the Poor Man 660 support thread

[ppa]

the quiescent currents of the loads at the two psu's outs,

when the power switch is turned off the psu caps, except c5, are discharged too fast if this current is high respect c5 , so c5 remains at an high voltage and it polarizes the transistors and the mosfet with abnormal voltages,

than D11 discharges fast C5 to avoid abnormal voltages to transistors, but for q4 is necessary even D13 is to protect it.

the problem is that in some 660 PSUs the abnormal voltages are so high to damage the transistors and q4, but in many other 660 PSU's don't broke theese ones. 

 

 

[radiance]

Thanks... I think I get it....took me some time to visualize...

 

[ppa]

infact Dingo use two channels with one psu so the load current was to high for that PSU to avoid the c5's abnormal voltages, but adding the protection diode q4 and the transistors now are good.

 

[mrclunk]

Just about to do some mods on my 670. The recent action in this thread has me excited about the poormans again.
I haven't had any problems with the psu apart from initial mistakes i made but i'll be implementing Piers mods, thanks!

I've a box of the Russian tubes which need a little more current, i think my transformer is at its limit so will add another heater transformer.

Is it possible to share the heater load on my existing transformer by adding another 9V Toroidal and paralleling them up together?
I'm thinking this is bad as the may short each other out?
Perhaps if i give them each their own rectifier bridge, would this work?

Otherwise i'll run the amplifier tubes from the existing rectified circuit and transformer.
Then the mu tubes on AC from a new 6V/50va torrid.

Any help would be appreciated.
paul

 

[Rob Flinn]

Why bother paralleling them, you could just run different heater circuits to different valves.  There's no reason to have them all supplied from the same supply.  In fact that is what I'm doing with my "not so pormans 670".  I have a filament transformer with 4 x 6.3v @2A

 

[mrclunk]

Rekon it'll be less faffing around and cutting pcb traces thats all.

Is having the heaters at 6.3 vac critical? I can pick up a cheap 6 Vac transformer that will fit in easily.

 

[Rob Flinn]

Rekon it'll be less faffing around and cutting pcb traces thats all.

Is having the heaters at 6.3 vac critical? I can pick up a cheap 6 Vac transformer that will fit in easily.

Normally 6v is within spec.

But if you supplied the left board with the original supply & the right with a subsiduary supply you would not have any trace cutting to do anyway.

 

[mrclunk]

Hmm, then one channel would be getting rectified 6Vdc and the other 6Vac.
Aiming to use this puppy for mastering so i'm not sure i'd be comfortable doing that, but i see your point.

 

[Rob Flinn]

Hmm, then one channel would be getting rectified 6Vdc and the other 6Vac.
Aiming to use this puppy for mastering so i'm not sure i'd be comfortable doing that, but i see your point.

Easy, make the 2nd supply rectified as well.

 

[mrclunk]

Then thats even more wiring!!
Back to the original question:-
How would i parallel two transformers to share the heater load? (Thru one rectification circuit)

 

[Rob Flinn]

Then thats even more wiring!!
Back to the original question:-
How would i parallel two transformers to share the heater load? (Thru one rectification circuit)

I'm really not getting why you are trying to do that at all ??  You would do better to just get a big second transformer & connect it on it's own to supply all heaters, leaving the insufficient tap of the other transformer disconnected or powering some meter back lights.  The difference in price will only be a few £'s.

 

[ppa]

Just about to do some mods on my 670. The recent action in this thread has me excited about the poormans again.
I haven't had any problems with the psu apart from initial mistakes i made but i'll be implementing Piers mods, thanks!

regarding my mods there are two type of problems that Dingo's pm660 had:

- q4 broken after any turn off state.

- voltage oscillations at both outs but only with two channels connected to the psu.

in my schematic some components are for the first problem and others for the second.
However, most of cases can be solved with only with some of the components in my mod schematic.

