the Poor Man 660 support thread

[tekno808]

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.

Hi,

You say "  4.5-5A is roughly the optimal for one channel " ???
6BZ8 heather current is 400ma, you need 2 of them for 1 channel so it's 800ma
5687 heather current is 900ma, you need 2 of them for 1 channel so it's 1800ma

So for one channel you have a total of 2,6 A or 5.2A for 2 channels , if you have a PT 9v 6A why is it not enough ?

Danny.

 

[dagoose]

I's just like driving a car at just below topspeed all day, not really good for the engine. It's better to have an engine that can run just a bit faster with lower RPM so that it's not that stressed all day.

 

[Kingston]

overhead and safety.

There is not a single transformer I would trust enough to run at the maximum rating, or even anywhere close to that. I have melted a few. With PSU transformers like this the core will start to saturate somewhere around 70-80% of maximum. Efficiency starts to drop, depending on manufacturer/quality that means more and more heat at an increasing rate, and sometimes dropping voltages and other more unpredictable things like life expectancy (yours and the transformers).

A good rule of thumb when you are rating transformer maximum current is exactly that 70-80% of maximum.

For our poorman case that means  2.6A / 70% = 3.7A. Notice also that the tube datasheet heater specs are averages and we should increase the overhead again. Now we land at a nice even number of 4A for each channel.

A dual winding transformer where one winding is providing high voltage B+ and another winding does heaters is another great example. If you run the heater near maximum, the B+ part (sharing the same transformer core) is now also saturating, and unpredictable things happen. If you care about stability and performance you don't allow this to happen.

 

[[silent:arts]]

all true ???

but a good transformer winder will keep all this in mind.
Mr. Müller is a good, old school transformer manufacture 8)

from various talks on the phone with him I know he is "over-winding" his products.
I remember a phone call about transformer heat & safety
the formulas / norms he instantly talked about for an hour made me a headache :
and his safety rule is winding one more norm higher than label it.

maximum power / core-saturation would mean heat from the transformer.
I have never heard of any issue with this (talking about Mr. Müller transformers only, not Edcor).
Mr. Müller transformers are fine up to 100 degree Celsius, but wound for 140 degree ...
go feature, this man is also doing transformers for medical care equipment.

just my 2 cents

 

[tekno808]

Thx Kingston and Silent:Arts for your good explanation, i dont use a edcor PT it's a toroidal PT.

@ dagoose , i don't drive with my PM670 , btw i see that you also only use 1 toroidal PT for your PM670 !

Grtzzzz all,

Danny.

 

[radiance]

All true ...again ;-)

But check the rectefier relationship notes below.

Slow start heater board will eat 38% of your power (AC current)

 

[dagoose]

Thx Kingston and Silent:Arts for your good explanation, i dont use a edcor PT is a toroidal PT.
@ dagoose , i don't drive with my PM670 , btw i see that you also only use 1 toroidal PT for your PM670 !

True, but i pulled 2 tubes from the sidechain otherwise things are getting way to hot and i can't even get the voltages higher then 5,9v.

 

[radiance]

Thx Kingston and Silent:Arts for your good explanation, i dont use a edcor PT is a toroidal PT.
@ dagoose , i don't drive with my PM670 , btw i see that you also only use 1 toroidal PT for your PM670 !

True, but i pulled 2 tubes from the sidechain otherwise things are getting way to hot and i can't even get the voltages higher then 5,9v.

Just put another 9V 8A toroid in there like I did and you'll be fine...well, things will be even hotter so maybe not...ah well... :-\

 

[Kingston]

things will be even hotter so maybe not

actually, things will be cooler. As was mentioned earlier, a saturated transformer core loses efficiency and becomes a heat generator. Much of that VAC from the mains is wasted or even sang as a 50hz mechanical song that you have to somehow damp with rubber.

A transformer that is not saturated and running efficiently will happily transform that VAC to your needs and won't waste it as heat.

 

[radiance]

things will be even hotter so maybe not

actually, things will be cooler. As was mentioned earlier, a saturated transformer core loses efficiency and becomes a heat generator. Much of that VAC from the mains is wasted or even sang as a 50hz mechanical song that you have to somehow damp with rubber.

A transformer that is not saturated and running efficiently will happily transform that VAC to your needs and won't waste it as heat.

Did not think of that but yes.....but I was more referring to the increased heat due to 2 extra tubes. What should be worse?
Dunno, Dagoose? Does your toroid get hot? Mine don't...over here the heat comes from tubes & transistors/regulators, and maybe a little from the bridge rectifiers...

