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    My ST-35 Build.............

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    atwageman

    Posts : 6
    Join date : 2009-11-08
    Location : North Carolina

    My ST-35 Build.............

    Post by atwageman on Sun Nov 08, 2009 10:18 pm

    I've got some PC-13 boards and parts laying around and thinking of building one from the ground up using my own chassis (hammond).

    I got to thinking as I was reviewing the schematic, why not run dc out to the heaters. But then again maybe I should just go with how Dynaco intended it to be.

    Anyways I'm reaching out to the group here to see if anyone here is running a ST-35 with DC heat and have they noticed any difference in how the amp sounds.

    Btw--Im new to the forum, but not new to tube amp building, although I've been away from diy stuff for about 12 years and I I'm now getting back into it.


    Last edited by atwageman on Tue Nov 10, 2009 5:22 pm; edited 1 time in total

    Bob Latino
    Admin

    Posts : 2376
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My ST-35 Build.............

    Post by Bob Latino on Mon Nov 09, 2009 4:27 pm

    atwageman wrote:I've got some PC-13 boards and parts laying around and thinking of building one from the ground up using my own chassis (hammond).

    I got to thinking as I was reviewing the schematic, why not run dc out to the heaters. But then again maybe I should just go with how Dynaco intended it to be.

    Anyways I'm reaching out to the group here to see if anyone here is running a ST-35 with DC heat and have they noticed any difference in how the amp sounds.

    Btw--Im new to the forum, but not new to tube amp building, although I've been away from diy stuff for about 12 years and I I'm now getting back into it.

    Hi,

    I see no advantage to running 6.3 volts DC on the heaters instead of AC like on the original ST-35. Some might say "the amp will have less hum etc." and "using AC on the heaters increases the hum level" but if an ST-35 is properly wired (always twist the AC heater wires) you won't have any hum at your listening position. Also consider this > Someone mentioned to me one time that there is the possiblity that you would have uneven "wear on the heater elements inside the tube with one being positive all the time and one being negative all the time BUT - I don't think that this is true either. IMHO I don't *think* the amp will sound any different with DC on the heaters but in all honesty I have never heard an A/B comparison of the two ..

    If anyone has tried a comparison of the two just weigh in here ...

    Bob

    atwageman

    Posts : 6
    Join date : 2009-11-08
    Location : North Carolina

    Re: My ST-35 Build.............

    Post by atwageman on Mon Nov 09, 2009 6:22 pm

    Uneven wear on the heaters....lol. Just when I think I've heard it all.

    btw thank you for your reply. I think I will let them run with AC.

    atwageman

    Posts : 6
    Join date : 2009-11-08
    Location : North Carolina

    My ST-35 Build

    Post by atwageman on Tue Nov 10, 2009 5:17 pm

    [quote="atwageman"]Uneven wear on the heaters....lol. Just when I think I've heard it all.

    btw thank you for your reply. I think I will let them run with AC.[/quote]

    Well I've changed my mind. I'm gonna run regulated/filtered 6.3vdc out to the heaters.

    Also I'm gonna make other changes to the power supply componets and values. Mainly just to use parts I have on hand. Instead of using a 4 section electrolytic can. I'm going with individual caps. The original values call for 60uf,40uf, and 20uf on the B+. I've got 3 caps rated 100uf@450v. These are large caps measuring 1.375"Dx2.125" and will be mounted up top like the transformers.

    I'm replacing D1 and D2 with a full wave bridge rectifier I have on hand. I haven't made my mind up yet on weather I want to replace the 50ohm 5watt resistor with a C354 choke. I have both parts on hand. Inrush current limiter will also be installed in series with the B+. I've got a 1kv 0.05uf ceramic cap that will be strapped accross the power switch to prevent pops.

    RCA inputs will be mounted on the backside instead of the front. Power switch and indicator lamp will be monted on the front.

    All this will be mounted on a hammond 17x10x3 steel chassis I have. Yeah I know such a large chassis is over kill in terms of size for a ST35 build, but I have 5 unused chassis that size, so it makes sense of using them versus ordering something smaller.

    Any thoughts or opinions any of you may have on the changes to the power supply circuit I'm gonna make would greatly be appreciated.

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