Results 1 to 23 of 23

Thread: Runaway current draw from single 6L6 tube

  1. #1
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1

    Runaway current draw from single 6L6 tube

    Just got an old RCA amp the other day, no schematic looked everywhere including here...

    Things were going well tonight testing, and I actually got to play through it for about a half hour, but with one caveat, the whole time the amp was running through my light bulb limiter, so the wall voltage was lower. I decided to run it straight to the wall and measure the plate voltages and current through the output transformer and I was shocked to find one tube with a 406vdc plate voltage, while the other was down around 354vdc. I checked the voltage drop between the center tap and each tube, and lets just say there was a HUGE difference, so I quickly got out my infrared temp gun and the tube with the low plate voltage and big voltage drop was 538 degrees Fahrenheit, while the other was 200 degrees.

    Now here's the weird thing, I ran the amp once again through the Light bulb AC voltage short detector and both plate voltages were identical and both tubes close in temperature.

    I substituted another tube in place of the "hot" one, same thing. The output transformer is a brand new Classic Industries one, and it wasn't hot.

    No schematic, but here's a pic of the underbelly of the amp. I couldn't measure the ohms on those big violet/blue (resistors ?) that were connected to the screens, so I cut them out, and just ran voltage to the screens on a second node coming after the first 40uf cap from the rectifier (replaced that cap), and then another 30uf cap to ground. That yields around 292vdc for the screens, at least through the light bulb short protection.

    Click image for larger version. 

Name:	RCA MI-6599 Bottom.jpg 
Views:	28 
Size:	96.4 KB 
ID:	56301

    Any ideas ? Thanks.

    EDIT #1 : Put a JJ 6L6 in place of the one super heating tube socket, and now it appears to be behaving even at the 125vac wall voltage, but... I think the 180 ohm cathode bias resistor is way to low, as one tube has a plate dissipation of 33.2 watts ! while the other is a more acceptable but still high 26.6 watts. I will straighten this out and see if it helps.

    EDIT #2 : Put a larger resistance between the B+ and screen nodes (now 2 x 5.6k = 11.2k) and screen voltage is back down to 33.2vdc. All seems well with the one JJ tube. I think I was just pushing the RCA tubes too hard, as the wall voltages are a lot more than when this amp was first built, around 1948.

    Still if anyone has an idea about anything else that may be an issue, I am all ears ! and thanks once again !!!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	RCA MI-6599 Bottom.jpg 
Views:	21 
Size:	139.1 KB 
ID:	56300  

    0 Not allowed! Not allowed!
    Last edited by HaroldBrooks; 12-11-2019 at 05:20 AM.

  2. #2
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    6,459
    Thumbs Up/Down
    Received: 1,308/1
    Given: 1,007/1
    Rep Power
    16
    There would have to be quite a large difference in OT primary resistance from each side to CT for plate voltages to be that different. If you measure resistance each side of the primary to CT what do you get? Were these plate voltage measurements taken with no signal at idle?

    As an aside, I wouldn't actually use an amp hooked to the limiter. That is for testing purposes only and initial fire up.

    1 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  3. #3
    Supporting Member Randall's Avatar
    Join Date
    Jan 2013
    Location
    Cape Coral, FL
    Posts
    2,470
    Thumbs Up/Down
    Received: 569/0
    Given: 104/0
    Rep Power
    9
    "I couldn't measure the ohms on those big violet/blue (resistors ?) that were connected to the screens"

    Why not? That seems easy enough.

    1 Not allowed! Not allowed!
    It's weird, because it WAS working fine.....

  4. #4
    Supporting Member eschertron's Avatar
    Join Date
    Aug 2012
    Location
    Great Black Swamp
    Posts
    2,267
    Thumbs Up/Down
    Received: 448/0
    Given: 1,207/1
    Rep Power
    11
    If you have questions about the amp, even - or especially - with questions about the component function, start drawing out a schem for us and yourself. Input circuitry, power supply, output section, etc., can be broken out from the rest of the design and handled (schem-wise) independently. I can't see under the mess of wires running over the tube sockets. Is this fixed bias? Cathode bias?

    Get some dissipation readings from each tube. One may not be 'hot', the other may be not conducting and the hot tube is normal. If there is a shared cathode resistor, however, a single operating tube will draw half the idle current and so the bias voltage will be very low. Possibly low enough to put the tube over dissipation limits?

    What exactly is "same thing" with a replacement tube. The running hot, I presume?

