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PAS2 voltages are negative on 5&9

89.3.153.155
Posted on October 7, 2009 at 14:37:08
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 Hi there. Was hoping someone could answer a question for me regarding my PAS2. When I received it, it had already been heavily modified. The tone controls removed, the caps and resistor all changed.

Anyway, it has been giving great sound for the last year, but this week, one of the tubes has gone out on one channel. I know it is the tube because the problem changes sides when I swap them.

These are new JJ ECC83S with only a years use, so I was worried that something was going bad.

So I put in some Chinese tubes and tested the voltages to the pins.

Now I'm no expert, but something look very strange. Here are my readings:

12AX7 Left Channel / Right Channel

Pin 1: 154V DC / 153V DC (spec: 175 V DC)
Pin 2: 1.2V DC / 1.2V DC (spec: 0 V DC)
Pin 3: 2.75V DC / 2.75V DC (spec: 1.45 V DC)
Pin 4: .04 V DC / .03 V DC (spec: less than 1 volt)
Pin 5: 11.4 V DC / -11.6 V DC (spec: 11 V DC)
Pin 6: 182 V DC / 186 V DC (spec: 200 V DC)
Pin 7: 0 V DC / 0 V DC (spec: 0 V DC)
Pin 8: 1.12 V DC / 1.1 V DC (spec: 1.25 V DC)
Pin 9: 5.6 V DC / -5.7 V DC (spec: 5.5 V DC)

Quad cap:

Square: 392V DC (spec: 405 V DC)
Triangle: 325V DC (spec: 355 V DC)
--------: 295V DC (spec: 330 V DC)
Semi-circle: 200V DC (spec: 210 V DC)

The negative voltages on Pins 5 and 9 are what I'm worried about.

Can anyone confirm whether this is a problem or not.

Thanks to any input.

EJ
RE: PAS2 voltages are negative on 5&9, posted on October 15, 2009 at 14:56:02
ebj29
 Problem solved!

I found that the phono section was very low on one channel even with good tubes. I know the phono section was fine previously. So I checked around for differences in resistance in different points, comparing them to the good channel, and then, found it. A wee bit of solder splatter crossing over. This probably came from when I rewired it. Strangely it didn't have this problem at first, right after finishing the rewire.

But the cross over was putting voltage into the bias, so that's why to tube fryed. Good thing this happened to JJ and not to the newly arrived Tesla E83CC gold pin.

Buy the way I started writing out the curcuit. This PAS really sounds killer. I'll post the schema of this as it is when I get it done to see if anyone recognizes the update that was done to it.
RE: PAS2 voltages are negative on 5&9, posted on October 22, 2009 at 16:02:33
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 I forgot to mention,
the voltage to pin 2 on the phono section did change considerably after I fixed the trace short, but I didn't right down the voltages at the time.
I'm pretty sure now that it must have been the tube in the phono stage that went first and then made the line stage sag in the same channel.

I got lost as to which ones where in the phono or line stage though as they are the same tubes, and I was swapping them around left/right, phono/line to try and diagnose if and which tube was bad. I shouldn't be trying to diagnose electonic problems at 1 in the morning I guess.

Eric
RE: PAS2 voltages are negative on 5&9, posted on October 15, 2009 at 18:30:15
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 So now all of the 2s & 7s have 0VDC? I would like to see what the mods are. The usual JJ 12AX7 problem was cathode to heater short, not on the bench, not while playing it, but only after it got shipped across the country and right out of the box. Very discouraging to the customer to say the least!!!!!

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 22, 2009 at 15:38:18
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
Sorry I didn't respond sooner Craig.
For some reason I didn't get an email signaling your follow message.

>> So now all of the 2s & 7s have 0VDC?

