6V6 in triode mode - big hum and blue glow

[octal]

The reason the amp is humming is that the screen grids are now connected to a node (the plate b+) with less filtering. When they were connected to the screen b+ node, they had an extra stage of R-C or L-C filtering. Remember, the screen grid is an input, just like the control grid, only less sensitive. You need to add extra filtering to the power supply if you're going to run in triode mode.

[Chuck H]

I agree with octal. If it's "two Champs in one chassis with a shared PSU", are you using a rectifier tube? If yes you may not want to add resistance to the power supply because the amp may get too squishy. But if you're not using a rectifier tube you could incorporate a Pi filter as the first supply node. You could also bump filter values up a bit. If you're using a sag resistor to simulate a rectifier tube you can just increase it's value a little and hang a filter (maybe 47uf) on the input side of that resistor.

[octal]

It also occurs to me that the bias point might shift if you run the screens at the same voltage as the plates. (i.e. triode mode, versus a lower voltage screen node.) If the bias goes hotter, the PS will produce more ripple under the heavier load. Do I have that right?

[Chuck H]

It probably balances out because the ideal load impedance decreases considerably in triode mode. I can't give particulars but this is what I read in my J.L. Hood book. Since the tubes stress less into a higher impedance it may balance the difference.

[Alan0354]

Just very hard for me to envision a Champ is too loud for a live gig. Something is really wrong with this picture.

Amp does not sound good in triode mode. Or else, why doesn't more amps doing that? My Marshall have a switch, it's loss all the Ooops switching to triode mode. I tried this on the Fender Prosonic, same thing. Get an attenuator.

[Chuck H]

Add me to the attenuator advocates. If you like the amp in normal, pentode (beam tetrode) operation, an attenuator is probably the best way to get that tone at a lower volume. Since your amp is stereo I suppose you'll need two attenuators. Here's a simple design that's cheap to build and sounds good. There is some notable tonal alteration at extreme attenuation, but this is true of any device.

If your amp has 4 ohm outputs simply half the resistance values. I use those aluminum cased resistors that mount to a chassis (implied in the diagram).

[soundguruman]

Just very hard for me to envision a Champ is too loud for a live gig. Something is really wrong with this picture.

Amp does not sound good in triode mode. Or else, why doesn't more amps doing that? My Marshall have a switch, it's loss all the Ooops switching to triode mode. I tried this on the Fender Prosonic, same thing. Get an attenuator.

Well, the reason it hums is that the screen grid supply is probably still connected....minor problem

Marshall is running amps in triode...sounds perfectly good.
Mesa is running in triode...sounds good.
Changed a Fender Supersonic 60 to triode, and it's the best Supersonic I ever heard....way better as a matter fact. (from standpoint of guitar player anyway...)
Changed a Hiwatt 100 to triode, no complaints and the owner loves it.
Changed a JCM 45 Combo to triode, and it sounded great.

"Amp does not sound good in triode mode...
" Well, a lot of players would probably disagree with that.
Most of the owners of these amps keep them in triode 100% of the time.

"Or else, why doesn't more amps doing that?"
Half the tube amps on the market are doing that, FYI. Perhaps you should pay more attention.
Everything from Seymour Duncan to JCM 900 are running triode...because it WORKS.

For small venues you get a better sound at a lower volume, and that's what we achieved.


Attenuator is OK too, but the more you attenuate -- the more tone of the amp is being lost.
So combination of Triode, a little attenuator, less efficient speaker, etc... can help achieve a better tone at small venue volume level.

It's ALWAYS a compromise. There is no perfect method.
BUT I guess you would have to be a musician to understand this....Which most technicians ARE NOT.

Triode is EASY, quick, cheap and very effective method.
Since I am established guitar player, I can verify that there is NOTHING wrong with this method.

I have no complaint about the sound quality. And none of the musicians complained about it either.
Rather, it was the opposite. They all liked it, a lot.

Just changed a 1959 100W plexi reissue to triode. It grinds like a chainsaw. But it's not blasting me out of the room either.
Once again, no complaints. I would play it, no problem.

[Dave H]

Could you use one of these, it's stereo?

High Power In-wall Stereo Volume Control

[walkman]

I have a friend who puts his screaming Marshall 4x12 cab and a microphone out in his van, and runs cables back in to the stage.

Strikes me as a kind of spinal tap thing to do. Reminds me of the work of Douglas Adams

"Disaster Area was a plutonium rock band from the Gagrakacka Mind Zones and was generally regarded as not only the loudest rock band in the Galaxy, but also as being the loudest noise of any kind at all.

Regular concert goers judged that the best sound balance was usually to be heard from within large concrete bunkers some thirty-seven miles away from the stage, whilst the musicians themselves played their instruments by remote control from within a heavily insulated spaceship which stayed in orbit around the planet - or more frequently around a completely different planet.

Their songs are on the whole very simple and mostly follow the familiar theme of boy-being meets girl-being beneath silvery moon, which then explodes for no adequately explored reason.

Many worlds have now banned their act altogether, sometimes for artistic reasons, but most commonly because the band's public address system contravenes local strategic arms limitations treaties."

Now I can say the reason that I play at home is that my amp is just way to loud to actually put in the venue. All I need is a extremely impossible low latency 3G/4G connection from my guitar to my amp and recording setup at home and i'm ready to rock anywhere!

This is where amp modelers may be a simpler approach

[Jot]

The guitar player in my band uses is a Deluxe and was always too loud. I finally convinced him to turn the amp around to face the back wall at the clubs we play, and now everyone's happy---not only is the sound less piercing, he can hear himself better now with the sound reflecting off the wall and so he plays at lower volume.

[Chuck H]

I use my attenuator because it's the least bad compromise. I hate playing quiet. The guitar and amp don't interact. Acoustic properties change for the worse. Very uninspiring. How much better to practice at band level so you actually know what the guitar and amp will do at a show? BUT... We need to keep the peace. And practicing with an attenuator is better than not practicing. Playing quiet... BLEH.!. I'd rather grate my shins with a salted hoof rasp.

[gui_tarzan]

Maybe dispersing the sound from the speaker up/down/sideways instead of directly facing the audience would help with the volume issue? I know it makes a difference to my ears when it's an amp with a bite. I had both eardrums burst at the same time about ten years ago and that affected my sensitivity to higher frequencies and how much actual sound pressure I can take.

We've tried side-washing, reversing (pointing at us from the front) and tipping the cabinets back so they shoot upward instead of out front. There are a lot of things you can do to help with volume issues aside from re-vamping the circuit.

[gui_tarzan]

Grrrrr.... double post.