the Poor Man 660 support thread

[Gus]

This is a long thread.  Page 80 and 81 has some information that might help.

What might be a good thing to do. Build  something simple like a adapter to measure the tube heater current and cathode current(should be close to plate current and safer than plate voltage) something like the bias setups used for the output stages of tube amps.    This should help determine what is going on with the tubes


Measure heater current for loading of the heater supply with different tubes

Measure plate current for transconductace changes between tubes and current in the output transformer.

This should answer the tube question.

 

[radiance]

Thanks Gus! In fact, I had your post (see below) on page 81 bookmarked already.
I'v ordered some other brand 5687's to see what that does....


Info on the box of the 5687's I'm using now reads:

JHS-5687WA
contract no  dsa 9-21370
MFG.  BY SYLVANIA IN USA
(a) date packed 2-66

similar to CV-5188


Does this mean they're from the year '66?

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.

 

[radiance]

Update:

I replaced the slow start heater heat-sink with a much bigger one and ditched the small heat-sinks.
After running the unit for 30 min with case closed the temp of the heat-sink was 65C.
That's 5C higher as the previous one. Better heat transfer I guess.
Heater voltages did not became higher because of this.
Bypassing R1 gave me a 0,10V increase in heater voltage.
Knobs of both channels don't interact with the meter of the other channel any more. (can't remember if they did actually... :-\)
Time constant pot does interact with the meter (of it's own channel) when turned fully clockwise.
Threshold pot only at the last two positions when turned clock wise.

Basically, running the unit with one 5687 tube inserted gives me a stable meter.
I've ordered another brand 5687's. We'll see if they'll make any difference.


Another thing I noticed: my 245V is actually 257V (and 136V is 139V). Would this cause any problems?
Over here I get 240AC from the power outlet  
I remember a post from InputOutput suggesting to lower the 136V rail.

If you are wondering if your PT has enough power OR if your meter is bouncing OR if you're getting random spikes in the sound, OR are wondering if your tubes are bad.  The cure might be as simple as lowering that R9 on the PSU-board. Try 176K as a start, and go lower to 170K if the problem is still there.

Here the post:  http://www.groupdiy.com/index.php?topic=28274.1740
Might give it a try as well.....


Also, would it be wise to lower the 257V I'm getting a bit?
If so, is this achieved by lowering both R2 & R3? Somehow, the 245V part of the PSU is a bit over my head....

Thanks.

 

[radiance]

Tried the new tubes. Still only 6V heater voltage. Slightly less knob / meter interaction on 1 channel, other channel no interaction.
This interaction might have to do with the transformers being to close to the meter....will check this.
I think that bigger caps in the slow start PSU will give me higher voltage as I've now 0,75 AC on top of the 6V DC.
Overall I'm quite happy with how the unit behaves and sounds. I've no bass roll-off problems.
Still have to try the SC booster and other in & output transformers.

 

[rrs]

Keep having PSU issues.

Twice had to replace Q3, D8, Q4 in the last year and a have burnt connectors for R15 on board, ground and heater over the same time.
Anyone able to give some help to find out why so many PSU issues. Everything is as stock with R15 being 47R.

 

[radiance]

Keep having PSU issues.

Twice had to replace Q3, D8, Q4 in the last year and a have burnt connectors for R15 on board, ground and heater over the same time.
Anyone able to give some help to find out why so many PSU issues. Everything is as stock with R15 being 47R.

Only thing I can think of is overheating. Does it get hot inside? How is the airflow? How hot does the Q4 gets anyway? I have not had my unit on for longer than a couple of hours so can't comment on that ....
Is the heatsink of Q4 big enough? Even when the toroid and R15 are close and generating heat as well? Does your toroid gets hot?

 

[rrs]

Well it's on for around a full day when I use it maybe once a week. The unit itself gets reasonably hot havn't measured the rectifier. The toroid dosn't get hot but R15 is the hottest part.

 

[idylldon]

Excellent ventilation seems to be imperative with this build.  My tubes are in a well-ventilated part of the chassis, but the power supply is relatively enclosed.  I ended up using two small computer fans (one pushing air and one pulling) at opposite ends of the chassis to ensure a good airflow.  Since I'm running the fans off an adjustable power supply, I have them spinning a bit slower to reduce noise.  So far (knock on wood), I haven't had any component failures or excess heat issues appearing on the PCB even after having the compressor on for a full day. 

Maybe this isn't your problem, but I thought I'd mention that this thing REALLY puts out the heat, which might explain your early component failures.

