Another 100W Low-Plate Skyliner

[David Root]

Exemplary work Martin!

I also found the std FET 8K2 is way off the mark. On my #124, with an NTE452 I also used 22k tail on the 150K, and a 2k5 to get the 10V/20V approx balance. I think a 2K2 would also work. I have a little higher B+ on V1 than you.

I have Jason's boards too, and plan to start using them soon.

[talbany]

Sweeett!! Build Martin.. Congrats

Tony

[Drumslinger]

that's a sweet build martin! congrats man! did the cat learn anything?

[martin manning]

that's a sweet build martin! congrats man! did the cat learn anything?

Nah, he's a cat... he slept through the whole thing!

[UltraHookedOnPhonix]

Holy haberdashery, Batman! That is one sleek looking build!

[67plexi]

Martin, Nice clean build, Sounds as good as it looks.........

[mdroberts1243]

Can't imagine that it wouldn't eventually sound good, given how great your build looks!

[mlp-mx6]

Martin,

That may be the cleanest looking build yet. The amount of thought and planning you put in is evident. I look forward to hearing the fruits of your labor.

Regards,
Michael

[erwin_ve]

Martin, what a neat build! Thnx for sharing.

[martin manning]

Thanks to all for the compliments, and again I can't say enough how much is due to the collective wisdom available here. Personally I'm most impressed by the amount of work required to build one of these things, even without the large measure of OCD. No surprise that the sale price of boutique amps is what it is, and the builders deserve every cent! I don't have much in the way of recording gear, but eventually I may get something I can share.

DR, I powered up the FET with a couple of 9V batteries to check the DC op point. I think once the right bias is found at 18V, it will hold up pretty well at 20 or 22.

[BobW]

Martin, Congratulations It's a very neat layout. It's difficult to tell from the pic but is the red wire on your leftmost relay soldered in place?

[CHIP]

Thanks very much for the kind words. I like nekid, er, inner beauty, yea, that's it. Gary, can you see the LNFB on V1b? The junction of the two 22-Meg resistors is right next to the ground lug on that rear terminal strip... ready for an on/off switch if desired. Your suggestion from a while back; thanks. Gil, I had a print of your photo of your "last amp" as a guide, and referred to it often. Mine seems to have no stability problems, and so with the right tubes, and maybe some tweaking, I'm hoping that there is a way to get it to sound as good as it looks. Thanks to you and others for posting all the details related to tuning... I've saved many of them, and will no doubt have some fun with that. Tom, the overdrive is great. I have to play with the entrance trimmer and see how to balance that with the full-on drive distortion level. Oh, and I forgot to give icracer props for the great #124 schematic and the others he drew up.

A couple of other details:

There are dual mica bright caps, 100p and 300p. This gives an option for somewhat subtle or a little more in-your-face... I like that feature a lot.

The FET is a metal can 2N4416A, and I ended up using 150k/22k voltage divider to get the Vcc, and a 2.0k source resistor to get Vd = ~Vcc/2. Should be as good or better than the NTE part.

The front panel LED (blue, of course!) runs from the 12V relay supply, with a 2k2 current limiter to keep the brightness down a bit. This helped to clean up the area around the power tubes, and I understand that the LM7812 is happier with that continuous current draw when the relays are both out, too.

Martin,
On your bright switch, are you using an on-off-on switch, where as your middle position is neither 100pf or 300pf, or is the 100pf is engaged when the switch is in the "Bright" postion and the 300pf is engaged when the switch is in the down position?

[angelodp]

Martin, very nice build. Superb craftsmanship.

Ange

[Structo]

I just have to say IMHO, that this Overdrive Special is the neatest and cleanest constructed one yet.
No offense to anyone else because there are certainly some others here that are great as well.

Makes me want to rewire mine......

[martin manning]

On your bright switch, are you using an on-off-on switch, where as your middle position is neither 100pf or 300pf, or is the 100pf is engaged when the switch is in the "Bright" postion and the 300pf is engaged when the switch is in the down position?

CHIP, the switch is a DPDT on-off-on with the center lugs connected to the pot, the 300p on the bottom, and the 100p on the top. Down connects the 100, up connects the 300. I decided "Up" should be the brighter position.

It's difficult to tell from the pic but is the red wire on your leftmost relay soldered in place?

It is, Bob. There is probably a bit of flux pooled in there. I noticed a bunch of artifacts from the flash in some shots too. Not a very sophisticated photo set up, just point and shoot.

Thanks again Tom, my face is red! To be sure, this kind of thing is over the top... I'd starve if I were selling them, and I'm sure the pro's here know that!