Kegger/blueglow kt88 project

[Ruidoso Bill]

Blown fuses are keeping me unhappy. Without KT88's & just 6N1P all seems to be ok. B+ = 536vdc. 6N1P pin1 = 271.2vdc & pin6 = 222.3vdc. LED's glowing. But when I add the KT88's pow, fuse blows. Using just one KT88 in either left or right, pow, fuse blows. Only gets to around 20vdc before fuse blows. Using slow blo 2A fuses..I have checked & double checked schematic several times. This is really getting to be a head scratcher.View attachment 1483025 View attachment 1483026 View attachment 1483027

OK Mr. Twirl, I certainly understand and totally appreciate your frustration, been there for sure. I first advise that besides my shorted ground issue I wrecked a GZ34. Of the 3 I had in the system at different times, (talk about head scratcher) one was wrecked, one tested lower on the tube tester or possibly semi damaged or degraded. I finally replaced most of the components around the KT88 sockets. Here is another option to try:



So even if the tube has cratered, this may help in the future. I have not read it affected audio performance in the least. I may just do this to my builds in the future.

It appears to me something involved with the KT88 wiring is shorted or as John suggested drawing to much current. You can unsolder components and try, keep a map of what you've done, at some point it will stop blowing fuses and then re install a component at a time. Do you have a capacitor tester? if you do that may be a time saver.

Earlier I had advised disconnecting the PS Transformer and looking for something shorted or leaking to ground, you haven't advised what you have done so don't know.

 

[Twirl]

First Wow, beautiful build, looks wonderful.

My advice is start with the simple, my issue was a combo of things, I had a wire (twice) pinched under the power transformer, there is zero room for a wire under the transformer, when I tightened it down it cut the insulation, second while messing with it the ground on the iec had broken off and moved ever so slightly to rest on the neutral lug, looked good but made the GZ34 go crazy shorting sounds buzzing etc, actually wrecked one brand new tube. I carefully unbolted and looked under the transformer and I thought I had pulled the wires through the grommet but not all. I actually took the ps apart and redid it and pinched another wire, sheesh, once this beast is assembled pulling the ps transformer is easier said than done. I did accidentally melt the bottom insulation on one of the 33uf caps, not sure if was shorting but redid and left more space.

I even tried disconnecting wiring in an attempt to isolate the problem, you might give it a try, mine would work when slowly brought up on the variac but if switched on with full ac it would make that sound and blow the fuse. One thing is for sure you have a short somewhere. Does it blow the fuse with the B+ disconnected to the KT88's? Maybe try disconnect one at a time B+ to the KT88's, and alternate. What does the heater voltage measure with no tubes? Discharge the ps caps and try to measure any of the transformer wiring to ground.

This thing cost me a lot of sleep but works great now, you'll find it, don't give up..

And of course what JohnT123 said!

Thanks Bill. I followed your build & admire your persistence. I did removed both opt for pinched wires. All was good. I have been out of town butback on it today. With 6n1p installed all voltages look per Mr Walker specs. But when I add those kt88’s, POW. Fuse blows. I tried just one same thing. Used same tube on other side, POW. I don’t near enough experience as you folks so I’m at a loss. From the very start before building the front end I tried the PS. All checked out even the6.3 filly’s. I went & got a tube tester & another pair of kt88’s. All checked out. I used pretty good parts & fairly good equipment to test. There are only 4 pin connections & ive checked those from several different schematics. All look correct. I would be happy to post any pics. I’m at a stand still. All suggestions are welcome.

 

[Twirl]

OK Mr. Twirl, I certainly understand and totally appreciate your frustration, been there for sure. I first advise that besides my shorted ground issue I wrecked a GZ34. Of the 3 I had in the system at different times, (talk about head scratcher) one was wrecked, one tested lower on the tube tester or possibly semi damaged or degraded. I finally replaced most of the components around the KT88 sockets. Here is another option to try:

View attachment 1483155

So even if the tube has cratered, this may help in the future. I have not read it affected audio performance in the least. I may just do this to my builds in the future.

It appears to me something involved with the KT88 wiring is shorted or as John suggested drawing to much current. You can unsolder components and try, keep a map of what you've done, at some point it will stop blowing fuses and then re install a component at a time. Do you have a capacitor tester? if you do that may be a time saver.

Earlier I had advised disconnecting the PS Transformer and looking for something shorted or leaking to ground, you haven't advised what you have done so don't know.

