the Poor Man 660 support thread

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
OK so installed new IRF 840 (Q4) still no go. Voltage fine with no load (253V close to 245V),
attach 1 channel board and down the voltage goes. Without the tubes all is fine but a little high (260V instead of 245V)

I have tried several IRF840/820 from different suppliers,

Any further ideas where to look would be much appreciated.
 
mitsos said:
OK, so I tried a 0.92R resistor in place of the 2R and it still drops my heater to 4.2 or so (should have written it down). My pre-resistor voltage is 6.25V, so can I just omit the huge resistor?
OK, definitely getting closer... I swapped in a new 47R for R8 and now my high voltages are pretty much right on.. EXCEPT for my heaters...

I put in a second 0.92R in parallel with the first and now have almost 4.92V or so on my heaters.. The 5687's are finally starting to glow. I'll see if it passes audio a bit later, but does anyone see a problem if I omit the big resistor seeing as my heater DC is 6.25V (loaded, it's something like 8.7V unloaded) at the rectifier/resistor junction.

cheers!
-d
 
rrs said:
OK so installed new IRF 840 (Q4) still no go. Voltage fine with no load (253V close to 245V),
attach 1 channel board and down the voltage goes. Without the tubes all is fine but a little high (260V instead of 245V)

I have tried several IRF840/820 from different suppliers,

Any further ideas where to look would be much appreciated.

So I am assuming the channel boards are OK and Lomo's SCamp booster is also ok along with audio transformers.

That leaves PSU board and mains Transformer or valves.
As Moby has brought up the mains transformer issue maybe this could be a problem. Has been working fine up to now and is still producing 390V up to Q4 but maybe it's something I am unaware of.
As Q4 also has been replaced many times maybe there is also a better alternative to this part (IRF840).
 
rrs said:
rrs said:
OK so installed new IRF 840 (Q4) still no go. Voltage fine with no load (253V close to 245V),
attach 1 channel board and down the voltage goes. Without the tubes all is fine but a little high (260V instead of 245V)

I have tried several IRF840/820 from different suppliers,

Any further ideas where to look would be much appreciated.

So I am assuming the channel boards are OK and Lomo's SCamp booster is also ok along with audio transformers.

That leaves PSU board and mains Transformer or valves.
As Moby has brought up the mains transformer issue maybe this could be a problem. Has been working fine up to now and is still producing 390V up to Q4 but maybe it's something I am unaware of.
As Q4 also has been replaced many times maybe there is also a better alternative to this part (IRF840).

So I'm looking into this a little bit more.....

The 245V goes to the PCB and then right out to the CT of TR4. With no transformer installed there should be no change once connected to the PM board. By chance have you verified the T4 transformer?

Check your T4 connections and the pinouts. The center of the PL8 connector should be the 245V and that goes to Pin #3 of T4.
 
All connections to T4 are correct . Double checked and nothing has been changed on channels boards since it was working fine.

Not sure how to confirm that T4's are not damaged. Connection between PSU 245V and T4 pin 3 is good.
 
swapped my 840s for the 6th time today, with one particular set the voltages went up to 380V(!) - after changing them again, I got them down to spec again, but the voltage still drops under load :( I'm ordering more of them and the MSPA42/92, since all the other components test fine.

christoph
 
I notice in an earlier post one user with the same problem was using IRF840a with no luck and went to 840b and with exactly the same specs and it worked for him.
The last one I have tried was 840a.

Maybe if we can document more closely which ones seem to have more luck.


Also could this be another option. IRFB11N50A
http://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5411944
 
A little update, finally hooked it up as is (with 4.9V heaters using the only high-watt resistors I have here) and it passes audio along with some crunchy rice-crispies distortion which I guess is from the low heater V?  Anyway, I can't get any super low R resistors (like 0.1R) for a little while, so I was thinking of winding my own out 20-22AWG enameled copper wire. With 22AWG, I think I can drop 0.1V with 1ft of wire, but can it handle the almost 3A?

I (still) don't have it in a case so wires flying all over the place but... I'd like to get rid of the crunchies...

What worried me when I tried it is I smelled something cooking (that familiar smell) from the audio PCB but nothing is visually marked nor did I see any smoke (it was on long enough that it should have left some kind of mark). The 5687s did get pretty darn hot.  They will only get hotter with higher heaters right? 
 
mitsos said:
A little update, finally hooked it up as is (with 4.9V heaters using the only high-watt resistors I have here) and it passes audio along with some crunchy rice-crispies distortion which I guess is from the low heater V?  Anyway, I can't get any super low R resistors (like 0.1R) for a little while, so I was thinking of winding my own out 20-22AWG enameled copper wire. With 22AWG, I think I can drop 0.1V with 1ft of wire, but can it handle the almost 3A?

