the Poor Man 660 support thread

[Kingston]

For example me and others here it seems are getting around 400V up to Q4

How's that possible? Even with 240V AC you should get only 336V DC measured after the rectifier.

It's the unloaded voltages thing again, unfortunately.

the transformer should spec at about 250VAC 0.2A, which loaded should be around 350VDC right at the first filter cap and bridge rectifier output.

Unloaded it's entirely possible it's as high as 400VDC. But nobody is drawing current so the parts should not break. Maybe.

Still, those puny low rated and too small package transistors in a high voltage (and relatively high current) PSU is a basically a design error. They work fine in what we call a "happy day scenario" at work. Not a lot of you have had a happy day with this PSU. Start up is a place where bad things might happen, surge currents killing the little things.

Time to start looking for better spec parts.

Simplification is also a good plan. Make the 250VDC regulator just like the lower voltage regulator already is, and rate the parts (voltage/watts) very high. There's no real need for the slow startup of the 250VDC here.

 

[rrs]

Time to start looking for better spec parts.

Sounds good where do we start.

 

[radiance]

At RS I could only find 2 PNP transistors with a  max collector emitter voltage higher than 300V, one with 400V and another with 500V.
However, both have a max dc collector current of 0,15A where as the MPSA92 has 0,5A. I don't know what's needed here...

...Also, those two alternatives I found (RS #  154-908  and 154-902 ) are smt ...might be possible to solder some legs on them though....

searching for NPN did give some more (non smt)  options. For example RS # 398-502  (530V, 1,5A)


May I ask, what other specs (other than max collector emitter voltage and max dc collector current) are we looking for here?

 

[Kingston]

It would be simpler to just simplify the first regulator and forget any exotic parts.

Just use the design that is already there, the lower voltage regulator section has proven itself already. Do that with a 100-120V 3W zener and a trimmer in place of the 182K resistor. There's your new 250VDC regulator section, what, 5 parts?

 

[rrs]

Well I have just re built myself a new PSU on a new board.Improved all my connections and wiring.
Under no load all voltages seem pretty good.

I think I will wait till tomorrow to test under load at least I will get a good night sleep that way.

 

[crisotop]

wicked - looking forward to hearing your results!

I need to order some more 840s, so my PM is on hold for some days...

good luck!
christoph

 

[rrs]

Unfortunately same old problem. Spent over $300 replacing parts and new boards.

Well I have no way to hide my disappointment with this POS project.
At least I know who to trust in the future if wanting to do a reliable build.

 

[radiance]

I'm very sorry to hear this.
You're having a faulty PSU, that's for sure. The rest of the compressor has been proven to work for you.
Maybe you should forget about the stock PSU and do what Kingston suggested i.e. build your own.
I don't know what's the VA rating of you're toroid but that might also be a cause of your problems.

So far both Edcor and "Holger" groupbuy toroids are underspecced, main PSU board uses 300V parts where they should have been at least 400V and the slow start heater board gives no were near DC due to underspecced cap values....
To me it seems the PSU parts of this project have been rushed / slightly overlooked.

 

[Kingston]

Unfortunately same old problem.

Time for a recap, as so many people are having PSU troubles and I forget what's what. Are you breaking parts, or is the voltage simply dropping too low under load.

Have you used the same PSU transformer the whole time?

 

[mitsos]

sorry about the problems.. I'm still waiting for a replacement power trafo to re-test mine.  My problem is the heater (I think) so I'm hoping a beefier (and better wound) PSU would take care of the issues and the hum. (speaking of hum, are there any ways of minimizing hum/noise while testing this thing outside of a case? So far I have the PSU ground tied to AC ground)

FWIW, I had some voltage weirdness too, some voltages dropping, etc. Not quite sure I figured out what it was, it kinda went away and hasn't come back (yet), but I also had a problem with R8 going open circuit which made my HV go very much off, so maybe the two were related.

But, if you're constantly changing (active) parts and getting the same problems, logic dictates that the problem is elsewhere.  Maybe after all the solder/desolder/modification of the PSU, lifting pads and such, is it possible you have a bad/intermittent connection somewhere on the board?  


ALSO: I'm surprised that the Edcor is underspec'ed... I thought they were ordered according to analag's specs? If that's wrong what are the correct PT specs for single/dual unit?  I still have time to change my order with the trafo winder!

EDIT: these are the specs for the Edcor XPWR063 (I think that's the one for a dual channel project?):

Power transformer for a 120V or 240V, 50/60Hz. line to 250V at 200mA, 30V (15-0-15) at 1A center tapped and 9V at 6A.

cheers and good luck!