    2 Not allowed! Not allowed!
    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


  5. #5
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by The Dude View Post
    There would have to be quite a large difference in OT primary resistance from each side to CT for plate voltages to be that different. If you measure resistance each side of the primary to CT what do you get? Were these plate voltage measurements taken with no signal at idle?

    As an aside, I wouldn't actually use an amp hooked to the limiter. That is for testing purposes only and initial fire up.
    224 ohms each side spot on. I just added some more resistance to the cathode resistor from 180 ohms to 230 ohms. I think I should have gone a bit further, as now one of the tubes is still at around 26.6 watts of plate dissipation. Ran the amp playing for about 15 minutes and nothing crazy happened yet... I think I need add a bit more resistance to the cathode resistor and use another new JJ tube, as the one I put it seems calm, while the old RCA metal can tubes are running hot. I won't be using the limiter anymore from this point on. I had to correct the shorted filter caps, so in the beginning it saved the amp, but you are correct, time to run wall voltage and fix what is left to be fixed.

    Thanks for pointing out the ohms measurement on the OT, I am new to all this, and still learning a lot as I go along (low on the learning curve).

    0 Not allowed! Not allowed!

  6. #6
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by eschertron View Post
    If you have questions about the amp, even - or especially - with questions about the component function, start drawing out a schem for us and yourself. Input circuitry, power supply, output section, etc., can be broken out from the rest of the design and handled (schem-wise) independently. I can't see under the mess of wires running over the tube sockets. Is this fixed bias? Cathode bias?

    Get some dissipation readings from each tube. One may not be 'hot', the other may be not conducting and the hot tube is normal. If there is a shared cathode resistor, however, a single operating tube will draw half the idle current and so the bias voltage will be very low. Possibly low enough to put the tube over dissipation limits?

    What exactly is "same thing" with a replacement tube. The running hot, I presume?
    I will try to do just that. I actually got a better view of everything just tonight. I am not quite as up on this stuff as I might seem, LOL, but maybe that would help. One thing I did was pull the 6SK7 tube out all together, and ran a cap from the plate of the 6J7 to the 6SN7 pin #1 grid. That worked out quite well, as the gain jumped considerably, and the distortion is now sweet sounding, whereas before it was a bit nasty. The 6J7 tube has a very high amplification factor, and I tied the screen grid to the screen supply for the 6L6 tubes using a 1 meg resistor and a .047uf cap to the cathode. I got this arrangement from one of my old National (Valco) model 50 schematics. Seems to work well here.

    Replacement JJ tube runs OK, and seems to take everything (unfortunately I only have one JJ). Only issue now seems to be reeling in the power tubes, specifically the old RCAs I am still using. For now the one cooler running JJ will stay put, and I will most likely buy another one to match. I like the "Chunky" and "Beefy" sound of this "New" amp ! different than my 6973, 6V6, or EL84 amps. I think it might have something at least in part do to the 6L6s, but that is probably only part of the picture, i.e. Power and OT transformers, etc...

    0 Not allowed! Not allowed!
    Last edited by HaroldBrooks; 12-11-2019 at 06:01 AM.

  7. #7
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by Randall View Post
    "I couldn't measure the ohms on those big violet/blue (resistors ?) that were connected to the screens"

    Why not? That seems easy enough.
    Tried again, this time using alligator clips attached to the leads so I could get a really good "Bite" on the wires of the two resistors, and they are out of the amp entirely... Nothing, not using any scale on my multi-meter, as if they were open, and perhaps they are or something else I am not seeing.

    One of them ran up the scale at the 20M ohm setting, and then just showed nothing, so there appears initially to be some continuity, just nothing I can measure ohms wise, so either they are shot, or not resistors, but they don't look like any type of capacitor, so there you have it.

    0 Not allowed! Not allowed!
    Last edited by HaroldBrooks; 12-11-2019 at 05:58 AM.

  8. #8
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    32,459
    Thumbs Up/Down
    Received: 2,013/7
    Given: 0/0
    Rep Power
    55
    Don't we already have a thread on this amp?

    1 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  9. #9
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Do you have the schematic for this amp ?

    That's what I was looking for in my other post.

    If you have the schematic, please post it, and I will be eternally grateful !

    And once again, Thanks for all your help Enzo !

