6L6's in Triode?

[leadfootdriver]

This is the amp. A Jet City JCA5012C. It's fixed bias. I have it a 70% in the pic.



If I run this 50 watt amp in Triode, what would the power output be? Also, what about longevity? I could use a heavy duty DPDT switch to do it as I did this to a Crate V30 some years ago. I also put a huge OT transformer on it. That amp was stupid loud for 30 watts.. But I digress...







The reason I thought about putting the JCA in Triode is because it's a 112 combo so there's no freq cancellation from additional speakers, and the EQ is pretty strong. I'm thinking that the Triode wiring might tame the harshness a bit. What do you think?

[Leo_Gnardo]

If I run this 50 watt amp in Triode, what would the power output be? Also, what about longevity? - - - snip - - - I'm thinking that the Triode wiring might tame the harshness a bit. What do you think?

I've put in lots of triode switches - you lose half to two-thirds of the power. Amps often start clipping well before the manufacturer's claimed power. Would be a fair guess that yours will clip @ 40W. So in triode, you'll be seeing 15-20 watts at clip. Hard to predict in advance but what's a couple watts among friends? Can't say I've seen tube longevity suffer by triode operation. Also expect a noticeable rolloff in high frequencies - yes it should tame the harshness. Short of putting the switch in, just wire it triode, should take 5 minutes, & give it a play. You might want to keep it that way, and you can decide to put in a switch after evaluating the triode tone.

[Chuck H]

Should tame harshness and reduce output (like Leo said). I just wanted to add that IMHO 15-20W is exactly the right amount if you plan to get the amp clipping in a live setting. The switch might be a good idea if you gig though. 15-20W won't carry a clean tone in a club on it's own. No way, no how.

[The Dude]

Well,.....that depends on how big the club's sound system and monitor rig is. I've done it plenty of times.

[Chuck H]

Well,.....that depends on how big the club's sound system and monitor rig is. I've done it plenty of times.

I've never been happy with the clean volume of even a DR type amp for a rock set in average sized clubs (say occ. 150- 200ish). It was a finite statement though, wasn't it? It depends on a lot of things, yes. Still, if you work clubs in a way where the amp needs to hold it's own I think most would agree that a 15-20W amp is too small.

[The Dude]

I don't disagree with your statement as a generalization. Spot on. I only piped in because, depending on the OP's particular situation, it may or may not work.

[Chuck H]

Sure! Sometimes a guy only has one or two regular gigs and they don't even want anything different. For about a year in my life when I 'wasn't gigging' I played a coffee house of similar occ. with a Champ style amp Great fun and lots of good joe.

[leadfootdriver]

Thanks for the replies! I'll definitely need to jumper the tubes out and see how it sounds.

I'm not sure what the stock screen resistors are at the moment, but what would be the minimum value I should use when I connect them to the plates? I assume I can just use whatever the amp came with tho.

[Leo_Gnardo]

I'm not sure what the stock screen resistors are at the moment, but what would be the minimum value I should use when I connect them to the plates? I assume I can just use whatever the amp came with tho.

Screen resistors are typically 470R in Fenders, 1K in Marshalls. Sure, start with whatever the amp has, as long as they're not roasted and out of spec. You can increase the value, which tends to reduce the amount of power the amp can produce. If you have enough time & patience & resistors you can select a value that will make your ears happy. I generally use 5W rated resistors. Some folks use lower power R's, perhaps in a bid to have the R act as a fuse should the grid go short circuit. And it does happen, just the day before yesterday for me.

[leadfootdriver]

Cool then..

BTW, do you guys prefer an EL34L in triode over a 6l6? I'll need to try that as well!

[leadfootdriver]

So, its kinda mushy like i remembered. I thought the fixed bias might keep it intact but not really.

But what about removing the negative feedback in triode?

[Chuck H]

So, its kinda mushy like i remembered. I thought the fixed bias might keep it intact but not really.

But what about removing the negative feedback in triode?

Probably a good idea on one front. IIRC the use of NFB reduces the ideal plate load. So does operating the tubes as triodes. So I should think that lifting the NFB could improve load matching in already less than ideal circumstances. OTOH, the NFB circuit is there to reduce distortions. Some of which can make the tone mushy. So by lifting the NFB this could be exacerbated. Then I've also read that once an amp is clipping hard the effectiveness of NFB is greatly reduced. The way it stands I'd say there's no harm in trying it.

[leadfootdriver]

I listened back today, and the Triode isn't really that bad. It's just a little bit looser. I lifted the NFB, and you get the volume back you lost when going Triode. But you're limited to the treble pot for highend adjustment. I haven't made my mind up about that yet. But I do like the more open and raggedness of the tone.

BTW, do you guys think a switch rated for 5 amps @ 120V or 2 amps @ 240V will be safe enough for a Triode switch?

[pdf64]

As there's significant Vdc, the switch should have a fast switching action.

[Leo_Gnardo]

BTW, do you guys think a switch rated for 5 amps @ 120V or 2 amps @ 240V will be safe enough for a Triode switch?

I use the biggest dam' Carling toggle I can find, rated 15-20A. Wouldn't use any mini switch here. What worries me is possibility of arcing to ground inside the switch. Breakdown voltage of air under "ideal conditions" zero humidity at sea level pressure is 8000V per inch. So 500V in a tube amp supply could jump 1/16 inch, and that's under the best conditions. Derate for humidity and altitude - better have lots o space inside the switch, between the electrodes and frame.

If anybody has a better switch suggestion I'd sure like to hear it, TIA!

leadfoot, I'm glad you're diggin' the triode tone. That's one thing I haven't tried yet, removing the feedback, thanks Chuck for that idea.