Gut and refurb old ss combo

[Greg_L]

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?

It's too late and difficult to do that now. I'm just adding a little flux to each turret and it's working out ok.

[Lt. Bob]

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?

It's too late and difficult to do that now. I'm just adding a little flux to each turret and it's working out ok.

well next time then.
With those turrets mounted to a board but before any components it would be pretty easy to grab that board and de-shine the shanks ...... and I'm thinking one of the nylon brushes rather than wire ...... pretty much every Dremel set has them

[Greg_L]

well next time then.
With those turrets mounted to a board but before any components it would be pretty easy to grab that board and de-shine the shanks ...... and I'm thinking one of the nylon brushes rather than wire.

Yup, definitely for next time....which will be as soon as this one is done. I'm doing a 2204 next.

[Lt. Bob]

well next time then.
With those turrets mounted to a board but before any components it would be pretty easy to grab that board and de-shine the shanks ...... and I'm thinking one of the nylon brushes rather than wire.

Yup, definitely for next time....which will be as soon as this one is done. I'm doing a 2204 next.

from scratch?

And lets get talking about colors and visuals ..... lol ....ya' know this old hippie likes a pretty amp!

For panels couldn't you just get a decal made?

[Greg_L]

from scratch?

Yes....well as "scratch" as I can. I can't wind my own transformers and stuff, but yeah, it'll be a fresh build.

And lets get talking about colors and visuals ..... lol ....ya' know this old hippie likes a pretty amp!

For panels couldn't you just get a decal made?

This Tender Assman is already sorted. Blue/white/black colors. None of my attempts at nice looking lettering worked out so I just hand scribbled some bullshit with paint pens.

The 2204 will be standard Marshall colors and appearance.

[Greg_L]

Well amigos....we're getting close to this thing being done now. Well, the amp portion anyway. I've still got a cabinet to tolex and stuff. But the amp part is close. Board is in and many hookups have been made.

Preamp tubes and phase inverter wired up. I've still got to connect the shielded grid wires, but they'll be done with the front panel stuff.


Power tube sockets, bias pot, and some node connections on the left side of the board. All of that shit on the left of the board is the rectifier, main B+ line, standby switch connections, OT center tap, choke connections, and the screen node connection (yellow). Lots of big voltage right there.




Here we got the pilot light, power and standby switches wired up.


And here's where it's at right now. Almost everything is connected at this point. I could actually power it on. But I still need to wire up the tone and volume controls. And the PPIMV. That's all front panel shit and it's the last step.



So unless something terrible happens, the next update should be......

[SweetDan]

What's up with those two resistors with the unfastened/unsoldered legs on the tube sockets? Looks familiar...



(Again, I'm personifying things too much...lol)

[JD01]

That looks like such a tidy job.

[Greg_L]

What's up with those two resistors with the unfastened/unsoldered legs on the tube sockets? Looks familiar...



(Again, I'm personifying things too much...lol)

Lol. Those are called "grid stoppers". They're not on the original 6G6B schematic, but they're a good idea on any amp. Grid stoppers block unwanted ultra-high frequencies that can wreak havoc in a tube. You'll always find them on your first preamp tube as they block the interference that can turn your guitar amp into an AM radio stuck on some random foreign language news channel. And on many pentode output tubes, that grid pin also carries the bias voltage. A grid resistor helps stabilize all that shit. Same with those large ceramic 5w resistors. Those are screen grid resistors. Same deal. They're much beefier because they have to handle huge voltage and current.

Anyway, those currently non-connected resistors will connect to the shielded leads coming from the PPIMV pot on the front panel.


If they were on the schematic they'd go right here:

1963-Bassman-6G6B-Schematic grid stoppers.jpg

[Greg_L]

Also, I think I forgot to mention this, I "blackfaced" the bias. The original design has a fixed bias that's not adjustable. It seems weird that an amp with an adjustable bias would be called "fixed bias" but that's how it is. Many fixed bias amps are adjustable. Anyway, the original 6G6B Bassman does not have adjustable bias. But the very next bigtime Fender circuit, the legendary AB763, does. And many of them also use two 6L6 tubes and the very same spec power transformer as the 6G6B Bassman. So in my mind, I thought "why can't this one have a blackface bias?" and I looked into other dual 6L6 Fender schematics. The Super Reverb has a very similar power section so I set my bias supply up like the Super Reverb. We'll see if it works. I hope it works. It needs to work. I might get bitten by not knowing what I don't know.

[WhiskeyJack]

What does adjusting bias do.

No let's back up. Wtf is bias?

[Greg_L]

What does adjusting bias do.

No let's back up. Wtf is bias?

