6L6 drop in?

chopperferrari · Post by **chopperferrari** » Sat Jul 25, 2015 7:39 am

Hi guys,

I have done a bit of a serch on the forum about swapping in 6L6s for the stock KT66 but haven't found all the info i think i need before going forward, anyone got some personal experience?

*Will any 6L6 work or do i need to aviod certain revisions i.e 6L6GC?

*I have seen that i need to check the voltage, is this the screen voltage? If so how much are too much? 450v? If my voltage is above that what should i do to bring it down?

i already have the bias range mod install because i sometimes swap in a solid state rectifier, any issues here?

Thanks,
Ben

chopperferrari · Post by **chopperferrari** » Tue Jul 28, 2015 8:18 am

Anyone?

neikeel · Post by **neikeel** » Tue Jul 28, 2015 9:05 am

The EL34 being a pentode and the 6L6 a beam tetrode are the obvious differences.

On EL34 pin 1 is the g3 connection so you cannot put an EL34 in an amp set up for 6L6 but you can put 6L6 in an amp set up for EL34s (or KT66s for that matter).

Same goes for heater current (EL34s consume significantly more heater current) and new production EL34s need at least 1k screen resistors (6L6s and KT66s are ok with 470R).

Your 6L6s will be fine in a JTM45 clone if your B+ is less than 450v.

I have an offset project with some Philips 6L6WGB https://www.watfordvalves.com/product_d ... sp?id=1313 (so quite like the orginal 5881 amps) but not had time to finish it yet, I will be using RS Deluxe OT.

chopperferrari · Post by **chopperferrari** » Tue Jul 28, 2015 10:40 am

Amazing, thanks! It's been a while since i build my kit and i'm a little hazy on some of the particulars. Am i right in thinking that the B+ is measured at the standby switch against ground?

Thanks so much,
Ben

neikeel · Post by **neikeel** » Tue Jul 28, 2015 11:12 am

Well B+ is a bit of shorthand, it is the HT from the rectifier.

I should have been more specific that it is the plate voltage (pin 3 of the output valves) and the screen voltages (pin 4) that are the correct things (they are usually a smidge lower than B+).

chopperferrari · Post by **chopperferrari** » Wed Aug 12, 2015 7:41 am

Great thank you. I'm a little stuck. Not sure if i'm measuring wrong, or what i'm doing. (Amp is working fine with KT66s) To measure the B+ i'm measuring pin 3 or pin 4 to ground with the tubes in, it's coming up as 240dc. Sorry if i'm being stupid. Can you help?

Ben

neikeel · Post by **neikeel** » Wed Aug 12, 2015 11:41 am

On the output valve base yes pin3 to ground, should be 400v plus. Daft question but your meter is ok?

chopperferrari · Post by **chopperferrari** » Wed Sep 02, 2015 6:42 am

Thanks Neil, it took me a while to work out what was happening. Good hunch, my meter was dud on the volts setting, got a new one. My B+ is coming in at 442v so i'm pretty sure i'll be fine with the 6L6s.

Thank you so much for your help!

Ben

neikeel · Post by **neikeel** » Wed Sep 02, 2015 9:00 am

Let us know how it sounds!

chopperferrari · Post by **chopperferrari** » Wed Sep 09, 2015 8:34 am

It sounds really good, I definitely perfer the cleans, bass is a little tighter. Thanks for your help!

neikeel · Post by **neikeel** » Wed Sep 09, 2015 9:22 am

chopperferrari wrote:It sounds really good, I definitely perfer the cleans, bass is a little tighter. Thanks for your help!

If you want tighter bass decrease the cathode cap on V1 to 25uF or lower (trial and error for your ears) and consider a 0.01uF coupler on V1b instead of the stock 0.022uF. Again trial and error on that, a 0.0022uF you will definitely hear, the 0.01 might be too subtle so then a 0.0068 or 0.0047 are next to try.

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