Cheers,
--
Don

 

[rrs]

OK still haven't fixed my latest PSU problem so hope someone can help me out.

Basically I only have around 30 volts coming out where there should be 245V and even less where there should be 136V.

I have traced down some voltages that may help out:
D4 cathode has 391V.
IRF820 has 391V on pin 2 (D) and 37 volts on both pin 1 (G) and 3(S).
(this is with one board attached)

I had just replaced the IRF820 as if was previously burnt out along with R5. So could this be a faulty IRF820 or something causing it to fail, not sure what voltages I should have where.

I also have 30 volts at D7,R2 that I also measured.

Also used my diode meter to check diodes and transistors and all seem ok. Does getting a forward voltage reading of around 500/600 on the diode meter mean they are working?
D13 and 14 are the only exception which measure around 115 but the diode out of circuit measure around 520.

 

[rrs]

Any help would be extremely appreciated.
This thing has given up on me just as I have almost finished some important mixes and having trouble stalling for time.

Maybe I can send a couple of Edcor transformers to someone for incentive  ;D  ;D

 

[TheGuitarist]

Hey guys just checking something with a few of the voltages.


Can someone confirm what the voltages from the toroid to the PSU is supposed to be? from HV to 17v i have  146, 164, 17.2,1.1,17.3

Now the rest are fine and my 17v rails are fine but i'm trying to trace down the HV problem i'm having and those numbers don't seem right to me.

 

[skal1]

Hi rrs

hope these voltages help you



can someone supply me with the ref voltages for the psu board for q1 q2 q3 q4 and d8 , thanks .

skal1
No prob, much easier than explaining point to point ) Here we go, this is the situation with my psu , I have a 300v after the bridge and 220u (c1)

Q1-E298.8V,B298.2V,C254V
Q2-C254V,B198V,E197.6
Q3-C197.6V,B100.5V, E99.9V

Q4-G254V,D299.4,S251.2
Q5-G137.4V.D251V,S135V


not loaded


skal 1

 

[rrs]

OK replaced the IRF820 and tried again.

Voltage on 245 went up to just over 245V then dropped down to 30V.
Tried later and similar thing but only got to 110V, couple more power up's and the same thing happened.

Any one know what could cause this ?

So when voltage drops to 30V I still have 391V on diodes D5,6 one end of D8 and one end of R3.

 

[kazper]

At some point there was a recommendation to use IR840's across the board. My guess is you have a issue with the MSA Transistors q1-3.

That or you damaged the PSU when R5 went out.

Are you in a 670 (2x1) configuration on one PSU or 660 (1x1) on one PSU.

 

[rrs]

I have 2 channels but testing with only one channel connected.

Would 2 IRF840 be safe to try?

I have replaced all the Q1,2,3 transistors but due to the solder pads peeling off so easily this section is virtually all point to point now. I am sure though I have copies all the traces from both top and bottom of the board.

 

[[silent:arts]]

...
Would 2 IRF840 be safe to try?
...

Yes - and recommended

 

[TheGuitarist]

Hey guys just checking something with a few of the voltages.


Can someone confirm what the voltages from the toroid to the PSU is supposed to be? from HV to 17v i have  146, 164, 17.2,1.1,17.3

Now the rest are fine and my 17v rails are fine but i'm trying to trace down the HV problem i'm having and those numbers don't seem right to me.

Anyone?

 

[skal1]

ok guys

rebuilding my fresh psu , just wondering can i use 1/4w for the resistor R2 TO R14 and use the closest values  to the ones on the bom , are the values critical?

thanks

skal1

 

[kazper]

Hey guys just checking something with a few of the voltages.


Can someone confirm what the voltages from the toroid to the PSU is supposed to be? from HV to 17v i have  146, 164, 17.2,1.1,17.3

Now the rest are fine and my 17v rails are fine but i'm trying to trace down the HV problem i'm having and those numbers don't seem right to me.

Anyone?

There all wrong... the voltage should be the same as the specified transformer you have. I think (off the top of the head) it's 250V, 15V CT, 9V
My transformer reads about 1-5% higher from the mains.

I have the Edcor XPWR063

These measurements should be lead to lead on the secondary side of the transf, AC measurements.

 

[TheGuitarist]

This was with reference to ground, Just checked lead to lead and i'm getting 280v... well that could explain it... probably burnt out a component somewhere then...

So i guess my xformer is bad... should have never bought anything off tat to begin with.