Bias is sort of like setting the idle and timing on a car. It's the base grid voltage setting that allows a tube to just sit there "idling" comfortably so when it's time to actually do work it'll operate at peak performance. You set the grid of a tube to a negative voltage so it repels electrons trying to escape from the cathode to the plate. If it's too negative then not enough electrons will flow during use. If it's not negative enough then too many will flow and exceed the rating of the tube.

[WhiskeyJack]

What does adjusting bias do.

No let's back up. Wtf is bias?

Bias is sort of like setting the idle and timing on a car. It's the base grid voltage setting that allows a tube to just sit there "idling" comfortably so when it's time to actually do work it'll operate at peak performance. You set the grid of a tube to a negative voltage so it repels electrons trying to escape from the cathode to the plate. If it's too negative then not enough electrons will flow during use. If it's not negative enough then too many will flow and exceed the rating of the tube.

Interesting. So how would a person know if their amp needs to have that looked at? And since were using car analogies? If looking into an amps bias was an oil change at what interval would you want to consider looking having it looked at / taken care of?

[Greg_L]

Interesting. So how would a person know if their amp needs to have that looked at?

When you replace output tubes it's not a bad idea to check and set the bias. If you blow up an output tube, check the bias. Otherwise, no need to fuck with it. It's not something you need to tinker with. Set it and forget it until there's an actual reason to mess with it.

And since were using car analogies? If looking into an amps bias was an oil change at what interval would you want to consider looking having it looked at / taken care of?

Well an oil change is a regular maintenance thing on a car. Bias is not that. You don't need to check or set your bias at any intervals.

Here's when I mess with bias....this is just me...
1) Get a new amp. I need to know what the bias is and set it accordingly. After that I never think about it again unless I replace tubes.
2) Replace tubes. If you replace tubes you should check the bias. Tubes, even of the same type, can conduct differently. If you have an amp bias set for old worn out tubes and you go to new feshies they may run too hot. You'll need to cool the bias for the new tubes.
3) Damage. If something bad happens in the output section always check bias. If a tube red plates or fails, you have to verify bias as part of the testing. Bias is controlled by resistors and capacitors just like everything else. That stuff fails sometimes. If you lose bias voltage the tubes die.

The good thing about bias is that it's pretty forgiving. And you can test for it with no tubes in place. Look for negative voltage on the grids of whatever tubes you're using. That's pin 5 on big bottle tubes like EL34s, 6550, 6L6, 6V6, etc. You need a negative number on pin 5 of the tube socket. If you have negative voltage somewhere in the -30 to -60 VDC range on pin 5 then you probably have safe enough conditions to install tubes and go from there. Now, this is important, that negative voltage is not your bias current. That just shows that there is negative voltage present at the grid and that means the bias circuit is probably working okay. Calculating your bias current is a few more steps. You need to do some math and measurements for that.

And this is all for fixed bias amps. Cathode bias is a different thing entirely. Those amps pretty much self bias.

[WhiskeyJack]

Interesting. So how would a person know if their amp needs to have that looked at?

When you replace output tubes it's not a bad idea to check and set the bias. If you blow up an output tube, check the bias. Otherwise, no need to fuck with it. It's not something you need to tinker with. Set it and forget it until there's an actual reason to mess with it.

And since were using car analogies? If looking into an amps bias was an oil change at what interval would you want to consider looking having it looked at / taken care of?

Well an oil change is a regular maintenance thing on a car. Bias is not that. You don't need to check or set your bias at any intervals.

Here's when I mess with bias....this is just me...
1) Get a new amp. I need to know what the bias is and set it accordingly. After that I never think about it again unless I replace tubes.
2) Replace tubes. If you replace tubes you should check the bias. Tubes, even of the same type, can conduct differently. If you have an amp bias set for old worn out tubes and you go to new feshies they may run too hot. You'll need to cool the bias for the new tubes.
3) Damage. If something bad happens in the output section always check bias. If a tube red plates or fails, you have to verify bias as part of the testing. Bias is controlled by resistors and capacitors just like everything else. That stuff fails sometimes. If you lose bias voltage the tubes die.

The good thing about bias is that it's pretty forgiving. And you can test for it with no tubes in place. Look for negative voltage on the grids of whatever tubes you're using. That's pin 5 on big bottle tubes like EL34s, 6550, 6L6, 6V6, etc. You need a negative number on pin 5 of the tube socket. If you have negative voltage somewhere in the -30 to -60 VDC range on pin 5 then you probably have safe enough conditions to install tubes and go from there. Now, this is important, that negative voltage is not your bias current. That just shows that there is negative voltage present at the grid and that means the bias circuit is probably working okay. Calculating your bias current is a few more steps. You need to do some math and measurements for that.

