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Blueman2

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Posts posted by Blueman2

  2. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    Nice!  Congratulations!!  I am loving the perspex case.  Though for heat dissipation, making the sides of the case heat sinks and using perspex for top, bottom, front, and back would seem better.  You must have a CNC to do all of those drill  holes so perfectly?  

    • Like 1

  5. Converting SRD-7 to pro voltage?

    in Do It Yourself

    Posted

    I recall some threads on people upgrading the trafos on SRD-7s, but not sure how much of a difference it made.  But wow, I am amazed to see how much these SRD-7s are going for on eBay these days.  I bought 4 of them a couple years ago for $100 each.  Now going for 3x that or more.  

  10. Kerry Design mini GRHV\GRLV and JoaMat mini T2 Group Buy

    in Do It Yourself

    Posted · Edited by Blueman2

    2 hours ago, boinger said:

    I have built a beta 22 and sigma 22 amps from amb. I have also repaired my blue Hawaii several times with live circuits for testing. I am just new to electrostatic amp construction from scratch. So I would love guidance.

    Having said that.

    I will take a full set for a mini t2 and psu.

    Plus a full psu.

    boinger,

    You will need to specify which boards and how many.  Also, if you want bare or partially assembled GRHVxxx boards.  That way, there will be no confusion.  

    Good luck!  

  11. SRX-Plus Build Thread

    in Do It Yourself

    Posted · Edited by Blueman2

    Right now, my SRX is the most stable amp I own in terms of L- to L+, R- to R+, L-L+R-R+ to ground. All rock steady less than 1V.  But before I did the better tubes and heater elevation, I had your issues.  Sounds like the offset issue follows your tubes?  So I would definitely try another set of tubes.

    As far as hurting your earspeakers, 20V between L- to L+ or R- to R+ does seem a bit high but I doubt it will cause any permanent damage.  But others can chime in on how dangerous this is.  I know I used my first SRX build at 20-30V offsets between -/+ and my SR-007 survived that.  It took about 2 weeks before a new set of tubes arrived, which solved the offset issue for me.  

    What is your L- to GND and R- to GND voltage?  Are they OK? 

  17. SRX-Plus Build Thread

    in Do It Yourself

    Posted · Edited by Blueman2

    5 hours ago, tomislavkufrin said:

    i used 500k and 100k what i had spare for 60V elevation. this is only for input tubes, output ones i left floating. C1 i need to buy first, after that i will try.

    now the hum is minimal. still present but not annoying. 

    edit: it seems the hum disappeared after the tubes warmed up a little bit . or at least it is at the level of my pc fan.

    Just for the heck of it, try tying Output to B- rail using 100K resistor and see if that does anything.  I think leaving them floating is probably OK since it is more likely that input tubes are source of hum.  But what the heck, worth a try.  

    And as @jose and @mwl168 mention, you might want to still try cleaning your tub connectors or switching tubes around to see how that impacts things.  And readjust the trim pots to null everything out.  

    All this talk about hum in the SRX-Plus really makes me feel nostalgic about my first build!!  

  18. SRX-Plus Build Thread

    in Do It Yourself

    Posted

    5 hours ago, tomislavkufrin said:

    heater5.jpg

    also what i found regarding separate trafo/windings.. what i understand, only separate windings are needed, not two transformers. somebody please correct me if i am wrong. 

    Correct, you just need separate windings, not necessarily separate trafos.  

    And the lower diagram would work fine.  For me, with 370V B+ rail, I have R1=470K and R2=100K.   That gave me 65V for filament elevation.   I did not use C1, but that could only help.  

    • Like 1

  19. SRX-Plus Build Thread

    in Do It Yourself

    Posted · Edited by Blueman2

     

    1 hour ago, mwl168 said:

    Hmm, I am using two separate secondary windings from the same and only transformer to supply the filaments - one for the output tubes (6.3v) and one for the input tubes (12.6v). Are you recommending to use two independent windings or two independent transformers? 

    Two independent windings.  And since Input uses 12.6V and Output uses 6.3V heaters for this SRX-Plus board layout, there is really no way to screw that up.  BUT, I modified the input tubes wiring to be able to use 6.3V (rather than 12.6V) since I had a trafo with 2x6.3V windings already.  I just wanted to make sure that if someone else did this, that they would not try to get away with just one 6.3V winding for both Input and Output.  That would be very bad due to different cathode voltages.

  20. SRX-Plus Build Thread

    in Do It Yourself

    Posted · Edited by Blueman2

    1 hour ago, mwl168 said:

    @Blueman2: care to elaborate your thoughts/experience on this topic? Thanks in advance!  

    MLA showed me a great article here: http://www.valvewizard.co.uk/heater.html

    Basically, there can be leakage between the Heater and the Cathode.  Since the heater is usually driven by AC at 60hz, some of this hum can come into the signal path.  Elevating the heater to a voltage near the Cathode can reduce the leakage and the hum.  If you have an isolated transformer for the heater, then it will allow the heater to eventually elevate itself as voltage on the Cathode drives to heater to 'float' to near its own voltage.  But this still results in hum in some cases.  So forcing the heater to a voltage that is near to the cathode can help.  

    Here is the way I constructed my divider:

    Quote

    I put the output stage to B- (-370V for my build).  For the input stage, I made a voltage divider using 470K and 100K resistors across ground and B+, which gave me 65V for the input stage.  Tweaking the 500K pots then removed what hum remained. 

    And, as stated before in this thread, do NOT use the same transformer to power both the Input and Output stage tubes.  You must you 2 totally independent windings, one for input stage, other for output stage heaters.    

    • Like 2

  22. SRX-Plus Build Thread

    in Do It Yourself

    Posted · Edited by Blueman2

    @tomislavkufrin,

    Congratulations!! My SRX-Plus remains one of my favorite builds, even with my Carbon and Blue Hawaii.  There is beauty in simplicity, and the SRX-Plus is all of that.  As for the hum, I too have had issues with hum in the past, but was always able to get rid of it by 1) using different tubes and 2) elevating the filament voltages, and 3) fine tuning the trim pot settings. 

    As for elevating the filaments, see my old post earlier in this thread:

    Quote

    I do have both filaments elevated.  12AT7s are at 60V (voltage divider off B+ rail) , and 6SN7s are at -340V (tied directly to B- rail).    I did this to eliminate hum.  I do of course have have 2 separate 6.3V windings (I modified my board to use 6.3V for 12AT7s) so they each are elevated to their own levels.

    Definitely do not give up and accept the hum.  I have 2 SRX+ builds, and both had hum at first but after doing some tube swapping and endless fine tuning of the trim pots, both are hum free.  

    Enjoy!!

    • Like 1
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