I’m perplexed by why supply works fine before applying load. Not sure what a dim bulb does?! I’ve tried bringing it up on a variac and it gets to maybe 21vdc then pop with either one tube or both. I have removed & tested capacitors at one point & yes I have a tester. Really appreciate your responses. I’m heading out of town but will tear back into upon return. Thanks a million. PS. I built Mr Walkers dummy load box & downloaded the software & have tested a few amps. Works great.

 

[Ruidoso Bill]

Thanks Bill. I followed your build & admire your persistence. I did removed both opt for pinched wires. All was good. I have been out of town butback on it today. With 6n1p installed all voltages look per Mr Walker specs. But when I add those kt88’s, POW. Fuse blows. I tried just one same thing. Used same tube on other side, POW. I don’t near enough experience as you folks so I’m at a loss. From the very start before building the front end I tried the PS. All checked out even the6.3 filly’s. I went & got a tube tester & another pair of kt88’s. All checked out. I used pretty good parts & fairly good equipment to test. There are only 4 pin connections & ive checked those from several different schematics. All look correct. I would be happy to post any pics. I’m at a stand still. All suggestions are welcome.

Twirl, like I said I was totally frustrated! checking, everything looked good. I am not one of the experts for sure, that's why I related to your problems. Turned 70, have a history with electronics, last stuff I worked with was radar, 1/2 megawatt out.I reached a point where I had memorized the schematic (dangerous place for Bill), so it's not the power supply from what you've said, not sure if that's 100% true, have you pulled the power transformer, do the checks of all of it's leads to ground?

my issue was worse, could go all the way up on a variac, playing test tones etc but would blow the fuse if turned off and turned back on after a cool down at full AC.

I reached a point I couldn't see the forest because of the trees!

Unsolder and remove after you verify everything with that power transformer. Anything can be possible, even Edcors warning about twisting wires.

I do know you will eventually find the issue and it will work! Keep trying...

 

[Twirl]

Thanks Bill....I'm turning 67 & have zero experience in electronics...Green eyeshade! But, I love building amp's. I have also rebuilt several Dynaco devices in the last year & have worked with Dan at updatemyDyna. He's a good guy. Pat4,5, 120, even a 4 channel integrated job & recently 400's. I saw this blueglow amp on u-tube & had to build one! Thanks for sticking with me & I will get on that PT as suggested. Thx

 

[Twirl]

BTW my name is Brian Frisbie. Not sure how to fix the twirl.

 

[Twirl]

Just checked my GZ34 & it tests replace. Why when installed with only the 6N1P would it say it's putting out B+ = 538vdc? I also checked on the same tube yester a 5V4 & 5U4 they tested good.

 

[Ruidoso Bill]

Thanks Bill....I'm turning 67 & have zero experience in electronics...Green eyeshade! But, I love building amp's. I have also rebuilt several Dynaco devices in the last year & have worked with Dan at updatemyDyna. He's a good guy. Pat4,5, 120, even a 4 channel integrated job & recently 400's. I saw this blueglow amp on u-tube & had to build one! Thanks for sticking with me & I will get on that PT as suggested. Thx

Great Brian, don't change the "Twirl", like that!, just add Brian in your signature. Same learning path as myself, did a Pat 5, St120, all thanks to Dan, he literally talked me through an issue, and I was lacking (disapointed} when completed, that's when I realized the Joy (or not) was in the building, Hell, not even sure my ears are that great! Know what I like and enjoy this hobby!

You will get this resolved and will learn in the process.

 

[JohnT123]

It's time to check all the components again. Double check component values and cap polarities and don't assume all the new components are good. The other thing I'd be looking for is accidental grounds. IT has to be something. IT could even be a tightly wrapped wire around a socket or terminal where the insulation is being pierced. Almost impossible to see.

 

[Twirl]

OK...without GZ37 or any tubes PT reads:
red wires to gnd..40.ohms each
6.3v fillys to ground..49 ohms each
5v fillys to gnd...no reading

 

[Twirl]

GZ34 not GZ37
Choke reads 79.8 ohms between leads.. Disconnected
All PS caps read as normal. I use an Atlas model ESR70.

 

[Ruidoso Bill]

GZ34 not GZ37
Choke reads 79.8 ohms between leads.. Disconnected
All PS caps read as normal. I use an Atlas model ESR70.

