is when biasing tubes. So as long as they can test their own tubes and send out matched pairs they're good to go.

I don't think there is too much "sound" in how hot or cold you bias an output tube as long as you're in a safe, usable range. There is some, but not enough to really get into the weeds over it. As long as you bias within the normal operating range of a tube it'll be fine. The sound difference between 55% and 70% dissipation in a push-pull amp is pretty minimal. The difference in tube life is pretty big though. Running a tube up against it's limit will significantly shorten it's life. I usually shoot for around 60% and call it good.

[Lt. Bob]

I don't think they are ..... Mesa wants to sell you tubes that they pick to fit the bias of their amps.

For me that's great since in 58 years I've never checked a bias in anything except the gRamp which you wanted me to dbl-check after shipping.

I think Mesa gets away with it by biasing their amps cold. They know our wall voltage across the U.S. falls within a certain range. They know what their plate voltages will be. They know how much wiggle room there is when biasing tubes. So as long as they can test their own tubes and send out matched pairs they're good to go.

when you buy tubes from Mesa ( I have ), they ask how you want the sound?
Do you want warmer and mushier or do you want cool and precise ..... if I remember correctly at the time they had 3 different choices in tubes.
Like cold, medium and hot are how they were described ..... been 15 years or so though, so who knows about now?

But other than that one time of buying tubes from Mesa, I have always just bought whatever and stuck them where ever ..... ya'll know my opinion on biasing for tube changes is that its importance is way overblown.

My policy of not giving a shit has worked well for 58 years and dozens and dozens of amps with not a single amp ever giving me trouble or having any significant detriment to the sound of any of them.

[Greg_L]

Lol. Tube bias is super duper important. But you're not wrong....if your amp works and you're just replacing tubes for maintenance or whatever, chances are the bias is set just fine.

[JD01]

My policy of not giving a shit has worked well for 58 years and dozens and dozens of amps with not a single amp ever giving me trouble or having any significant detriment to the sound of any of them.

I think people only started giving a shit about unimportant stuff in about 1998.

[SweetDan]

I like how the resistors are giving the capacitors a little hug with how they're positioned.

[Greg_L]

I like how the resistors are giving the capacitors a little hug with how they're positioned.

I think it's more like a tea-bagging.

[Greg_L]

I tell ya wut....I'm not really a fan of these turrets. I mean, I love turrets, I prefer them to fiber eyelet boards or PCBs, but these particular turrets are kind of...too slick I guess? The solder doesn't want to bond as easily as I'd like it to. It's taking a lot of heat. The parts that can go into the holes are fine. But soldering a wire lead around the stepped shank parts is being kind of a bitch.

[Lt. Bob]

I tell ya wut....I'm not really a fan of these turrets. I mean, I love turrets, I prefer them to fiber eyelet boards or PCBs, but these particular turrets are kind of...too slick I guess? The solder doesn't want to bond as easily as I'd like it to. It's taking a lot of heat. The parts that can go into the holes are fine. But soldering a wire lead around the stepped shank parts is being kind of a bitch.

they look really shiny to me and that has always seemed to correspond to needing to sand things to make solder stick.
I don't do turrets but if I have a pot or jack that's really shiny, the solder never seems to stick well.

Maybe grab a Dremel and use one of those little flat brush fittings to get around that shank area?