the Poor Man 660 support thread

[Gus]

Looked in the GE book found 5 with the 9H pinout
one has a 20Volt heater 7370
6900 1 amp fil at 6.3VDC and a 7044 .9amp fil at 6.3VDC different Rps.
7892 is noted as a Pulse amp

I spent hours on the phone with Kevin.  There were numbers of things tried, different transformers, different tubes from the same purchased group of tubes, voltage and heat measurements and calculations and a lot of thinking.   After the voltage readings of working units were posted and every thing else was checked and rechecked I asked Kevin to install one tube.  When one installed tube node readings matched two tubes node readings of working units the readings were telling me the first tubes were conducting about X2 in the circuit.

Some of the other crazy stuff was maybe caused by the 10K to 600 transformer having too great a current in the windings and maybe being saturated and having a larger magnetic field affecting the meters and causing distortion.

When you build the circuit check your voltages to the posted ones that will help figure out what is going on if you have an issue. Use Ohms law and calculate power.

The answer might be found comparing the tubes with a curve tracer.

There are classes given in troubleshooting systems, processes etc that show/teach you will not get the correct answer if you tell yourself it can't be something when all the logic shows it is in that section.

 

[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?

Yep, it does work.  ;D

 

[khstudio]

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).

My PT Temp read about 135' F after the FULL unit was on for about 1.5 hour.
At Gus's request, I disconnected the everything but the AC Heater lines & let that run for an hour & it went up to about 125' F (& rising)
So I'd say the heaters are drawing a lot.

I will try to let it burn in more but in no way will I let it run unattended!

Thank you lolo-m for helping me.  ;D

 

[khstudio]

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:

Thanks Volker... I needed that.
If I can get this hot PT worked out I can put the lid on it, then move on.
I can't say enough about the way this thing compresses... even with the ONE tube, Rowans original 10uf (stock) setup souds & works great on the 2 buss.  ;D
My other added time-constants are better for individual instruments. 

 

[khstudio]

Gus & Doug,
I can't thank you guys enough for all your help & advise... many hours of talking, measuring, etc...

Kevin

 

[analag]

I'm glad you got itsorted out, me and Gus spent a few hours discussing your PM670. I must say this is a learning experience. Personally I have never seen eight bad tubes, well not like that.

 

[khstudio]

I'm glad you got itsorted out, me and Gus spent a few hours discussing your PM670. I must say this is a learning experience. Personally I have never seen (8) bad tubes, well not like that.

Me either... that's why I spent so much time chasing my tail. 

I'd be more than happy to send you a pair of these tubes for testing if you like?
... just let me know. (PM or Email me your address)

& thanks for a cool comp.  ;D

While I have your attention I have a few questions:
- Does the 10uf across the trimmer to GND have anything to do with the time constants?
...if so, could you explain?

- Concerning the Trimmers:
I think it was you who said to set RV3 to 2.4v & RV6 to 4.5v...
But are those voltages set in stone? ...meaning, is there any other reason to set them different... like for "Balancing" stereo signal OR the control voltage?

- Any other tips you may have for calibrating or tuning this thing into perfection would be cool too. ;D

 

[mikeyB]

Don't forget Kevin - if you can squeeze a 30 or 50 VA transformer in there just to do or share "heater-duty" - your main tx should run cooler!!

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:

Thanks Volker... I needed that.
If I can get this hot PT worked out I can put the lid on it, then move on.
I can't say enough about the way this thing compresses... even with the ONE tube, Rowans original 10uf (stock) setup souds & works great on the 2 buss.  ;D
My other added time-constants are better for individual instruments. 

 

[tommypiper]

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!
...
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.

Well, OK.  It's just we've never heard of 8 out of 8 NOS tubes all being defective.  Very unusual.

I believe we've all been through the sh#t with you on this.  Trust me.  

I'll be curious to hear more details about the bad tubes.  Maybe some of us will suffer similar issues since many of us bought them at the same place as you.

 

[analag]

I'm glad you got itsorted out, me and Gus spent a few hours discussing your PM670. I must say this is a learning experience. Personally I have never seen (8) bad tubes, well not like that.

Me either... that's why I spent so much time chasing my tail. 

I'd be more than happy to send you a pair of these tubes for testing if you like?
... just let me know. (PM or Email me your address)

& thanks for a cool comp.  ;D

While I have your attention I have a few questions:
- Does the 10uf across the trimmer to GND have anything to do with the time constants?
...if so, could you explain?

- Concerning the Trimmers:
I think it was you who said to set RV3 to 2.4v & RV6 to 4.5v...
But are those voltages set in stone? ...meaning, is there any other reason to set them different... like for "Balancing" stereo signal OR the control voltage?

- Any other tips you may have for calibrating or tuning this thing into perfection would be cool too. ;D

I'm gonna send you my email address.

 

[khstudio]

EDITED: Your right Rowan. 

If someone with a "Curve Tracer" wants to test any of these tubes, let me know?

 

[analag]

Hey I have a curve tracer...be nice guys, it's only electronics.

 

[Moby]

Kevin I'm glad you removed your last comment  8)

 

[idylldon]

While I have your attention I have a few questions:
- Does the 10uf across the trimmer to GND have anything to do with the time constants?
...if so, could you explain?

- Concerning the Trimmers:
I think it was you who said to set RV3 to 2.4v & RV6 to 4.5v...
But are those voltages set in stone? ...meaning, is there any other reason to set them different... like for "Balancing" stereo signal OR the control voltage?

