HawkeyeKane
2220 posts
Dec 18, 2013
9:22 AM
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I just read somewhere that it's possible to run a 6L6/5881 or EL34 in a Special 6 without performing any mods to the amp. I know you can run an EL84 by way of socket adapter, but a 6L6 type tube? How is that doable? In my mind, it seems like that would burn something up!
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Hawkeye Kane
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Kingley
3320 posts
Dec 18, 2013
9:41 AM
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Yes apparently you can run a 6L6 without any mods and without any detrimental effect to the circuit, but only in the head version. In the combo version there isn't room to fit a 6L6 in due to the speaker. How it's doable is beyond my technical knowledge, I'm sure someone like Mark Burness can explain the details of how.
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HawkeyeKane
2221 posts
Dec 18, 2013
9:52 AM
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Funny...VHT's site and manuals don't say anything about it. The Special 12/20 boasts about it, but they also have a voltage switch installed to go from the 12W max for 6V6's and EL84's to the 20W max for 6L6's and EL34's.
What would that do to the Special 6's output rating I wonder? Would it be like the LW 6L6SE or the Fender Ramparte and kick it up to around 10 or 12 watts? The OT on the Special 6 certainly looks beefy enough to accomodate the extra from the 6L6.
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Hawkeye Kane
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5F6H
1720 posts
Dec 18, 2013
10:54 AM
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When you put a 6L6/EL34 in an amp running a 6V6, the bigger tube draws more heater current, this will pull down the voltage on the plate & power. The bigger tube will draw more plate current, also pulling down plate voltage. So there's a degree of swings and roundabouts.
Usually, you get a change in tone, rather than noticable hikes in power, unless you have some way of correcting the plate voltage (you don't in the VHT).
A lot of transformers in Champ style amps are over engineered (2A heater current rating), so as long as they can take the hike in heater current you are OK (e.g. a Champ PT is also used in a 2x6V6 Princeton, so we know it can take twice the heater current of 1x6V6 & 1x12AX7 - an EL34 would need further mods to the wiring in any Fender), but check with manufacturers first.
The bigger plate current draw of 6L6/5881/EL34 means you also get more cathode voltage, so the power tube cathode resistor & bypass cap often need uprating accordingly...but it depends on what plate voltage & ratings the parts start with.
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Last Edited by 5F6H on Dec 18, 2013 10:56 AM
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HawkeyeKane
2222 posts
Dec 18, 2013
12:26 PM
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Interesting. Would a KT66 also be an option?
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Hawkeye Kane
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HarpNinja
3649 posts
Dec 18, 2013
12:40 PM
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I always had a 5881 one in mine.
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5F6H
1721 posts
Dec 18, 2013
1:14 PM
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"Interesting. Would a KT66 also be an option?" If the amp has a 1K screen grid resistor (which it would also need for a EL34)...I can't access the VHT schem from this computer. I run a JJ KT66 in my modded champ, there isn't a whole bunch of reliable choices in that tube type though. The new Tung Sol KT66 is a 6L6 in a big bottle & has same specs as 6L6 so probably the safer bet.
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5F6H
1722 posts
Dec 19, 2013
1:34 AM
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Just checked the schem & the Special 6 has a 470ohm screen grid resistor, not suitable for a true KT66 (OK for the new Tung Sol) not a great idea for EL34.
2W power tube cathode resistor is borderline for a 5881/6L6/EL34 etc...you'll probably get away with it for a while but a 5W resistor would really be best if sticking with a big tube.
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HawkeyeKane
2223 posts
Dec 19, 2013
12:21 PM
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In theory, I suppose someone could rig a 5W cath resistor alongside the 2W, and a toggle switch to alternate between the two for swapping between 6V6 and 6L6....
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Hawkeye Kane
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MJ
656 posts
Dec 19, 2013
12:44 PM
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I don't believe it would do any harm to run the 6V6 with the 5W resistor, no need for a toggle. I have a couple of my 5F1s set up with higher values for 6L6 and run the 6V6 without a hitch.
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HawkeyeKane
2224 posts
Dec 19, 2013
12:54 PM
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@ MJ
No noticeable reduction in output running a 6V6 with the 5W resistor?
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Hawkeye Kane
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arnenym
245 posts
Dec 19, 2013
12:55 PM
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I have a toggle and a 560 ohm 5W beside the original 470 ohm 2 w resistor. I have 470/2W for 6V6 but mostly go for a 6L6 and 255 ohm and watts enough.
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SuperBee
1588 posts
Dec 19, 2013
4:15 PM
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I'm interested in this concept, since Arne mentioned swapping a 6L6 into my 6V6 valve junior.
So this is primarily a change in tonal character?
I'm going to demo my 6V6 vj to a guitarist friend. I'm thinking if he likes it he may be interested in having me build one for him. If I was to mention the 6L6 option it may be more interesting to him, as his other amps run these tubes also. But how would you characterise the difference between 6v6/6L6?
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HawkeyeKane
2225 posts
Dec 19, 2013
5:18 PM
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@SuperBee
If your guitarist friend likes it, you could also make mention to him that he could run the original EL84 in it by way of a YellowJacket socket adapter. Even MORE versatility!
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Hawkeye Kane
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