the Poor Man 660 support thread

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dagoose said:
The 'regular' sidechain is stock (ok, via the scamp circuit) and the scamp booster is build exactly like in the attached schematic.
Click to expand...

The connection labelled "R-L Conn_2"  & "C-L Conn_2" allows you to connect a rotary (or whatever) to switch between different caps and resistors. That was what I was asking.

dagoose said:
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.
Click to expand...

Why do you think it's the input trafo's?


dagoose said:
I have no way to match tubes so no.. tubes are not matched. How did you match 'm?
Click to expand...

Read this thread again starting here: http://www.groupdiy.com/index.php?topic=28274.2160

Lolo-M posted a schematic for a tube matcher which can be made on vero board.
I might have mine left somewhere...plus some tubes from my matching endeavours...PM me if you're interested. I've also some russian tubes (which I ended up using BTW) left.
But really, if you want to resurrect your poorman, read the thread starting at the link I posted above.
A lot has been learned about this project since you finished your poorman I guess....
 
dagoose said:
@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.
Click to expand...

I tried an upside-down cinemag output used as input transformer, and then finally a multipurpose-lundahl LL16XX something. I forget what numbers exactly. All my experimentations are well documented earlier in this thread, recap here: http://www.groupdiy.com/index.php?topic=41807.0
 
Kingston said:
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.
Click to expand...

So the SCamp booster is to boost the sidechain ? but why ?
Most people use there PM without SCamp booster and just mod the TC network ! so you don't need this SCamp booster ??

It's all a little confusing....

So i build my PM670 with a extra PT for the heater, mod the TC network and mod the PSU with the protection mod from ppa and use matched tubes !

What's better the 6BZ8 or 6BC8 ? they have a little different plate voltage, grid circuit resistance and some other values....

Sorry for all the questions but i want a good build from the first time .

thx.....

Danny.
 
Kingston said:
Time to start reading the thread from the beginning. Yes, it's long, but all of this has been gone through about 4 times already.
Click to expand...

I already go trough the whole thread but didnt find info about why the Scamp booster and why 6BC8 or 6BZ8. I have the 6BZ8 .
I understand what the Scamp booster does but you can modify the TC network to have shorter attack and or release without it.

i'm gonna give a try for the third time !  :eek:
 
Ah, I see.  Well that explains why I couldn't find it then : - )
I would guess that the info only becomes available if you buy the pcb yes?
Fair enough, was just curious that's all.
Thanks Doug for letting me know. 

Jean.

Almost forgot to mention - Kingston, while I was searching for the schematics, I came upon your rasberry baby here:
http://www.groupdiy.com/index.php?topic=41807.0

Very nice : - )
 
Hello,

I'm building one of your tube matching circuits to use for the 6BC8 that I'm using in my PM 670 and had a quick question:

You said to use a pot 4X higher in value than the one used in the PM, which would mean use a 20K (probably 25K since 20K isn't a common value).  In the PM, there is also a 22K resistor (R6) in parallel with the meter.  Do you have to use that in addition to the pot or is the pot all that is needed here?

Thanks,
--
Don



lolo-m said:
Ok, I never checked the additional options  :-[ !

To supply the filament you can set the +17V rail of the PSU660 to 6,3V, it'll work to test one tube without any problem.

The principe of the match is : plate current is fonstion of grid tension. If the plate current of one of the triode is close to plate current of the other triode at several test points (let's say 6, it's enough), your tubes are matched.

Procedure :
not to damage your tube never set the grid pot at more than -2V
1°) set the pot to -2V and adjust the vu pot to read 0dB.
2°) set the pot to -4V, and note on and excell sheet the value of the vu
3°) set the pot to -6V, and note the value... and so on...
4°) change the triode connection, and start the second triode test from -2V without readjusting the 0Vu reading

I talked about an excell sheet as it's easy to trace curves with it and it's really easy to see which triodes tracks well together.

You can easily add some lorlin to do the test quickier, for grid tension and cathode/grid/plate connection. A PCB is easy to do so...
Click to expand...
 
idylldon said:
Hello,

I'm building one of your tube matching circuits to use for the 6BC8 that I'm using in my PM 670 and had a quick question:

You said to use a pot 4X higher in value than the one used in the PM, which would mean use a 20K (probably 25K since 20K isn't a common value).  In the PM, there is also a 22K resistor (R6) in parallel with the meter.  Do you have to use that in addition to the pot or is the pot all that is needed here?

Thanks,
--
Don



lolo-m said:
Ok, I never checked the additional options  :-[ !

To supply the filament you can set the +17V rail of the PSU660 to 6,3V, it'll work to test one tube without any problem.

The principe of the match is : plate current is fonstion of grid tension. If the plate current of one of the triode is close to plate current of the other triode at several test points (let's say 6, it's enough), your tubes are matched.

Procedure :
not to damage your tube never set the grid pot at more than -2V
1°) set the pot to -2V and adjust the vu pot to read 0dB.
2°) set the pot to -4V, and note on and excell sheet the value of the vu
3°) set the pot to -6V, and note the value... and so on...
4°) change the triode connection, and start the second triode test from -2V without readjusting the 0Vu reading

I talked about an excell sheet as it's easy to trace curves with it and it's really easy to see which triodes tracks well together.

You can easily add some lorlin to do the test quickier, for grid tension and cathode/grid/plate connection. A PCB is easy to do so...
Click to expand...
Click to expand...

If you still use the 22k in your PM670, use a 88k. Then the same way+components to connect the vu.
I just suppress the 22k in my PM670 and replaced it by a pot...

The reason of the X4 is simple : we're dealing with only one plate in the tester while there are 4 plates in the PM670. That means that we pump trough the resistor 1/4 of the current pumped in the PM670. As the vumeters are more or less voltage meters, we need to multiply by 4 the value of the voltage creator : R6 in stock PM660/670.

I hope I'm clear...
 
Thanks.  I added the 88K resistor to the VU meter but it really didn't make any difference in the measurements so I just left it out.

I have some Russian tubes coming and I'll hopefully get some matching tubes.

Cheers,
--
Don
 
Thats what i'm doing.
Use a brand new Stanley blade and slice into the trace, then heat the trace chunk with your soldering iron and it'll just lift off. 
 
hi guys

dont know if this is a silly ?  . i am rebuilding my power psu but i can not get these resistors

2 x 475R
2 x 121K
1 x 182K
2 x 221K

can i use  a value which is close to the original ones

cheers

skal1
 

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