the Poor Man 660 support thread

[khstudio]

I'm VERY concerned about how HOT my Q4 IRF820 is getting... I mean it's smokin' hot!!!!!!!
Could this be a sign of a problem or even cause the distortion I'm hearing somehow???

Also, I'm going to get yelled at for this one...
It's time to completely remove one channel but I need to adjust the Heater resistor & I'm having a brain fart with the math. :-[
I'm currently using .33 ohm for 2 channels. (assuming aprox 5.2 amp @ 6.3v)
Could someone refresh me on how to calculate for one channel?

Thanks

 

[lolo-m]

x 2, more or less ;D !

 

[khstudio]

x 2, more or less ;D !

Thanks man.

 

[Moby]

Kevin, can you please measure the voltage drop around R6 with max and no gain reduction? I can't find did you mentioned what value U used in place of R6.

 

[khstudio]

Kevin, can you please measure the voltage drop around R6 with max and no gain reduction? I can't find did you mentioned what value U used in place of R6.

I left the 22k but added a 5k Trimmer... not sure how the trimmer will effect the measurement.
Let me know what you want me to do & I'm there.

Right now I'm increasing the Heater resistor so I can remove one channel completely for testing.

 

[khstudio]

UPDATE:

Using the EDCORE PT = These are the resistor values I needed to get proper voltages:

For 2 channels
.33 ohm
Voltage drop across was = 1.852v
Total Current Draw = 5.6 amps
Final Output Voltage = 6.2v

For 1 channel
1.35 ohm
Voltage drop across was = 3.8v
Total Current Draw = 2.81 amps
Final Output Voltage = 6.3v

The sad part is, I had to use a 10watt 1 ohm in series with the .33 to get the voltages close & the 1 ohm started SMOKING 
I don't have any other high wattage resistors around so this project is being put aside for a while. 

Days of working on this thing with no resolve at all... not cool.
I've built & worked on a lot of gear and have NEVER felt like giving up like I do with this one.
There are TOO many variables & not enough data or feedback with this project (I'm sorry to say)
I'm afraid that with the schematics being "Private"... other knowledgeable people around hear that COULD help, can't.

I'm going to the bar 

 

[Moby]

I'm asking about voltage drop around meter because U  mentioned that PSU fet is hot. Looks like some serious current is going there , so if you have few Kohms in series it's possible that voltage drops a lot below 136V when compression start. It's normal that current is different in steady mode (lowest current) and with max GR current will be "max" . It will be cool if you can measure those values (voltage drop or current consumption) in both situation . I presume that distortion is caused because low plate voltage in max GR (gain reduction). What about tubes ? Did you checked them with tube tester? Did you measured T2 static resistance from CT to plate? And again, it's possible that PSU transformer is saturated so voltage drops with small current change  :-\ just my 0.2c 

 

[[silent:arts]]

...
Days of working on this thing with no resolve at all... not cool.
I've built & worked on a lot of gear and have NEVER felt like giving up like I do with this one.
There are TOO many variables & not enough data or feedback with this project (I'm sorry to say)
I'm afraid that with the schematics being "Private"... other knowledgeable people around hear that COULD help, can't.

I'm going to the bar  

I'm wondering why we would have seen quite a few finished and working units if there isn't all needed information available ???
if the designers "private" decision doesn't work here the only other way to do such projects in the future would be completely private, meaning hidden
but some people around here don't like this either ...  :
you might feel better after the bar  ;D

 

[radiance]

(max 6A winding running at some 5,2A)

Where is this current draw meassured? Before or after the rectefier?

5,2A is from the tube datasheets. A stereo poorman, meaning 4X 6BC8 and 4X 5687 will eat about that much.

A brave man does not rectify, and feeds AC for the heaters. Did anyone try this with poorman? noise?

When feeding the heaters AC you'll have enough juice and the transformer will likely run cooler.

Volker, I'm not trying to be a PITA here but have a look at this "rectefier relationship" data sheet from the RS site.

http://documents.rs-components.com/EITC/UK/infozone/rectifier_relationships.pdf

Please correct me if I'm wrong but as far as I understand it, to get 1A rectefied DC you'll need a transformer that puts out 1,61A AC.

you should rate the required current to about 60% of the maximum for the winding. In this case, the 5,2A should be pulled from something like 8A max rated windings.

This might be to compensate for the current loss caused by the rectefier.

 

[kambo]

hi, new to tubes, and i am about to order some tubes for this project.
there are some options at tubedepot

1. Matched+balanced Triodes
2. Low Noise and Microphonic

matching is good, but low noise is good too...  so i am little confused....

for stereo build, which option i should go for...

thank you
kam

 

[jdbakker]

1. Matched+balanced Triodes
2. Low Noise and Microphonic

matching is good, but low noise is good too...  so i am little confused....

for stereo build, which option i should go for...

Tube matching has been discussed a few times in the past; please read the earlier posts in this thread (which is not a bad idea anyway when embarking on any of the DIY projects around here).

Good luck,

JDB.

