the Poor Man 660 support thread

[Gus]

I was thinking more about the transformer.  One thing to check with series connected filaments is how well the filaments share and power up.

I see your point about reducing the heat in the reg if you run just over the in to out voltage needed to have the regulator work well you will dissipate less heat in the regulator if the current is reduced.  You can add a series resistor before the regulator to drop the voltage down and dissipate some energy in the resistor.

 

[mrclunk]

http://www.groupdiy.com/index.php?topic=28274.msg347004#msg347004

Volker the image dosnt load, has the url changed?

 

[CJ]

did you burn the tubes in?
the plate current might drop after the cathode gets set up.
if you have 16 sections, like the 670, that could be a big reduction.

the 670 guy at aes said that the bias shifted on his reissue tubes after about a 30 hr burn in, weird, i wonder if the original GE 6386 did that?

 

[emrr]

DC Power = VDC X amps.

Some numbers for simple math  

12VDC x 2amps =24 watts

6VDC x 4 amps = 24 watts

12.6 volt or 6.3 volt wiring of the fil still equals the same watts.

Thanks Gus.  I've been running up and down the street punching babies over that topic.  ;D

 

[[silent:arts]]

http://www.groupdiy.com/index.php?topic=28274.msg347004#msg347004

Volker the image dosnt load, has the url changed?

yes, but you didn't miss anything important:

 

[geoff004]

Here's latest on the unit I'm working on with Undercarriage-
checked it tonight.  We didn't go through all the voltages, but all the basic ones really are spot on.
We also checked the switches and they're all good too.

A couple observations:
1. the unit acted quite different from the first 3 minutes or so vs. the 10 minute mark.  I guess that's just the whole thing warming up.
2. the power transformer never got so hot that it was remotely uncomfortable to touch.  We had the thing running for at least 30 minutes.
3. the headroom still seems low.  Driving what seems like a reasonable amount of signal results in distortion.
4. the thing is compressing (basically working as it should) but to hear much difference it needs to be set at extremes.

Here's the big question: how much difference will not having a meter make?
I noticed (I remember reading in an earlier post too) there's a good +55 volts or so on the meter.  We're still waiting on meters - that's all the unit is lacking.  Could we use a resistor in there temporarily?

Does anyone else have similar experiences with their units?

 

[emrr]

consider the current limiting presented by NOT having a meter in circuit.  I think that's where your headroom falls down at the moment. 

 

[stanz]

Geoff004 - what power transformer are you using?

 

[analag]

I remember choosing not to regulate the heater in the prototype for obvious reasons. If I were to do it again I would AC heat the 5687's and run the 6BC8/6BZ8 regulated. In my final mu compressor I went totally AC with exceptionally low noise due to proper symmetrical activity which should be the case with the PM670.

 

[geoff004]

what power transformer are you using?

It's the Edcor - XPWR063
The 50w resistor (R15) is .33 ohm, giving me 6.2v on the tubes for a stereo unit.

 

[stanz]

Thanks Geoff. Getting ready to build a PM670 with the Edcor PT. Had seen an issue with one, so checking to see if it was universal. Already have most parts except tubes and sockets.

 

[[silent:arts]]

Thanks Geoff. Getting ready to build a PM670 with the Edcor PT.

check if the voltages of the secondaries follow the color code before connecting ...

 

[veermaster]

Just got my unit working again, big thanks out to Volker again! A little fire destroyed my PSU board, that was no fun.
Please everybody be very careful when measuring voltages here. Try to find some measuring points at not too close placed parts.
For instance if you want to measure V after R1 don´t measure R1 but D6 and so on!
Today I´ll take mine to the studio and try it in a mixing session  ;D
Good luck to everybody, emre

 

[mrclunk]

Got my stereo unit working ;D ;D ;D
Had a few teething troubles but its working almost perfectly now.

I have one final (hopefully) problem.
One channel is compressing the low frequency part of a signal alot less than the other channel.

As a test i fed a 100Hz sine into both channels and channel 2 compresses about 6dB more. (This is with threshold control set fully up, CW.)

If i sweep the sine wave, when it hits approximatly 1000Hz the compression is equal on both channels.

I've swapped over tubes between channels but this dos'nt make any difference.
could it be that one of the sidechain transformers is off spec?

any help would be apprieciated.

p.s Huge thanks to Volker and analag, i've had alot of fun (plus a few tears) building this beast, hope to have more using it!

 

[Kingston]

could it be that one of the sidechain transformers is off spec?

yes, if for example one side of the dual winding is disconnected, it might behave that way.

Edcor does the transformers cheap, but has a bit relaxed quality control. Try swapping the transformers between the two channels, and/or compare resistances of all of them. Should be easy to find the broken one.

Also have a look at the VERY thin wires soldered on those metal connectors. I've seen a few that were broken during shipping. Simply solder them back.

 

[mrclunk]

Thanks Kingston, checked the transformers but they all measure about the same. i'll try swapping over T3 and T4 between the channels and see what that does.
Just had a loverly pair of old Dbx 165 arrive so i'm gona get them racked up first for my session tommorrow.

 

[stanz]

Thanks Geoff. Getting ready to build a PM670 with the Edcor PT.

check if the voltages of the secondaries follow the color code before connecting ...

Yes, that would be wise. Thanks

 

[mrclunk]

Kingston you were correct. Pin 5 of T4 wasn't connected. Unfortunately it must be an internal fault as i couldn't fix it. Luckily i have a few spare. Swapped it out out and now both channels track together.  ;D

Just need to print out my meter scales and receive my knob back order and it'll be done. I post some pictures when its all finished off.
I'm mixing at the weekend so I'll put it through its sonic paces then.
thank you all
paul

 

[W DeMarco]

Just wondering if anyone bought a spare PSU board to make two mono units and ended up building a single stereo.  I might need a new board if I cant work out the problems.

Will

 

[Kingston]

Unfortunately it must be an internal fault as i couldn't fix it.

ah well. at least they're cheap.