    0 Not allowed! Not allowed!
    Last edited by HaroldBrooks; 12-11-2019 at 09:00 AM.

  10. #10
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    32,459
    Thumbs Up/Down
    Received: 2,013/7
    Given: 0/0
    Rep Power
    55
    If I had one I would have posted it, I suggested you draw one from the circuit.

    1 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  11. #11
    Supporting Member
    Join Date
    Dec 2009
    Location
    UK
    Posts
    3,557
    Thumbs Up/Down
    Received: 290/0
    Given: 39/0
    Rep Power
    14
    I always suspect leaking caps in older amps and these can be a source of trouble if ignored. The leakage isn't always evident at lower voltages and an amp operated at reduced voltage (as with a limiter) can behave fairly normally. The leakage can jump right up when under full voltage and cause an excessive bias voltage to appear on the tube grids. Caps that have a small leakage usually get worse so for longer-term reliability it's worth checking. I install 470R screen resistors with 6L6 tubes by default and I like the flameproof fusible resistors that Fender uses in some amps.

    1 Not allowed! Not allowed!

  12. #12
    Supporting Member
    Join Date
    May 2006
    Location
    Staffordshire UK
    Posts
    3,812
    Thumbs Up/Down
    Received: 549/1
    Given: 480/2
    Rep Power
    18
    I guess a 1948 PT would be intended for 110V; feeding it 125V will probably result in all secondaries running too high, resulting in limiting values being exceeded. eg what are the heater voltages?
    Bear in mind that the amp was designed around early 6L6, which had much lower voltage and dissipation limits on plate and screen grids.

    2 Not allowed! Not allowed!

  13. #13
    Supporting Member eschertron's Avatar
    Join Date
    Aug 2012
    Location
    Great Black Swamp
    Posts
    2,267
    Thumbs Up/Down
    Received: 448/0
    Given: 1,207/1
    Rep Power
    11
    Quote Originally Posted by HaroldBrooks View Post
    I just added some more resistance to the cathode resistor from 180 ohms to 230 ohms. I think I should have gone a bit further, as now one of the tubes is still at around 26.6 watts of plate dissipation.
    What was the other tube's calculated dissipation? Also, posting the voltage across your 230R cathode resistor will help me get a better idea of what you're facing. And I'm assuming the plate voltages are different now with different tubes and a different Rk. Please share.

    0 Not allowed! Not allowed!
    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


  14. #14
    Supporting Member eschertron's Avatar
    Join Date
    Aug 2012
    Location
    Great Black Swamp
    Posts
    2,267
    Thumbs Up/Down
    Received: 448/0
    Given: 1,207/1
    Rep Power
    11
    Quote Originally Posted by HaroldBrooks View Post
    Tried again, this time using alligator clips attached to the leads so I could get a really good "Bite" on the wires of the two resistors, and they are out of the amp entirely... Nothing, not using any scale on my multi-meter, as if they were open, and perhaps they are or something else I am not seeing.

    One of them ran up the scale at the 20M ohm setting, and then just showed nothing, so there appears initially to be some continuity, just nothing I can measure ohms wise, so either they are shot, or not resistors, but they don't look like any type of capacitor, so there you have it.
    Drawing and posting at least the section of the circuit where these devices were, showing them in circuit (identified with a question mark?) will help us answer those questions. Really, take a half-hour and sketch it out on a piece of paper. Don't worry about how bad it looks, it will jump start your understanding of this amp tremendously.

    2 Not allowed! Not allowed!
    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


  15. #15
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by Mick Bailey View Post
    I always suspect leaking caps in older amps and these can be a source of trouble if ignored. The leakage isn't always evident at lower voltages and an amp operated at reduced voltage (as with a limiter) can behave fairly normally. The leakage can jump right up when under full voltage and cause an excessive bias voltage to appear on the tube grids. Caps that have a small leakage usually get worse so for longer-term reliability it's worth checking. I install 470R screen resistors with 6L6 tubes by default and I like the flameproof fusible resistors that Fender uses in some amps.
    I checked the 6L6 coupling caps and no DC voltage leaking from one end to the next. Those are the best looking caps of the lot, so I left them in, but I will take your advice under advisement just the same. There are a couple of other caps I have not changed that visually are a wreck, and today I will swap them out. It's possible they were causing an imbalance that I did not understand, so they need to go.

    Thanks !

