radiance
Well-known member
lolo-m said:
As in: all the way up till -17V?
the Poor Man 660 support thread
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As in: all the way up till -17V?
lolo-m
Well-known member
I bet you will reach -20 dB way before a grid value of -17V. 6 points from 0 dB to reach -20dB is really enough to match the tubes. More is a pure overkill.radiance said:
For info : JJ TESLA match their 6386 with 3dB tolerance on 8 points from -2V to -30V of grid bias.
lolo-m
Well-known member
Yes !jackies said:
Notice that in the test circuit as in the comp the CV doesn't swing a lot.
lolo-m
Well-known member
ERRATA:
With my tube tester circuit, the Vu pot must have a resistance 4 times higher than the Vu pot you use in the PM670.
It's obvious, you're checking the current of one plate while the PM660 vu is checking the current of 4 plates.
Sorry for this mistake ;D !
With my tube tester circuit, the Vu pot must have a resistance 4 times higher than the Vu pot you use in the PM670.
It's obvious, you're checking the current of one plate while the PM660 vu is checking the current of 4 plates.
Sorry for this mistake ;D !
radiance
Well-known member
P1 = 20K instead of 5K?
lolo-m
Well-known member
Yes, if you use a 5K in your PM670.radiance said:
If you use a 1K in the PM, it will be a 4K (4K7) in the tester...
radiance
Well-known member
miko said:
I don't think these are for sale at the moment. However, they do show up on the black market sometimes...
Kingston
Well-known member
there's finally a light at the end of the tunnel.
I built lolo's grid-voltage/plate-current matcher. I went through a batch of 20 6BC8/6BC6, various brands. Then I went through a 12-batch of russian 6N5P, roughly an equivalent.
In a "pm670 environment", one never needs to match outside the grid voltage range of -1.5V to -8V. The curve will always fall there (as about 3dB to 25dB on the VU meter).
Anyway, out of the batch of 20 6BC8/6BC6, there was only a one "equal triodes" match. And that would not be a problem, but the rest of them were all over the place, and in the batch I could not even cross-match to get two equal triode channels of four tubes total. ie. cross matching triode sides to create a roughly equal current draw.
And I had actually found the best match with my own crude matching set up. It sounds like crap, with odd distortion, and no headroom, and unequal stereo image. That's what I've always been complaining about.
Enter 6N5P. Out of a batch of 12 there were four perfect matches, all values pretty much equal. With cross matching I can actually use most of the rest of the tubes in the future as well! Incredible tolerances! About a third of them have an odd unstable heater (no 6BC8 has this), and some of them can be heard doing a "shuffling paper near the mic" type of distortion. I'll test if these are simply duds, or if they just need a burn-in.
Headroom is finally there, now in the range of the rest of the studio! And the "roof" of the headroom is very very soft saturation, just wonderful! I've never heard anything like it. This will find a LOT of use. 6N5P is simply a great tube.
The unfortunate Edcor lack of quality can stil be heard, but that's an easier (if a little costly) fix. Lundahl to the rescue.
Now that the unit is in perfect working order, I found a new source of distortion, very much measurable: the VU meters. Is there some way to buffer up - or somehow isolate - the VU meters so that they don't affect the sound? They do odd things to midrange frequencies, and show up as added THD, in a slightly different shape than unbuffered VU meter on 600-ohm balanced outputs.
I guess an easy fix would be to put in a switch with a choice of VU meter and a dummy resistor equal to the VU load (about 50ohm for me).
[edit] while I was writing this it turned out russian the tubes just needed a burn in. No more "paper shuffling" distortion.
I built lolo's grid-voltage/plate-current matcher. I went through a batch of 20 6BC8/6BC6, various brands. Then I went through a 12-batch of russian 6N5P, roughly an equivalent.
In a "pm670 environment", one never needs to match outside the grid voltage range of -1.5V to -8V. The curve will always fall there (as about 3dB to 25dB on the VU meter).
Anyway, out of the batch of 20 6BC8/6BC6, there was only a one "equal triodes" match. And that would not be a problem, but the rest of them were all over the place, and in the batch I could not even cross-match to get two equal triode channels of four tubes total. ie. cross matching triode sides to create a roughly equal current draw.
And I had actually found the best match with my own crude matching set up. It sounds like crap, with odd distortion, and no headroom, and unequal stereo image. That's what I've always been complaining about.
Enter 6N5P. Out of a batch of 12 there were four perfect matches, all values pretty much equal. With cross matching I can actually use most of the rest of the tubes in the future as well! Incredible tolerances! About a third of them have an odd unstable heater (no 6BC8 has this), and some of them can be heard doing a "shuffling paper near the mic" type of distortion. I'll test if these are simply duds, or if they just need a burn-in.
Headroom is finally there, now in the range of the rest of the studio! And the "roof" of the headroom is very very soft saturation, just wonderful! I've never heard anything like it. This will find a LOT of use. 6N5P is simply a great tube.
The unfortunate Edcor lack of quality can stil be heard, but that's an easier (if a little costly) fix. Lundahl to the rescue.