 

[kambo]

i cant believe i missed it... its even on the first page...
human error  ;D

 

[khstudio]

I'm asking about voltage drop around meter because U  mentioned that PSU fet is hot. Looks like some serious current is going there , so if you have few Kohms in series it's possible that voltage drops a lot below 136V when compression start. It's normal that current is different in steady mode (lowest current) and with max GR current will be "max" . It will be cool if you can measure those values (voltage drop or current consumption) in both situation . I presume that distortion is caused because low plate voltage in max GR (gain reduction). What about tubes ? Did you checked them with tube tester? Did you measured T2 static resistance from CT to plate? And again, it's possible that PSU transformer is saturated so voltage drops with small current change  :-\ just my 0.2c  

I did check all tubes with Tube tester & all looked good + I tried different combination (I bought double the amount of tubes needed for spares)
I also measured all the transformers Resistance & Inductance to make sure they matched each other & had correct connections.

I will test the Plates in both modes & post back.

Also, I just found a FREED 6.3v 8amp Sealed power TX... I guess I could try this out & hook up the heaters AC for testing.

Do you think it's the current draw of the heaters that's possibly pulling the Power down or saturating?
if so, this Freed might help.

 

[khstudio]

Could someone with a working unit PLEASE make a "Voltage Chart"

Here's a list of test points:

POWER SUPPLY
R1 - 47r (BEFORE & AFTER)
R8 - 47r (BEFORE & AFTER)

CIRCUIT
PL1 - Control Voltage (Threshold Off, Med & Full on) This one is tricky but important!
...Must have audio going thru unit, say 1.2v Test tone & then set gain to have 1.2v at the output (with Threshold fully off)
Obviously everyone's measurements will be slightly off due the differences of Threshold controls, Taper & values chosen...
but if you KNOW your switch & values, posting the value along with the Voltage reading will be more accurate!

R1 - 330r (BEFORE & AFTER)
R10 - 330r (BEFORE & AFTER)
R11 - 47r (BEFORE & AFTER)

Even if not perfect, these measurements taken from a GOOD WORKING UNIT will help others troubleshoot none working units & narrow down problem areas.

I will be testing these points on my unit today.

Thank you in advance.
Kevin

 

[lolo-m]

Could someone with a working unit PLEASE make a "Voltage Chart"

Here's a list of test points:

POWER SUPPLY
R1 - 47r (BEFORE & AFTER)
R8 - 47r (BEFORE & AFTER)

CIRCUIT
PL1 - Control Voltage (Threshold Off, Med & Full on) This one is tricky but important!
...Must have audio going thru unit, say 1.2v Test tone & then set gain to have 1.2v at the output (with Threshold fully off)
Obviously everyone's measurements will be slightly off due the differences of Threshold controls, Taper & values chosen...
but if you KNOW your switch & values, posting the value along with the Voltage reading will be more accurate!

R1 - 330r (BEFORE & AFTER)
R10 - 330r (BEFORE & AFTER)
R11 - 47r (BEFORE & AFTER)

Even if not perfect, these measurements taken from a GOOD WORKING UNIT will help others troubleshoot none working units & narrow down problem areas.

I will be testing these points on my unit today.

Thank you in advance.
Kevin

Here's a list of test points with results I made on my unit :
DON'T TAKE THIS AS A VOLTAGE CHART (I made those test quickly today just to help  )

POWER SUPPLY
R1 - 47r (BEFORE & AFTER)    350/346
R8 - 47r (BEFORE & AFTER)      259/254

CIRCUIT
PL1 - Control Voltage (Threshold Off, Med & Full on):
I use a switch made with the log pot to switch xls file:

NO COMP : 4,5V
Approx half taper : 6V
Fully on : 7,2V

With no signal applied :
R1 - 330r (BEFORE & AFTER)  1,28/0
R10 - 330r (BEFORE & AFTER) 12,06/0
R11 - 47r (BEFORE & AFTER)  12,5/12,06

 

[RedNoise]

very helpfull lolo , thanks!

 

[khstudio]

lolo-m,

Thank you VERY much.  ;D

Here's a list of test points with results I made on my unit :
DON'T TAKE THIS AS A VOLTAGE CHART (I made those test quickly today just to help

... Better than No voltages at all to compare.

It would be great if others can take measurements too... I'd be happy to compile a "working unit voltage chart".
It would also be nice to see an EDCORE PT units voltages.

 

[kambo]

Kevin,
"working unit voltage chart" is a great idea...

thank you
kam

 

[khstudio]

Well... the Voltages that LOLO-M posted have REALLY helped me out.  ;D
I've seemed to narrow my problem down to one section & will post my finding & working voltages (& the bad ones) when I get done.

Once again... PLEASE post your Voltage readings if you have a working unit - following the guidelines posted on the previous page.

Thanks for helping!

 

[lewilson]

kevin, I got your message.  my edcore power transformer does not get very warm. But the fil. resistor and ic's do. I did put some mu metal between the pt and audio transformers due to low level hum .
Looks like you did a mod to the time constants. Im curious what you find.