GZ34 not GZ37
Choke reads 79.8 ohms between leads.. Disconnected
All PS caps read as normal. I use an Atlas model ESR70.

Went back and these were my readings:

1. I'd disconnect the transformers and check the DC resistance on each one to see if they are different. Edcor does have a bulletin cautioning people not to stress or over twist the leads because of possible shorts or open winding's. One side of your B+ filter cap could be shorted, there are a lot of things it could be. I'd start taking test measurements on you components and see what's failed. When you check the wiring get in there with a good light and magnifier. I've seem all sorts of hard to spot grounds and shorts. Your problem is right in front of you waiting to be found. I'd separate the circuit into small blocks and just work through each one. If there are no faulty components then the fault must be in the way they're connected together.
   
   
   Resistance readings OPT
   
   Right Blue "Plate" red "B+" = 85.8 ohms, Red "B+" to Blue/White "Screen" = 54.5 ohms, Blue "Plate" to Blue/White "Screen = 33.5 ohms, Outputs Yellow & White = 2.5 ohms
   
   Left Blue "Plate" red "B+" = 86.5 ohms, Red "B+" to Blue/White "Screen" = 54.8 ohms, Blue "Plate" to Blue/White "Screen" = 33.8 ohms, Outputs Yellow & White = 2.5 ohms
   
   Both transformers appear nearly identical, no wire twisting on these.
   
   Last edited: Feb 24, 2019
   Ruidoso Bill, Feb 24, 2019EditDeleteReport
   #151+ QuoteReply
   
   
2. 
   Ruidoso BillAK SubscriberSubscriber
   Messages:
   159
   Location:
   Ruidoso, New Mexico
   ↑
   I'd disconnect the transformers and check the DC resistance on each one to see if they are different. Edcor does have a bulletin cautioning people not to stress or over twist the leads because of possible shorts or open winding's. One side of your B+ filter cap could be shorted, there are a lot of things it could be. I'd start taking test measurements on you components and see what's failed. When you check the wiring get in there with a good light and magnifier. I've seem all sorts of hard to spot grounds and shorts. Your problem is right in front of you waiting to be found. I'd separate the circuit into small blocks and just work through each one. If there are no faulty components then the fault must be in the way they're connected together.
   Resistance readings OPT
   
   Right Blue "Plate" red "B+" = 85.8 ohms, Red "B+" to Blue/White "Screen" = 54.5 ohms, Blue "Plate" to Blue/White "Screen = 33.5 ohms, Outputs Yellow & White = 1.5 ohms
   
   Left Blue "Plate" red "B+" = 86.5 ohms, Red "B+" to Blue/White "Screen" = 54.8 ohms, Blue "Plate" to Blue/White "Screen" = 33.8 ohms, Outputs Yellow & White = 1.5 ohms
   
   Both transformers appear nearly identical, no wire twisting on these.
   
   Last edited: Feb 24, 2019
   Ruidoso Bill, Feb 24, 2019EditDeleteReport
   #152+ QuoteReply
   
   
3. 
   primosoundsPowered with pure tube sounds.Subscriber
   Messages:
   3,151
   Location:
   Terra, 21st century CE
   ↑
   Resistance readings OPT
   
   Right Blue "Plate" red "B+" = 85.8 ohms, Red "B+" to Blue/White "Screen" = 54.5 ohms, Blue "Plate" to Blue/White "Screen = 33.5 ohms, Outputs Yellow & White = 1.5 ohms
   
   Left Blue "Plate" red "B+" = 86.5 ohms, Red "B+" to Blue/White "Screen" = 54.8 ohms, Blue "Plate" to Blue/White "Screen" = 33.8 ohms, Outputs Yellow & White = 1.5 ohms
   
   Both transformers appear nearly identical, no wire twisting on these.
   Since both trannys have the same resistances it is not a likely problem, although sometimes under load or full voltage a short can show up. But that would mostly be on a very old transformer where corrosion has created some insulation of the short to the chassis. If you are desoldering suspect parts try using test leads between components when you put them back in circuit. If the fuse blows you have your bad part, if it doesnt then you are good. This is true if the circuit has checked.
   I have found that when i have an issue similar to yours, i mostly incorrectly wired a tube socket, which is very easy to do.
   
