the Poor Man 660 support thread

[mich]

anyone with a working unit yet?
mine is compresing and sounding fine - but there is a dip in the high frequency....i measured -3 db at 9Kh...since we all use the edcor iron-can someone do a measurment and confirm?

 

[[silent:arts]]

[quote author="khstudio"]Maybe it's time to update the Parts list with some of the new or updated info so some of the same questions don't swamp the thread[/quote]
feel free to to this. personally I don't have the time right now to follow or correct order codes, and the parts theirself haven't changed.
haven't seen a project here with full order codes for any possible supplier anyway.

[quote author="SIXTYNINER"]see at resistor
where voltage about?[/quote]
in my parts list there is stated: "HALF WATT METAL FILM RESISTORS"
(I used 1/4W with no problems)
in the PSU there are two "2 WATT METAL FILM RESISTORS"

[quote author="elektrovolt"]I am thinking of a power rheostat. what value should I buy ? the BOM says something with 0,3 ohm to 1,5 ohm, so a 10 ohm should be ok ?[/quote]
sure, but anything smaller (5 ohm, 2 ohm) would be better

 

[Moby]

again about the heater resistor, I am thinking of a power rheostat. what value should I buy ? the BOM says something with 0,3 ohm to 1,5 ohm, so a 10 ohm should be ok ?

To be honest I will go with regulated supply for heaters because it saves the tube life. But, since this should be under 660 pimp thread I will not going into details about :wink: Rheostat should allow you to determine right resistor value and later with parallel combination of few fixed values you will save the pain with ordering bunch of them. Rheostat you buy will be better to stay for some future projects as "lab device" since it's possible to change the value during the time ... heh it's"mechanical thing" :grin:
And yes, since resistors will be hot it's good idea to mount them on some heater to keep exact value :thumb:

 

[[silent:arts]]

[quote author="mich"]mine is compresing and sounding fine[/quote]
congrats - where are the pictures :thumb: :grin: :green:

[quote author="mich"] - but there is a dip in the high frequency....i measured -3 db at 9Kh...since we all use the edcor iron-can someone do a measurment and confirm?[/quote]
mhm, I wouldn't call this normal compared to mine.

 

[elektrovolt]

smaller values , indeed. but I could only find 10 ohm as the smallest.

Moby, yes I know, that is why I am thinking of some locking thing and mounting it in the back. no knob, loctite, superglue... only thing is, that I hope it would dissipate enough of it's heat to the case. but a 60 watt should do the trick

 

[khstudio]

[quote author="[silent:arts]"][quote author="khstudio"]Maybe it's time to update the Parts list with some of the new or updated info so some of the same questions don't swamp the thread[/quote]
feel free to to this. personally I don't have the time right now to follow or correct order codes, and the parts theirself haven't changed.
haven't seen a project here with full order codes for any possible supplier anyway.
[/quote]

I don't have time either.

But I can say this... I have ALL my parts & found them using the Parts list posted, reading the thread & asking a few questions. :wink:

 

[emrr]

It's hard for me to imagine spending significant time theorizing over the exact value of R15, versus buying an assortment and measuring the results in your unit. My time is worth much more than the $3 x 5 (or whatever) I might spend trying a selection in this $900 beast we're building. Wiring in a rheostat permanently doesn't strike me as a particularly good idea either; we're not on battery power with a need for constant adjustment. An internally mounted adjustable tap resistor makes more sense. The Ohmite adjustable tap 1 ohm 50W is $14.20 at Mouser.

 

[Siegfried Meier]

Where are you guys getting your tubes for these?

Thanks,
Sig

 

[mich]

www.tubesandmore.com :wink:

 

[seavote]

sorry to ask the same question again but i think it got lost in all the poating as of late
as per the heater supply. is there a reason why an unregulated heater supply is preferred in this application? can we use a regulated supply or is it not practical in this circuit? heat an issue???
sorry if its obvious i'm teaching myself electronics. im only 2 years into this/thanks

 

[Sorr]

Seavote,

You could use a regulated heater supply.
At 2.6A per channel, you could use one LM338 per channel.
Make sure they are mounted on a large heatsink with mica insulators and thermal grease.
If its more than 6 inches away from the input filter cap, you need to use an input bypass cap.

 

[jdbakker]

[quote author="seavote"]as per the heater supply. is there a reason why an unregulated heater supply is preferred in this application?[/quote]
This has been discussed a few times in this thread; have a look at the posts by [silent:arts] and emrr on page 15.

JDB.

 

[CJ]

There are a ton of threads on heater stuff, but I do not know where they are.

I posted about 6 different heater supplies from VTV a while back.

There is a startup sequence in the original 670 that might be worth considering:

1) 6386 Tubes get heater current - GZ34 gets heater current
2)6386 heaters now pretty warm - GZ34 is still a few seconds out
3)6CA7/EL34 pass tube heater is now hot
4)GZ34 now on, plate current flows to OC3 Regulator via EL34
5)OC3 conducts after a few seconds
6)B+ now on banks of 6386.

Since the plate voltage is so high, the tubes take a beating during startup if you do not pre bake.

I was told by the 670 guy at AES that the original 6386 did not last that long, as they are being run close to their max rating.

But worry not, 6386 on the way!

 

[Moby]

Thanks CJ. The stereo PM 660 will need 5A at 6.3V . (4x 5687 + 4x6BC8) , so for regulated heater supply (what I prefer because saving tubes life) we need some "stronger" PSU.

 

[Kingston]

[quote author="Moby"]regulated heater supply (what I prefer because saving tubes life)[/quote]

Tube doesn't care if it's getting filament voltage somewhere in the ballpark, so a perfect 6.3V regulation won't make your tubes last any longer.

Some say heater voltages affect sound, but I personally think the design is broken if it can't handle slight deviations. Remember fairchild was designed at the time when 10-20% or something equally ridiculous was the normal deviation for all parts so that was taken care of in the circuit. AFAIK any good tube design still does this, including the poorman.

 

[emrr]

i wrote a nice little post and erased it. :razz:

 

[mich]

o,k , back to the frequency response thing...i measured the Edcor (xsm600/10k) alone - without any termination, and i get the same roll off that starts at about 2K and is -3 db at around 10K and -6db at around 16K....
the test was made using RTA and like i said, no termination - just from the soundcard output (hot & cold) into the primarys and secondries back to the soundcard input.
cant think what else is causing this...

 

[[silent:arts]]

mich, I will measure some Edcors tomorrow to compare
what is the input impedance of your soundcard ?

 

[jdbakker]

[quote author="emrr"]i wrote a nice little post and erased it. :razz:[/quote]
I think you forgot the picture link.

HTH,

JDB.

 

[mich]

what is the input impedance of your soundcard ?

its an M-audio Delta 1010 -spec's sheet says 10K minimum..