the Poor Man 660 support thread

[W DeMarco]

OK guys,  

Ive put the beast aside for a couple of weeks now hoping to clear my brain.  Its fully built but after a big spark somewhere in the psu, probably related to my non-isolated regulators, I lost the two high voltage rails on the output of the PSU.  I do have good voltages coming out of the transformer.  I think something like 260 Volts and 150 Volts.  I'm not sure where to begin with the tracing.  Another problem is that my schemes have disappeared somewhere along the line.  I have things isolated and replaced both regulators now.  I checked with my continuity checker all of the diodes in the path and they seem to be working correctley.  Can someone post some key places I can test along the high voltage rails to see where the problem lies.  After the big spark incident Im a bit wary of sticking anything in that case.

For more info on my dilemna check here
http://www.groupdiy.com/index.php?topic=28274.msg413283#msg413283

Thanks

Will

 

[khstudio]

Anyway - right now I have 1 channel working correctly & the voltages match others... BUT, I'm STILL getting DISTORTION while compressing!!!  I don't get it & may never at this point.

How much are you compressing ? If it's more than 20dB reduction you reach the cutoff point of the 6BC8... And you'll have distortion.

I'm glad you brought this up.
With a 1.2v input & output signal - As soon as I turn on my threshold to the 1st ON position - the output gain drops about (.6 ) Volt or so... this is a LOT if you ask me.
Keep in mind that my control voltages closely matches other working units.

You've got a real problem here. Must I understand pos1 as threshold all way down ? If it is, check / double check / triple check your switch, someting isn't normal here.

Sorry, I thought I was clear...
Position #1 is OFF.
Position #2 is the "1st ON Position"

 

[khstudio]

Update:
I spent another full day replacing TX's, Tubes, checked for shorts & finally got a chance to swap the PCB card positions to see if the problems followed the PCB or the Pots & TX's.
It looks like the PCB #1 (left Channel) has the most issues.

Still working on it.

 

[[silent:arts]]

can you give us a "resistor chart" of the switch?

 

[Moby]

if you suspect at threshold switch try to replace it with double pot just to check out situation.

 

[khstudio]

can you give us a "resistor chart" of the switch?

I used the Excel file posted on page one - LOG = 15k for both Gain & Threshold

 

[khstudio]

if you suspect at threshold switch try to replace it with double pot just to check out situation.

read my post just above yours.
Also, if you missed it... my CH2 (right CH) is working OK except for distortion (which could be going too deep into Comp)
I was able to get my voltages to match what others sent me & posted. Also, my voltage fluctuation @ R10 = 330r was stable when moving the threshold. (I talked about this a lot. This was the 1st spot I could see a problem thanks to others posting their Voltages!

My ch 1 (even after swapping the channels) still has a problem with voltage fluctuation @ R10 = 330r when moving the threshold.

 

[radiance]

my CH2 (right CH) is working OK except for distortion (which could be going too deep into Comp)

So did you try this OK channel with less compression as well?

 

[khstudio]

my CH2 (right CH) is working OK except for distortion (which could be going too deep into Comp)

So did you try this OK channel with less compression as well?

Not sure how deep I was going but I CAN say this... I LIKED what I heard & tried it on some tracks = Bass, Guitar, Vocals... VERY cool but if pushed I got distortion. Just when I got it to the "Sweet spot" it was on the edge.
This can be tweaked when other problems sorted out but it at least gave me some excitement about this Comp.
But still, with this single channel test - my PT got HOT!  ???
(keep in mind I ONLY pulled the Tubes from the other channel so maybe the was still some problem or shorts on the other PCB (ch1-Left) the one that still seems to act up.

Thanks for hanging with me everyone.

 

[emrr]

With a 1.2v input & output signal - As soon as I turn on my threshold to the 1st ON position - the output gain drops about (.6 ) Volt or so... this is a LOT if you ask me.

That would be a matter of the taper of your 12 position threshold switch.   Sounds like you need a different taper or more and finer steps.    Your Daven dual 10K log step switches sound like a perfect immediate on-hand sub to try for troubleshooting purposes.   To confirm, you current threshold is MBB, rather than BBM, to avoid open grid condition?  I still think 1M safety resistors from grids to ground is a good idea, to avoid open grid condition from switch or connector faults.  I am personally leery of the vast use of circuit board connectors versus hard soldering between grid/transformer/switch/etc contacts.    Any single contact fault could cause a world of trouble, and could be very tough to spot.  

