Tube amps!

[moto fugazzi]

MESA Boogie Bass here. 6 6L6GC just enough to keep up with you screaming guitar types.

The Mesa Boogie 400 is an amazing bass amp. Well done, Sir!

[GuzziMoto]

I do like Mesa Boogie amps. My Subway Rocket Reverb is small but loud with great tone. I have an old 80's Kramer and a 90's Schecter with a solid quilted maple top and birds eye neck.

If only I was any good.........

[docc]

I do like Mesa Boogie amps. My Subway Rocket Reverb is small but loud with great tone. I have an old 80's Kramer and a 90's Schecter with a solid quilted maple top and birds eye neck.

If only I was any good.........

 

It's a little chilly, now, here in The Den. But those 6L6 outputs heat up to some serious temps. Should I worry that one of them gets to some 325ºF?

 

Seems pretty cozy to me!

[Trevini]

As long as they're not red plating you should be ok.  If they are, it could be a bias issue.  At the last valve change, was the amp rebiased to match the new valves?

[moto fugazzi]

 

I do like Mesa Boogie amps. My Subway Rocket Reverb is small but loud with great tone. I have an old 80's Kramer and a 90's Schecter with a solid quilted maple top and birds eye neck.

If only I was any good.........

 

It's a little chilly, now, here in The Den. But those 6L6 outputs heat up to some serious temps. Should I worry that one of them gets to some 325ºF?

 

Seems pretty cozy to me!

 

Docc, is it red plating? Just one of the tubes gets to 325f? What's the temp on the others? What happens if you swap the tubes around?

Ken

[docc]

This is a new experience for me! How would I know of the "red plating?" Is it visible on the glass like "silvering" on a light bulb?

 

Seems like the other output tube was ~275ºF, but I'll recheck it in a few minutes after it warms up.

 

I understand this second gen Bassman RI, has a bias adjustment, but I don't know where it is or how to set it . . .

 

If it had a TPS and a tight tappet, I'd be all in!

[docc]

The Fender's been on for a little over an hour, played it some in that time at about 1/4 volume and the output tube temps look almost identical (~340ºF)

 

I do have an owner's manual, so can look at the bias control (the manual is not very informative) and read further on the "red-plating" business.

 

Thanks, gents!

[Zooter]

Red plating is when the big metal bits inside get red hot. I have only seen pictures. ( The heater filament glows orange in the bottom, normal ) After a while a red plating tube will fail and often pop resistors supplying the plates. The tube may be fine with a tuneup of the bias.

[Trevini]

Docc  This is a pretty good site for sorting out valve amp issues  For info on biasing, click on the link to tube amp FAQ in this link     You'll need to make up a tool to check the bias on your amp and any others that aren't fixed bias.

 

BEFORE doing any work at all inside a valve amp, make sure the electrolytic capacitors have been drained as they can hold lethal voltages.  You can make up a tool to drain them using a wooden chopstick (do not use a graphite pencil under any circumstances), a short length of wire, crocodile clip and a 220k 1w resistor. Solder one end of the resistor to the wire with a crocodile clip on the end. tape or heatshrink the resistor/wire assembly to the chopstick so the end of the resistor not connected to the wire is at the sharp end of the chopstick. without touching any bare wiring on your tool (you shouldn't have any), connect the croc clip to earth and hold the chopstick end against the positive side of the first electrolytic capacitor  on the power supply circuit (it'll be the one nearest to the mains transformer/rectifier. measure the dc voltage across the cap.  Fully charged, it'll be in the 300-450v range. once it gets below 10, you're ok to work on the amp. 

 

You'll obviously have to have the power connected and the amp switched on to check the bias, but most amps with adjustable bias have a socket to do it and don't require the amp to expose any live wiring.  Have a good read of the articles in the above links. All interesting reading.

 

edited to add links.

[moto fugazzi]

Here's a vid on how to bias a HR Deluxe, and yours should be very similar. 

 

Chances are your amp is fine, and you won't need to do anything. If the tubes are about the same temp, they're most likely matched (especially if they're the factory tubes). If you replaced the tubes at any time, you will need to bias them if it hasn't been done already. And like Trevini mentioned: Be very careful around those caps!

 

Just think of the bias pot as your TPS, and you'll do just fine. 

Ken

[docc]

Thanks again, guys! Looks like I've got some studying-up to get on with!

 

As soon as I can put this guitar down . . .

[al_roethlisberger]

Used to have some Ampeg tube heads, now have a variety of 1950s mono Fisher and Magnavox consoles and components I tinker with.

 

I recently restored a Fisher FM-50 early FM receiver and 30a amplifier, both mono.

 

I have a late 50s Fisher Philharmonic, "mostly" mono console, which has a stereo phono, and supports stereo FM with an outboard FM tube multiplexer.  

 

Fun stuff

[Kiwi_Roy]

Not a player or an audiophile for that matter but I am a pretty big music nerd. You guys know anything about vintage/tube receivers?

Back when I was growing up we had lots of 6 Volt radios, previously much of the area didn't have power so you took your 6 Volt battery up to the local garage every few days for re-charging.

They had a vibrator to generate the high Voltage and tubes (we called them Valves) had a directly heated filament, they would start from cold almost as quick as a transistor radio and had great tone.

[Kiwi_Roy]

BEFORE doing any work at all inside a valve amp, make sure the electrolytic capacitors have been drained as they can hold lethal voltages.  You can make up a tool to drain them using a wooden chopstick (do not use a graphite pencil under any circumstances), a short length of wire, crocodile clip and a 220k 1w resistor. Solder one end of the resistor to the wire with a crocodile clip on the end. tape or heatshrink the resistor/wire assembly to the chopstick so the end of the resistor not connected to the wire is at the sharp end of the chopstick. without touching any bare wiring on your tool (you shouldn't have any), connect the croc clip to earth and hold the chopstick end against the positive side of the first electrolytic capacitor  on the power supply circuit (it'll be the one nearest to the mains transformer/rectifier. measure the dc voltage across the cap.  Fully charged, it'll be in the 300-450v range. once it gets below 10, you're ok to work on the amp. 

 

Now you've taken all the fun out of it

[Trevini]

I can charge a capacitor up and post to you if you like, that'll be fun lol