New ~26W Build

Dr Tony Balls · Post by **Dr Tony Balls** » 08 Jul 2011, 16:55

This design is the brainchild of user ScottVA on the Weber forum. Scott called the basic design the "Phat Ass". Its basically the initial preamp from an 18W lite, the tone stack from a 5E3 deluxe, a long-tailed-pair phase inverter, and a cathode biased power section. The members of that forum have hit the ground running with his initial deign and they've made everything from dual el84 power sections, to dual 6V6, to quad el84, etc. This one is dual KT-66s (referring to it by PA26-66) and it is a monster sounding amp clocking in somewhere under 30W.

The idea is to keep things minimal, so the preamp is sparse, as is the iron, and it keeps the whole things pretty light. The sound out of it is amazing. Its not too gainy and has a lot of clean head room (with a tele) but it gets a good bit of crunch at the end of the dial. The cleans are VERY blackface bassman to me and that is wonderful. The crunch is straight plexi.

If anyone wants the schematics or the basic layout I used, lemme know and i'll post em.

diggum12 · Post by **diggum12** » 08 Jul 2011, 19:02

I would be interested! Very cool! I love that giant-ass copper ground wire off-board too.

Dr Tony Balls · Post by **Dr Tony Balls** » 08 Jul 2011, 19:40

Here's the schematic from the original author for EL34s:

For mine I used KT-66s, with the Weber W025130 power transformer and the Weber W404248 output transformer. With KT-66s the secondary impedances on that OT wind up being 16, 8, 4 for Yellow, Green, White, respectively. Then the only other thing to change is the KT-66 cathode resistor to 500R/10W. Here's my layout:

KindaFuzzy · Post by **KindaFuzzy** » 08 Jul 2011, 21:59

Cool.

Greenmachine · Post by **Greenmachine** » 11 Jul 2011, 22:05

Sweet amp.

theundeadelvis · Post by **theundeadelvis** » 12 Jul 2011, 22:27

Very nice amp! I'm may have to build one of those in the near future. Do you have any recordings of how it sounds? I'd love to hear it.

Also, it looks like you may have omitted it in your build, but in the layout you have an SPDT switch on V1. Does this switch just ground half the tube to lower gain? And if so, why did you decide to leave it out (or am I missing it in the pictures)? Thanks!

*edit* Thought of another question. What size chassis did you use? Thanks again!

Dr Tony Balls · Post by **Dr Tony Balls** » 13 Jul 2011, 19:40

theundeadelvis wrote:Very nice amp! I'm may have to build one of those in the near future. Do you have any recordings of how it sounds? I'd love to hear it.

Also, it looks like you may have omitted it in your build, but in the layout you have an SPDT switch on V1. Does this switch just ground half the tube to lower gain? And if so, why did you decide to leave it out (or am I missing it in the pictures)? Thanks!

*edit* Thought of another question. What size chassis did you use? Thanks again!

no clips of mine yet. various people have put up clips of their similar builds over on the Weber forum though. I'll probably have a clip before long.

I omitted the switch because I liked it best this way. It was basically running V1 as a single triode or as paralleled triodes. I liked the sound better with them paralleled so I just left it at that.

I used a 12.5" x 6.5" x 2.5" chassis from www.turretboards.com

DeanM · Post by **DeanM** » 13 Jul 2011, 21:54

Google....Weber forum

results...
A "friendly forum" for those just starting out with the Weber Smokey Mountain Cooker.

Wanted to check out sound samples. was thinking of building something like this recently...a cathode biased KT66 amp. I have a 100watt marshall VM and i love the sound of it and the KT66s but its stuck in my tiny bedroom! so was thinking of a smaller kt66 amp. Really nice work man! i bet it sounds awesome?

theundeadelvis · Post by **theundeadelvis** » 14 Jul 2011, 02:06

Thanks a bunch for your reply!

DougH · Post by **DougH** » 14 Jul 2011, 19:11

Nice work! Do you have any sound clips?

Dr Tony Balls · Post by **Dr Tony Balls** » 15 Jul 2011, 15:44

HA! Sorry, the Weber forum being the forum related to Weber Speakers and tube amp kits. Here's the link, but I think you have to be a member to view: http://www.weberorders.com/forum/index.php#1

Here's a clip from someone else that's basically the same as what I built, but EL34s instead of KT-66s, and he has a master volume on his:

I'll get clips of mine up sometime soon.

theundeadelvis · Post by **theundeadelvis** » 01 Nov 2011, 22:42

Started building mine yesterday. Quick question. What diodes did you use for the rectifier? I've got some 1N4007's and I'm wondering if they'll suffice. Thanks!

Dr Tony Balls · Post by **Dr Tony Balls** » 02 Nov 2011, 00:39

theundeadelvis wrote:Started building mine yesterday. Quick question. What diodes did you use for the rectifier? I've got some 1N4007's and I'm wondering if they'll suffice. Thanks!

Nah, the current through em will be too much. Use some 1N5408s or something similar.

theundeadelvis · Post by **theundeadelvis** » 02 Nov 2011, 04:12

Thanks Dr. T. I'll get some ordered. Evidently I have plenty of time, since I ordered the Edco transformer. Everyone says they take upwards or 2 months to fill an order.

Dr Tony Balls · Post by **Dr Tony Balls** » 02 Nov 2011, 12:47

Are you building the KT-66 version? I love that but there are documented builds of this guy with EL84, EL34, 6V6, and 6L6 power sections, too!

theundeadelvis · Post by **theundeadelvis** » 03 Nov 2011, 22:18

I am doing the KT66 version, because I already have a matched pair of Saratovs. Now that you've had some time with yours, what are your impressions? Thanks for your help!

Dr Tony Balls · Post by **Dr Tony Balls** » 04 Nov 2011, 00:50

I love it! Its really blackface-y and definitely fills that middle-power notch in my stable. Its just so simple and easy and sounds great. You'll dig it for sure. are you using my layout?

theundeadelvis · Post by **theundeadelvis** » 04 Nov 2011, 01:20

Glad to hear you dig it! I am using your layout. Pretty much sticking to it, using the Edcor power transformer, and a 40 watt OT from musical power supplies. I may add either VVR or bypass cap attenuation (not sure which yet), but other than that, it's exactly like yours. Looking forward to getting to play it!

Dr Tony Balls · Post by **Dr Tony Balls** » 04 Nov 2011, 14:28

Rad! If you need any pics or my original voltage sheet they're all here: http://www.flickr.com/photos/thetonybal ... 482881523/

Be warned that I goofed when drilling my chassis and so the orientation is flipped (looking into the open chassis, the input is on the left instead of the right). No biggie, it just wont exactly match my layout.

Also, I just hardwired V1 in parallel operation, instead of using the switch.

theundeadelvis · Post by **theundeadelvis** » 04 Nov 2011, 21:34

Thanks Dr. T! I noticed your build was reversed (I've done that before too). Also, as reference for future viewers of this thread, since I don't have 1N5408 diodes, I'm using 1N4007's but doubling them in series. Since they are rated a 1kv each, two in series should be more than robust enough. I''l post some pics, once I get a little deeper into the build. Thanks again for your help!