Your Amp's Bias is Key to Getting Good Tone - Check it Frequently

If I was a touring musician, I would have my amp tech check the amp's bias before every gig. After a while, if you see it is fairly stable, cut back to once a week but for amp owners, check it at least every 3-6 months. I show you how simple it is to do in this video. It can make a huge difference in the way the amp sounds. Components and tubes drift over time so check to be sure everything is dialed in correctly. You'll be rewarded for it.
Also, for all you amp builders and modders, let me know what kind of results you get when you match the two 470 ohm screen resistors.
Weber Bias Calculator and Tube Bias Chart - elecurls.tripod.com/biascalc.htm
VHT Tube Tester and Bias Meter - www.stewmac.com/luthier-tools...
Eurotube's Bias Probe (two required, and two DMM's) - www.amazon.com/Eurotubes-Bias...
Nobsound Dual Bias Probe - www.amazon.com/Nobsound-Curre...
USA Made Dual Bias Probe - www.ebay.com/itm/Dual-Bias-te...

[@PeterDad60]

It's good to see your face as I have been tuning into your channel and heeding your advice for years. I purchased my new Fender '59 Bassman LTD. in November 25, 2019. I have spare tubes, a dual port bias probe with 2 needle style meters and and several multi meters. I am grateful for the bias port on my Bassman and also my Hot Rod DeVille III 410 purchased March 23, 2015. These are kind of similar amps as both are 4 x 10" speakers and similar wattage being powered by 2 of the 6L6 power tubes, which are similar to the 5881. Of course the Bassman still uses a 5AR4 rectifier tube which I prefer over the solid state rectifiers because the tube rectifier has the tube sag which I crave. I even use a Variac to control the voltage going into the amp. I use 110 and 120 VAC depending on the sound I'm going for. The Variac has a large rotary knob on top with a dial pointer than I align with the desired voltage. So changing the voltage takes all of several seconds.- Peter age 73

[@millstap]

Hey Peter. Thanks for watching. I need to practice what I preach and check mine soon. The last time I checked I think they had drifted apart quite a bit and I replaced one tune to match the other one better.

[@grantonian4142]

Great info as always.

[@barbmelle3136]

From LeoM: If it is drifting very much and very often, you have some resistors that need replaced. Those old compressed carbon resistors dry out and change. Just like the capacitors, nothing lasts forever.

[@millstap]

Thanks for this Barb. I’ve realized this and just this weekend I started replacing resistors in my 1963 Fender reverb unit because it was making noises. I am due to check the bias on this amp again. I replaced some resistors years ago but probably not all of them. My problem is I still go back with NOS carbon comp resistors if I have them but I have been ordering some newer carbon film resistors for my reverb unit. I hate the look of new resistors and if you use the wrong type, the amp can start to sound very sterile.

[@TheCleaner6969]

They had 2 different resistor values to bias the tubes to a closer match. More resistance on the higher mV to bring it down & closer to the lower one.

[@deandee8082]

cant you install on the amps that have no bias pot one of those rotary pots like on Lucille? just a click type pot that has a multitude of different caps each position, just load that rotary pot with pots in the same range or very close so you can run it hotter when you like, or colder, OR, dial it in as you say, maybe install bias meter that's always running or just plug in a VHT Tube Tester + Amp Bias Meter every so often as you say? click type pot to dial it back where you want if it drifts..

[@jpalberthoward9]

Both my Princeton and Tremolux make 6.3 on the filaments at 114.5 Small world. Tweeds are some of the finest products this country has ever produced. Leo Fender should have gotten the Nobel Prize.

[@millstap]

Exactly. Leo was a utilitarian genius. I guarantee these amp will be in service well into the end of this century and beyond if they don't figure out how to run everything on something other than electricity.

[@jpalberthoward9]

@@millstap I just hope they don't declare some kind of "green" war on tubes like they did on light bulbs, or blow up the Reflektor factory in Russia or do some kind of other demented thing to make the tubes extinct. So far as I know, the only uses they still have in the world are guitar amps, Hammond organs and Leslies, and super high end stereo. Now I see the younger folks looking towards simulators for all that stuff.

[@whimpypatrol5503]

Indeed, but the actual designer behind the original 1954 bassman 4x12 amp apparently wasn't Leo Fender himself but either an employee or steel guitar virtuoso.

[@sidewaysrain7609]

If those are your original power tubes I would swap out a set of matching tubes. Once biased that will fix your problem!

[@Rhythmicons]

Man it would be cool to hang out with you. I'm such a huge Hendrix fan and I've commented numerous times about my '64 6G6B. Thanks for this valuable information.

[@millstap]

Thank you for all of your comments. How is your Bassman doing? I haven't followed my own advice and checked the bias on this amp in some time. I think I will soon.

[@Rhythmicons]

@@millstap I got it in Sep 2019 and haven't had it serviced. I haven't opened the doghouse to look but everything with the exception of the tubes is all-original and dates to 1964 (transformers are '63). I'm the second owner. It's clean. The wood between the speakers that runs front to back is fragile though. Oxfords fart out a little bit when I run the Clavinet through it. I'm about to get it recapped and serviced but hesitant. Still has the 2-pronged plug. There's a guy I'm taking to that supposedly has a stellar reputation in the state but wants me to meet him at a gas station to hand it off. Paid 3200 for it.

