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Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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Bob Latino
New2Tubez
rjpjnk
vtshopdog
deepee99
Drummerboy2
tubes4hifi
nmchiefsfan
Mr C
HarryY
LeGrace
Dale Stevens
Peter W.
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    A bright flash, a low dull thunk and diminished volume

    Bob Latino
    Bob Latino
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    Post by Bob Latino Sun Aug 25, 2019 3:07 pm

    Mr C wrote:Thanks Bob.  I haven't short cycled it.  And it's been on and off just a few times with all it's tubes.  I went over some of the solder joints this morning, specially the quad cap and SCM.  This morning my line voltage is 119.6.  I have seen it a little over 121.  most the time its in the 120 range.  My speakers are rated at 89dB, they are Polk monitor 10s.  I did have it turned up a little at the time.  It had been on for about 2 hours and I had it on for about 2 hours earlier.  I cant do anything till I get the tube.  Any preference between the Weber SS rectifiers?

    Either the Weber WS-1 (with thermistor) OR the Weber WZ68 will work fine in the ST-120. Note that if there is a problem with the amp itself, you can also blow either of the Weber's. What deepee99 has said is also good advice. If you can find a GZ33 or GZ37 tube rectifier, these are the best tube rectifiers that you can use in your amp. Unfortunately these are not made anymore and the remaining stock are priced in the $100 range.

    Bob
    vtshopdog
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    Post by vtshopdog Sun Aug 25, 2019 3:28 pm

    I purchased my GZ33’s from this British seller on eBay.
    https://www.ebay.com/itm/GZ33-VINTAGE-MULLARD-NOS-VALVE-TUBE/312538946993?hash=item48c4c5ddb1:g:pb4AAOSw6d9clPKC

    Happy with their service and product.
    deepee99
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    Post by deepee99 Sun Aug 25, 2019 4:03 pm

    vtshopdog wrote:I purchased my GZ33’s from this British seller on eBay.
    https://www.ebay.com/itm/GZ33-VINTAGE-MULLARD-NOS-VALVE-TUBE/312538946993?hash=item48c4c5ddb1:g:pb4AAOSw6d9clPKC

    Happy with their service and product.
    Yep, good outfit. I've bought Mullard El-34s from them too. I think they're sitting on a monster stash of Mullard production and dribble this stuff out when they need beer money. It would be worth a trip to the U.K. to locate and raid said stash.
    Smile
    -d-
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    rjpjnk


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    Post by rjpjnk Sun Aug 25, 2019 5:58 pm

    Mr C wrote:Bob is sending out another 5AR4.  In the mean time I went down to the local guitar store and got a GT 5AR4.  All they had where the Groove Tubes.  With the new tube it blew the fuse.  I replaced the fuse and tried again.  The 5AR4 flashed and blew the fuse.  Is something else going on for it to take out the 5AR4?  Could guitar center have had a bad tube?  Is there some trouble shooting to do before trying a another 5AR4?  This amp worked for about 5 hours before loosing the tube.  Bad quad cap?

    You didn't mention how quickly this happened. How long was the amp running with the new 5AR4 before the first fuse blew? And again before the flash and second fuse blew?

    If it was only a short time after turn on (or instantly) then it is probably not tube related, but more likely a short somewhere.
    LeGrace
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    Post by LeGrace Sun Aug 25, 2019 6:17 pm

    Of all the folks I have seen comment that they are running a GZ37 or GZ33 I cannot recall anyone ever commenting they had one die on them; impressive when you think about it. Mine are still going strong.
    deepee99
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    Post by deepee99 Sun Aug 25, 2019 6:31 pm

    LeGrace wrote:Of all the folks I have seen comment that they are running a GZ37 or GZ33 I cannot recall anyone ever commenting they had one die on them; impressive when you think about it. Mine are still going strong.
    And they're so damn studly! If I open the curtains at night with those guys and a quad of 6550s glowing, I can't fight the women off. Say that about solid-state gear. Even blue meters can't fool the truly discerning female.
    Mr C
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    Post by Mr C Sun Aug 25, 2019 6:46 pm

    rjpjnk, The first one blew after about 4 hours of play. It took the fuse out after I put it on the bench and turned it back on. The second one went immediately and the fuse went with it. I went over some of the soldering today. Specially the quad cap. I took a little acid brush and brushed out around everything thinking there may be a wire remnat floating around. I didn't find anything. I also looked around with my magnifying glass looking for a solder bridge. Everything looked okay. Before first power on I took the little vacuum and tried to vacuum out around everything. So I don't know. I'll keep looking and going over the solder joints today.
    Mr C
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    Post by Mr C Sun Aug 25, 2019 7:00 pm

    Looking at the Weber WS-1, would you get the one with the thermistor? It's a delay. It comes with and without.
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    Post by New2Tubez Sun Aug 25, 2019 8:04 pm

    Mr C wrote:Looking at the Weber WS-1, would you get the one with the thermistor?  It's a delay.  It comes with and without.  
    Bob answered this a couple posts up.

    I have the WS1-t in my ST120. I just put it in after having a Tungsol 5AR4 for over a year w/ no problems. I’m using the s/s to go with the newly installed auto bias board which has delay so keeps the power tubes happy. I did the yellow sheet diode mod just after completing the build in 3/2018.
    Mr C
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    Post by Mr C Sun Aug 25, 2019 8:08 pm

    Oops.. senior moment, he did say with thermistor
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    Post by New2Tubez Sun Aug 25, 2019 9:27 pm

    No worries "C".

    Don't quote me but I don't think the Weber WS1-t has enough delay to help the tubes. The VTA-TDR is in the vicinity of 17 seconds. The Weber only does a few seconds w/ thermistor.
    Maybe someone with more knowledge knows better.
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    Post by rjpjnk Sun Aug 25, 2019 10:01 pm

    Mr C wrote:rjpjnk, The first one blew after about 4 hours of play. It took the fuse out after I put it on the bench and turned it back on.  The second one went immediately and the fuse went with it.  I went over some of the soldering today.  Specially the quad cap.  I took a little acid brush and brushed out around everything thinking there may be a wire remnat floating around.  I didn't find anything.  I also looked around with my magnifying glass looking for a solder bridge.  Everything looked okay.  Before first power on I took the little vacuum and tried to vacuum out around everything.  So I don't know.  I'll keep looking and going over the solder joints today.  

    Well if the new tube arced immediately at power-on and the fuse blew I think you almost certainly have a short circuit somewhere. Replacing the tube will not fix this.

    I would start by testing for obvious shorts on B+ using a multimeter after unsoldering the can capacitor. Of course the cap itself could be the problem. So is the new tube toast now or do you think it still might work? I would try removing all the tubes except the rectifier and see if you develop proper B+ voltage with no load. If it blows the fuse again I would remove the can cap and retest. I once heard of a choke that shorted to ground. In any case, get the rectifier up and running with nothing connected to it and then add things one at a time. Something is drawing excessive current. This is a fairly easy thing to fix but only if you are experienced. If you are not comfortable working with high voltage power supplies you should get someone else to help you. Especially with a potential short.

    If the new tube is no longer working I would get two 1n4007 diodes for about 10 cents and not waste money on tubes until the problem is fixed.

    What is the amperage of the fuse you are using?



    HarryY
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    Post by HarryY Sun Aug 25, 2019 10:22 pm

    I was reading in one of the threads on another site from a link in
    the diode mod thread and came across a post mentioning this:

    GFCI Plug with Surge Protection

    A bright flash, a low dull thunk and diminished volume - Page 2 41if9a4qmhL


    If the power gets interrupted it turns off and you have to press the reset button to turn it back on.

    I'm considering ordering a few of these. That way if I have a case of the power
    going on and off the device will shut off and stay off instead of cycling on and off.

    They seem like cheap insurance
    Mr C
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    Post by Mr C Sun Aug 25, 2019 10:35 pm

    Yea the new tube arced immediately.  blew the fuse.  Removed the 6550s, replaced the fuse and same thing.  I'm using 5a slo-blo fuses.  So replaced fuse and put in the original tube.  It doesn't blow the fuse.  The filament glows.


    Last edited by Mr C on Mon Aug 26, 2019 1:07 am; edited 1 time in total
    deepee99
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    Post by deepee99 Sun Aug 25, 2019 11:09 pm

    HarryY wrote:I was reading in one of the threads on another site from a link in
    the diode mod thread and came across a post mentioning this:

    GFCI Plug with Surge Protection

    A bright flash, a low dull thunk and diminished volume - Page 2 41if9a4qmhL


    If the power gets interrupted it turns off and you have to press the reset button to turn it back on.

    I'm considering ordering a few of these. That way if I have a case of the power
    going on and off the device will shut off and stay off instead of cycling on and off.

    They seem like cheap insurance
    They are indeed cheap insurance, and almost a requirement for our power supplies, to which a quick power on-off-on cycle is anathema. So it protects your system in two ways. Don't leap for the restart switch on the GFCI. I wait for the electrical disturbance to pass, where we live it's either lightning or some bozo taking out a power poll, at least a minute or two, then restart. Don't leave home without it.
    Mr C
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    Post by Mr C Sun Aug 25, 2019 11:10 pm

    Yea, there is something terribly wrong. It arcs and blows fuses with just the rectifier in it.
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    Post by New2Tubez Mon Aug 26, 2019 12:18 am

    HarryY wrote:I was reading in one of the threads on another site from a link in
    the diode mod thread and came across a post mentioning this:

    GFCI Plug with Surge Protection

    A bright flash, a low dull thunk and diminished volume - Page 2 41if9a4qmhL


    If the power gets interrupted it turns off and you have to press the reset button to turn it back on.

    I'm considering ordering a few of these. That way if I have a case of the power
    going on and off the device will shut off and stay off instead of cycling on and off.

    They seem like cheap insurance
    I got the 5A variac Bob recommends and the instructions say a surge protector shouldn't be used . I stopped using it after this but honestly don't know why I shouldn't.
    Anyone who knows, please chime in...
    deepee99
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    Post by deepee99 Mon Aug 26, 2019 4:38 am

    New2Tubez wrote:
    HarryY wrote:I was reading in one of the threads on another site from a link in
    the diode mod thread and came across a post mentioning this:

    GFCI Plug with Surge Protection

    A bright flash, a low dull thunk and diminished volume - Page 2 41if9a4qmhL


    If the power gets interrupted it turns off and you have to press the reset button to turn it back on.

    I'm considering ordering a few of these. That way if I have a case of the power
    going on and off the device will shut off and stay off instead of cycling on and off.

    They seem like cheap insurance
    I got the 5A variac Bob recommends and the instructions say a surge protector shouldn't be used . I stopped using it after this but honestly don't know why I shouldn't.
    Anyone who knows, please chime in...
    Since it's my job to make all the mistakes around here, let me advise that the instructions don't lie. The variac will have a melt-down. If there's a workaround, I've not heard of it.
    LeGrace
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    Post by LeGrace Mon Aug 26, 2019 6:43 am

    Mr C wrote:Yea, there is something terribly wrong.  It arcs and blows fuses with just the rectifier in it.  

    Yeah I went through boxes of fuses in the early going, like gum drops. Perhaps you made a mistake, but it sounds so similar to my experience from my 5AR4 days. Soon as I went away from it things calmed down immediately.

    Do you have a cap meter? Handy tool to have in your back pocket. Allows testing of caps in situ. Especially nice for checking up on the condition of the quad cap. Or any other for that matter.
    Bob Latino
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    Post by Bob Latino Mon Aug 26, 2019 7:17 am

    Mr C wrote:Yea, there is something terribly wrong.  It arcs and blows fuses with just the rectifier in it.  