 

[ppa]

just to be clear around the mods I propose to Dingo.


regarding D11, D12, D13 , C6, they are to avoid the transistors and Q4 broken


regarding R13 and R11 is to avoid the oscillations on +136V out, often adding R13 is the only thing to do.


regarding D14, D15, D16 are to upgrade the regulations on +136V out


regarding R5 and C10 they are to avoid Q4 local oscillations, just I can write that I like this schematic very much because here Q2 reduce the power dissipated by Q3, moreover, it does the frequency compensation with R2 and R3.
Compliments to Analag for Q2. Very cool Analag !!!!

Moreover, I can say that I like very much the signal section, very good.
I seen Analag in a picture here in this forum, Analag is an elegant guy and I see his elegance in his pm660 too.  

 

[Kingston]

That's great Pier Pablo.

My PSU isn't broken now but all that information & improvements convinced me to upgrade the PSU. Thanks!

 

[mrclunk]

Then thats even more wiring!!
Back to the original question:-
How would i parallel two transformers to share the heater load? (Thru one rectification circuit)

I'm really not getting why you are trying to do that at all ??   You would do better to just get a big second transformer & connect it on it's own to supply all heaters, leaving the insufficient tap of the other transformer disconnected or powering some meter back lights.  The difference in price will only be a few £'s.

I haven't the space for one big heater transformer hence why i want to supplement the existing xform with another smallish one.
Why waste the 5-6amps @ 9vac i have available already IF i can just parallel in some way another 9vac xform.

 

[Kingston]

Are the two transformers perfectly equal? same manufacturer and specs? Then you can parallel them just like you parallel two windings within a single transformer.

If they are not equal I would not recommend it. There is no guarantee that they will share the load equally. At worst case one transformer will be loaded significantly more than the other and will die, burn and cause various types of unpredictable havoc. Guess what then happens to the other transformer trying to cope with the full load?

Or worse!  

The only way to safely conduct this situation is to make two separate heater circuits. Can't avoid the increased wiring and extra rectifier + big filter caps here.

That 5-6amps @ 9vac is only really enough for one poorman channel, despite the fact it works for two channels for some people here (I call that gambling). You actually need that much overhead for safety and reliability of one channel. 4.5-5A is roughly the optimal for one channel. Getting a new big 9VAC transformer to power another channels heaters is not wasting anything. This is a brute force beast and I think you too will appreciate safety and reliability.

And further, I think you will just have to fudge in some space for that extra transformer. Think outside the box. And I mean literally.

 

[mrclunk]

Thanks for that kingston.
So I'll  power the amp tubes with my existing transformer and rectification and then run the mu tubes on ac from a smaller 6vax Torroid that will just squeeze in.
Should have built this beast in a 4U case as advised at the beginning!
I can't actually remember the spec of my current xform but its been running for the past year (a touch warm) without problems.

 

[lolo-m]

Thanks for that kingston.
So I'll  power the amp tubes with my existing transformer and rectification and then run the mu tubes on ac from a smaller 6vax Torroid that will just squeeze in.
Should have built this beast in a 4U case as advised at the beginning!
I can't actually remember the spec of my current xform but its been running for the past year (a touch warm) without problems.

You need to cut traces on the PCB to do that... Just do a second heater PSU on the same schemo than the one you already use. Use another 9 VOLTS transformer with the same specs than the first one (voltage+amps). The price of that additional transformer isn't a deal compared to the overall cost !!!  If you've got space problems, put the 2nd transformer out of the box. Use the first PSU for one channel and the second for the other. As the carracteristics of both heater PSU will be the same, noise and sound will be the same on both channels.

 

[tekno808]

Hi,

I have almost all the parts for building the PM 670.

Now i'm searching for the the SlowStart Heater PSU PCB, can someone tell me where i can find it ?

Thx.....

Danny.

 

[Majestic12]

Sorry for the dumb question, but where do I get the pcbs for this build, or at least a layout for home etching ?