the Poor Man 660 support thread

[mitsos]

Today's bench test of the side chain amp; I'd show you a picture but you'd be scared.   Pile of loose parts and test clips, bench PSU. 

247VDC = 38 mA
13.7VDC at top of R10

-15dBm into T3 = -3.2dBm on sec
20.5dBm T4 pri = 8.3dBm sec
23.3dB gain through SC amp

Then disconnected T4 sec from rectifier, put 5K load on it, and did level listening tests. 
By ear, looks like approximately 10 dBm max into T3 pri with threshold control fully open, which matches T4's max rating of 2.5W. 

Worth considering when planning threshold attenuators. 

This 2.4W is only for the threshold right? I mean, for the input attenuator we can use those little state ones (0.25W) like in the 1176?

 

[emrr]

SC amp output max of 2.4W.  No attenuator involved. 

 

[tomcat]

If you have a good cutter like my beloved knippex you can do that:

1. you cut the pin lengthwise
2. you cut of half of the split pin

Works like a charm

 

[tomcat]

second pic

 

[mitsos]

Hey emrr, I was referring to that:

Worth considering when planning threshold attenuators. 

tomcat, I should have sent you my sockets.. I tried doing that but ended up destroying the third pin and stopped. Then did the "wrap a piece of leftover resistor lead around the pins" thing. Worked so far, everything is soldered and solid, but been too busy to wire the thing up though for testing...

 

[Kingston]

Mitsos, there won't be 2.4watts at the threshold control!  emrr certainly didn't mean that.

Just that the sidechain amp has plenty of gain and you'll want enough range (attenuation) for your threshold control so you won't distort everything all the time.

 

[lewilson]

Id like to figure something out. If I remember right my pm670 side chain puts out on average about -14 volts. Maybe im using the wrong math but that calculates to less than 1 watt into a 600 ohm load? Anybody?

 

[mitsos]

Mitsos, there won't be 2.4watts at the threshold control!  emrr certainly didn't mean that.

Just that the sidechain amp has plenty of gain and you'll want enough range (attenuation) for your threshold control so you won't distort everything all the time.

ok, cuz reading that the first time got me scared of burning up all my 1/4W resistors  ;D

I found an old mallory 500 ohm T pad I might stick in the input. Not sure how well it's working, gives some odd infinite resistance measurements at certain points in the rotation, but I stuck it at the output of a 312 and it seemed to work.. but maybe I should just cough up the dough and buy some new ones.  :

 

[Kingston]

Id like to figure something out. If I remember right my pm670 side chain puts out on average about -14 volts. Maybe im using the wrong math but that calculates to less than 1 watt into a 600 ohm load? Anybody?

the sidechain puts out 2.4W if you want to just listen audio through it, at the primary of the output transformer. But then it goes through 4:1 step down, into the bridge rectifier, and finally the time constant network. You need a much more powerful sidechain amp if you want more than the 10-20V voltage swing poorman offers for the grid control signal. 6BC8 tubes crap out before this anyway, so you would also have to change your vari-mu tubes in that case as well, or at least significantly increase B+.

 

[emrr]

Pretty sure I was getting +33 dBm off the secondary, into distortion.  Yep, follow my previous math.

 

[radiance]

Finally finishing this thing. It's so quiet, can't hardly believe it's actually switched on. Everything works as should.

One thing: 1 channel has it's polarity reversed. Can this be an Edcor issue? Pretty darn sure it's not my wiring...

 

[crisotop]

Have you got a scope to trace a sine? (Could easily be a trafo with reversed connectors)

still fighting with mine, so thumbs up for your working baby!
Christoph

 

[radiance]

Thanks Christoph! It probably is what you've said.
I'll check with the scope..,.
...or I just randomly reverse the wires of one of the input or output trannies and be done with it. 50% chance I get it right.....

 

[crisotop]

Not sure if it actually would make a difference, but theoretically it could alter the stereo performance when linked if the channels are reversed?

anyone? christoph

 

[lolo-m]

It shouldn't alter the performance in stereo link mode as you link the control voltage.
In some compressors you add the signals and look what's hapening then, in "Fairchild like" compressors you only add the 2 control voltages so it should not change anything...

Congrats radiance for your working baby !
Did you put the mains transformer inside the box ?
Did you use a slow start heater mod and if so, what's your mains transformer ?

 

[loopermc5]

Finally finishing this thing. It's so quiet, can't hardly believe it's actually switched on. Everything works as should.

One thing: 1 channel has it's polarity reversed. Can this be an Edcor issue? Pretty darn sure it's not my wiring...

Same thing happened to mine it was the transformer so I just reversed it at the output.I was also surprised how quite it runs. where's the pics!

 

[radiance]

Al tough far from finished...here's a pic.

As you can see the  lower compartment is finished. Above needs some more work.
Below are two toroids, one extra for 1 heater so the main toroid only has to power the other one. Would have been nice to have 1 big toroid which would have handled it all...meh
...it works like this and I've no heat problems.

Still to do:

Connecting Sc-booster board (mounted on the upper right behind the birds nest of wires waiting to be connected)
Experiment with different input transformers (you can see the HAufe)
Tube matching
Making wiring more tidy
Frontpanel

Will probably take another two months or so given the pace I'm going at....

 

[loopermc5]

Al tough far from finished...here's a pic.

As you can see the  lower compartment is finished. Above needs some more work.
Below are two toroids, one extra for 1 heater so the main toroid only has to power the other one. Would have been nice to have 1 big toroid which would have handled it all...meh
...it works like this and I've no heat problems.

Still to do:

Connecting Sc-booster board (mounted on the upper right behind the birds nest of wires waiting to be connected)
Experiment with different input transformers (you can see the HAufe)
Tube matching
Making wiring more tidy
Frontpanel

Will probably take another two months or so given the pace I'm going at....

Nice!! Really like your mounting the tubes like that neat.

 

[rrs]

That looks really well set out.

I have just installed Lundahl LL1676 on the inputs which over the Edcors to me sound tighter and cleaner. The Edcors a re a little hazy.

Anyway it's noticable but to the average listener very subtle. Kinda like getting better digital convertors.

I wonder wether changing the output with the same trannies will give equaly as noticable difference.
Earlier Kingston said the Edcor out's wern't that bad.

RE: Matching tubes I have been using 6CZ8 and just brought 6n5p russian tubes.
Have not matched but seem to sound decent enough. There is a schematic to build a test rig on page 110 but I have never built anything straight from a schematic so a little scared to try.

 

[radiance]

Nice!! Really like your mounting the tubes like that neat.

Thanks....I guess it helps for shielding as well. As I said before, it's soooo quiet. Even with gain set to max and listening on headphones set to max as well there is no hum or even noise. Never had a unit this silent before....

That looks really well set out.

I have just installed Lundahl LL1676 on the inputs which over the Edcors to me sound tighter and cleaner. The Edcors a re a little hazy.

Anyway it's noticable but to the average listener very subtle. Kinda like getting better digital convertors.

Anybody find a suitable output transformer replacement yet? One that does not break the bank he he....