    0 Not allowed! Not allowed!

  16. #16
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by pdf64 View Post
    I guess a 1948 PT would be intended for 110V; feeding it 125V will probably result in all secondaries running too high, resulting in limiting values being exceeded. eg what are the heater voltages?
    Bear in mind that the amp was designed around early 6L6, which had much lower voltage and dissipation limits on plate and screen grids.
    6.8 vac, again a bit high, and I think you are correct about the wall voltage being a part of the problem. I do have an inexpensive surge protector that automatically limits wall voltage to 114vac from the normal 125vdc I see here, and I'm not sure how this get's done in the unit, but it's consistent and the unit can handle 3k watts. I don't use it because it weighs a lot ! and I don't want to be tied to lugging that around when I use this amp. I was just thinking of employing some Zener diodes I have, as I used those in the past with another amp, and they worked well.

    QUESTION : the B+ on this amp peaked last night to 462vdc, am I running any real risk in using 450vdc rated brand new filter caps exposed to 462vdc ? I would think it's close, but I would like to here from the voice of experience as to what the potential risk is !

    0 Not allowed! Not allowed!

  17. #17
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by eschertron View Post
    Drawing and posting at least the section of the circuit where these devices were, showing them in circuit (identified with a question mark?) will help us answer those questions. Really, take a half-hour and sketch it out on a piece of paper. Don't worry about how bad it looks, it will jump start your understanding of this amp tremendously.
    Till this point I haven't had the confidence to draw any circuit, but I think your advice is good, and I will attempt it as part of my learning and initiation. Probably have something later today. Verbally now I can say that each one of those Blue/Violet assumed resistors were connected to the screens #4 pin of the 6L6 tubes, and someone here mentioned as a voltage divider. Here's the weird thing for me though, one was connected to pin #2 of the rectifier, and the other just to ground. Again I may not see the obvious implications of this.

    0 Not allowed! Not allowed!

  18. #18
    Bent Member Chuck H's Avatar
    Join Date
    May 2007
    Location
    pacific north west
    Posts
    15,767
    Thumbs Up/Down
    Received: 2,607/4
    Given: 3,063/0
    Rep Power
    30
    I think it's probably that in your first observation there was a tube that wasn't conducting. 200°F isn't indicative of a tube that conducting, but 538°F might be about right for a hot bias on the surface of a metal can tube. Possibly one tube was not conducting due to the bad screen grid resistor/s. After replacing those there was some mismatch in the current between the power tubes. The RCA's ARE old tubes, so there may be a problem with one or both. And I wouldn't expect the JJ to match up with them at all. I think you need a pair of good tubes in there for more evaluation and before any further circuit adjustment.

    1 Not allowed! Not allowed!
    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

  19. #19
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,554
    Thumbs Up/Down
    Received: 1,906/1
    Given: 1,103/2
    Rep Power
    5
    Here's the weird thing for me though, one was connected to pin #2 of the rectifier, and the other just to ground. Again I may not see the obvious implications of this.
    As pin 2 of the rectifier is B+, the 2 resistors constitute a typical voltage divider if screens are jumpered (looks as if they are). Screen voltage being R1/(R1+R2) times B+, with R1 to ground, R2 to B+.

    2 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-11-2019 at 06:44 PM.
    - Own Opinions Only -

  20. #20
    Supporting Member mozz's Avatar
    Join Date
    Oct 2015
    Location
    NEPA
    Posts
    839
    Thumbs Up/Down
    Received: 196/1
    Given: 136/0
    Rep Power
    5
    Could you post the tube lineup again, i may have the schematic on my old Rider PA. manual. Does it have a interstage transformer?

    0 Not allowed! Not allowed!

  21. #21
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by mozz View Post
    Could you post the tube lineup again, i may have the schematic on my old Rider PA. manual. Does it have a interstage transformer?
    Only a power and an output transformer, no chokes. The tubes are 6J7, 6KS7, 6SN7, and two 6L6s.

    Thanks for any help !

    0 Not allowed! Not allowed!

  22. #22
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,027
    Thumbs Up/Down
    Received: 1,795/24
    Given: 4,607/11
    Rep Power
    23
    Quote Originally Posted by HaroldBrooks View Post

    [B]QUESTION : the B+ on this amp peaked last night to 462vdc, am I running any real risk in using 450vdc rated brand new filter caps exposed to 462vdc ?
    Quote Originally Posted by Helmholtz View Post
    As pin 2 of the rectifier is B+, the 2 resistors constitute a typical voltage divider if screens are jumpered (looks as if they are). Screen voltage being R1/(R1+R2) times B+, with R1 to ground, R2 to B+.
    Yes, that is how the screen supply was configured. In the other thread, I had mentioned that judging by the size (power) of those resistors they were probably pulling the whole B+ down somewhat and it may put the main filter caps & power tubes at risk to remove them.
    That seems to be the case, or at least it is a contributor along with the higher modern line voltage.

