Inverted back plates build

[grapplesaw]

Check for cold solder joints around those two sockets, if not that you could have some issues on the foil side of that backplane....

They look good to me please see if you can tell any thing from these shots

 

[laatsch55]

They certainly don't look bad...

 

[grapplesaw]

I have some 0.009 ones. Your welcome to use them now as long as I get replacements.....

Thanks for that offer

I have to order from mouser anyway so I double up for now if nessary
I have some around here I think but don't remember were I put them

 

[grapplesaw]

So lots of thought through the night. I have made some assumptions throught the trouble shooting steps.

both channels acted the same so testing one would be uniform to both
Re and re trans in both banks left and right looking for common problem

I only load tested the right channel through this test thinking what happens to one happens to other

This was not smart

I tested the right channel just now with right 5 and 6 unpopulated with no distortion showing although the crest of the wave was not totally sharp.

I then tested Left fully populated rows and found distortion in that channel.
I removed bothe Row 5 and 6 and distortion went away. I re polluted just row 6 and left row 5 open
Retested and distortion was back.

Conclusion distortion comes to both channels with rows 5 and 6 populated

Something is realy messed up here. Same voltage output with all rows populated has distorted output compaired harder driven four rows populated with same output current and no distortion

The distrortion is in either channel depending on total populated rows. Is this a current thing or induced field somehow
I just ordered an other load resistor so in future I can load test both together.

 

[grapplesaw]

Going to remove rows three and four and populate rows five and six and retest. This would give some indication of load vs total # of drivers and if this is truly a row five and six problem or a current problem

 

[kevin]

WOW !!!! What a thread !!!! Cant wait to see what you find Glen !! Good luck man !

 

[grapplesaw]

Had a few minutes so moved row four to six and retested
No distortion

Will move row three to row five later today

This is looking like a combined load problem

Should we check the bridge rectifier further??? Any thoughts anyone???

 

[Gepetto]

Had a few minutes so moved row four to six and retested
No distortion

Will move row three to row five later today

This is looking like a combined load problem

Should we check the bridge rectifier further??? Any thoughts anyone???

What type of load are you using?

 

[grapplesaw]

What type of load are you using?

OK I will fess up

I stripped it down today after blowing some 1 amp fuses on B fuse supply.

Pulled the back plates and had a good look around

A couple of connects to the control were protruding a little to far and may have contacted the chassis , or close to it. Trimmed up all possible protrusion and put back together and now have the first to third row in and tested good so far.

Will finish tomorrow and see if that was it. So thank you all for your thoughts and concerns to date
Not out of the woods yet but looking better.

 

[laatsch55]

I have done the same thing Glen....there is soooooooo much that has to be done right the first time......or.......

 

[grapplesaw]

I have done the same thing Glen....there is soooooooo much that has to be done right the first time......or.......

Thanks for the support Lee

I can tear it down in about 30 minutes now
The transistors are popping in a lot easer using the magnet but get leg off a little and five minutes can go by quick. Getting the legs square and space exact can make it a piece of cake

And Dennise got his high volt caps in this one
I guess I will soon need more

 

[NavLinear]

Thanks for the support Lee

I can tear it down in about 30 minutes now
The transistors are popping in a lot easer using the magnet but get leg off a little and five minutes can go by quick. Getting the legs square and space exact can make it a piece of cake

And Dennise got his high volt caps in this one
I guess I will soon need more

I'm glad to hear that you may have found the problem Glen. It sure sounded like those protruding leads on the bottom of your backplane boards were a bit long. My guess was the board was pulled a smidgen closer to the chassis when the screws were torqued down but my guess was it was only a few thousandths. I've seen a similar problem a time or two with some prototype hardware.

I do feel better that you got rid of the 100 volt electrolytic reservoir caps and replaced them with the higher voltage ones.

 

[grapplesaw]

So I could not wait and got up and put in row four
All good
In went row five and both channels same distortion came back as before. I changed the fuses from one to amp just to see if that helped, but no it made no changel

As I pondered what next as I left the distorted current run on the scope
What I saw was over a few seconds it cleared up
So I turned up the gain a little and more distorted bottom half of wave
But once again over a few more seconds it smoothed out

Not to push my luck I turned it off, as I still have one row to go

So what is going on? Like its learning. Maybe I have recreated the Hal 5000 from space odyssey!!

I will set up input scope and track both in and out tomorrow

So is the load causing this, it did not on the other amp?
Is there bad caps in there some were?
Do these transistors need breaking in?
Why is it only on the bottom half of the wave, some difference in PNP vs NPN?

Used same test equit setup on other amp at far greater output and no sign of any signal distortion

It is not control board it was swapped out
Could be back plate, but why both channels identical?

Joe asked what I had for load test and it is open Center core 7 ohm 300 watt Ribbon wire would resistor

I will try an other one which is 8.5 ohm 1000 watt GE open wire one. Need to make amount for it

 

[grapplesaw]

What type of load are you using?