I used larger Dale 1/2W resistors on my amp boards, and find the small resistor spacing problematic and limiting.  There is at least one possibility of resistor short in the R10-R14 area, when using larger 'custom choice' resistor bodies.  

I will add that I've found that to be an oversight in most of the (very few) project boards I've ever purchased; no capacity for variance in personal selection of parts, because of tight part spacings intolerant of variance.  The Drip boards go way overboard in the other direction; somewhere in between would be a wise path to tread when designing a layout.

To confirm, when swapping channels, you are using entirely different sets of everything; power wiring, pots, and transformers?  Board move to other position, correct?  

 

[Nele]

you did mount all the heatsinks isolated?

something which nearly drove me insane once..

 

[idylldon]

you did mount all the heatsinks isolated?

something which nearly drove me insane once..

Other than for safety reasons, why?  The heatsinks aren't grounded.

Cheers,
--
Don

 

[Nele]

oops.. :-[
they looked to be connected to ground, but after measuring they're not.. sorry

 

[emrr]

oops.. :-[
they looked to be connected to ground, but after measuring they're not.. sorry

Yes, only a (very real) problem if you drop another shorting element across them, or need to get fingers in there while powered up.  Mine aren't insulated, but I may well go back and rework, if only to frustrate Murphy.

 

[emrr]

it should have been mentioned it is not a beginners project.

It was, I believe.

it is getting scary.
won't do this anymore.

I'm not sure what's scary to you.  I simply suggest that as a matter of PR, the lack of input or commentary from the designer appears to be both frustrating and scary to many who wish to believe the project is both good and worth finishing.  Many have clearly finished it to success, and moved on.   Others clearly feel the baby has been left in a basket on the steps of the church, without even a note pinned to it's blanket.   I think it's correct to say we've experienced that range of emotion, right or wrong, in this thread. It's disheartening to watch, as a bystander, and I suggest the effects worth observing, as anyone offering a project of any type will find their reputation affected by the public reaction to the follow-through aspect.   A simple observation.  

at the end, you don't buy support with PCBs.
Volker

Sure, but a private party like this has to have more internal support, to cover that support which is lost with an open-source project that all can view freely.    It took extra requests to get the +/- 17V supply schematic published; to simply state that the +/-17 section is 'standard circuitry' assumes that all builders are well versed in all types of PSU's, which is at best wishful thinking.  It took extra requests to get any detail whatsoever on the setting of the trimmers.  I don't recall seeing any descriptive about what variance in the trimmers might do, and that would seem to be another piece of useful knowledge, especially in a troubleshooting situation.  These are extremely basic support issues, and I would think the effort put into extra support documentation would be worth it, if only to shut down the endless related questions that we experience now.  

Eventually I will find the time to finish mine (boards built since last August), and feel confident I have the necessary abilities to reverse document and comprehend the subtleties through the magic of test equipment and observation, but it's obvious that many project builders lack many of those skills.   The difference here is the fact that this is an entirely new design, with no previous immediate body of commentary and knowledge to draw upon.  A GSSL, LA-2A, or 1176 is an entirely different matter, even at minimum different because of the fact that they are clones of desired proven technology.  

Please know that I only wish this commentary to help; I have no desire to lay out pointless criticism, and wouldn't waste my time on it if I thought it were so.  I am a vested player in this project, only moving too slowly to be much help in troubleshooting at this date.  

 

[tommypiper]

Just a wild hunch, but Kevin I still think the hot Edcor is a clue.    No one else is having that issue.  It could be a defective PT or who knows what...

I suggest you replace it.  Or at least replace the heater supply with another toroid, if only for testing (they are cheap).

Since you're going through everything else like crazy, I suggest you not overlook this PT (and PS in general) while you're trouble shooting.  Because you should not be getting that heat, particularly when others with the SAME PART are not getting that heat.  

We need to solve this heat mystery!

If there is a defective winding in the PT it could be causing all kinds of whackiness... Doug could tell us more.  I feel this possibility has not been exhaustively precluded from the potential causes of your problems.  And it needs to be.