I (still) don't have it in a case so wires flying all over the place but... I'd like to get rid of the crunchies...

What worried me when I tried it is I smelled something cooking (that familiar smell) from the audio PCB but nothing is visually marked nor did I see any smoke (it was on long enough that it should have left some kind of mark). The 5687s did get pretty darn hot.  They will only get hotter with higher heaters right? 


Less V = More I 

Heat should be the same, remember those 5687's can do 12V heater for 1/2 the amperage that they pull under 6V

if you have 6.4 V just go for it for now replace later...
 
OK, so I removed the heater V-dropping resistor and still only have 5.75VDC... so the trafo winder guy screwed me. It was an impulse buy, the guy wound it on the spot kind of thing, and it sucks. I'm going to take this to a local winder and have him fix it and hopefully be done with this.

Anyway, the comp functions for the most part, but I have some crazy noise which goes away when a signal is present (and comes back as soon as signal goes away). It also goes away for a sec as I take V measurements, when I touched any DC terminal with the positive probe of my DMM, but it comes right back a second later, while still touching said terminal.

BTW, has anyone taken temp measurements on the 5687 tubes? My DMM has a temp sensor and it read close to 140 deg C!  wow!

thanks guys!
 
mitsos said:
BTW, has anyone taken temp measurements on the 5687 tubes?

I'm used to yanking out tubes shortly after turning off a unit when testing or measuring them. They are usually only mildly hot. But not the 5687! Yowza! Second degree burns are nasty. Hurts like a ***** on the day after. Same with soldering iron related injuries.

So yeah,
I've taken temp measurements, using highly sophisticated organic equipment.

On a safety and longevity stand point, it's probably not a good idea to install the optional reservoir caps next to the 5687 and the high voltage terminals. They won't last a year.
 
Kingston said:
mitsos said:
BTW, has anyone taken temp measurements on the 5687 tubes?
I've taken temp measurements, using highly sophisticated organic equipment.
:D :D :D  I burned myself on the heater resistor... that hurt... I also gave myself two shocks so far building this thing, nothing serious thank god!
On a safety and longevity stand point, it's probably not a good idea to install the optional reservoir caps next to the 5687 and the high voltage terminals. They won't last a year.
I never ordered them(options=more$$ which I didn't have. But yeah, 105C caps next to 140C tubes is not good I guess.
mich said:
Yes,5687 is the hottest ,current sucking triode...very good for cold winter sessions..
no cold winters here I'm afraid. It's only spring and it's already hit 30 C... Fun times ahead!

Fixed an issue with the input wiring and I think it's working as well as it's going to for now. This week I'll hopefully fix the power trafo and finish up the case design to send it off to fabricate. Then, proper grounding and a case should get rid of the noise, (that's the plan at least).  Is there a ground plan for non-cased (in testing) tube circuits that would give me the best idea of how well this thing is working? Tying PSU ground to mains ground helped a bit but not THAT much.
 
I'm finally having at least some luck (sheer expertise?  ;)) - it's definately Q4 that's causing my problems at the psu side. I socketed Q1 - 3 and put in another brand IRF840 and my high voltages are stable again with just the left channel connected (+Slow Start Heater & SCAMP Board), as soon as I put tubes in the right channel my voltages drop again and I have to replace Q4. Not sure if I'm just quick enough to not damage Q1-3, but I never had to replace them (and I burnt 5 pc. 840 since yesterday :D)

Don't know what's causing the problems on the right side though, the channel pcb is definately fine, all transformers + connectionsmeasure fine, as do the switches. Don't think that the Heater PCBs, or the Scamp Board would cause trouble on the high voltage side? Well, off to the bench again....

heads up David, sooner or later the PSU will be up and running again,
Christoph
 
I just cut off "regular" IC sockets:
4-way-2.54mm-single-in-line-socket-rc.jpg


The 840 I got from a local shop, can't really tell the brand, but I've got a couple of working ones from Conrad and they are Vishays.

hth, Christoph

EDIT: Got the next setback, seems like the PSU is only "randomly" holding the high voltage. The unit was running for 20min+, then I turned it off (took a break, didn't touch/change anything), on the next power up the HV rails are dropping again :( Unfortunatly I ran out of 840s (10 pieces now), so I'll have to wait until tomorrow... This thing is slowly driving me nuts  ???
 
Unfortunately same thing happened to me also. One IRF840 worked fine so went to bed that night feeling like I solved it. Next day fired it up and voltage dropped again.

One thing that also bothers be with some of the parts for this is voltage wise they are rated below what the PSU is producing in some areas. For example me and others here it seems are getting around 400V up to Q4 yet the MPSA 42 and 92 are only rated at 300V. Also C1,2 are listed in the BOM at 400V which is right on the limit.
 

Latest posts

Back
Top