the Poor Man 660 support thread

[Gus]

It is a guess on my part.  I am not sure it is caused by the tubes.  It seems like a possible answer I could be wrong and it might be caused by something else.

The way to tell if this is true would be to curve trace the tubes and compare to others that work correctly.

 

[khstudio]

If you or anyone has any more test points or procedures that you feel should be added or changed, Please let me know & I'll fix it up.

In the power supply, R2 should probably be R8, right?

I've filled out the chart and have attached it.  Since I have a stereo unit, I separated L/R measurements with a /.

http://www.mediafire.com/?yjzqt3mztzr

Cheers,
--
Don

Thanks for filing out the Chart Don!  ;D

YES -

In the power supply, R2 should probably be R8

As you guys upload your voltage charts I will gather them & upload them to one spot.
I'll post a link that can be added to page one when I get a chance.

Thanks

 

[Kingston]

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.

I noticed you mentioning about this earlier in the thread as well but forgot to ask. What exactly might an open grid condition cause?

 

[emrr]

An open grid (infinite ohms to ground) is a basic thing one doesn't do.  Every tube has a maximum resistance to ground on the data sheet.

As Gus and I were moaning the other eve, you see pots wired as rheostats all the time with the unused lug floating.  It should be tied to the wiper, so when and if wiper contact fails there is at least the safety factor of the pots' maximum resistance, rather than an open circuit.  

Also slightly related, why one uses a MBB versus a BBM switch for controlling opamp gain in a preamp; full open loop gain in the spaces between contacts with a BBM switch.  


Kevin can remind me which variants; there are only 5 tubes shown in the GE book with the same base as the 5687.  Most look essentially like the same tube on the data sheets.  In the Sams substitution book, none of them are listed as a sub for the 5687 (nothing is), but one lists the 5687 as a sub which will work in some circuits.   I wonder if that points to a silk screening mixup; doubtful.   He's seeing double the expected current, and it sounds like his T4's and cathode resistances are all quadruple verified and substituted. B+ correct, PSU overheating.  It's a weird one.  

 

[khstudio]

Yea... I ordered new tubes today (different Brand) we'll see if that makes a difference.
If it does I'm gonna puk... but be happy.

UPDATE:
I'm running ONE 5687 tube in my output stage!
As Doug pointed out, a Single 5687 tube in my PM670 output stage measures EXACTLY like everyone's posted voltages.

- My Cathode voltage @ R10 330r = 11.9v
- My Meters is now perfectly stable & actually show the 20dB Gain Reduction, whereas before they only showed about 3dB.
They don't move around at all like before... they were sensitive, like to a magnetic field or something, even just touching the wires.
- Total 245v B+ Current Draw with 1 tube is around 36ma
- Total 245v B+ Current Draw with 2 tubes was around 82ma
- The Large Volume drop (when kicking the Threshold ON) is GONE!
- The Distortion when compressing is also GONE! (Unless I get close to -20dB on my meter)
- BUT - My Power TX still gets a little too HOT!!! around 125 Degrees F - With the lid OFF

This things sounds GREAT!!!!!!!!!
I ran audio thru it for hours last night & today... even on mix buss & it's so damn cool.

BUT - Obviously, it still isn't right. Hopfully the new tubes will fix it, if not, I ordered 4 DUAL 10k LOG Taper Pots & will add 5k to the ends to make the needed 15k... this will help rule my Stepped attenuators out & the tubes.

I tried so many things before eventually removing one output tube.
I tried 4 NEW Edcore TX's & even tried a Push-Pull EL84 output TX, loaded the secondary with 10 ohm & ran the 245 B+ thru it to see if it would solve my problem & it didn't... it did exactly the same thing as my EDCOREs... so I can rule them out too.

New tube sockets, New resistor, Re soldering, Measured Everything 1000 times, you name it... I may have a bad batch of tubes.  :-\

Thank you everyone for hanging with me... I'm really burnt from this one... but feel I'm close.

 

[[silent:arts]]

eight bad tubes with the same mistake
nothing you think about at the beginning ...

would be a bummer but nice if this was the only fault

 

[khstudio]

eight bad tubes with the same mistake
nothing you think about at the beginning ...

I've had worse luck in my life.

Think about in the beginning?

No, not until I started asking others to post "Voltages" which really helped me narrow down the problem to the Current draw of the 5687's. The Voltage @ R10 was instantly apparent, which is why I focused on that over the past 20+ posts.

I NEVER would have thought all 8 tubes could be bad... I bought double of every tube just to avoid this.
I'll have a new set of Tung-Sol 5687's in on Friday... so we'll see then, if this is really the problem.

would be a bummer but nice if this was the only fault

Yes & YES! 

And what a learning experience this will be... for Everyone.
You can't rule anything out when troubleshooting... even when your using the EXACT same parts (or tubes) as everyone else.
These tubes are even from the same batch & date code as others... that will be strange if so.

 

[Freddy G]

Holy Smokes!
I've been following this thread closely.
Kevin, your ordeal is making me nervous about building my own PM670....just ordered most of the parts and am about to start.
I guess the lesson is to go slow and test every building block along the way and as you say "you can't rule anything out"!

 

[Moby]

Kevin I'm glad you fixed the beast but as I remember I asked did you measured tubes. You answered "yes" but... Just to notice that besides measuring current it's very important to check  microphonics . I purchased my tubes from Antique Electronic Supply and checked all of them, found 4 from 25 5687 sensitive to "knocking".

