Tube amp maintenance questions

[Yooper]

For the standby, my Boogie DC-5 manual says, "Perfect for set breaks..."

[Guest HRB853370]

Another question: Why do some small amps (e.g. Champs, Princetons, Blues Jr., etc) NOT have a Standby Switch?

Same thing for the Delta Blues, no standby switch. I was told once that it depends on the circuit whether or not it has the SB switch. I am not complaining, one less thing to deal with on that amp.

[Guest HRB853370]

Should make this a sticky..

 

What the hells a sticky? Is there another name for it?

 

Should be pinned somewhere.

I am gonna pin it on my lapel.

[bolero]

Another question: Why do some small amps (e.g. Champs, Princetons, Blues Jr., etc) NOT have a Standby Switch?

 

they might have a tube rectumfrier, which means it may not need a standby

 

also those were budget amps, maybe they wanted to save some $$ on production, by using less inventory?

[HANGAR18]

I turn the power switch on when I plug in the power cord, and then wait till everything else is setup to

turn on the standby switch. Soon as I'm done playing, I turn the standby switch off. When I'm ready to

slip the cover on my amp for loadout I turn the power switch off.

 

This ^^^^^

[HANGAR18]

Has anyone mentioned having the BIAS adjustment checked periodically?

[Yooper]

 

BIAS adjustment

 

Another Mesa Boogie advantage. No bias adjustment required.

[MartyGrass]

Has anyone mentioned having the BIAS adjustment checked periodically?

 

You just did! What do you suggest? I've never had that done before.

[RhoadsScholar]

I use the standby switch when I switch guitars so as not to pass a harsh sound of plugging/unplugging the guitar into the speakers. Other than that, I just turn the amp on and off.

[Kuz]

Has anyone mentioned having the BIAS adjustment checked periodically?

 

Yep, sure do. Again, this will probably bring the "I can't hear a difference anyhow" statements.... but there is a bias sweet spot based on how hot you are running the power tubes. Too cold and the amp sounds bland, too hot and you are burning up tubes and could have an issue with possible damage/malfunction/ect.

 

here is the formula:

 

(how hot you want the tubes to run ; 50% usually is cool to 70% which is hot) times the tube wattage rating divided by measured volts the amp is running = the milliamps you should bias your amp.

.65 (65%) X 25watts / 425 vols = .038xxx thus 38mAmps

[Guest HRB853370]

 

You just did! What do you suggest? I've never had that done before.

Likewise PV amps. FIxed bias is the way to go.

[Billgelder]

I use the standby switch when I switch guitars so as not to pass a harsh sound of plugging/unplugging the guitar into the speakers. Other than that, I just turn the amp on and off.

If you had one (or two) of Steiner's cords you would not have to turn the standby off when changing guitars.

[111518]

A lot of modern amps make bias adjustment much easier than it once was by putting probe points and micro-pots on the rear panel. If you have to go into an amp to do this, be careful --pcb or p to p, there are some wicked exposed voltages in there, potentially stored in caps even if the amp is off, and the amp has to be running to set the bias.

 

What I'm doing, and would suggest, is that each time I have an amp serviced, I pay the repair guy to take me through the biasing process for that amp --how to get to the pots, easiest way to get to measurement points, where the danger points are. Then, the next time, I at least have a sense of what's involved and can do it myself if it is reasonably easy and safe, or make an informed judgement to let the expert do it. Some techs --including the guy I work with-- actually make their own settings with an oscilloscope --an expensive investment if you are only doing occasional adjustments. However, he shows me how to get close with a multimeter.

[MartyGrass]

Here's how do the bias adjustment.

 

Yes, boys and girls, someone will get hurt doing this. That adds to the excitement.

 

Note the teacher discusses keeping one hand in the pocket at all times when in the amp but doesn't do it. I'm sure I'm the same way when I get comfortable around danger.

 

 

 

 

[JeffB]

I put a bias kit in my Mesa. Im still alive and so is the amp.

For me it was a worthwhile upgrade. Mesa are biased to cold and it affects the way it breaks up the way I run it.

Thats one of my concessions to tube voodoo. They have to be biased right.

EL34 amps in particular to my ears.

[HANGAR18]

 

You just did! What do you suggest? I've never had that done before.

 

Yep, what they said. If the bias isn't right, it can shorten the life of your equipment. Depending on how your amp is built, it can be very dangerous (deadly) but some of the newer amps have easy access to the adjustment screw (or whatever it is). There are a number of videos on youtube on the subject. Watch many of them if you are going to try it yourself or else just have a professional amp service technician do it for you. A service manual for your particular amp ought to mention the range it ought to be operating within. Stay safe!