[@JimmyDevere]

Thanks for the video Stan. Always great to start off the day with vintage amp work to take I ones mind off of everything else. I think I may try the mismatch tubes just to see what it it sounds like. I have the Alienist and it’s a great pedal. I may look at getting his wah too. I didn’t get the notification for the interview with Aaron. I hope I get this one. Maybe post a short video when you set the date and time. I usually get a notification when you post a video. There’s a couple questions I have regarding mods for the Alienist. If I send it in can he put a battery option in? Is there a easy way to correct the phase so it doesn’t reverse phase? I have had it happen a few times running dual amp wet/dry rig where it was an issue. Not too often though.

[@millstap]

I'm pretty sure the reason Dan didn't put a battery in the Alienist is because of space. I don't think it can be done without changing the enclosure but I will check with him. We are setting up the next interview with Dan. It should be great. His old drop-in kit is still my #1. It was the first time I ever bought a new wah after the Cry Baby I bought in the '80's. Interestingly, I recently put the old Cry Baby pot in my drop-in because the other one was getting too noisy. That old Cry Baby pot made it sound really good. I immediately started looking for some more of the old Allen Bradley pots but they are few and far between. The pot is key, I am finding. If I ever wear out this A/B pot. I will start a pot search because I didn't realize how much difference they make. There are so many options. I'm not sure what Dan is using now. He's been down the pot road a lot in his career and should be able to shed some light on the situation. On the phase issue, I would just get a good A/B box that has phase switches on it so you can change the phase of the amp with just the flip of a switch. Why do you need the battery option on the Alienist? Just curious.

[@JimmyDevere]

@@millstap Thanks for the info on the wah pot - that would be good info for a discussion with Dan. The phase is not that big of a deal. I do I have a Lehle psplit that has phase reverse but it's just one more thing I need to pack for rehearsals etc. Regarding the battery, and with the band I was in recently, I found myself simplifying things a lot to make it simpler for rehearsal and gig set ups. The last two shows we played it was really critical to get things up quick and fast. Not to mention save my back.... Anyways, I found myself wanting to take the alienst like I might just grab a fuzz or wah but I didn't want to have to bring a messy power supply.

[@JimmyDevere]

BTW, you have probably heard that Mike Fuller is closing shop.A lot of the guys who were passionate about vintage gear and recreating that are now reaching retirement. I hope people like Aaron, Greg G., Dan and all the other great custom builders of guitar gear find a way to pass on their knowledge and experience and not just let it go. With Fulltone, I was hoping one day to save up for a tape echo, but that doesn't look like it will be happening soon....

[@millstap]

@@JimmyDevere I understand. Taking one wall wart power supply shouldn't be too much to take. Do you have an individual Boss PSA? I know what you mean though. I got frustrated with my old power supply at one point because it was noisy and I dumped it for a time and just used Boss PSA's. What a tangled mess when you take 6 or 7 of them. Now I use some Boss's and a Strymon Ojai which is very quiet. The wah pots discussion is going to be a sensitive subject in my opinion because there doesn't seem to be a lot of great options out there that are vintage correct and sound right. Dan tried to get some custom built I think. He may talk about that. I was thinking of trying the Dunlop HotPotz II which I have seen on a few high end wahs lately.

[@JimmyDevere]

Gotcha regarding the sensitive subject. Will keep an eye out for the interview notification. Regarding power supply, my preference for playing is keep it simple and have a good base tone (guitar/amp). At home I’ll throw in a bunch of pedals but I’m always mixing it up and it’s a rat nest. 90% it’s just fuzz/wah and sometimes Alienist which is why a 9v option would be perfect.

[@garyeckel1656]

Marshall DSL40 I bought used at Guitar Center, just barked at me, way too hot, no matter what settings they all were unusable to my ears...bought a Celestion 65w Creamback still didnt help. so I tossed in a smaller pair of matched EL34`s and lowered the bios, its now playable Im going to tweek it some more but I was about to take this amp back. It made sound , it just sounded like a solid state on steroids.

[@samchipner1131]

Hi nice video but what you were pointing to for ground is a 6.3 vac heater😊

[@millstap]

Actually I was pointing at the bare braided wire that goes to the chassis ground but no biggy.

[@djesus8307]

no need for the Weber board ! (5881 heat dissipation tubes 26w triode connection) 26/436x0.7=0.04174 multiply by 1000 to move the comma to the right place (0.04174x1000=41.74). For your bassman 26/434x0.7=0.04193 x1000=41.93 it works with all tubes if you are aware of their thermal disipation. Be aware that the 5f6a and a pentode amp and therefore the 5881 lamps must not exceed 23w of heat dissipation (37.09ma for 434v @70%)

[@Electrondivize]

I see you have not replaced the old selinium bios diode will help.

[@millstap]

Yes, I should probably change that. I do have some good diodes. I just need to figure out how best to do it.

[@DemonKingOFFICIAL]

It was the bias. The screen grid resistors shouldn’t change the sound that much. I have a Peavey Valveking that I use as a modding / tinkering platform, and at one point in time, I just took them off of the screens in general… simply to see how they affected sound. I couldn’t tell much of a difference without them.

[@mikegLXIVMM]

Is that selenium rectifier being used?

[@millstap]

Yes.

[@monroegadoury384]

⭐ 𝙥𝙧𝙤𝙢𝙤𝙨𝙢

[@toneswithtommyrobbie450]

Your fulltone pedals are gold bricks check reverb prices its ridiculous

[@Ottophil]

Thats cause fullers a dork. I thru mine in the trash.

[@UnremarkableMarx]

@@Ottophil boo hoo. Fuller ran a good USA business, said the wrong thing, got unnecesary flack, retired. Dorky, but who cares. I rescpect that guy