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KT66 (6L6) conversion?

Posted: 09 Sep 2014, 11:04
by malc_p
Hi guys
New to the forum (but not to Marshalls) so please be gentle with me!
I'm picking up a Haze40 at the weekend and after I've spent some time checking it out (I have an SG with Burstbuckers in it plus a strat with Bareknuckle Rory Gallaghers) I may find that I want to try some of the tweaks mentioned in this forum. One thing I would really like to try, though, is a pair of JJ KT66's that I have lurking around; trying to get the early plexi smoothness?

Should really be just a bias setup(32 - 35ma or so should do it), I tried them in my JTM60 and they were OK, but I'm wondering if anyone's modded a Haze 40 to use them?

Thanks

Malc

Re: KT66 (6L6) conversion?

Posted: 14 Sep 2014, 07:07
by Anitoli
The smoothness of the Plexi that you are reffering to is more than just the power tubes. It takes the combination of all of the amps stages to really produce that tone. You can get very close but 9 out of ten times these mods don't give you what you are looking for. Unless you really know what you are doing you are better off sticking with the tubes that the amp was designed for. A lot less headaches that way.

Re: KT66 (6L6) conversion?

Posted: 14 Sep 2014, 10:39
by malc_p
Yup Anitoli I get your point, you can't make an amp sound like a 1967 plexi unless it's a 1967 plexi...
However, the character of an amp is, as you rightly say, contingent on all the various factors - quality of component, voltages, tolerances, sheer luck and so on but you can gently steer it in the direction you want with judicious substitution and tweaking. So, once I've got the hang of how this one initially sounds with the SG and the Strat and can form my opinion of it's 'basepoint' sound, I fancy doing some experimentation (I am a qualified electronic engineer and spent my training years learning on valve gear). I was really putting my toe in the water to see if anyone's tried KT66's in a Haze 40 and what they thought of them, is all.
That, and I'm a born meddler!
*This* is my Holy Grail tone (yes yes I know, pie in the sky, four 4X12's with G12/30's etc...): https://www.youtube.com/watch?v=OWTJVNPu_r4

Re: KT66 (6L6) conversion?

Posted: 14 Sep 2014, 11:14
by Anitoli
Isn't the Haze 40 originally manufactured for EL34's? Was this head converted to 6L6GC's?

As in the Vintage Modern the KT66 is not a suitable drop in for the EL34/6L6GC due to the large differnce in plate impedence. The transformer's primary winding will not match the KT66, resulting in a more innefficient operating amp.

Re: KT66 (6L6) conversion?

Posted: 14 Sep 2014, 11:50
by malc_p
Seems to depend on which source you read...posters on the Gear Page seem to be of the opinion that they're broadly similar; ditto MetroAmp. One other place I looked thought you'd need to use a 16ohm speaker on the 8 ohm tap but I can't find corroboration of that anywhere else. I'll keep a watch on anode current and hence dissipation if I ever get round to trying it. It will only make a difference to the sound at power levels above 8 or so anyway so it may be unnecessary as I'll rarely be using it at that level.

Re: KT66 (6L6) conversion?

Posted: 14 Sep 2014, 13:13
by Anitoli
KT66's also have a higher heater current draw if they are the original ones, not the 6L6GC's stuffed into a bigger bottle made by JJ..... :bgrin