No I still have voltage on 2 ( 1.2V)

Pin 1: 154V DC / 153V DC (spec: 175 V DC)
Pin 2: 1.2V DC / 1.2V DC (spec: 0 V DC)
Pin 3: 2.79V DC / 2.8V DC (spec: 1.45 V DC)
Pin 4: .049 V DC / .049 V DC (spec: less than 1 volt)
Pin 5: 11.4 V DC / -11.6 V DC (spec: 11 V DC)
Pin 6: 187 V DC / 187 V DC (spec: 200 V DC)
Pin 7: 0 V DC / 0 V DC (spec: 0 V DC)
Pin 8: 1.12 V DC / 1.1 V DC (spec: 1.25 V DC)
Pin 9: 5.6 V DC / -5.7 V DC (spec: 5.5 V DC)

Don't think I goofy, but,
I confused myself on what voltages are showing up as I kept changing the tubes. Turns out that the voltages change quite a bit depending on what tubes I have in.
The reading I showed earlier were with a pair of chinese tubes in just in case it fries them. But I changed them to a pair of JAN GE tubes and then to another pair of JJ and took more readings and that's when I found that problem I spoke of earlier (shorted trace with solder splatter).
I'm rather certain that it fixed something important as the phono section works correctly in both channels now and did not when I was testing and probing earlier in the evening. At first it was very low sound in one channel.

The readings with the JJ tubes in look like this:
JJ
Pin 1: 140V DC / 143V DC (spec: 175 V DC)
Pin 2: 1.3V DC / 1.3V DC (spec: 0 V DC)
Pin 3: 2.9V DC / 2.8V DC (spec: 1.45 V DC)
Pin 4: -2.48 V DC / -2.48 V DC (spec: less than 1 volt)
Pin 5: 11.3 V DC / -11.6 V DC (spec: 11 V DC)
Pin 6: 182 V DC / 186 V DC (spec: 200 V DC)
Pin 7: 0 V DC / 0 V DC (spec: 0 V DC)
Pin 8: 1.12 V DC / 1.1 V DC (spec: 1.25 V DC)
Pin 9: 5.6 V DC / -5.7 V DC (spec: 5.5 V DC)

The big jump is Pin 4. Very strange.

Anyway it sounds good now in both channels in both phono and line.
So I've put in some New (16 years old but never used) JJ ECC83S and will use it for a while and see if the tubes live or not.

I have 60% of the schematic drawn out so far. I'll try to get the rest done soon, but I got lost on one section and had to back track and redo a section.

Eric

RE: PAS2 voltages are negative on 5&9, posted on October 22, 2009 at 15:54:47
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 Eric,

If I remember correctly the heater voltages are dependent on the tubes used, ALL four should be the same type/brand. If that rule is followed the voltages should check correctly. As for pin2 not at 0VDC, finish your schematic and see if that explains anything. If there is only a resistor on pin3 and the other end is grounded you should not have any voltage on pin2. PC5 tubes Pin2 should also go to ground thru a relatively large (Ohmage wise) resistor, the volume control in a stocker. Might want check if there is DC on the volume control. The new schematic should reveal all when you're done.

Craig
RE: PAS2 voltages are negative on 5&9, posted on October 23, 2009 at 09:43:22
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
Wow thanks Craig. This is valuable info.

It will be Monday night when I can get back on it. I work away from home and go back to the family the weekends. The bonus is I can play with my hifi electronic and listen to music during the week as I like.

Will post Tuesday.

Eric
RE: PAS2 voltages are negative on 5&9, posted on October 15, 2009 at 16:58:55
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 So now all of the 2s & 7s have 0VDC? I would like to see what the mods are. The usual JJ 12AX7 problem was cathode to heater short, not on the bench, not while playing it, but only after it got shipped across the country and right out of the box. Very discouraging to the customer to say the least!!!!!

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 00:52:07
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 Thanks Craig.

I have
Pin 2: 1.2V DC / 1.2V DC (spec: 0 V DC)
Pin 3: 2.75V DC / 2.75V DC (spec: 1.45 V DC)

So you say that I have +2.75V bias?
Or do I need to test between pins 2 and 3 and the diff will give me the actual bias? So 1.2-2.75= -1.55VDC which is close to spec.

EJ
RE: PAS2 voltages are negative on 5&9, posted on October 7, 2009 at 17:52:40
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 Do you have the PAS manual? If you do you will note that those voltages are correct. If you don't you'll find it on the Dynaco Doctor site.

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 8, 2009 at 00:41:23
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 Found the manual and the voltage ratings.

Thank-you for sending me to the right place to find the manual.

Yes, I see now that it is + or - for pins 5&9.

Can you tell me how I test the grid voltage? The specs for the JJ tube says -2v and -3v max and that pin 2 is the grid.

