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    Prototype 125 watt monoblock tube amplifier KIT

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    Bob Latino
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    Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Sat Jun 05, 2010 1:07 pm

    Since business slows down during the summer I will be experimenting with a prototype monoblock tube amplifier which should be capable of 125+ watts. I don't want to give the details of the circuit right now because the circuit is still in the development stage. I had a pair of larger output transformers made for me by my transformer company (see photo comparisons below). This 11.5 pound output transformer has a very large core so it won't saturate at higher current flow levels. The manufacturer assured me that these have been tested up to 200 watts (continuous power) with no core saturation. The plates are M6 grain oriented silicon steel like the VTA ST-70/ST-120 output transformers. The primary and secondaries are interleaved/layer wound just like the VTA ST-70/ST-120 output transformers. The primary impedance is 1800 ohms. I won't be able to work on this for a couple of weeks but will let you know in this thread how (if any?) progress is being made on the project.

    Bob




    Last edited by Bob Latino on Fri Jul 29, 2011 11:54 am; edited 7 times in total

    PeterCapo

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by PeterCapo on Sat Jun 05, 2010 9:51 pm

    Hey Bob,

    Pretty exciting possibility there! It could be a successor of sorts to the Dynaco Mk-VI.

    Suggestion: make the amp user-configurable for either the new KT-120 as well as KT-88/KT90/KT98/KT100 (in the event KT-120 ever ceases production).

    Good luck.
    Peter

    baddog1946

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by baddog1946 on Sun Jun 06, 2010 9:35 am

    Hi Bob:
    What are the specs on that transformer? What voltages does it have output, bias etc.

    baddog1946

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by baddog1946 on Sun Jun 06, 2010 9:38 am

    Oh yes! Can we buy them soon?

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Sun Jun 06, 2010 9:56 am

    baddog1946 wrote:Oh yes! Can we buy them soon?

    Right now all I can tell you is that the primary impedance of the OUTPUT transformer is 1800 ohms CT. The POWER transformer secondaries will be able to deliver 415-0-415 VAC @ 450 milliamps.

    Re: "Can we buy them soon?". These amps may or may not see the light of day as a production amp kit? I am having two prototype chassis made which I won't see until the end of this month. I will post some photos of the chassis when they arrive ..

    Bob


    Last edited by Bob Latino on Wed Jul 20, 2011 9:03 am; edited 5 times in total

    JunkyJan

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by JunkyJan on Wed Jun 09, 2010 4:55 pm

    Hi Bob

    I assume to get that kind of power output, you'd be looking at running 4 X KT88 in a PP configuration (per monoblock)? I admit to being very curious and even more so VERY interested - that would be serious fun building it (assuming you'd have it available as a kit).

    The power levels would right up there ("Oh-my-gawd-I'm-calling-the-police")...

    -- JunkyJan

    Falcon4646

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Falcon4646 on Tue Jun 29, 2010 12:23 pm

    Bob,

    Very interested in your 125-150 watt monoblock effort. My 4 ohm floorstanders go from 20-400 watts of power handling capability. Had been considering the ST120 but your new effort seems more suitable to my needs.

    natoe

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by natoe on Tue Jun 29, 2010 1:17 pm

    Bob, I think it might be interesting just to buy the parts off of you for the mono blocks and do your own chasis.I have had some ideas for a chasis for a while and I think this would be the proper platform to do them. Almost the same is Jim McShane and the pre-amps he will be offering up when he gets the r&d done on them.They will come with no chasis, kit form to keep the cost down.

    always,thank you
    pete

    davidnes
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    Any update on the new amp project?

    Post by davidnes on Wed Sep 01, 2010 10:05 am

    Bob,

    Any update on the status of this project?

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Wed Sep 01, 2010 10:09 am

    davidnes wrote:Bob,

    Any update on the status of this project?

    Hi,

    Yes - I should have the two prototype chassis by the end of this week. I will post photos of the chassis when I get them ...

    Bob

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Thu Sep 02, 2010 12:17 pm

    Hi All,

    I have one of the two prototype chassis for the VTA M-125 power amp. The photos are below. The chassis will be 10" by 12" and made of 16 gauge brushed stainless steel as seen in the photos. The chassis will have no silk screening. The amp will have a parallel push pull circuit using a modified VTA Mark III driver board. The complete circuit details have not as yet been worked out. The chassis will have on the front face three bias test pins - one grounded to the chassis and the other two for biasing one pair of the 4 output tubes. The ON/OFF power switch will be on the front. On the rear face will be the input jack, fuse post, IEC AC connector and a single output binding post terminal. The amp will use four KT88, 6550, KT-90 or KT-120 output tubes. The amp should be capable of 120 to 140 watts ...

    I will not be able to really work on this until Monday Sept 20th. I am helping someone with a project all next week and and will be on vacation the week of Sept 12 to Sept 18.

    Chassis photos below ..