 

[radiance]

Power transformer for a 120V or 240V, 50/60Hz. line to 250V at 200mA, 30V (15-0-15) at 1A center tapped and 9V at 6A.

I think the Edcor is designed for a mono unit
For a stereo unit the heater secondaries are underspecced. It also depends on if you're going to use a slow start heater board or not.
My stereo unit with slow start heater boards draws 5,6A. To be on the safe side I would go for 10A or so.

 

[mitsos]

That makes sense. I think they doubled the current (which I think is OK for the rest of the voltages) but for the heater maybe 5A would be good for a mono unit? I think I asked the guy to do about 4.5-5A on the heater winding.... will double check..

Does the slow start need much current?  I am pretty sure my mono pulls about 2.8A (could be 2.6, working from memory here).

cheers!

 

[loopermc5]

I used the edcor for my stereo unit but got a separate heater tranny works great the edcor barely gets warm I got a 10a hammond for the heater

 

[kazper]

Does the slow start need much current?  I am pretty sure my mono pulls about 2.8A (could be 2.6, working from memory here).

I get about that on my Mono.

 

[tommypiper]

I'm probably not going to use my power supply PCBs, so if anyone wants to rebuild their supply or make a modified version, or have a spare, let me know.

 

[horvitz]

For whatever it's worth, I just recently finished my PM670 using the Edcor XPWR063 and so far no problems at all.  Nothing gets too hot, even when left running for hours.  Seems to work just fine.  Pretty strange that it should be fine for some people and not others.  I mean, we're all building pretty much the same thing here.

  Brian

 

[rrs]

Mine had been working for around 2 years.


Problems? ... yes blew the transistors Q3 twice. Other issues I had though were of my own doing when building.
While troubleshooting latest problem (high Voltages due to problems around Q3 and D7) burnt Q4 and 475R. Ever since replacing those I have had this low voltage problem.

I have the Avel Lindburg toroid from the US group buy.

Some Thoughts?

1) Even when voltages drop (245/136 only under load) I am still getting between 390-400V before Q4 IRF840. I assume this means toroid is working fine??

2) I notice this problem has occurred to others through this thread after mine was built. Originally I used IRF 820 and was fine. The exact same parts no longer available and I noticed in Analags BOM part numbers for IRF 820B are probably what I brought and what others also did. One person around page 50ish noted having success with the B version. These no longer seem available anywhere. Using IRF 840's now due to Volkers advice but no difference.
Maybe some were lucky with IRF 840/20 parts but now we need a substitute??

3) not using slow start heater. Could this help??

4) Dose this mean Q4/ IRF840 is blown ?? In the past for other reasons I have had a unit ( different build) shut down like this but transistor wasn't blown just lowered voltage and was fine.

Volker/ Analag
I would strongly urge a rethink on the PSU in this project. Yes most including me have had working versions but seems only a matter of time till it breaks. Considering the voltages we are dealing with here I think it highly irresponsible to keep selling these until this issue is sorted.

 

[rrs]

Unfortunately same old problem.

Time for a recap, as so many people are having PSU troubles and I forget what's what. Are you breaking parts, or is the voltage simply dropping too low under load.

Have you used the same PSU transformer the whole time?

Voltage is dropping too low under load. Yes using same PSU transformer.

 

[mich]

No problems with the Edcor power for me....

yes, it gets a little hot after hours working - but a lot less than the 5687 tubes....also,you can always
mount it outside of the box(on back panel).i wouldnt call it underspeced...try touching any fender amp(tube) power transformer....and they are designed to last years....

 

[mitsos]

What voltages are you getting after Q4? I get near 400V before also before and after R8?

The only problem I have with these boards is that they are small and everything is cramped together. Combined with the tube heat and dangerous voltages makes it extra fun to poke around....  Remember the game Operation?  ;D

If the PSU is giving you nothing but problems, why not build a new one? Breadboard a passive one or grab Tommypiper's extra board
and be done with it. I was thinking to go passive if the new PT doesn't fix my issues. 

TommyP, what PSU are you planning on using? Care to share the design?

I wonder if it's possible/reasonable/worth it to filter the heater DC? The way it is, there is no filtering right? I haven't measured, but there should be quite a bit of ripple, does this not make a difference in a heater?  How much capacitance does one need for 3A?

OR, anyone run this thing on AC heaters? Any reason not to?