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    4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

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    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Mon May 07, 2012 1:20 am

    chassis is in, dry fitting stuff to it


    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Fri May 11, 2012 12:30 am






    davidness

    Posts : 39
    Join date : 2010-09-15

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by davidness on Fri May 11, 2012 10:20 am

    You would be good at Tron. Very Happy

    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Fri May 11, 2012 10:30 am

    davidness wrote:You would be good at Tron. Very Happy

    ive never played it but possibly if my wiring style translates well.

    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Fri May 18, 2012 3:04 pm


    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Sun Jun 10, 2012 9:56 pm

    recent gut shots

    follow the links they are hi res

    http://img38.imageshack.us/img38/7584/img1494bx.jpg

    http://img708.imageshack.us/img708/6144/img1495nb.jpg

    http://img694.imageshack.us/img694/817/img1496kc.jpg

    http://img534.imageshack.us/img534/7998/img1497wb.jpg

    http://img526.imageshack.us/img526/4176/img1498hq.jpg

    Alan-14

    Posts : 46
    Join date : 2012-03-31
    Age : 56
    Location : Melbourne - Australia

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by Alan-14 on Mon Jun 11, 2012 1:29 am

    Wow ... that's a really impressive wiring job!
    Kudos to you ... beautiful work!

    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Tue Jun 26, 2012 8:17 pm

    up and running now, pretty loud and destructive


    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by Bob Latino on Tue Jun 26, 2012 8:25 pm

    Hi Nick,

    Looks great !

    Define "pretty loud and destructive"? The VTA M-125 output transformer was designed for Hi-Fi work but should do pretty well on a guitar amp since (I believe) that the lowest note on any guitar amp is about 41 Hz.

    Bob

    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Tue Jun 26, 2012 8:35 pm

    Bob

    Generally speaking HiFi bandwidth OTs and PTs out preform guitar ones because they dont need such bandwidth and usually run up the THD to get more output and distortion since thats not a concern. Here I am getting excellent bass response with guitar or bass so the extra low end I can get is great. The fundamental frequency on a standard tuned guitar is ~82 hz but I normally tune lower than standard where the thickest string is a C note, 2 notes below the usual E. Probably around a 60 hz fundamental I would think

    So I have been testing/tweaking the amp and here is a short demo I did in my room through a 4x12 which in guitar world is a speaker cabinet with 4 12" speakers and I am using a few hi gain fuzz boxes to add a lot of extra volume/distortion to pushing the amp even harder to get it louder. I was essentially shaking the walls and everything in my room but the amp kept giving me whatever volume I wanted. The sort of customers I sell to are looking for this kind of guitar sound, a lot of available power and a lot of clean headroom. The design is a smidge different than pictured earlier on the forum. I converted to a cathodyne phase inverter for better balance in the outputs and then added more driver stages post phase inverter to increase gain into the power tubes along with DC coupled followers on the output to drive the amp into AB2 operation under heavy load so that I can conduct grid current into the output tubes without going into blocking distortion.

    http://www.youtube.com/watch?v=mXyi7DJbrJw

    I should mention I am running it in Pentode output mode but theres a switch to put it in Ultra Linear as well. Pentode has more power and more THD which is sometimes nice. Dynaco style amps have been used in the past for guitar and bass amps famously made so by a company called Sunn back in the 60s I believe. They took Dynaco kits and converted them into guitar and bass amps with slight mods to the preamp to add more control but the power amp is distinctly Dynaco.

    dunwichamps

    Posts : 36
    Join date : 2011-10-20

    Re: 4 x KT88 Guitar Amp using M-125 Iron Set, now with pic of driver circuit

    Post by dunwichamps on Thu Jun 28, 2012 9:43 pm

    Another shot, fired up. Rattling the house away. Breaking in everything and tweaking it. Iron is staying nice and cold during heavy play so thats a solid thing.

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