Bottlehead Forum

General Category => General Discussion => Topic started by: corndog71 on February 03, 2014, 06:09:35 AM

Title: My VTA ST120 KT88 Amp
Post by: corndog71 on February 03, 2014, 06:09:35 AM
For years I've been wanting a KT88 amplifier.  Most of the manufactured amps out there are out of my price range so for a while now I've been looking at building the Dynaco Mk 3 monoblocks as a less expensive alternative.  But then I found Bob Latino's ST70 kits and his upscaled version called the ST120.  It's basically a stereo version of the MK3 but with a more modern driver circuit.  Bob really likes the ST70 "look" and even added other refinements to his kits like  the stainless steel chassis and triode/pentode switches.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.tubes4hifi.com%2FVTA120top.jpg&hash=c711679fb960f8922916d093dde8ed731c749e7a)

I got my ST120 kit sans chassis because I wanted to build it a little differently.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8362_zpsfc7bbb41.jpg&hash=9d4fa879435556a95ce5dec5696903706c5d248a)

Ok, a LOT differently.

Here's my sketch and inspiration. 

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FD479369D-9068-4915-AE6A-678F9B9BA8F3_zps7r18ivqq.jpg&hash=407e14184d336058d0a45251635958ded6893041)

The idea was to use a big 17"x17"x4" Hammond box.   I went with a similar layout as my modded ST35...http://www.bottlehead.com/smf/index.php/topic,4690.msg44489.html#msg44489 (http://www.bottlehead.com/smf/index.php/topic,4690.msg44489.html#msg44489).

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8373_zps1246f6bf.jpg&hash=5c8ecc7141796b9720e88e1e66fd70dde6265309)

I wanted to forgo the big circuit board and go point to point wired as much as possible.

Another feature is that I'm using Clarity Cap TC series 700V film power supply caps.  These are why I got such a big box.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8379_zpsdc346ff9.jpg&hash=933f0dbda3f09c3e7871aac3f16799edf8476ece)

I got the Russian PIO caps from Bob as well as a pair of Clarity Cap ESA caps for C1 & C2.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8453_zpse4895657.jpg&hash=610116aa8e32804080e1ef5fb657a6ef0dbdb30c)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8383_zps835263a7.jpg&hash=5706601ab88a7a06e916bf1e91dd835a6d970768)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8423_zps1c259b1a-1.jpg&hash=facd2202d8f8400329dfbe6a2ec72c8a6a8bdc46)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8438_zps7ba257c2.jpg&hash=60894be2fe9364a22e6d063fb355df937c4aa75a)

The caps are held down with cable ties and industrial strength velcro.  They don't budge.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8462_zpse0e52262.jpg&hash=0cfe278fe1f7f7fb6c2751f056b16ed4d67d7262)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8480_zps24404161.jpg&hash=235b87f43d5953079a0c0d2a6dc819a9e6107e94)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8515_zps322052ad.jpg&hash=fc75eee9a2476c82c764247b10ca2a8aaeca5cb0)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8514_zps18e29525.jpg&hash=5f4ef875bb7025d6b92a4c44c66793670f950750)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8516_zps108bfabe.jpg&hash=43a1548f026c3a5101a7472659fd536321737ac7)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8500_zps08e6ca54.jpg&hash=503386ffdf9feb46c36f0b0b5a68308a5b6a42b6)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8496_zps53ee9a49.jpg&hash=58e78f8bf3de478693177dd62ff36cbcc4307598)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8492_zps4cafec5a.jpg&hash=b48eab5774965816ce3c20fc3a686734c641a2a1)

I still have to do the main power connector, speaker connectors, input wires and a few ground wires.  And then I have to buy tubes.  :o
More to come!
Title: Re: My VTA ST120 KT88 Amp
Post by: Downhome Upstate on February 03, 2014, 06:26:32 AM
Holy Smoke! Infreakin'credible!! You 'da man, and its 'da bomb!!!
Title: Re: My VTA ST120 KT88 Amp
Post by: corndog71 on March 01, 2014, 06:14:20 PM
Done.  New Tung Sol 6550's.  I'm currently using EH and NOS RCA cleartops in the driver stage although I have a new set of RAM Labs 12BH7s coming in a few days.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8572_zpsdfa8ab66.jpg&hash=eb774c387c78635c7ddf6ba165055282b756e531)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FVTA%2520ST120%2FIMG_8569_zps9ea4c40d.jpg&hash=2c0db24403b9e921d4f1ea760593f098d517ad06)

The VTA kit is pretty nice.  If you need more power, it's a great choice.
Title: Re: My VTA ST120 KT88 Amp
Post by: Paul Birkeland on March 01, 2014, 06:29:33 PM
Very nice! 

Have you popper her on the scale?
Title: Re: My VTA ST120 KT88 Amp
Post by: corndog71 on March 01, 2014, 08:45:19 PM
34 pounds.  The transformers alone are 25#.  She's a sweet-talking beast!
Title: Re: My VTA ST120 KT88 Amp
Post by: JamieMcC on March 01, 2014, 11:34:12 PM
Nice work those kt88 tubes look sweet.
Title: Re: My VTA ST120 KT88 Amp
Post by: corndog71 on March 02, 2014, 07:20:28 AM
Quote from: JamieMcC on March 01, 2014, 11:34:12 PM
Nice work those kt88 tubes look sweet.

Thanks.  These are actually new Tung Sol 6550 tubes.  Eventually I want to get some KT88s and KT120s.
Title: Re: My VTA ST120 KT88 Amp
Post by: johnsonad on March 02, 2014, 09:38:58 AM
Nice!  I had McIntosh MC75's for a while and they were awesome amps!  That should help this winter but wait until summer ;)  6550's are real room heaters!
Title: Re: My VTA ST120 KT88 Amp
Post by: pdxgrampa on March 02, 2014, 10:46:57 AM
Nice job Rob

I built an ST-120 for my daughter and son-in-law(and my 5 year old grandson who is an AC/DC fan :)) about 3 years ago. They have had zero problems with the amp and they are not techies.

The amp drives a pair of Zaph Audio SR-71's.I installed kt-120s on the last trip out .It does Rock n Roll!
Title: Re: My VTA ST120 KT88 Amp
Post by: corndog71 on March 04, 2014, 08:10:07 AM
Both of my amp projects.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi576.photobucket.com%2Falbums%2Fss207%2Fcorndog642%2FMisc%2520Audio%2F307CFBBA-3A09-45BC-A9CC-9F03FE332DDF_zps2bntpynb.jpg&hash=dc6604f46fa16af73c3e4a1c7d6d4e0e8e018ae9)
Title: Re: My VTA ST120 KT88 Amp
Post by: Guy Boisvert on March 04, 2014, 10:40:47 AM
Nice work....however, I don't think you could bring that on an airliner as a carry-on  ;) ;)

Guy