the Poor Man 660 support thread

[crisotop]

I'd check for shorts on the psu pcb high voltage path (this is where the fault is occurring right? - your 245V rail is way off?)

 

[TheGuitarist]

Thats the next step... so the buzzing transformer i should just ignore if the voltages are correct?

Could someone also send me the schematics, even just for the PSU so i can trace down this issue?

 

[crisotop]

yes, secondaries voltages seem fine, at least if they are not under load. Schematics should have been included with the pcb's? I would contact Volker if he can help you out, since redistribution is prohibited.

hth, Christoph

 

[TheGuitarist]

Ahh i see, i'll send him a pm. 136v has nothing either.

 

[mitsos]

from the first post of this thread

PM660 Component Placement and Dimensions
PSU660 Component Placement and Dimensions

hole diameters are 3,1mm

yeah, well, you can't really expect me to read the first post in the help thread, can you?!?!? 

thanks!

 

[radiance]

I've a couple of Lundahl 1517 transformers laying around.These are 1+1:1+1, so not ok as T2 replacement. But what If I used two of them, primaries of both in series, secondaries of both parallel. Result would be a 4:1 transformer with center taps.
Are these transformers ok for this ? http://www.lundahl.se/pdfs/datash/1517.pdf

I know the edcors can handle  2,5W. Can't find this info in the Lundahl datasheet though...

 

[Kingston]

I've a couple of Lundahl 1517 transformers laying around.These are 1+1:1+1, so not ok as T2 replacement. But what If I used two of them, primaries of both in series, secondaries of both parallel. Result would be a 4:1 transformer with center taps.
Are these transformers ok for this ? http://www.lundahl.se/pdfs/datash/1517.pdf

I know the edcors can handle  2,5W. Can't find this info in the Lundahl datasheet though...

dBm to power (watts) conversion on the bottom of this page.

http://www.sengpielaudio.com/calculator-db-volt.htm

LL1517 is loud enough for input and barely enough for output stage usage (but not sidechain output), but it's still not the best of ideas to parallel them. You'll end up with the weirdest phasing issues most likely.

Or not.

It's certainly an oddball combo to test so if you have the time let us know how you wind up. And don't get the many (4!) parallel secondaries mixed out of phase in output 4:1 usage.  

This kind of thing is sometimes done internally to the transformers so you won't even know it, but the windings would be designed for the task. Lundahl is actually very open about it in their datasheets but not all manufacturers ever let you know what kind of tricks they pull behind the curtains.

 

[radiance]

It's certainly an oddball combo to test so if you have the time let us know how you wind up. And don't get the many (4!) parallel secondaries mixed out of phase in output 4:1 usage.  

Ha, cool..I will keep you posted.

Order of things to do:
1) build tube matcher + match tubes.
2) replace input trannie
3) Lundahl experiment....so it'll take some time.

thanks!

 

[SmokingGun]

I've been looking into the 600 ohm attenuators use for gain control as a option posted a few pages back.  Would you also be able to do the same attenuator thing between PL5 and T3 skipping the 15K dual switches used for threshold and wiring the PL7 up with PL7 Pin#2 the secondary Center Tap on T-3 ? From what I can see your still controlling the level to the side-chain 2x 5687 amp.

I'm guessing that the threshold control really is just the side chain amp gain?

One other question I have is there an need for zobel networks on these transformers?

 

[Kingston]

I'm guessing that the threshold control really is just the side chain amp gain?

correct.

But notice how the output of the 6BC8 amp already goes to an isolation pad (just another attenuator), then to the sidechain input transformer. But this is a 10k load. Adding a 600-ohm attenuator in between here will hurt output drive capability.

But you can replace the 15K dual pot/rotary with, say, a dual 20-50k log pot.

 

[emrr]

But notice how the output of the 6BC8 amp already goes to an isolation pad (just another attenuator), then to the sidechain input transformer. But this is a 10k load. Adding a 600-ohm attenuator in between here will hurt output drive capability.

It's a 1K8 load with a 10K shunted across it.  It's being driven by a 600 ohm source, so a 600 ohm attenuator would work fine, and the existing R7-9 isolation pad would still present a minimum condition as designed.  A 600 ohm T that is set for almost minimum attenuation is about a 5K shunt load, so no damage at all.  But, a 600 ohm T or ladder here potentially affects the balance of T2 output to the outside world, if you care about such things.  I don't. 