- Any other tips you may have for calibrating or tuning this thing into perfection would be cool too. ;D

I'd be interested in your answers to these questions as well.

Cheers,
--
Don

 

[emrr]

Very, very weird.  I find it extremely hard to believe that all 8 out of 8 tubes are defective.  Possibly counterfeit?  Mislabeled?  

I've not ever had 8 bad 'new' tubes, but have had as many bad 'new' neon bulbs drive me insane in the same manner.  I think these are way too cheap for counterfeiting.  Mislabeling of one of the 4 other variants seems more likely, but they all look about the same in regards to performance.  They are all the same batch and date code, so I'll bet on some really poor tolerances and attention to detail in the xmas/new years week of '86. 

 

[khstudio]

Hey guys, I took a break for a few days.

My PT is still getting hot, even with just the heaters hooked up.
Heater current draw is 5.25 Amps (after warmed up) everything else measures good.

I called Brian from Edcore today after exhausting all other possibilities & he said it should not get that hot.
I measured it at 145 Deg. F after 1 1/2 hour... & this is with the lid off!
He offered to send me a new PT, so that should rule that out & hopefully fix it.

About the tubes:
Before I even focused on the tubes as being a possible problem, I would randomly put different sets of the 8 tubes in the unit.
It's possible that a few MAY be OK.  I'm going to test them one at a time tonight to see.
I also plan to send one (or so) to Rowan to check them out on his curve tracer but wanted to make absolutely sure they ALL were bad or wrong... I'll bet most are.
The reason I'm thinking a few could be good is... now looking back, I thought that at one point I had a good working channel.
But it was so random I forget.


Hey Doug, I got your message.

 

[noulou]

I have to say a big thanks to Kevin for the push to solve the problems he was having.

I missed it while it was going on, but when I went through his postings I realised I had exactly all the same issues with my pm670 as him.

Namely large distortion only with gain reduction, wobbly metering, rf meter interference ...

I had tried everything and had almost given up. I had also bought a second set of 6bc8 and 5687 tubes to try out.
Unfortunately I bought the 5687s again from the same person on ebay
http://cgi.ebay.de/5687WB-Roehre-neu-new-5687-Tube-OTL-Headphone-Amp_W0QQitemZ370230727572QQcmdZViewItemQQptZRöhren?hash=item5633789394&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1229%7C293%3A1%7C294%3A50

The other day I tried the trick of pulling one 5687 from the pcb like Kevin. The comp started working fine. I immediately pulled out the credit card and got some NOS 5687s from the States.
Now the whole thing works beautifully. 
There is a little bit of a buzz and the german torroid is getting quite hot but what isn't inside this beast? Maybe installing a fan is a good idea.
There is distortion while doing large amounts of gain reduction, but that is normal for a vari-mu.
Lessening the release time is something to try out also.

anyway, the thing sounds great! BIG thanks to everone involved!

 

[[silent:arts]]

noulou,

now where are the pics ;D ;D ;D

this tube thing is scary. my tubes are from just the same eBay seller ...
and I don't have this problems 8)

anyhow it seams there might be something wrong with some 5687 tubes.

 

[Gus]

6900 and 7044 9H pinout tubes from the Ge "Essential Characteristics" book.   Also note the Rp is lower at lower plate voltage with the 5687.  Also note the GE book specs them at different -grid voltages.  Like emrr posted the tubes seem to be close in specs

from The Ge "Essential Characteristics" book

6900 plate volts 120, Rp 1.6K, Gm 11,500, u 18.5,  1amp at 6.3VDC fil, -2VDC grid, max volts 600
7044 plate volts 120, Rp 1.7K, Gm 12,000, u 21,  .9amps at 6.3VDC fil,  -2VDC grid, max plate volts 300

5687 plate volts 180, Rp 2K,  Gm 8,500,  u 17, -7VDC grid
       plate volts 250, Rp 3K, Gm 5,400,  u 16,, -12.5 grid

I would order a 6900 and 7044 and try the tubes in the circuit as a test.

I don't think the term "bad tube" is correct to use at this time.  I would GUESS what ever the tube is it DOES meet the specs of the 5687.  Maybe using one tube is a good thing?  Could it be tubes that fall at one end of the normal distribution?  http://en.wikipedia.org/wiki/Normal_distribution


noulou  Could you post the datecode and brand on the tubes you bought?
 

 

[idylldon]

noulou  Could you post the datecode and brand on the tubes you bought?

Kevin posted this earlier in the thread:
[blue]
PHILIPS ECG 5687WB (NOS) From Antique Electronics Supply
BLUE Lettering - DATE CODE 8652 = 1986 (December I think?)[/blue]

I have these exact tubes in my unit and haven't had any issues, but since Kevin has had some problems with his I might get some from another mfg. to see if there's a difference in my unit.

One other thing.  These aren't not just normal tubes; they are JAN (Joint Army/Navy) tubes and, as such, they undergo more strident testing procedures and are built "tougher" for the military.  While there's always a possibility for a bad tube out of a batch, I would find it strange if there were a whole bunch UNLESS there was some mfg. defect on the line that wasn't caught for a period of time.  Nowadays the NOS tubes have been pretty much picked over, especially regarding the common tubes, so it wouldn't surprise me to find out there are some bad 5687s floating around.  I think Kevin is going to test them again one at a time to see if this is a global issue or something more confined.

Cheers,
--
Don