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sorenb

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Posts posted by sorenb

  2. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    5 minutes ago, bui501 said:

    Help!  So...  After waiting several months for replacement SiCs, I replaced all the 10m90s, SiCs and DN2540s on both GRHV boards and amp boards.  I've only started testing the psu boards.  The low voltage outputs measured right around +/-15V.  However, the -400VDC lead only measures -5V even though the leads from the transformer correctly reads ~390VAC (measured directly at the pads on the board).  The high voltage outputs correct (+/-400VDC) before the SiC and 10m90 meltdowns from a few weeks ago, so the only parts I've replaced are the 10m90s, SiCs, and DN2540s on the board.  Any suggestions?

    On a side note, when a manufacturer advertises their silver-looking thermal paste as "electrically non-conductive", they might not be thinking high-voltage...  One of the 10M90S on my other psu board just let off a spectacular spark and a "Pop!" after a few minutes at full 220VAC from the variac.  I was using PEEK screws, Protronix Series 7 Silver Thermal Paste, and standard aluminum oxide pads.  The paste was advertised as "electrically non-conductive.":angry:  The little explosion blew the al oxide pad right out from between the component and the heatsink.

    check the terminal where the leads from the transformer is attached. Might also be that you populated the CPC1117?
     

  3. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    1 minute ago, Blueman2 said:

    Thanks.  Sorry for my confusion on the OpAmp.  But is there any advantage to engaging Servo2 rather than Servo1?  As I recall, only one should be enabled at a time.    

    only one at a time. Both will keep the amp offset ~ zero, and both are altering the operation point of the particular stage.

    • Like 1

  4. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    27 minutes ago, Blueman2 said:

    I currently have the Op27a based servo (Servo 1) in use on my Carbon.  Works great.  I just got hold of a couple 4N25's for the Optocoupler (Servo 2) and was going to plug them into the board.  Is there any advantage to the optocoupler servo over the op-amp servo?  Just curious why both were put on the board.  For now, I am leaving Servo 1 enabled and Servo 2 disabled.  

    in any case the OpAmp is needed. Servo1 acts on the input, and Servo2 on the output stage rather. You need  some ~ +15V offset to use the Servo2.

    • Like 1

  5. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    1 minute ago, Blueman2 said:

    Thanks.  Is there much of an issue running a BH BJT at only 375V?  Either that or I will get a 350V rated trafo.  Just not sure the larger trafo will fit into this case.  Things are really, really tight in there right now.   

    no issue running it a bit low, and leave it at that.

    • Thanks 1

  6. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    44 minutes ago, Blueman2 said:

    Details are:

    Raw AC from trfo: 2x 315V @ 330ma each

    Unregulated DC: 436V

    Regulated B+: +404 no load, +392 load

    Regulated B-: -410 no load, -383 load

    SiC drain is 8.3V under load. 

    will measure other in a bit...  Thanks sorenb.

    secondaries are too low for getting 400V out ... try 375V rather ...lower the two 390k to 365k, or parallel to get there

    • Thanks 1

  8. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    17 minutes ago, Blueman2 said:

     ...But stays in a range of about 390 +/-3v.  Enough to allow me to get offsets down to under a volt and confirm the outputs to 20ma.  

    assume you GRHV voltage out is 390V under load and +404 and -410 without? what is the voltage at the drain of the Sic (middle leg) against ground? 
    and what is the voltage between R9/R7?  both with and without load

    • Thanks 1

  9. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    13 minutes ago, Blueman2 said:

     

    I got the BH BJT up and running today.  Everything seems great and I was able to dial all the voltages and currents in just right.  One issue I am seeing is filament voltage.  My Antek PSU is giving me 6.8V under load for the EL34s.  Our voltage here is always around 125V, and the PSU was rated for 115, thus the higher value for the 6.3 feeds.  I put a pair of 5W 1Ω resistors in parallel to create a 0.5Ω resistor for each amp board filament supply.  That got the voltage down to 5.5VAC.  Is that too low or should I go out and buy another 1Ω resistor to add in parallel?      

    you need > 6.0V, 3x 1ohm might get you there, else use 4x
     

    • Thanks 1

  10. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    1 hour ago, bui501 said:

    Problem 1:  The low voltage outputs from the GRHV boards goes up to only +/-10V even at 220VAC input on the transformer (17.8VAC unloaded measurement from the transformer's output, low voltage winding).

    Check your CT from the transformer  is really going to CT at the board.

    1 hour ago, bui501 said:

    Problem 2:  I hooked up the power supply boards to the carbon boards anyways and started to play with the current adjustment pots.  At the test point FURTHEST away from the servo 2 jumpers, I can get the current to 20mA (started out at 18mA).  However, at the test point/pot closest to the servo 2 jumpers, the current started out "normal" at close to 20mA, but after 10 or 20 seconds, it rose to 36mA -- I cannot/cannot get the current to go much lower at that test point.  This is the same for BOTH amp boards, so I'm assuming it's a problem with the PSU boards.

    Sounds like thermal runaway for the 10m90; the dissipate as much heat as the SiC and thus needs to be properly heatsinked.
    Cannot see from your pics how you have attached the 10m90 to the sink ...use an alu oxi pad, thermal past on both sides of the alu oxi pad, and a screw to tighten )
    If not the above check the CSS using 2xbattery9V or similar, and see if you can adjust the current - if not, the DN2540 has probably gone south

  14. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    45 minutes ago, Blueman2 said:

    1) Is it necessary or common to have soft stop on the BH?  I am hoping I do not need this.

