BTW, don't hook it up to the high volts DC!
Or you will have tweakers incense permeating your domicile.
Or you will have tweakers incense permeating your domicile.
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- Thread starter Scenaria
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Paul B
Well-known member
oop. no 100K. used a 3.9k and a 330 k . measured zero VAC around the 3.9. too high of values?
Paul B
Well-known member
well Im fading away here. gotta be up at 4 again tomorrow.
I appreciate you also having no life and being around to help. Or maybe its what ever is turning you into one of the furry freak brothers. hey, got any more? type at ya later.
I appreciate you also having no life and being around to help. Or maybe its what ever is turning you into one of the furry freak brothers. hey, got any more? type at ya later.
lets bump that 3.9 k up to 10k and try that.
or even 20k or 30k if you have that.
make sure meter is back on ac volts.
when you see this hi volts ac, is it stable or is the display bouncing around?
or even 20k or 30k if you have that.
make sure meter is back on ac volts.
when you see this hi volts ac, is it stable or is the display bouncing around?
OK Paul, a couple of thoughts. Do you have another piece of tube gear laying around? You could measure the high volts dc and see if your meter does the same thing. It might be the dc playing havoc with the a/d converter when on ac volts. I have seen this before.
Also check your grounds. Hook your meter ground right to that res/yel centertap. There were some paint-in -the -way of- ground issues a while back.
Also check your grounds. Hook your meter ground right to that res/yel centertap. There were some paint-in -the -way of- ground issues a while back.
Paul B
Well-known member
I found the 100k's strapped the 1k-100k around A24 and A25 and I still got a zero voltage reading. :? The wierd readings I got were steady save for C7d which would slowly drop about 20V and then stay steady.
other tube gear is an old marshall head at the rehearsal studio, I can get it but I wouldnt know where to measure the high volts dc.
Grounds should be ok, paint has been scraped at all star washer points and pots as well and have been checked for continuity.
other tube gear is an old marshall head at the rehearsal studio, I can get it but I wouldnt know where to measure the high volts dc.
Grounds should be ok, paint has been scraped at all star washer points and pots as well and have been checked for continuity.
Paul B
Well-known member
Ok I replaced the cheap DMM and the bad readings went away. Here's what I am getting now, all VAC:
C7a- 10.12 VAC 7b- 9.88 7c- 2.45 7d- 980mVAC
C11 tube side: 963mVAC pin3 t4b side: 18-24mVAC
C9 tube side: 960mVAC R37 side: 1.2mVAC
How about those low AC readings on C11 and C9? CJ said he got 60VAC on both sides of C11.
C7a- 10.12 VAC 7b- 9.88 7c- 2.45 7d- 980mVAC
C11 tube side: 963mVAC pin3 t4b side: 18-24mVAC
C9 tube side: 960mVAC R37 side: 1.2mVAC
How about those low AC readings on C11 and C9? CJ said he got 60VAC on both sides of C11.
SSLtech
Well-known member
The C7 a-d readings look reasonable.
The C9 and C11 look as though the caps might possibly be be too low value... what are they?
If C11 is too low value, you'd probably find that it compresses better at HF than LF (Kinda like a de-esser) Likewise C9. Try with R37 wound one way then the other and see if the difference between thr two ends of C9 is any different.
Keith
The C9 and C11 look as though the caps might possibly be be too low value... what are they?
If C11 is too low value, you'd probably find that it compresses better at HF than LF (Kinda like a de-esser) Likewise C9. Try with R37 wound one way then the other and see if the difference between thr two ends of C9 is any different.
Keith
Paul B
Well-known member
Hi Keith,
C11 is .01uf and c9 is .02uf. On the tube side of C11 I got 1060mVAC, slowly dropping a few millivolts every few seconds- I got this no matter where I turned R37. On the R37 side of C11 I got .9 mV when turned full up and 1.6mV R37 all the way down.
C11 is .01uf and c9 is .02uf. On the tube side of C11 I got 1060mVAC, slowly dropping a few millivolts every few seconds- I got this no matter where I turned R37. On the R37 side of C11 I got .9 mV when turned full up and 1.6mV R37 all the way down.
Paul B
Well-known member
A little good news - I replaced C12 and my ground noise went away. The voltages at C11 and C9 barely changed, a little higher.
AnalogPackrat
Well-known member
Paul,
The tag-team debug continues... Glad you got a better meter. There's nothing worse than not being able to trust your tools when you're debugging.
What's this about "ground noise?" Do you mean that you had hum/buzz on the output before you replaced C12? If so, that's strange since C12 is in the sidechain. Have you taken CJ's advice and printed a copy of the schematic so you can trace it against your build using a hilighter pen? I'm wondering if maybe you got a grounding problem somewhere. Have you checked your ground tree?
Analog Packrat
The tag-team debug continues... Glad you got a better meter. There's nothing worse than not being able to trust your tools when you're debugging.
What's this about "ground noise?" Do you mean that you had hum/buzz on the output before you replaced C12? If so, that's strange since C12 is in the sidechain. Have you taken CJ's advice and printed a copy of the schematic so you can trace it against your build using a hilighter pen? I'm wondering if maybe you got a grounding problem somewhere. Have you checked your ground tree?