Now that the unit is in perfect working order, I found a new source of distortion, very much measurable: the VU meters. Is there some way to buffer up - or somehow isolate - the VU meters so that they don't affect the sound? They do odd things to midrange frequencies, and show up as added THD, in a slightly different shape than unbuffered VU meter on 600-ohm balanced outputs.
I guess an easy fix would be to put in a switch with a choice of VU meter and a dummy resistor equal to the VU load (about 50ohm for me).
[edit] while I was writing this it turned out russian the tubes just needed a burn in. No more "paper shuffling" distortion.
inputoutput
Well-known member
good to hear Kingston!!
Well, I installed LL1676 in a 1:1 configuration at the input and at T3. Unfortunately, I haven't had the opportunity to hear if it improved the sound yet, cause it now starts to PUMP(in lack of a better word) when sound are driven through it. Everything seems nice, at startup. It feels like the circuit is pushed totally out of stability, and the meters and compressor goes up and down - (almost in the tempo of the release-time). It is even worse with the russian tubes. I remember struggling with this in an earlier buildingstage too, but I then solved it by lowering the 136V rail a little from the PSU and by experimenting with different tubes.
now, what's going on here?
Well, I installed LL1676 in a 1:1 configuration at the input and at T3. Unfortunately, I haven't had the opportunity to hear if it improved the sound yet, cause it now starts to PUMP(in lack of a better word) when sound are driven through it. Everything seems nice, at startup. It feels like the circuit is pushed totally out of stability, and the meters and compressor goes up and down - (almost in the tempo of the release-time). It is even worse with the russian tubes. I remember struggling with this in an earlier buildingstage too, but I then solved it by lowering the 136V rail a little from the PSU and by experimenting with different tubes.
now, what's going on here?
Well, 1:1 is wrong ratio, has to be 1:4.
Also, T3 (if I'm not mistaken) is sidechain amp input which wouldn't (directly) affect your audio quality, and (again imho) you should upgrade T1 and T2 first, to improve the sound.
inputoutput
Well-known member
ah, well, thanks. Should have checked this thread again before throwing them in. Felt there was something wrong when I wired them as 1:1. It's been a long time since I worked on my Poorman
radiance
Well-known member
Encouraging post Kingston!!
Thanks...
Thanks...
Kingston
Well-known member
inputoutput said:
I'm surprised it worked at all!
The input impedance of the sidechain (generating current for time constants) amp is completely ruined. The tube's can't make much use out of 600 ohms and go "haywire" as you've now probably heard. The 1:1 at makeup-varimu stage also completely ruin the working abilities of the 6BC8 and variants. I can't even imagene what voltages the grids are seeing.PS, how are you even able to wire LL1676 as 1:1?
You would do better to leave the sidechain alone. It's perfectly fine with the edcors.
Wire the LL1676 as 1:4 to input and 4:1 to output. As T1 and T2. Remember 1:4 is 600/10kohms. And 4:1 is 10k/600ohms with the transformer reversed.
Look at the datasheet for example, the picture shows how you'd wire the output with a center tap, but can/core go to ground (and NOT to B+). And then we reverse the transformer for 4(+center tap):1 configuration. It's more complex than edcors, even if it ends up in the same configuration.
inputoutput
Well-known member
thanks for the info Kingston. Can't wait to get them correctly wired.
in+ 1
in- 4
2+5 together
out+ 6+10
out- 7+9
ground 8
in+ 1
in- 4
2+5 together
out+ 6+10
out- 7+9
ground 8
Silvas
Well-known member
Very nice, Kingston ! good to know that. I´m still preliminary testing my PM and have to wire the bypass...and yes, you have to be very careful with your input levels. What about heaters current draw with the 6n5p ? will be good idea to beef up the power trafo ? i think i´ll order a small lot to play with them on my PM...
Kingston
Well-known member
Silvas said:
heaters draw roughly the same as 6BC8. It varies a bit, as shown on datasheet as well. It's always a good idea to over design PSU trafo requirements. I calculated a worst case scenario for all the heaters of two channels together, and specified that as using 60% from the max of dedicated heater winding, ie. lots of safety-, stability- and playroom.
Kingston
Well-known member
I happened to have a Cinemag CM-9589 output transformers (4:1 10k/600) waiting for another project. I decided to strap then in as input transformers, reversed. They have no dual windings (or a centertap obviously) so they can't be installed as poorman output, but they work fine as input (T1), even if hopelessly oversized at 1.7W (then again, so are the edcors).
And what a difference! It seems the original edcor output transformer causes far less problems than the input XSM 600/10k. I have used the XSM10k/600 in other projects with very satisfactory results, so I kind of expected it would be the same for poorman.
Anyone who hears the Edcor hi frequency "sand", I can report that changing the input (T1) transformer is enough. CM-9589 is a very good sounding combo with the original output edcor. I personally want to experiment with mid-side configations, requiring open dual windings so this is just a temporary solution.
And what a difference! It seems the original edcor output transformer causes far less problems than the input XSM 600/10k. I have used the XSM10k/600 in other projects with very satisfactory results, so I kind of expected it would be the same for poorman.
Anyone who hears the Edcor hi frequency "sand", I can report that changing the input (T1) transformer is enough. CM-9589 is a very good sounding combo with the original output edcor. I personally want to experiment with mid-side configations, requiring open dual windings so this is just a temporary solution.