Hi Joe
This what I have been using
A ohmite 7 ohm 300 watt Robison wound



And this is what I have to upgrade to a GE 1000 watt 8.4 ohm

 

[laatsch55]

Hook the amp to some speakers scope it while you test through the speaks. What voltage does distortion start??

 

[grapplesaw]

Hook the amp to some speakers scope it while you test through the speaks. What voltage does distortion start??

Ok

I want to spend a little more time on this before the speakers
Let you know
Glen

 

[Gepetto]

So I could not wait and got up and put in row four
All good
In went row five and both channels same distortion came back as before. I changed the fuses from one to amp just to see if that helped, but no it made no changel

As I pondered what next as I left the distorted current run on the scope
What I saw was over a few seconds it cleared up
So I turned up the gain a little and more distorted bottom half of wave
But once again over a few more seconds it smoothed out

Not to push my luck I turned it off, as I still have one row to go

So what is going on? Like its learning. Maybe I have recreated the Hal 5000 from space odyssey!!

I will set up input scope and track both in and out tomorrow

So is the load causing this, it did not on the other amp?
Is there bad caps in there some were?
Do these transistors need breaking in?
Why is it only on the bottom half of the wave, some difference in PNP vs NPN?

Used same test equit setup on other amp at far greater output and no sign of any signal distortion

It is not control board it was swapped out
Could be back plate, but why both channels identical?

Joe asked what I had for load test and it is open Center core 7 ohm 300 watt Ribbon wire would resistor

I will try an other one which is 8.5 ohm 1000 watt GE open wire one. Need to make amount for it

Glen you want a load bank that is wound as non-inductive. Wire wounds resistors are usually quite inductive (especially these big ones) which is why I do not use them for the emitter resistors (although PL did). Wire wounds can be had in non inductive but they are specially wound to cancel the inductance normally created when you coil up (spiral up) a lot of wire around a tube.
You probably do not have an LCR bridge to test the load resistors. As a quick test, see if a 0.1uF mylar or ceramic type cap tacked right across the resistor itself makes the situation better or worse to give us a clue.

How long are your test wires that go out to the load resistor (these are also inductive if not paired closely together)?

 

[grapplesaw]

Glen you want a load bank that is wound as non-inductive. Wire wounds resistors are usually quite inductive (especially these big ones) which is why I do not use them for the emitter resistors (although PL did). Wire wounds can be had in non inductive but they are specially wound to cancel the inductance normally created when you coil up (spiral up) a lot of wire around a tube.
You probably do not have an LCR bridge to test the load resistors. As a quick test, see if a 0.1uF mylar or ceramic type cap tacked right across the resistor itself makes the situation better or worse to give us a clue.

How long are your test wires that go out to the load resistor (these are also inductive if not paired closely together)?

Thanks Joe
Will follow the instructions
I will see if my Sencore can test that

 

[grapplesaw]

Glen you want a load bank that is wound as non-inductive. Wire wounds resistors are usually quite inductive (especially these big ones) which is why I do not use them for the emitter resistors (although PL did). Wire wounds can be had in non inductive but they are specially wound to cancel the inductance normally created when you coil up (spiral up) a lot of wire around a tube.
You probably do not have an LCR bridge to test the load resistors. As a quick test, see if a 0.1uF mylar or ceramic type cap tacked right across the resistor itself makes the situation better or worse to give us a clue.

How long are your test wires that go out to the load resistor (these are also inductive if not paired closely together)?

Joe the 300 watt had inductance of 2 uh. The 100 watt is 14.5 uh

I put the 0.01 uf cap across the resistor and it made it worse
I then undid the small call and the single was good. Some time had past from powering on

I then left it with smooth sine at 15 volt current. I had 2 amp fuses installed and then after about 3 minutes the b- fuse when out.

I guess it was close to load but should not have gone I thought. I wil put in some three amp and run again at 15 volts to see.

So it looks like for now this signal distortion settles done after some ideal time, powered on
Still looking into things. I will retest the cap over the resistor again , as well inverting the leads,

Still missing row six transistors.

Joe how about the .01 caps on the bridge, could one of those influence the output?

 

[Gepetto]

Joe the 300 watt had inductance of 2 uh. The 100 watt is 14.5 uh

I put the 0.01 uf cap across the resistor and it made it worse
I then undid the small call and the single was good. Some time had past from powering on

I then left it with smooth sine at 15 volt current. I had 2 amp fuses installed and then after about 3 minutes the b- fuse when out.

I guess it was close to load but should not have gone I thought. I wil put in some three amp and run again at 15 volts to see.

So it looks like for now this signal distortion settles done after some ideal time, powered on
Still looking into things. I will retest the cap over the resistor again , as well inverting the leads,

Still missing row six transistors.

Joe how about the .01 caps on the bridge, could one of those influence the output?

Very unlikely on the bridge snubber's Glen...thanks for running the test.