Kt66 amp done

[JoshBernstein]

Hello all,
I just finished another amp. This one is the most "from scratch'' that ive done so far, as i designed a lot of the layout myself. Its a cathode biased kt66 amp with a kinda matchlessy-voxy ef86 preamp. I added a tone control similar to the one in my marshall 2061x, a bright switch which parallels another bright cap, and a sort of 'deep' switch, which parallels another cap accross the first coupler. Running the kt66's at about 400 volts using an ac30 power transformer and gz34 rectifier, giving me around 15 watts of output. I think is sounds very nice. Vert glassy/chimey and full. Dead quiet. I wanted to thank everyone on the amp garage for all of the knowledge and advice that has allowed me to put together something like this. It'll be my last one for a while as im off to college in a month.

I do have a question as well. I put a ppimv in there, but i cant get the preamp to clip at all. With the master cranked i can get a bit of crunch from the power amp, but is there a way to lower the preamp's headroom?

I dont have any gut shots yet but ill take some if anyone is interested.

Thank you all!
-Josh

[JoshBernstein]

Also meant to say im going to be mounting it in a recycled bad cat head cab and i have a piece of rosewood that i will use for a faceplate.

[strelok]

With a pair of KT66's you should be getting a bit more than 15 watts into a 4k load (assuming standard AC30 primary). You might want to check the bias and tweak your cathode resistor. Unless of course you like that operating point.

Without seeing a schematic, I'm assuming you're using a long tailed pair for the PI? With the single EF86 stage you simply might not have enough voltage gain to get much distortion out of the PI. You can try tweaking its operating points, bigger plate load, screen voltage etc. But if you want a fair bit of distortion you might just have to add another stage, or use a boost/OD pedal.

[JoshBernstein]

Im very happy with the 15 watts, any more is usually too much for what i do.

And i may just add another stage like you said. To add some more gain. I just wanted to see if i could get away with a little less difficult of a modification.

Assuming i just add another standard 12ax7, would you recomment using one or both triodes? Thanks

[JoshBernstein]

I just thought of something else. Does anyone think a dumble style fet input would be effective or sound good?

[martin manning]

The D FET is basically a clean boost. If you have a pedal that does that, then you can try it out. Re adding a stage or two, I see you have an available 9-pin socket hole, but of course you'll have to find room for the other components somewhere. If you go there, maybe you could arrange a pentode input and a triode input, and then use the other triode as a common stage to drive the PI.

[strelok]

I'll throw in another alternative just for the hell of it.

You could convert your PI to a Cathodyne style and free up a gain stage. If you feel like getting extra fancy you can direct couple the cathodyne to the previous stage and bootstrap it for even more gain.

You may or may not like the sound of the cathodyne though. Just a thought.

[JoshBernstein]

I'll throw in another alternative just for the hell of it.

You could convert your PI to a Cathodyne style and free up a gain stage. If you feel like getting extra fancy you can direct couple the cathodyne to the previous stage and bootstrap it for even more gain.

You may or may not like the sound of the cathodyne though. Just a thought.

That is an interesting idea. How does the sound of a cathodyne pi compare to the ltp?

[strelok]

Hard to say. I've built amps using both, however I've never done a direct comparison between the two using the same circuitry otherwise. I will say if you're not careful how you set it up it can be prone to blocking distortion and other weird distortion effects, though this can be mitigated in theory if you use direct coupling to the previous stage.

Perhaps someone else can chime in and offer some input on how the two directly compare to each other in terms of sound.

[martin manning]

A cathodyne has less than unity gain so it will need a gain stage just to equal the gain of a LTP.

[strelok]

According to Merlins page on the cathodyne you get more gain using it in conjunction with the free'd up gain stage in comparison to both triodes used for the LTP. I don't know how he arrived at that or if its correct. Maybe OP could do an expirment and verify it for us . I'm fairly certain the bootstrapped version would.