   primosounds, Feb 24, 2019Report
   #153Unlike+ QuoteReply
   You like this.
4. 
   Ruidoso BillAK SubscriberSubscriber
   Messages:
   159
   Location:
   Ruidoso, New Mexico
   ↑
   I'd disconnect the transformers and check the DC resistance on each one to see if they are different. Edcor does have a bulletin cautioning people not to stress or over twist the leads because of possible shorts or open winding's. One side of your B+ filter cap could be shorted, there are a lot of things it could be. I'd start taking test measurements on you components and see what's failed. When you check the wiring get in there with a good light and magnifier. I've seem all sorts of hard to spot grounds and shorts. Your problem is right in front of you waiting to be found. I'd separate the circuit into small blocks and just work through each one. If there are no faulty components then the fault must be in the way they're connected together.
   Choke = 1 ohm
   
   Power transformer
   
   Primary measures 1.5 ohms
   
   Secondary red to red = 86 ohms, red/black CT to both reds 45 ohms
   
   Brown & Brown 6.3 heaters = 1.2 ohms
   Yellow & Yellow 5v 1.5 ohms
   
   Nothing to ground from any wire

At least this may help you compare

 

[Twirl]

Thank you Bill!
I have requested resistance checks from Edcor for all 3 trannies. I Should have measured before starting!! My numbers are identical (checking same way as u2 did) with following exceptions: output trannies yellow & white were both .6 ohm. Blue/white to red were both 31.6 ohm. On the PT, brwn to brwn & yelo to yelo were both .3 ohm.

 

[Ruidoso Bill]

Thank you Bill!
I have requested resistance checks from Edcor for all 3 trannies. I Should have measured before starting!! My numbers are identical (checking same way as u2 did) with following exceptions: output trannies yellow & white were both .6 ohm. Blue/white to red were both 31.6 ohm. On the PT, brwn to brwn & yelo to yelo were both .3 ohm.

I sure wouldn't have thought to measure before installing, I did check components prior but nothing major, if you disconnect the output transformers and with the tubes in wonder if you are still blowing fuses. Mine was so bad I had the mini fuses, no where local to replace so went to the full 30 mm fuses, replaced the fuse holder, only because I could find them local. Hope my measurement aren't misleading due to my meters.

 

[Ruidoso Bill]

Brian, sounds like you've done some good work, don't give up, you will find the issue, when you do it will be one of those moments when one says darn, can't believe I missed that.

 

[JohnT123]

What was the outcome from the bad GZ34? You say it shows bad under test and that would be the first thing to be ruled out. I could see the rectifier running ok with a near zero load but shorting once a real load (the output tubes) was applied.

 

[Ruidoso Bill]

An update on my first build, I have been running this amp now for several weeks, lots of hours (400+) and I have been using it in Triode mode for the last several days, UL starting to sound a little harsh, think I figured out the listening fatigue I have read about. Maybe it is burn in? anyway finding triode mode more enjoyable.

 

[Ruidoso Bill]

Thank you Bill!
I have requested resistance checks from Edcor for all 3 trannies. I Should have measured before starting!! My numbers are identical (checking same way as u2 did) with following exceptions: output trannies yellow & white were both .6 ohm. Blue/white to red were both 31.6 ohm. On the PT, brwn to brwn & yelo to yelo were both .3 ohm.

Maybe this could help Click while trying to sort everything out.

 

[Ashutosh]

This is kind of primary level, but do I require phono preamp with this amplifier to use with turntable? If yes, then can you guys suggest one?

 

[Tubeglowpio]

Thanks very much.
Vent holes in both the top and bottom covers really help to lower operating temps especially over the course of a long session here in sunny Ca. central valley.
The ones around the kt88 are spaced properly, the ones around the rectifier should be closer to the tube.

I've always wondered how much the vent holes really help because doesn't the air m

An update on my first build, I have been running this amp now for several weeks, lots of hours (400+) and I have been using it in Triode mode for the last several days, UL starting to sound a little harsh, think I figured out the listening fatigue I have read about. Maybe it is burn in? anyway finding triode mode more enjoyable.

What kind of coupling and power supply caps did you use again? I experienced burn in before where the mix of caps seemed to have good synergy at some point and after 100 or more hours I don't hear any change and the amp sounds good but seemed to sound a bit sweeter at the 30 to 60 hour point. First 4 or 5 hours sounded harsh up top and it wasn't just my ears breaking in because others noticed the same.