Keep at it...

 

[khstudio]

Nice post Doug. 
I try to be a diplomatic as possible & also mean no harm in my post... I just want to share my findings for 2 reasons, Help & to help others. The voltage chart IS & will be VERY Important to everyone.

I too am more interested in the "Trimmer" settings... I seriously doubt that "One setting fits all"
This will become more apparent when more builders fill out the "voltage charts" & follow the test procedure for the Control Voltage & post those as well. I've already noticed, from the few already posted, that those control voltages don't exactly match or track the same for each channel... what role does the "Trimmers" have to play in this???

 

[khstudio]

Just a wild hunch, but Kevin I still think the hot Edcor is a clue.    No one else is having that issue.  It could be a defective PT or who knows what...

I suggest you replace it.  Or at least replace the heater supply with another toroid, if only for testing (they are cheap).

Since you're going through everything else like crazy, I suggest you not overlook this PT (and PS in general) while you're trouble shooting.  Because you should not be getting that heat, particularly when others with the SAME PART are not getting that heat.  

We need to solve this heat mystery!

Keep at it...

You are right & I'm doing my best to narrow this thing down... you have no idea how much time I've spent on this thing... it's crazy.
I've had several VERY knowledgeable techs on the phone  (from this forum) helping me trouble-shoot this thing & even they are stumped.
Just when I think I have it narrowed down, I don't.

 

[khstudio]

Doug,
I did install the 1meg resistors from each GRID to GND for safety... this was highly advised by a few guys I spoke with on the phone too.

When I 1st tested the ONE channel idea, I only removed the Tubes from CH1... this left CH1's PCB still connected. So, even thought CH2 worked  & measured better doesn't mean CH1's PCB (no tubes installed) isn't shorting or effecting the Power Supply somehow... still looking into it.

 

[emrr]

We need to solve this heat mystery!

If there is a defective winding in the PT it could be causing all kinds of whackiness... Doug could tell us more.  I feel this possibility has not been exhaustively precluded from the potential causes of your problems.  And it needs to be.

It makes it more difficult that there are at least 3 power transformers in play with this project.  I don't have the Edcor.  We know a lot of heat means a lot of current is going somewhere.  If we get very specific current measurements on Kevin's unit, it should point to something.  If the current draw of the entire circuit AFTER the transformer is correct, then we can assume there's a short in the power transformer.  My intent, back when I had the boards built long before the arrival of my power transformer, was to fire up sections of the circuit on a bench supply, and take readings from that.  It would be a helpful approach to diagnosis, if power trans or supply is suspect. 

The grid to ground safety resistors are certainly not a standard approach seen in most designs, but they certainly don't hurt.  They prevent compound problems, at least.  It only takes one position of the threshold connector going funky to throw some or all of the grids into an open condition, and that assumes the home made threshold switches are working correctly. 

The trimmers may have useful effect at varied settings; I don't know the answer to this, and have missed it if addressed.  Again, I don't have mine ready to experiment with. 

For anyone building this beast, I'd certainly advise testing one channel at a time before firing up two together, so you can ID and troubleshoot anything that arises in a modular fashion.  That seems like common sense to me, but I think a lot of people don't have any real troubleshooting methodology.   

There seems to be multiple instances of concern surrounding the tolerances of the heater voltage, and that concern may make one feel it dangerous to fire up only one channel.    The value of a modular approach to verification of function trumps all, IMO.  There is nothing worse than a complete and tidy build that must then be torn apart while chasing faults.    I believe you will not endanger your tubes if you fire up one channel of a two channel build long enough to do basic testing.    If one actually pops at a slight over voltage, it was not long for this world anyway, and better to discover it now.  These tubes are cheaper than time, and you should have bought spares anyway, right?  Even simpler if you purchased an adjustable tap resistor for use with the stock power supply, as you can simply reset it as needed, when needed, and forget about it otherwise.  It doesn't get any simpler. 

I was glancing at the PSU board the other night, and thought that if the layout was ever redesigned for reissue, I'd vote for a layout that avoided the sort of canyons amidst skyscrapers that currently exist.  I'd hate to have to replace anything in the center part of the board, down between the heat sinks and the caps. 

Sorry to be a pain in the ass Volker; I hope you can take something constructive from the comments!