    Bob

    Chassis top and front face



    Chassis top and rear face


    PeterCapo

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by PeterCapo on Thu Sep 02, 2010 8:11 pm


    Outstanding! Looking forward to hearing more about it.

    Corona

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Corona on Thu Sep 02, 2010 9:13 pm

    Nice can't wait to see this project come together What a Face

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Sep 03, 2010 8:34 am

    Hi,

    I found some minor "glitches" in the translation of what I wanted as to spacing of certain parts on the chassis. The IEC connector is too close to one of the mount screws for the power transformer. On this prototype it's no real problem because I will just shorten the screw about 1/4 inch and it will go in there fine. The IEC connector will have to be moved 1/4 inch toward the fuse post and the fuse post will be moved 1/8 further towards the input jack.

    Also, the four holes that mount the SCM, main grounding tabs, 3 lug and two lug terminal strip were too small. I told them that I wanted a hole for a 4-40 screw. What they gave me was 4 holes that could be TAPPED for a 4-40 screw. I just drilled the 4 holes out. They also got one dimension wrong by 3/8 of an inch. The triode/pentode switch is too close to the mount screw for the SCM module. It will be moved 3/8 of an inch towards the two lug terminal strip. On production models a heavier duty DPDT triode/pentode ultralinear switch will be used. On production models a 15 amp rated SPST ON/OFF switch will be used. I just used some smaller switches I had around the shop here on the prototypes.

    Photo below of progress so far. I will be able to work more on the amp next week because the project that I was going to help someone with has been postponed.

    Bob




    Last edited by Bob Latino on Sat Nov 06, 2010 6:13 pm; edited 1 time in total

    baddog1946

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    new amp

    Post by baddog1946 on Fri Sep 03, 2010 10:01 am

    Hi Bob:
    The new project looks like it is coming along quickly. I noticed you are sticking with the quad cap on this one. Is there a particular reason you are doing so?
    I would think that a board with the option of modifications and swapping out better caps would have been the call. Got any other specs for that thing yet?
    I hope to see the completed project soon. Will it be a kit or a complete amp?
    a very curious
    Baddog1946

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Sep 03, 2010 10:34 am

    Hi Baddog,

    On this amp and the ST-120 amp the Authenticap quad cap is rated at 550 volts continuous and 600 volt surge. The SCM on this amp and the ST-120 is rated at 800 volts, the ESL capacitors that will also be used are rated at 630 volts.

    Example > Why not use the Triode Electronics/SDS Mark III under chassis board for this amp? Reasons why not below ..

    1. Other than the first section of the Triode/SDS board which is 800 volt rated, the other 4 sections are 500 volt rated - too low for this amp which operates at 500 - 515 volts continuous with a solid state rectifier.

    2. I could change out their (500 volt rated) caps and buy my own higher rated caps which may or may not fit the diameter spacing on their board?

    3. I don't want to depend on Triode Electronics to supply me with this board. I could have it copied but probably Sheldon Stokes who developed this board may have it patented.

    This basic design which has been used sucessfully on the ST-120 will be tried first. If it doesn't work out I have other things in mind which can be tried.

    Bob

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Sep 03, 2010 2:29 pm

    This is as far as I got today ... Transformers and quad cap on. The driver board is all built. I won't be able to work on this amp for another week or so as I have other obligations at home here ..

    Bob



    avi.inc

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by avi.inc on Fri Sep 03, 2010 3:11 pm

    Hi Bob

    I wonder will this amp be optimized for the kt-120's or will this be like the st-120 using the kt-120.
    That's a lot of 120's in that sentience.

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Sep 03, 2010 3:27 pm

    avi.inc wrote:Hi Bob

    I wonder will this amp be optimized for the kt-120's or will this be like the st-120 using the kt-120.
    That's a lot of 120's in that sentience.

    Hi,

    The amp will not be optimized for KT-120's but you could use them in there. This amp will run a B+ of about 500 - 515 volts. To optimize an amp for the KT-120 tubes you would probably have to get the B+ voltage above 600 volts and if you do that it would be too hard on KT88 or 6550 tubes IMHO.

    The other thing is that the KT-120 tubes are only made by Tung-Sol. What would happen if they decided to stop making them because the didn't sell well? You would be left with an amp optimized for a tube that doesn't exist. Not a good thing ... I think that if this amp ever becomes commercial most audiophiles would choose to use KT88 output tubes in there.

    Bob


    Last edited by Bob Latino on Tue Nov 09, 2010 5:48 pm; edited 1 time in total

    baddog1946

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by baddog1946 on Fri Sep 03, 2010 4:16 pm

    Hi Bob:
    Good points, sounds like the can quad will do the trick and the rest is looking like I may have to start saving some dough for a pair of these.
    What do you think the R&I period will be? Are you using a modified VTA board on this amp? Will there be a cage for it? Is it the same dimensions as the MK III?
    Finally and I know I ask a lot of questions but got any idea of what a pair would be worth?
    Baddog1946







    7D

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Sep 03, 2010 4:34 pm

    baddog1946 wrote:Hi Bob:
    Good points, sounds like the can quad will do the trick and the rest is looking like I may have to start saving some dough for a pair of these.
    What do you think the R&I period will be? Are you using a modified VTA board on this amp? Will there be a cage for it? Is it the same dimensions as the MK III?
    Finally and I know I ask a lot of questions but got any idea of what a pair would be worth?
    Baddog1946

    7D

    Hi Baddog,

    To answer your questions ..