    Harold, was the 462V just during power up, or while running?

    1 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  23. #23
    Member HaroldBrooks's Avatar
    Join Date
    Mar 2019
    Posts
    259
    Thumbs Up/Down
    Received: 133/0
    Given: 749/0
    Rep Power
    1
    Quote Originally Posted by g1 View Post
    Yes, that is how the screen supply was configured. In the other thread, I had mentioned that judging by the size (power) of those resistors they were probably pulling the whole B+ down somewhat and it may put the main filter caps & power tubes at risk to remove them.
    That seems to be the case, or at least it is a contributor along with the higher modern line voltage.

    Harold, was the 462V just during power up, or while running?
    426vdc is While running, and as you know there is a brief exposure to higher voltage (peaks briefly at 540vdc) on startup. I will order a few 600v 47uf caps. It's the first one off the B+ that will take the beating, as the others are reduced I believe by the resistance later in the chain.

    Thanks for solving the mystery of the big resistors. I think at this point they will stay out as the amp sounds good with the current voltages.

    Update :

    I found another JJ 6L6 lurking in one of my forgotten single ended amps ! So I popped it in, and the balance is restored ! one tube is biased now at 21 watts for just the plate dissipation, and the other is 24 watts, so all is well I believe. Today I added a bunch of my usual safeguards, i.e. Varistors, Diodes for the rectifier. I also put the amp through the paces with a few different type speakers, and it sounds best playing through my twin 10" Celestion Greenbacks (So Far). I don't think this amp is producing all that many more watts than my 6V6 amps, but It handles the bass transients a whole lot better and cleaner. I don't think the power tubes are being driven into distortion all that much, and that may account for it.

    So I still haven't drawn a "modified and current state" schematic, but I may get to that later tonight. I abandoned using the 6SK7 tube in the amp, as it was wired in concert with the 6J7 in a way that I don't understand, and I saw little advantage at this point (Famous last words !), so I just hooked up the 6J7 to the 6SN7 through using a .01uf coupling cap off the plate to the grid (pin #1) of the 6SN7. That works rather well ! Also this amp runs a higher plate voltage for the 6J7 then I've seen in the past, right around 250vdc, but using a 1meg screen resistor and as a result it's only running a modest screen voltage of 77vdc. In any event, the gain is very good, but not too much to overload the 6SN7 too much it seems. I also reduced the size of the coupling caps to the 6L6s, from .1uf to .047uf 630v metalized Polyester caps. This seems to have sharpened up the sound a bit. Still there is a lot of bass in the very low region (below 100hz) and I filter that out up front with my EQ, but I probably should nock it out in the amp itself with some changes to the bass pot, or perhaps an even smaller coupling cap from the 6J7 to the PI tube.

    I boosted the heck out of the amp and it sounds superb even with punishing levels of gain !

    Great for 80's rock (think AC/DC, Scorpions, etc..) Fat and big sound, and clear as a bell when playing 7th and even on a 7th#9 chords, the ones that are normally chaotic. This amp for me is a winner so far !

    Thanks for everyone's help so far. I will try to make a "schematic" the best I know how, and get further input from you guys. There is always room for improvement !

    2 Not allowed! Not allowed!
    Last edited by HaroldBrooks; 12-12-2019 at 06:13 PM.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. EL84 current draw help
    By lion in forum Maintenance, Troubleshooting & Repair
    Replies: 17
    Last Post: 11-24-2013, 02:52 AM
  2. Power tube current draw changes unevenly over time?
    By jamesmafyew in forum Maintenance, Troubleshooting & Repair
    Replies: 2
    Last Post: 06-15-2010, 02:33 PM
  3. Cathode Bias current draw
    By MikeT in forum Theory & Design
    Replies: 3
    Last Post: 11-10-2009, 08:33 PM
  4. Mains current draw
    By lowell in forum Theory & Design
    Replies: 0
    Last Post: 05-20-2008, 12:41 AM
  5. grid current draw
    By JC@ in forum Theory & Design
    Replies: 7
    Last Post: 09-30-2007, 09:12 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •