Forums https://www.decware.com/cgi-bin/yabb22/YaBB.pl SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> Blowing fuses Rev 12 2018 https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1608074217 Message started by jbohlscheid on 12/15/20 at 23:16:57

Title: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/15/20 at 23:16:57 First attempt a building a tube amp, and I require assistance. First attempt at firing up my Zkit#1 and I am blowing fuses. Fast blow, time released, and slow blow 2, 3 and 5 amp. I get a 1 second buzz on the power transformer, then pop. I have the board wired up and tubes in. I am building on wood and attempting to follow all of the directions to the "T". The chassis ground solder point is connected directly to the ground on the iec socket. Black primary leads connected directly to iec socket. I tried three different types with switches, fuses and just a straight socket. The ground of the RCA connection are connected to the shield (see photo). I am looking for suggestions to diagnose the problem. The soldering looks acceptable. Capacitors and diodes are in the correct orientations. I have been checking the ground continuity and it appears to be ok. I have attached photos for reference. I have connected the 6 jumpers. I used a 18 awg solid conductor that is rated for 150 V, low energy circuit (what I had on hand). The speaker connections are bolted directing onto the board. https://ibb.co/WfSVsSP https://ibb.co/Wc4Lk8R https://ibb.co/s6D1VD2 https://ibb.co/fDX55x9 https://ibb.co/tJRyWWY https://ibb.co/3Nk09t3 https://ibb.co/WKg8MFJ

Title: Re: Blowing fuses Rev 12 2018 Post by JBzen on 12/16/20 at 00:22:52 Double check the 33uf capacitors. Look to be in backwards. John

Title: Re: Blowing fuses Rev 12 2018 Post by Radarek on 12/16/20 at 00:28:38 Take a picture direct from the top with all components installed but it looks like those two blue electrolytes capacitors you have installed in wrong direction...

Title: Re: Blowing fuses Rev 12 2018 Post by Radarek on 12/16/20 at 00:29:49 Use slow blow fuse as well...

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/16/20 at 00:51:24 Thanks for the comments on the Nichicon Caps. I misunderstood the notation on the outside. As for the fuse spec, the 3/10/2019 revision I downloaded notes 3A 250V. I am using a slow blow. Darius, did not have a jumper from the RCA input ground to the shield on the back side of the board? I have been admiring your work for some time. Thanks for photos.

Title: Re: Blowing fuses Rev 12 2018 Post by JBzen on 12/16/20 at 01:04:06 Looking at the other photos, it seems the grid resistor (1K 2W) on the left channel 6P15P leading to pin 7 might be a cold joint. This could create issues with sound quality. Best of luck. John

Title: Re: Blowing fuses Rev 12 2018 Post by Radarek on 12/16/20 at 01:45:47 I have shield connected on board side only...almost invisible...look at right one as it shows a bit better, shield you only connecting on one side either to ground on rca side or pcb side ...never on both ends...

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/17/20 at 00:48:33 Thanks for the suggestions. I turned the caps around and we have light. And I addressed the potential cold solder. However there may be more as the voltages are off. A. 341 vs 346 (within spec) B. 293 vs 309 (off by 6) - check solder at 6.8K resistor C. 9.26 vs 10.25 (within spec) D. 0.04 vs 2.60 (way off) If I understand the schematic, the two cathodes int he 6N1P input tube are not receiving the appropriate voltage/charge. I suppose I will trace back through the parallel 47K resistors and the socket pin soldering. Cleaning up the solder at the 6.8K resistor might help. Back to the bench. Being new to the tube world, I thought there might be a bit more glow out of the tubes. They are warm.

Title: Re: Blowing fuses Rev 12 2018 Post by JBzen on 12/17/20 at 11:33:29 Is the volume control all the way down?

Title: Re: Blowing fuses Rev 12 2018 Post by Denizen on 12/17/20 at 18:20:18 Check your plate voltages (pins 1 and 6) on your input tubes they will determine your cathode voltages.

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/17/20 at 18:36:24 Denizen - Thanks for the idea. Checking the plate voltages is while the unit is running, correct? I need to check the appropriate value. Also to the question on the volume, it is all the way down. One thing I have noticed is that the schematic is a bit different from the silk screen and the parts list. Two 330K resistors replace two 1K resistors int the output stage and the associated caps are 0.1 uF 400V vs 0.1 mF 600V.

Title: Re: Blowing fuses Rev 12 2018 Post by Denizen on 12/17/20 at 18:49:38 The 2 watt 1k resistors on the output tubes are connected to pins 7(plate) and pin 9(screen grid) the two 330k resistor go from the .1uf coupling caps to ground.

Title: Re: Blowing fuses Rev 12 2018 Post by Denizen on 12/17/20 at 20:58:21 After checking the schematic against the board you should use the values printed on the board, those are the correct values.

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/17/20 at 23:05:20 The voltages at pin 1 of the input socket is 108 V and pin 6 is 115 V. At pins 8 and 3 it is 3 V, and 2 and 7 zero V. I'm not sure of the appropriate value expected.

Title: Re: Blowing fuses Rev 12 2018 Post by JBzen on 12/17/20 at 23:34:08 Pins 3 & 8 check at 3 volt. Should be good to go.

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/17/20 at 23:56:28 Ugh! I was taking the voltages at the wrong spot - across the resistors not against the ground. At 3.02 - within spec. Thanks for the help and hopefully no undo excitement on attaching sources and speakers.

Title: Re: Blowing fuses Rev 12 2018 Post by JBzen on 12/18/20 at 00:00:28 Good thing you used fuses or else there would have been fireworks when the 33uf caps popped. Seems like all should be good without harm done. Enjoy! John

Title: Re: Blowing fuses Rev 12 2018 Post by jbohlscheid on 12/18/20 at 04:34:01 I kept an appropriately rated fire extinguisher handy just in case. Hooked up though Rotel RA 1572 as preamp and ran CD from Marantz ND8006 and Paradigm Atom stand mount speakers to check out the work. Julie London and Tom Waits sounded great (not together of course). Sounds good, no notable odd sounds outside of the purring of the transformer. Tomorrow on to the Heresy 1 pair and some vinyl - Need to celebrate Beethoven's 250th. I wonder if I can hook up my Rel sub also? Thanks for all of the help. I'm going to draw up "A bucket head's instruction manual" for this. My notes to give to my kids so they can get the fundamental system set up.

Title: Re: Blowing fuses Rev 12 2018 Post by Radarek on 12/18/20 at 06:53:00 Great, congratulations and enjoy...

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