And this is all for fixed bias amps. Cathode bias is a different thing entirely. Those amps pretty much self bias.

COOL!!! This surprisingly makes a tiny bit of sense to my little brain. I won't screw with any of it or go poking and prodding. Just leaving it alone.

Cathode bias is a different thing entirely. Those amps pretty much self bias.

I have an amp that has both apparently. Fixed and Cathode. It's a finger switch on the front. NO idea what it does. I know it get's a bit less loud in the cathode bias mode. Lower wattage rings bells but i could be wrong? Fixed = 40W and Cathode is 15W? Maybe? I really ought to know this stuff but i don't.

[Greg_L]

I have an amp that has both apparently. Fixed and Cathode. It's a finger switch on the front. NO idea what it does. I know it get's a bit less loud in the cathode bias mode. Lower wattage rings bells but i could be wrong? Fixed = 40W and Cathode is 15W? Maybe? I really ought to know this stuff but i don't.

Yup, that is a thing. Cathode vs Fixed Bias. Both work great but they have different characteristics. Very generally, amps with fixed bias tend to have better headroom and punch. Cathode bias amps have more compression and output overdrive but less output overall. It just depends on what you want. The beauty of cathode bias is that it constantly sets itself depending on how you're using it. When you're digging in it sets itself. When you lay off, it sets itself. It all depends on current draw.

Some cathode bias amps brag about being able to use "any tube" as long as it fits in the tube socket. That's mostly true. They will set themselves. But it's a huge compromise. The amp will work best with a certain tube type depending on what kind of cathode bias resistor it has and the primary impedance of the OT. This is stuff you can't easily change. So maybe you wanna use EL34s. Great, but they might be only running at 50%. 6V6s might be better. You won't know unless you throw a bunch of tubes at it and try them....or do the measurements with a bunch of tubes to see which ones the amp really wants. Who wants to do all that? Or maybe you do the work and set it to work best for 6L6s. Cool, but now any other tube you might wanna use won't work that well and you've defeated the "flexibility" of the amp. And who the hell really wants to constantly swap around output tubes anyway?

[Lt. Bob]

I have an amp that has both apparently. Fixed and Cathode. It's a finger switch on the front. NO idea what it does. I know it get's a bit less loud in the cathode bias mode. Lower wattage rings bells but i could be wrong? Fixed = 40W and Cathode is 15W? Maybe? I really ought to know this stuff but i don't.

I'm pretty sure that is a mode switch that changes the the operation of the power tubes from pentode to triode.
triode will have about half the power of pentode.
Pentode is tighter and triode is a spongier 'feel'.

My 6101 has this and also my Tiny Terror had it , my little Ampeg GVT-5 does and I believe my Mark V also uses it.

I doubt very much that you can switch between fixed and cathode biasing ...... that would make no sense and it's also such a basic part of an amps design that I don't think you could easily switch between the two.

Greg may correct me on whether this is possible ..... but the pentode/triode thing is quite common.

[Greg_L]

Yeah pentode/triode is different.

When you switch from pentode to triode you're basically killing two of the protection grids inside a pentode tube. This makes it way less efficient, thus reducing it's output...and usually sounding worse. But it's a quick and dirty "half power" method.

Switching from fixed to cathode bias is very different. It's doable, and probably wouldn't be that hard to do, but I'm not aware of any common amps that have that feature.

[Greg_L]

Also, just FYI @Lt. Bob your Deluxe Reverb is fixed bias. Your little 18w Marshall TMB is cathode biased. You can set the bias on your Deluxe. Your 18w was set by me and you can't do jack shit about it!

Well, you can, but please don't.

I had to fine tune the cathode bias resistor on your 18w. The schematic value had your tubes running at like 130% and that will kill them fast. I got it set right at 95-100% with EL84s which is right where you wanna be with a cathode bias amp.

[Lt. Bob]

Yeah pentode/triode is different.

When you switch from pentode to triode you're basically killing two of the protection grids inside a pentode tube. This makes it way less efficient, thus reducing it's output...and usually sounding worse. But it's a quick and dirty "half power" method.

Switching from fixed to cathode bias is very different. It's doable, and probably wouldn't be that hard to do, but I'm not aware of any common amps that have that feature.

plus it wouldn't cut the power in half.

I generally prefer pentode myself but I like a precise clean.

I can see preferring triode for some things ......... I used to prefer the Tiny Terror in triode ....... but pentode and triode are fairly different sounding and most of the time I have liked pentode better.

But it's been years since I fooled around with this and I'm not sure which I'd like better these days so I guess I'll fire up the 6101 next week and fiddle with that.