 

[khstudio]

Kevin I'm glad you fixed the beast but as I remember I asked did you measured tubes. You answered "yes" but... Just to notice that besides measuring current it's very important to check  microphonics . I purchased my tubes from Antique Electronic Supply and checked all of them, found 4 from 25 5687 sensitive to "knocking".

Lets not jump the gun too soon... Friday I'll have the new tubes to know for sure but I'm about 99% sure the tubes are the problem.

I did test them ALL with my (Basic) tube tester but in the circuit is a different story.

 

[khstudio]

Holy Smokes!
I've been following this thread closely.
Kevin, your ordeal is making me nervous about building my own PM670....just ordered most of the parts and am about to start.
I guess the lesson is to go slow and test every building block along the way and as you say "you can't rule anything out"!

Freddy, Don't be nervous!
This is really a simple circuit which is what drove me nuts.

It also sounds GREAT!

Nobody really focused on the tubes as being the problem but instead, the PS, wiring, Pots, etc...
All of which kept me guessing for the last 2 weeks.

All new builders now have some voltage charts to help resolve problems & also learn from my dilemma.  8)

 

[khstudio]

I Got 4 NOS Tung-Sols's in today!

sorry for the caps but:

THE TUBES WERE MY PROBLEM!!!

TUBES I'M USING & had trouble with

PHILIPS ECG 5687WB (NOS) From Antique Electronics Supply
BLUE Lettering - DATE CODE 8652 = (52nd week of 1986)

I don't know how the hell this happened but I have the EXACT same tubes as many others... even the same "Date Codes"  
But it is now CONFIRMED... so if your voltages look funny & you're drawing too much current or reading voltages @ R10 330r much higher than 13v (mine was almost double) then you may have the same problem.

I don't have time right now but I'd like to go back & refine all my posts to point to this conclusion to save others from having to read thru all of it.

Thanks to ALL who stuck with me thru this one & I'm sorry if I pissed anyone off BUT there was no way I could have known it was the tubes... I bought 8 just to be sure but they're all from the same batch. I checked them with a "Basic" tube tester & also checked with others to see if they were using the same ones.

2 weeks of hell is over.  ;D

I'll post my final voltage chart when I have time.
(BTW, My PT is still getting a little too hot for my liking... still need to do some work on that)
It sounds GREAT but strangely, it sounded great with just the SINGLE, old tube in there too.
Doug & Gus are going to try to help me figure out what other tube it may possibly be (wrongly labeled maybe ?)

 

[skal1]

Glad to here you solved the problem,  h a p p y  your  h a p p y  i now i am i'am sure are your h a p p yyyyyyy.

skal1

 

[Moby]

2 weeks of hell is over.  Grin

;D

 

[tommypiper]

Very, very weird.  I find it extremely hard to believe that all 8 out of 8 tubes are defective.  Possibly counterfeit?  Mislabeled?  Something is not right in this story.

And you are still getting a hot power transformer?  Are you sure it was the tubes?  Are you sure your issues are over?

You were able to run it on one tube?  Does this make sense?  Can it be replicated by others?

This defective tube solution sounds too simple and too unlikely. ( I'll buy it if they are mislabeled or counterfeit.  Still, the chances of that as really true are slim.)

I'm open to explanations, just expressing the obvious reaction to such a story...

 

[khstudio]

I'm not sure how to respond to your post.

The tubes were DEFINITELY the main problem.

Yes, I still have a hot PT.
But ALL the other problems I mentioned several times already are GONE!

like:
Distortion while compressing
Wacky Meter movement + not showing correct gain reduction
Abnormal (Double) voltages @ R10 (compared to others units) They got 12v... I got 22v
R10 voltages moving around when moving the Threshold, etc...
double the current draw of my PHILIPS 5687WB tubes.

What else do I need to say... I put a NEW set of tubes in & ALL voltages are on the money & it works & sounds GREAT!

Believe it bro... I got a bad or mislabeled set of tubes.
maybe I should leave all my posts up so you & others can see the **** I went thru before finding this out, the hard way.

 

[MartyMart]

Kevin, I'm very pleased to see that you sorted it out !!
I have not got to my 2 x 670's yet so hadn't really been keeping an eye on the thread.
I got my tubes from a different source so hoping they will be fine !!
I sympathize with the time you've put in and all the "head scratching" I have personally been very
lucky with builds and only had a day of "weirdness" with my D-AOC - due to the higher voltage here
in west London of about 248v AC, my 220v AC rated traffo was pumping out too much for the circuit.
A simple 1k 25w power resistor sorted that out !

Is the traffo overheat due to the rating being a little on the low side ?
Did you see that mentioned somewhere .... pulling 5A from 6A winding is a "no no" ?

ENJOY

Marty.

 

[lolo-m]

Yes, I still have a hot PT.

I'm happy you sorted out  !!! I never thought about 8 bad tubes  ...
Now your PM670 is working, let the tubes burn about 48 hours like EMRR said earlier in the topic... NOS tubes need some time to get their definitive values. My PT was hotter than it is now during that time... After this pre-burn, if your PT is still too hot, maybe you'll have to think about an additionnal transfo for the heaters (I would say 9V/8A).

 

[[silent:arts]]

I'm happy you sorted out  !!! I never thought about 8 bad tubes  ...

me too ;D ;D ;D ;D

Kevin, this one is for you:

 

[dagoose]

Just wondering;
I blew up one of the 2n6107 transistors while calibrating (shorted two legs) and it's a bit hard to get a new one (i want it fast) but according to a local electronic store the BD244c is the same. Before i install it i wanted to know for sure. Is it the same?