[bobmeyrick]

Can't remember where I encountered this analogy, but biasing was compared to setting the correct mixture on a carburettor. My hifi power amp (a conrad-johnson MV55) has a very user-friendly way of biasing the output valves - each one has a trim pot and associated LED. Adjust the trim pot so the LED is off and the valve is correctly biased. The trim pots are easily accessed through holes in the case with a long thin screwdriver (supplied with the amp). A great sounding amp! (I'm listening to BBC Radio 3's "Jazz on 3" as I type this, with a live recording of the Wayne Shorter Quartet from this year's London Jazz Festival... )

[TalismanRich]

If you had one (or two) of Steiner's cords you would not have to turn the standby off when changing guitars.

 

RIght you are Bill! They take care of all the buzzing and screaching.

[TalismanRich]

I had to set the bias on my DSL401 and its a royal PITA! You have to remove the whole chassis, lay the thing out on the back of the cabinet and find the small plug and pot on the circuit board.Luckily I had a spare connector to hook up so I could run a pair of wires away from the plug for hooking up the meter. Theres no way you can safely get a meter probe onto those little pins.

 

 

On the other hand, the Patriot has the bias points on the back of the chassis, ready for the probes to go in, plus the trim pot right there. That's the way it should be if you have to bias an amp.

[Guest HRB853370]

Here's how do the bias adjustment.

 

Yes, boys and girls, someone will get hurt doing this. That adds to the excitement.

 

Note the teacher discusses keeping one hand in the pocket at all times when in the amp but doesn't do it. I'm sure I'm the same way when I get comfortable around danger.

 

 

 

 

I used to keep one hand in the pocket all the time but then I was accused of doing something kind of perverted.

[peterbright]

Too Funny. I have the probes and have set the bias on a number of amps when changing tubes. You can bias hot (more output/shorter life) or cold (less output/longer life). Sometimes the diassembly/reassembly is more difficlult than it needs to be. It's still nice to be able to do it yourself.

[Kuz]

Guys, not many people bias with the probes anymore. Weber makes an affordable Bias-Rite meter where the power tubes fit in the Weber meter coupler. The coupler & power tubes are then plugged in the tube sockets. You fire your amp up, let it warm up, turn on the meter and read the Volts & mAmps of the tubes. If you have an external bias pot outside of the chassis, then you don't even have to open the chassis to bias your amp.

 

The Weber Bias-Rite meter cost between $125-175 and has at least paid for itself 10-15x over that. I can safely bias my amp and no cost from a tech required. Mike, is obviously capable of using the pin method, but he uses the easier Weber Bias Rite meter.

 

Link...

 

https://taweber.powweb.com/biasrite/br_page.htm

[t0aj15]

My newest amp eliminates all that hassle. Not only is it self biasing, but it also has a biasing circuit I've yet to see on another amp. This circuit checks and sets the bias for each of the four output tubes every time the amp is turned on so that even non matched tubes can be paired just as long as they are 6L6's. Furthermore there is a selection switch that allows you to choose hot/normal/cool biasing to suit your particular style. That coupled with the loose/normal/tight damping switch put this amp well ahead of the pack IMO and figured prominently in my choosing this amp over others I was considering.

[MartyGrass]

My newest amp eliminates all that hassle. Not only is it self biasing, but it also has a biasing circuit I've yet to see on another amp. This circuit checks and sets the bias for each of the four output tubes every time the amp is turned on so that even non matched tubes can be paired just as long as they are 6L6's. Furthermore there is a selection switch that allows you to choose hot/normal/cool biasing to suit your particular style. That coupled with the loose/normal/tight damping switch put this amp well ahead of the pack IMO and figured prominently in my choosing this amp over others I was considering.

 

 

Wow. If that amp was any smarter it would be solid state!

[H]

My newest amp eliminates all that hassle. Not only is it self biasing, but it also has a biasing circuit I've yet to see on another amp. This circuit checks and sets the bias for each of the four output tubes every time the amp is turned on so that even non matched tubes can be paired just as long as they are 6L6's. Furthermore there is a selection switch that allows you to choose hot/normal/cool biasing to suit your particular style. That coupled with the loose/normal/tight damping switch put this amp well ahead of the pack IMO and figured prominently in my choosing this amp over others I was considering.

That sounds like the Orange Divo bias circuitry. Is your new amp an Orange?

 

It's available as an aftermarket kit also: https://www.orangeamps.com/products/accessories/amplifier-management/divo-ov4/