Analog Packrat
Paul B
Well-known member
Well the noise is "back", or maybe the disappearance was just a figment of my hallucination. :? I mentioned the low level hum in one of my earlier posts. Might be a power conditioning situation, going to check it at another power source -
In fact I did print out and trace the schematic - it was a good lesson. Fortunately (or not) I didnt find any problems with the wiring.
In fact I did print out and trace the schematic - it was a good lesson. Fortunately (or not) I didnt find any problems with the wiring.
AnalogPackrat
Well-known member
Well, the hum may be a clue. Mine's pretty quiet. Have you messed with C4 (the big trimmer cap that soldered onto the terminal strip)? I set mine to ~300pF before I installed it. Try cranking it CW (clockwise) if it's not all the way CW already.
So your situation is still that the meter has weak response and you don't get any noticable compression, right? You can get a strong and clean output without compression (PR at 0), right?
Did you try CJ's suggestion to disconnect one of the meter leads? <grasps handfull of straws>
Analog Packrat
So your situation is still that the meter has weak response and you don't get any noticable compression, right? You can get a strong and clean output without compression (PR at 0), right?
Did you try CJ's suggestion to disconnect one of the meter leads? <grasps handfull of straws>
Analog Packrat
Paul B
Well-known member
Thanks for reminding me!! Before plugging it in, i did in fact screw C4 all most all the way counter clockwise - I will put it back where it was.
Situation is strong output, weak compression (7-10db max w/ PR at 100) and weak needle response (no PR until 70, on +4 must turn Gain to 70 (horribly distorted) to get meter to 0db)
It seems there is definitely a situation around C9 and 11. Not getting anywhere near the 60 VAC that CJ got at C11 on both sides.
No change in the noise as I adjust C4 :?
Situation is strong output, weak compression (7-10db max w/ PR at 100) and weak needle response (no PR until 70, on +4 must turn Gain to 70 (horribly distorted) to get meter to 0db)
It seems there is definitely a situation around C9 and 11. Not getting anywhere near the 60 VAC that CJ got at C11 on both sides.
No change in the noise as I adjust C4 :?
AnalogPackrat
Well-known member
Have you taken a look at CJ's T4 page?
http://www.vacuumbrain.com/docs/t5.html
He has some nice photos of the module. Does yours look like these? I'm still wondering if maybe you've got a minor error inside the T4 itself. You can just remove the cover without yanking the whole unit out since that has caused trouble before. Check the way the cap and EL panel are wired.
Do you have C6 and R30 in your build? They're related to the stereo link, but they are in the sidechain circuit.
http://www.vacuumbrain.com/docs/t5.html
He has some nice photos of the module. Does yours look like these? I'm still wondering if maybe you've got a minor error inside the T4 itself. You can just remove the cover without yanking the whole unit out since that has caused trouble before. Check the way the cap and EL panel are wired.
Do you have C6 and R30 in your build? They're related to the stereo link, but they are in the sidechain circuit.
Paul B
Well-known member
I actually used those pictures to help me with my t4b. I checked that area again earlier today.
I do have C6 and R30. for C14 I am using a 100pf.
I do have C6 and R30. for C14 I am using a 100pf.
Cool on the new meter!
When I measured 60 vac on C11 both sides, that was with a music input and the GR turmed up all the way. Just to verify...
Let's get a good sounding line amp first. Do you have some 100K 1/2 watts laying around? Change the two 220K plates resistors on V1 with 100K 1/2 W.
Do you have a 12AY7 laying around? This tube makes a much better input stage than the 12AX7 for two reasons:
1) On the average it will sound nicer than the harsh 12AX7
2) It will reduce your gain so you can turn up the Gain pot above 1 with a CD type level input.
It has the same pinout as the 12AX7, so all you do is pop it in.
There is a mil version of the 12AY7 which is very cool.
Fogot the number. 6001 or something.
Anybody?
When I measured 60 vac on C11 both sides, that was with a music input and the GR turmed up all the way. Just to verify...
Let's get a good sounding line amp first. Do you have some 100K 1/2 watts laying around? Change the two 220K plates resistors on V1 with 100K 1/2 W.
Do you have a 12AY7 laying around? This tube makes a much better input stage than the 12AX7 for two reasons:
1) On the average it will sound nicer than the harsh 12AX7
2) It will reduce your gain so you can turn up the Gain pot above 1 with a CD type level input.
It has the same pinout as the 12AX7, so all you do is pop it in.
There is a mil version of the 12AY7 which is very cool.
Fogot the number. 6001 or something.
Anybody?
Thanks Wilebee!
6072A 19.95 at www.tubesandmore
I am sure you can find cheaper. And you can change the tube later, so just do the resistor mod for now and we can hook up the VU meter on audio outout and that will leave us the side chain to trouble shoot.
6072A 19.95 at www.tubesandmore
I am sure you can find cheaper. And you can change the tube later, so just do the resistor mod for now and we can hook up the VU meter on audio outout and that will leave us the side chain to trouble shoot.
Paul B
Well-known member
OK, the 100k's are in.
Strangely, I am finding myself more and more concerned with your tag line...
:wink:
Strangely, I am finding myself more and more concerned with your tag line...
:wink:
