Wiring 6L6's

[Tdale]

I noticed on Normster's(?) layout, that the 1 ohm resistors that go from lug 8, also connect to lug 1, which is not used on 6L6 tubes. However, on EL34, lug 1 is used for a grid, that looks like the one that is internallyl connected to lug 8 of a 6L6

Does connecting lug 8 and 1 mean that I can use EL34 tubes also? Or isn't it as simple as that?

By the way, I checked my 1 ohm resistors, and I found some 3W Vishay-Dale resistors that measure 1.5 ohm. I checked my meter, and it turns out that it shows 0.5 ohm when the probes touch, so it seems like the resistors are dead on!

I also paralelled two 1K resistors for the control grid, which gives me 500K, which is the same as most Fenders use...so I should be good?



Tommy

[Bob-I]

Sounds like you're in need of a new meter. You'll have to measure mv range to bias the amp so if it's not calibrated well you could have problems.

[Icetech]

Tdale, if 1 and 8 are connected you should be good to go on el34's.. that was the only mod i did on mine and rebias'd and they been running for a week..

I am barely able to build things though.. so double check.. but according to the torres book also, which is what i followed and it worked fine for me:)

[mhuss]

The "spare" pin to use on octals (for screen Rs, etc.) is 6. This is N/C on 6V6, 5881/6L6/KT66, EL34, and 6550/KT88.

Also, it' s safe to connect pin 1&8 on all of these (and somewhat necessary for the EL34 )

--mark h

[Tdale]

Yes, I used pin 6 for the screen resistors.

Cool that I can try EL34 too, without doing anything else but bias..

Tommy

[Luthierwnc]

Hi Tommy,

I agree with the other replies and would add that Fender amps usually use pin 1 as a tie point for the grid stopper resistor and pin 6 as the tie point for the screen resistor. Pin 8 is the cathode on a 6L6 but it is internally wired to the supression grid so pin 1 is unused. On an EL34, pin 1 is the suppression grid which is why you have to do it at the socket.

You can use an EL34 if 8 and 1 are together as far as the socket goes but the bias control might be out of the useable range. Be prepared to change resistors to get the current in the sweet spot.
For screen (control) resistors I have always used 1k for the 40+ watt amps. Usually sandbox 5 watters but sometimes more boutique types. They will get a little warm.

There's another safety feature I haven't seen posted here. A lot of homebrewers use metal oxide varisters (MOV) on the wall input in the event of voltage spikes. In the US we use a 130 volt MOV most of the time. You would need one to suit Norwegian voltage. I've never had mine shunt but a friend did a gig on a yacht and it saved his amp when the generator got frisky. The bass player wasn't so lucky.

FWIW, Skip

[Pete]

I also paralelled two 1K resistors for the control grid, which gives me 500K, which is the same as most Fenders use...so I should be good?

I think most fender amps (and/or schems of) I have seen are 470 ohm (though 500 would be close enough, no?).

[jaysg]

Cool that I can try EL34 too, without doing anything else but bias..

As long as the filament supply can handle an extra 0.6A per octal....6L6 0.9A....EL-34 1.5A

[Tdale]

Normally I run a pair of wires to each tube for heaters. This time I did it the "normal way" running wires from tube to tube. I use 1mm diameter wire..I think that's about 18 gage... Is that enough for two 6l6 and three 12AX7... ? all tubes are about 2A together, aren't they?

Tommy

[Zippy]

You only need to run the heavier gage wires to the output tubes. The current to the remaining tubes, as you have noted, is sufficiently low that many builders only use 22 AWG wire for the preamp tubes.

[Tdale]

I ran the wires directely from the transformer to the first power tube. Then I used 18gage to the next power tube, and on to the three preamp tubes....

Should the power tubes have one set of wires, and the preamp a different set, or will it work to use heavy wire for the power tubes, and then just keep wiring from second power tube to the preamp tubes?

Tommy

[Zippy]

Yes, heavy gage to the power tubes then from there to the adjacent preamp t
tubes using the lighter gage.

(Yes, Funk', I had a brain fart. I apologize for thinking of something else whilst typing.)

[Funkalicousgroove]

Zippy,
Why would you rectify your heater voltage?? I mean DC heaters on PReamp tubes make little to no difference in the noise floor, and are TOTALLY un necessary on output tubes.

Tommy,

Your wiring sounds correct, except you never mentioned if your fillament wind has a center tap or not. If it doesn't you'll need to put a couple of 100 ohm resistors to ground from your filament circuit to balance the wind, otherwise you'll get major hum.

RE: EL34's If you are going to use these you MUST use at least 1K 5W Screen resistors, otherwise they'll just go up in a cloud of smoke.

[Tdale]

Yes, I have a center tap.

I'll remember the 1K if I ever try EL34... Would it be possible to have switchable screen resistors, to make the change between 6l6 and el34 easier.

Tommy

[dobbhill]

MY 6L6's don't mind the 1k screen resistors.
HTH, D