    It will be a few months before these are ready for any production "kit" version of this amp - hopefully by the end of the year ..

    The amp will use a modified VTA Mark III driver board. This amp is larger than a Mark III. A Mark III is only 9 X 9 inches (81 square inches). This amp is 10 X 12 inches (120 square inches). A Mark III is about 27-28 pounds. This amp will weigh in at about 40 pounds

    There will be no cage for the amp.

    I have not done a cost analysis of the amp as yet so I don't want to go out on a limb and project right now what a kit version of this amp would cost.

    Bob


    Last edited by Bob Latino on Tue Nov 09, 2010 5:49 pm; edited 1 time in total

    baddog1946

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by baddog1946 on Sun Sep 05, 2010 8:54 am

    Hi Bob:
    Well my ST-120 has been running fine since the Weber blew up I have checked it over internally and everything tests within normal tolerances. But I was wondering about something else. I live in a hot place (at the beach in Costa Rica) and I use my amp at least 4-8 hours a day here. It seems to be running fine but the main power trannie is always pretty hot.
    I mean too hot to leave your hand on for more than a second or two. My question is are the trannies you had made for the mono block project for sale? Would they swap into my 120? At least the main. Do you think it would run a little cooler? Or at least not be running as hard? I play a lot of jazz, blues and a bit of the rock and roll but not at extreme volumes the thing is I use it a lot so it is on a long time every day.
    Those trannies are a little more robust. The main thing might be they look a little bigger which might crowd the other two but if it can fit and it could give a little insurance then it might be worth it to me. Our average temp here in the rainy season is 80 degrees.
    I am running some Decware NFX's I built with 99dB sensitivity which by the way are some of the best speakers I have ever heard in my 40 year audiophile career they have unbelievable detail and they actually have some decent bass although I have a small sub as well.
    Which brings me to another question; what would I have to do to swap my VTA high gain board to a low gain board?
    I have a stepped attenuator on the amp but often I have to turn it down to 2-3 or it has too much volume and one click makes a huge difference.
    Thanks for listening
    Baddog1946

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Sun Sep 05, 2010 9:50 am

    Baddog,

    The reason your ST-120 runs a little warmer than normal is that the ambient temperature around you is warmer than normal and the thermal gradient (the relative difference between the transformer's temperature and the surrounding temperature) is lower than normal. As such, the transformer will run a little warmer. The transformer will take the extra heat just fine. I have one customer in the military who runs his ST-120 in the jungles of Brazil. He probably has a higher surrounding temperature than you do and his ST-120 has been running fine for over 2 years.

    The transformers for the M-125 monoblock won't fit the ST-120.

    The ST-120 had a little more gain than the average tube amp and in combination with the very efficient (99 dB) speakers that you use will give you less volume control at the lower end of the volume control.

    Email me directly at Bob01605@aol.com and I can give you the resistor differences between the standard gain board that you have and the lower gain board.

    Bob

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Thu Sep 09, 2010 9:03 am



    Well - it works and sounds great .. Noticeably more headroom than a single channel of the ST-120. The two driver tubes are 12BH7's and the resistors on the driver board have been optimized to give higher voltage swings than a Mark III driver board. The amp has somewhat less gain than the ST-120. Some of the chassis holes are slightly off from where they should be and some of the components inside are not quite where they should be - off by 1/8 to 1/4 of an inch. The triode/pentode switch is not connected yet. The amp runs (right now) in ultralinear mode only. Since this is a prototype I don't want to show the interior wiring just yet until everything is where it should be. Since I only have one amp and won't have the time to build another one for 2 to 3 weeks, I can't comment on imaging or soundstaging. I will be on vacation starting Sept 20 but should be able to build a mate for this one near the end of the month.

    NOTE - The driver board in the above photo is not a production driver board. The production driver boards will be green colored and have all the part numbers silk screened on the top like the VTA ST-70/120 driver board. See production driver board photo below ...



    Bob


    Last edited by Bob Latino on Thu Jan 01, 2015 10:46 pm; edited 3 times in total

    davidnes
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    Suggestion

    Post by davidnes on Thu Sep 09, 2010 10:51 am

    Small suggestion:

    Can the VTA board be mounted the other way around to allow the bias adjustment posts to be toward the front of the amp? I keep my amps in a rack, and reaching over hot tubes to reach the 'blind spot' pots would not be my first choice.

    Just a minor suggestion.

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