    You should not ever do this (JUST the rectifier in the amp). Without the output tubes in the amp as a "load", the B+ voltage can rise above the limits of the voltage rating of the electrolytic caps in the amp. You could take out some of the parts that receive DC high voltage. (quad cap, SCM, ESL, Russian PIO caps, power caps on the driver board etc.)

    Bob
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    Post by StevieRay Mon Aug 26, 2019 8:45 am

    I use the Weber WS-1 with thermistor.  I also have the time-delay (TDR) module.  While I have a pasion for vintage stuff, I don't believe in tube rectifiers, better sound or not.  Sure, I like better sound, more relaxed, or whatever, but cannot justify the heat and waste of the tube rectifier.  Yes, the vacuum tube is the absolute best thing ever made to reproduce music, but not to turn AC to DC.

    However, I believe the TDR is not absolutely necessary, especially with the thermistor.  I've checked the ramp-up of DC voltage on the Weber; it's nice and steady rise, and probably takes 8 to 10 seconds to level out.

    There's a big debate on whether the time-delay is necessary for audio amplifier tubes vs. radio transmitter tubes, etc.  Just google "cathode stripping".  A lot of manufacturers of tube gear use solid-state rectifiers with no delay for B+ (including lots of McIntosh stuff, conrad-johnson, etc.).

    ASAP -- All of your caps in the B+ signal path (as Bob noted above that might get an over-voltage without the power tubes installed) need to be checked for a short to ground!  The Quad cap first, and note that some or all of your connections to it might need to be unsoldered.  A capacitance checker would be ideal, but a multimeter can also be used to check for cap shorts.
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    Post by New2Tubez Mon Aug 26, 2019 9:45 am

    Look at Peter W's posts about fuses, etc. They're numerous and helpful.

    I'm using these but they're specific to your current draw:

    https://www.alliedelec.com/product/eaton-electronics/mdq-5/70149818/

    Ex:
    https://dynacotubeaudio.forumotion.com/t4016-vta-st-120-and-variac-5-amp-fuse-help-appreciated?highlight=fuse
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    Post by rjpjnk Mon Aug 26, 2019 10:23 am

    Mr C wrote:Yea, there is something terribly wrong.  It arcs and blows fuses with just the rectifier in it.  

    But the good news is it is a relatively simple problem and 100% reproducible. It is straight forward to fix this, but it can be dangerous to troubleshoot without proper experience. Do you feel comfortable troubleshooting it on your own? An alternative is to just start replacing stuff. No risk in that other than possibly wasting money. Do you have someone local who could help you? If you want to mail it to me in NJ I will fix it for you no charge if all else fails, but I realize the shipping is probably too much.
    Mr C
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    Post by Mr C Mon Aug 26, 2019 11:49 am

    Bob Latino wrote:
    Mr C wrote:Yea, there is something terribly wrong.  It arcs and blows fuses with just the rectifier in it.  

    You should not ever do this (JUST the rectifier in the amp). Without the output tubes in the amp as a "load", the B+ voltage can rise above the limits of the voltage rating of the electrolytic caps in the amp. You could take out some of the parts that receive DC high voltage. (quad cap, SCM, ESL, Russian PIO caps, power caps on the driver board etc.)

    Bob

    Phew, Thanks for the warning. I'll back off here till I get the new tube. I was doing rjpjnk's suggestion in his post where he said "I would try removing all the tubes except the rectifier and see if you develop proper B+ voltage with no load."
    LeGrace
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    Post by LeGrace Mon Aug 26, 2019 4:33 pm

    Recently I had someone advise me, in very strident language, that I needed to immediately replace the rectifier leg of my quad cap with a standalone cap 1/10 the value when running a GZ37, for safety reasons. I now always pursue a 2nd opinion, so posted a checking question here. Turns out this advice was same quality as your rectifier only advice, ie not good. Soon after someone else posted an actual literature reference confirming that the quad cap as currently configured is appropriate for use with a GZ37. Sadly many posers out there.

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