    Not needed.
    Soft START is a good thing to be easy on the tubes. T2 uses 60 seconds delay.
    Some uses constant current sources to feed the filament, to avoid the high current when the tube is cold  - high current is stressing the tube (and usually why incandescent bulbs fail)... some runs the filament a bit below spec e.g. 6V rather than 6.3V,  (even seen 5.5V) as far as I have measured 6V is pretty safe, where as lower voltage increase the risk for "cathode stripping" 

    • Thanks 1

  16. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    35 minutes ago, Blueman2 said:

    I need some advice on modifying an early GRHV board that does not have the delay circuit (no CPC1117N).  I want to add the delay circuit to it for use with the BH BJT I am building. 

    It appears from looking at the attached diagram (for the board with the CPC1117N) that the delay circuit effectively puts a 600R resistor across the 12V (or 10V on my older board) zener D1 to shut down high voltage output.  Is that all that is needed to shut the board down? 

    I plan to make an off board circuit using a 600R resistor on the output of a CPC1117N, and tie that output across the D1 using about 6" of 20awg wire.  The CPC will be driven by a timer circuit I got off of eBay.   It seems pretty straightforward, but I wanted to see if my thinking was valid.  

    goldenreferencehvsic.PDF

    Yep - you might mount D1 on the separate board and use it's legs for connection to the main pcb

    • Like 1
    • Thanks 1

  18. grounded grid

    in Do It Yourself

    Posted

    7 hours ago, bbest said:

    Hello all!

    How many mA in transformer prefer to use for GG? Voltage 360 (=> 450V output) and 350 mA is it will be enough? On another forum recommended 500VA transformer for tubes amps.

    ( 2 channels x (2x Output stage current  + 10mA for input stage )*sqrt2*360VAC + 4x 6.3VAC*1.5A ) * some_factor depending on how much overkill  ~ 100VA * some_factor 
    I usually end up using a factor somewhere above 2 and close to 3 

    • Like 2

  19. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted

    5 hours ago, bbest said:

    Hello all!

    Successfully run one board of GRHV (boards 1.7 version). Wanted to turn it on 450V. Could I use three resistors instead of two R8, R9 ? Is not it criminal?

    For example 390K + 390K + 100K = 880 = 2x 442 .

    only reason to use more resistors is spreading the heat dissipation 

    • Like 1

  20. goldenreference low voltage power supply

    in Do It Yourself

    Posted

    What is the drop of those special diodes you are using? 2.8V drop seems to be about twice what could be expected.
    In any case you might consider using higher secondaries to provide the regulation some 'room' ... as far as I have experienced 3V is minimum to get regulation, but if the current is above 1.5A is more likely to be 4V .... as for your experience it seem like you have some loss between the VAC input and collector of the pass transistor 

    • Confused 1

  21. goldenreference low voltage power supply

    in Do It Yourself

    Posted

    5 hours ago, mwl168 said:

    Checked 3 GRLV and observed very similar measurements. 

    Under load, which is only 300mA - 400mA in these cases, the transformer secondaries measured right around spec. However, I am getting < 3VDC Vce on MJW21194 and MJW21193 and it seems to drift a bit, I measured between 2.3VDC - 2.9VDC at different time and the lower Vce is also reflected as dimmer LEDs next to the MJF190303/19031. I don't have the GRLV schematic on hand. What do I need to do to raise the Vce of the MJW devices to 3 - 4 VDC? 

    EDIT: Forgot to mention that I did measure the input pins of the OP (pin 2 and 3) and pin6 of LT1021 and they all measured 10VDC.

    So you have 24VAC 100VA connected to a GRLV configured for 24VDC, and have less than 3VDC drop, while the transformer secondaries are at 24VAC? numbers doesn't seem to add up - at least 3-5V is missing as far as I can see: 24VAC*1,4VDC/VAC - 3VDC (regulation drop) - 2VDC (diode drop) - Load_drop = 24VDC =>  Load_drop ~ 3-5V
     

  24. goldenreference low voltage power supply

    in Do It Yourself

    Posted

    6 hours ago, mwl168 said:

    Fed by a transformer with 2 X 24vac/2A secondaries, my GRLV was not able to sustain regulation for 24 VDC output when the current draw was about 1A per rail. The output sagged down to about 23 VDC.  

    The same setup works fine when I reduce the current draw to about 500mA pre rail. It also works fine for 1 A per rail draw once I lowered the regulated output to 22 VDC.

    As you can see from my previous post (edited to include transformer information), I was able to pull 4.2A at 20V without any problems (had a scope on the output).
    I suggest you measure the actual input pins of the OpAmp and pin6 at the lt1021, to verify all those are at 10V when you experience the output is sagging. If that is ok Check if you have >4V Vce across the pass transistor (for my experience it works already at 3V when the current is 1A) 

  25. goldenreference low voltage power supply

    in Do It Yourself

    Posted · Edited by sorenb

    2 hours ago, mwl168 said:

    Drawing about 1A per rail, my GRLV could not maintain regulation for 24VDC rails when supplied by a transformer with 24vac/2A secondaries.

    "could not maintain regulation" meaning what exactly?

    (edit after adding the transformer info to the previousposting)
    You probably want to check the voltages in the input pins of the OpAmp (directly on the OpAmp) against the pin6 at the LT1021, when you experience the regulation doesn't work

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