 

[dagoose]

things will be even hotter so maybe not

actually, things will be cooler. As was mentioned earlier, a saturated transformer core loses efficiency and becomes a heat generator. Much of that VAC from the mains is wasted or even sang as a 50hz mechanical song that you have to somehow damp with rubber.

A transformer that is not saturated and running efficiently will happily transform that VAC to your needs and won't waste it as heat.

Did not think of that but yes.....but I was more referring to the increased heat due to 2 extra tubes. What should be worse?
Dunno, Dagoose? Does your toroid get hot? Mine don't...over here the heat comes from tubes & transistors/regulators, and maybe a little from the bridge rectifiers...

The toroid doesn't get hot but it's more the fact that i don't trust the circuit with all tubes in. I know it's working to hard because of the fact that i can't get the voltage over something like 5,9v while with 2 tubes removed i can easily adjust it over 7v. So these 2 tubes are indeed saturating the trafo.
I must also confess that the last time i actually used the PM was over a year ago. I just don't like the sound of it.  ???

 

[radiance]

. I just don't like the sound of it.  ???

Did you've matched your tubes? What time constant cap's and resistor combinations are you using?

My stock unit (non matched tubes & analag mode) did not sound nice at all....after I matched my tubes and added the side chain booster with time constant settings this did all change dramatically...It really is capable of many colours now, from mild distortion to smooth inaudible compression to sledge hammer style and what not...

EDIT: with matched tubes the analag mode DOES sound nice!

 

[idylldon]

Did you've matched your tubes? What time constant cap's and resistor combinations are you using?

My stock unit (non matched tubes & analag mode) did not sound nice at all....after I matched my tubes and added the side chain booster with time constant settings this did all change dramatically...It really is capable of many colours now, from mild distortion to smooth inaudible compression to sledge hammer style and what not...

Agreed.  While I didn't install the side-chain booster, I redid the time constants to have a selection to choose from, which made the compressor much more versatile.  I love using it.

Cheers,
--
Don

 

[radiance]

..... the fact that i don't trust the circuit with all tubes in. I know it's working to hard because of the fact that i can't get the voltage over something like 5,9v while with 2 tubes removed i can easily adjust it over 7v. So these 2 tubes are indeed saturating the trafo.

To get back on this...it's that toroid you use that you should distrust, the circuit is fine.

 

[Kingston]

Just to not get dagooses hopes up too much, I didn't like the stock poorman sound one bit either.

The single best modification you can do is probably the variable attack/release time constant network. The original was nearly useless to me. Most of the time I could not hear what it was doing.

time constant example below, mine is similar, but I couldn't bother to redraw.

Next in line, in order of importance:

1. matched tubes
2. better I/O transformers. Just changing the input transformer makes quite a dramatic difference. The Edcor outputs are decent.
3. russian alternative vari-mu tubes
4. I have the option to switch between plain, and boosted sidechain on mine, but I find myself using the plain mode almost all the time.

 

[mitsos]

Is that a 2x6 switch or two separate ones?

 

[Kingston]

depends on personal preference, as do all the values of course. resistance is release, capacitance is attack.

 

[dagoose]

..... the fact that i don't trust the circuit with all tubes in. I know it's working to hard because of the fact that i can't get the voltage over something like 5,9v while with 2 tubes removed i can easily adjust it over 7v. So these 2 tubes are indeed saturating the trafo.

To get back on this...it's that toroid you use that you should distrust, the circuit is fine.

That's what i meaned, the trafo is satturating/overloading when i insert the extra tubes, so when it's drawing more power from the trafo. I think i might add a dedicated heater trafo indeed.

@kingston: what input trafo's did you use? i think that the sound of the edcors is indeed mostly the sound i didn't like. I had th same thing with my d-aoc, when i replaced the input edcors with lundahls it really came alive and it sounds brilliant.
I have some lundhals, might be worth the try.
I allready have the scamp sidechain booster in my unit, sounds a lot better indeed but it's just that i don't like the overall sound.

 

[radiance]

but it's just that i don't like the overall sound.

But did you match your tubes? Cause that's what has THE biggest impact on the overall sound....

Also, what caps and resistor combination did you use for your side chain booster?

 

[dagoose]

The 'regular' sidechain is stock (ok, via the scamp circuit) and the scamp booster is build exactly like in the attached schematic. The compression in the scamp mode is pretty good i think, nothing to complain and it can really add some nice touch/glue. It's the sound, it's just a bit muddy/dark and missing bottom-end which i really think is coming from the input trafo's.
I have no way to match tubes so no.. tubes are not matched. How did you match 'm?

I'm checking some trafo's for the heater and came up with something like this at RS: 223-7951
Is that ok? i could use the secondary in parallel.

Right now my PM is just used as rackfilling which is a shame so it would be nice if i could acutally use it.