 

[kazper]

But notice how the output of the 6BC8 amp already goes to an isolation pad (just another attenuator), then to the sidechain input transformer. But this is a 10k load. Adding a 600-ohm attenuator in between here will hurt output drive capability.

It's a 1K8 load with a 10K shunted across it.  It's being driven by a 600 ohm source, so a 600 ohm attenuator would work fine, and the existing R7-9 isolation pad would still present a minimum condition as designed.   A 600 ohm T that is set for almost minimum attenuation is about a 5K shunt load, so no damage at all.   But, a 600 ohm T or ladder here potentially affects the balance of T2 output to the outside world, if you care about such things.   I don't.  

So your thinking it would work? EMRR are you saying that it's a 600:10K:600/600 in what Smoking was sayin?

I've been looking for pots for my build, I've found 10K, 25K and 50K Dual log pots at Digikey and there ruffly the same cost as the attenuators from HBA or CAPI.

I was planing on building a couple units, and got some cases recently off the black market for a dual mono set which changed me up a bit. I do have a set of switches already and would just need to purchases the resistors to make them happen. I'd really like to try it out with some pots and go from there before wasting some nice switches for something I don't use or sell.

 

[emrr]

I plan to use dual pots.

Not considering tube drive into T2, it's really 600 -> 2465, considering the U-pad.  That's with the output disconnected.  In use, it's 600 driving 2465 in parallel with the output load.  10K load, it's then 1977 ohms.    A T cares about none of this; the taper just changes. 

 

[radiance]

Basicly, I'm a tube noob.
So now I'm matching tube's for the first time using  lolo-m's test setup. (thanks for that lolo!!)

Question, what is a close match?
For example: with the VU meter at -1dB, one tube reads -2,45V and another reads -2,35V. I know, the whole curve should be matched but is a 0,1V difference a close match? I have tubes with 0,5V differences as well BTW.

Also, should tubes be burned in (& for how long) before I match them? AND is it OK to match to use tubes from different manufacturers as long as the curves match?

Maybe we should make some kind of "tube curve pool". A place where everybody can post curves of tubes so that you can swap...

Thanks!

 

[melville]

Basicly, I'm a tube noob.
So now I'm matching tube's for the first time using  lolo-m's test setup. (thanks for that lolo!!)

Any info on this knocking around? Very curious. Just about to start my poorman build and this would be very useful since I
also have some more guitar amps to build.

Thanks

Dominic
ps. I have tried searching 

 

[radiance]

Let me "search engine" this for you....

http://www.groupdiy.com/index.php?topic=28274.2160

 

[Kingston]

what is a close match?
For example: with the VU meter at -1dB, one tube reads -2,45V and another reads -2,35V. I know, the whole curve should be matched but is a 0,1V difference a close match? I have tubes with 0,5V differences as well BTW.

Also, should tubes be burned in (& for how long) before I match them? AND is it OK to match to use tubes from different manufacturers as long as the curves match?

you can let the curves vary some 1-2V from tube to tube, and even more in the higher gain reduction end of the curve. I went through like 40 tubes (zen time!) and found out there can be no exact match. The curves can dip in somewhat unpredictable ways especially when you're past around -10 to -15dB point on the VU meter.

Burning them in should have little or no effect. As long as the heaters have heated and all voltages stabilised up you're ready to trace.

 

[radiance]

Thanks Kingston! It's indeed Zen...

 

[melville]

Thanks for that Radiance. Am I missing something with the search function?
"tube tester" didn't find that for me. The site search not the google search.

Anyway enough off topic.
Sorry  :-[

 

[radiance]

Thanks for that Radiance. Am I missing something with the search function?
"tube tester" didn't find that for me. The site search not the google search.

Anyway enough off topic.
Sorry  :-[

Sorry, I was kidding you. I knew where to find this. I did not use the search...
Search function on this forum is not very good.
With google you can use the "inurl" function which would look like this:

inurl:http://www.groupdiy.com/index.php?topic=28274 matching

Matching is the word we search for. Unfortunately it still gives 4 pages of google results....