Do I need to test between 2 pins?

thanks,
EJ
RE: PAS2 voltages are negative on 5&9, posted on October 8, 2009 at 09:22:52
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 You will find that the control grids will have 0 VDC on them because the tubes in the PAS are cathode biased. The grids (2&7) are referenced to ground and there will be a positive voltage on the cathodes (3&8). That voltage could be considered the bias voltage. Use the PAS manual to see what it should be.

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 04:27:11
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 Thanks Craig.

I have
Pin 2: 1.2V DC / 1.2V DC (spec: 0 V DC)
Pin 3: 2.75V DC / 2.75V DC (spec: 1.45 V DC)

So you say that I have +2.75V bias?
Or do I need to test between pins 2 and 3 and the diff will give me the actual bias? So 1.2-2.75= -1.55VDC which is close to spec.

EJ

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 09:57:02
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 You absolutely should have NO DCV on pins 2 or 7. Check the coupling capacitors (.05 in the phono, .02 in the line level), if they are the originals they are probably leaky. Leaky as in DCV not "stuff oozing out". Replace them or lift one end and see if the voltage goes away.

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 16:20:13
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 thanks again Craig.
It'll be Monday night before I can test it.
None of the caps or resistors are original on this though. They are all mylar caps. The sound is great; been playing it for the last year hooked up to a Sumo Nine. It is better sounding than my Sumo Athena and maybe even better that my Sumo Artemis! If it hadn't burned a rather new tube, I wouldn't be fretting with this. But I recently bought some Tesla E83CCs and before receiving them, the JJ burned up. I really want to be sure the PAS is playing nice to the tubes before I put the Tesla tubes in.

I'm not great at electronics, but my love for hifi and music has forced me to embrace and learn it. I have a Fluke 75 meter so it is quite accurate. I have an oscilloscope and frequency generator to that helped me a lot fixing a problem with my Sumo Artemis.

I'm sure that with determination, the PAS2 can be tamed.
Thanks very much for the help.

EJ

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 17:20:53
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 Having a JJ tube go bad is no big deal, that's the norm for them the last couple years. We quit using their preamp tubes years ago and just recently stopped using their E34L and 5AR4, just can't trust them anymore. I too have a Sumo Nine, used to have an Athena. When I bought my Athena, late 80s, it took three tries to get one that worked correctly. I finally took the power transformer out and put it in another box, that is one noisy xfmr. Sold it in the early 90s. I haven't used my NIne in several years forgot what is sounds like. Had two Andromedas to go with the Athena, sold one and traded the intermittent one to same guy I got the Nine from, it was broken when I got it. As far as learning goes tube electronics are relatively easy to repair and there is MUCHO info on the Dynas.

Craig
RE: PAS2 voltages are negative on 5&9, posted on October 10, 2009 at 00:41:18
ej29
Audiophile

Posts: 9
Joined: October 7, 2009
 WOW! Never expected to run into some else with a Nine!
I think it is amazing sounding with out doing anything to it but rewire. I rewired it with Audio Consultants cryo silver wire. I have a Polaris III. None of my Sumo gear has had problems that I didn't create myself, so I guess I've been lucky so far. The Nine sound much better (coherent, seperation of sounds) than either the variuos Perreaux amps I've had or the Polaris III (that I use with the Artemis).

If you have a Nine and don't use it, what do you use? Tube amps?

As for this PAS2, the layout is not much like in the manual, especially the phono stage. I should try to transfer the actual layout into a schematic; as you say it is very simple compared to ss.

EJ

RE: PAS2 voltages are negative on 5&9, posted on October 11, 2009 at 11:56:25
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 My Nine is the first version with the super beta transistors (2SC1831) which are now made of unobtainium so I don't use it. It works now but ya never know. Right now I'm using a Manley 50/50 integrated.

Craig

RE: PAS2 voltages are negative on 5&9, posted on October 9, 2009 at 10:33:36
llwhtt
Audiophile

Posts: 26
Location: SOCAL
Joined: October 28, 2008
 I just reread the original post and saw that it's been modified along with new caps and resistors. Depending on the mods done the original PAS manual may not give you the correct voltages. If you are able, draw your own schematic of what you have then compare it to the PAS manual, it may keep you from chasing your tail.

Craig

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