PV11 troubleshooting help

[Dr.Greenthumb]

I picked up this unit a couple years ago and it's been the box since it arrived. I opened it a couple weeks was not happy.The preamp was suppose to be in working order but is not. Some one had their fingers in this one so who knows what they did or why.

Here are the issues:
- Excessive heater noise - better with some tube, worse with others, but always too loud.
- Tubes 5 and 6 extremely microphonic. I can lightly tap anywhere on the stand, away from the unit, and you can hear them ring.
- It's not tube specific. I tried 10 pairs 12AU7 and they all rang.

- Every capacitor in the power supply has be replaced with Solen caps
- Every solid state device replaced

Here are the voltages from the tubes and the pin numbers. Are these correct?
V1: 1-124, 2-0, 3-0, 4-31, 5-44, 6-124, 7-0, 8-0, 9-0
V2: 1-123, 2-0, 3-0, 4-44, 5-32, 6-124, 7-0, 8-0, 9-38
V3: 1-148, 2-0, 3-0, 4-32, 5-44, 6-140, 7-0, 8-0, 9-38
V4: 1-325, 2-140, 3-148, 4-44, 5-32, 6-325, 7-148, 8-155, 9-38
V5: 1-149, 2-0, 3-7, 4-33, 5-44, 6-325, 7-149, 8-157, 9-38
V6: 1-325, 2-151, 3-159, 4-44, 5-32, 6-152, 7-0, 8-7, 9-38

Relays - what are they for?
Schematic shows couplings caps as 2uF, but they are 4uF on the board. Which one is correct?

[admin]

First, welcome to CJO. Great to have you with us.

Sorry to hear the trouble. This may be difficult as clearly a lot of work has been done on this unit,... sounds like most of the major components were replaced. I'm not sure what the correct voltages on the pins should be, but the tubes on V1/V2 are the same, V3 is unique, and V5/V6 are the same. Not sure why the voltages would be so different on the same tube types,... but I could be wrong and maybe that's normal?

As for the coupling caps, I think both 2uF and 4uF are ok but we have some people here on CJO who are much more knowledgeable so hopefully they will chime in.... roberto, I'm talking about you.

[roberto]

Hola...voltages seems to be ok. Noises are due to have tubes usually in wrong position or different types...here is what the the PV11 manual says:

The audio circuit of the PV11 uses six vacuum tubes of three different types: two 12AX7 (V1 and V2), one 5751 (V3) and three 12AU7 (V4, V5 and V6). The PV11L uses two type 12AU7 (V5 and V6). Each type has been carefully chosen for its circuit application. It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive audi- tioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11. Also, the tubes in your preamplifier have been tempered by a controlled burn in procedure that permits them to perform for a greatly extended period with out sonic degrada- tion. We anticipate two or three years of operation without degradation in normal use. We highly recommend that when the time comes to replace the vacuum tubes you purchase replacement tube sets from conrad-johnson design.

Usually 2.2 uF or 4.7 uF are coupling caps and this values are to prevent DC from one stage to other, but AC (signal) will pass through.

Hissing tells too, bad tubes.

[AnotherJohnson]

Yes, hiss is virtually always attributable to one or more noisy small tubes.

This unit sat for a long time. Caps probably will benefit from some charging cycles. Give it a week and see how it evolves.

For many years, the PV11 was my bucket list preamp. It was eventually displaced by the ET3SE, which led to ET7 and ET7S2. I’m now on to ARC LS28 SE and REF 6, so bucket lists change.

I hope your PV11 hasn’t been molested beyond restoration. A little loving care may pay dividends.

[Dr.Greenthumb]

Hola...voltages seems to be ok. Noises are due to have tubes usually in wrong position or different types...here is what the the PV11 manual says:

The audio circuit of the PV11 uses six vacuum tubes of three different types: two 12AX7 (V1 and V2), one 5751 (V3) and three 12AU7 (V4, V5 and V6). The PV11L uses two type 12AU7 (V5 and V6). Each type has been carefully chosen for its circuit application. It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive audi- tioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11. Also, the tubes in your preamplifier have been tempered by a controlled burn in procedure that permits them to perform for a greatly extended period with out sonic degrada- tion. We anticipate two or three years of operation without degradation in normal use. We highly recommend that when the time comes to replace the vacuum tubes you purchase replacement tube sets from conrad-johnson design.

Usually 2.2 uF or 4.7 uF are coupling caps and this values are to prevent DC from one stage to other, but AC (signal) will pass through.

Hissing tells too, bad tubes.

Double checked that tubes are in the right places. If I take a microphonic tube from line stage and put it in V3, it doesn't ring. The tubes are only microphonic in V5 or 6. It seems like there is excessive gain in the line stage? The pre-amp has way more gain than I need. I can't get knob past 9 o'clock without it over driving the amp. Any thoughts on how to lower the gain?

The volume pot was leaking oil, so I changed that out and overall noise was reduced. not sure why the p.o. needed to oil the pot.

What do the relays control?

[admin]

Has the unit had any modifications? You can lower the gain by adding a resistor at the output connectors.

Not sure what relays you are referring to, but relays typically control on and off states. For example, disconnecting the audio path until tubes warm up.

[AnotherJohnson]

Double checked that tubes are in the right places. If I take a microphonic tube from line stage and put it in V3, it doesn't ring. The tubes are only microphonic in V5 or 6. It seems like there is excessive gain in the line stage? The pre-amp has way more gain than I need. I can't get knob past 9 o'clock without it over driving the amp. Any thoughts on how to lower the gain?

The volume pot was leaking oil, so I changed that out and overall noise was reduced. not sure why the p.o. needed to oil the pot.

What do the relays control?

CJ preamps are known for having a lot of gain. But how they pair with an amp depends on the amp. I’ve had 6 CJ preamps dating back to the PV5, and 6 CJ amps dating back to the MV-52. They’ve all matched up to suit me.

The volume pot probably had some dead spots and the PO tried to clean them. Deoxit would have been a better choice.

It is likely that the OEM pot is no longer available.

Relays are also problematic. As admin pointed out, they’re there to allow the circuit to stabilize before hitting it with full function. The OEM relays have aged out. CJ has told me not to bother to replace them because the few they have are as old and disfunctional as the ones they’d replace.

Isn’t this the one with aftermarket caps? Share a picture and we may be able to identify how far it is from stock.

Regarding tubes, if it were an unmolested survivor, it would be worth investing in a set of new, high quality tubes. But it’s clearly been molested. Good money after bad etc.

I’m assuming you didn’t give much for this unit. Obviously you didn’t need it when you bought it. You may have given a fair price.

You say the solid state devices were all replaced too.

I don’t think anyone can give you good advice on this one. Pics would help. Best of luck.

[AnotherJohnson]

FWIW, here’s an early review.

https://www.stereophile.com/content/con ... eamplifier

I am pretty sure the PV11 was not a hybrid, and not buffered, so I’m not clear on the reference to SS devices having been replaced.

Is this a Backert (or other) “improved” version?

The line stage gain is 18 dB … much less than the 25ish of more recent CJ preamps.

[roberto]

Hola...voltages seems to be ok. Noises are due to have tubes usually in wrong position or different types...here is what the the PV11 manual says:

The audio circuit of the PV11 uses six vacuum tubes of three different types: two 12AX7 (V1 and V2), one 5751 (V3) and three 12AU7 (V4, V5 and V6). The PV11L uses two type 12AU7 (V5 and V6). Each type has been carefully chosen for its circuit application. It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive audi- tioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11. Also, the tubes in your preamplifier have been tempered by a controlled burn in procedure that permits them to perform for a greatly extended period with out sonic degrada- tion. We anticipate two or three years of operation without degradation in normal use. We highly recommend that when the time comes to replace the vacuum tubes you purchase replacement tube sets from conrad-johnson design.

Usually 2.2 uF or 4.7 uF are coupling caps and this values are to prevent DC from one stage to other, but AC (signal) will pass through.

Hissing tells too, bad tubes.

Double checked that tubes are in the right places. If I take a microphonic tube from line stage and put it in V3, it doesn't ring. The tubes are only microphonic in V5 or 6. It seems like there is excessive gain in the line stage? The pre-amp has way more gain than I need. I can't get knob past 9 o'clock without it over driving the amp. Any thoughts on how to lower the gain?

The volume pot was leaking oil, so I changed that out and overall noise was reduced. not sure why the p.o. needed to oil the pot.

What do the relays control?

Just thinking loud: I remember my old times when I tweak some units. At that time I used a logarithmic volume pot. What it does is to be more resistive at the beginning and at the half or about it, stat to work as a regular pot. I think that they are available...perhaps you have to do some adjustments, but it will work beautiful.

Happy listening!

[roberto]

The relays are for prevent any odd noise while the tubes are warming up. Also the timer built in is the right time to have all the voltage stages to be stabilised, then they click and the preamp sends the signal to the amp. On later models, the power on LED flashes, and with the click, stays on.

[roberto]

https://www.ebay.com/sch/i.html?_from=R ... &_osacat=0

Here are log pots. A great variety so you can find the one that suites you best.

[Toberius]

Schematic shows couplings caps as 2uF, but they are 4uF on the board. Which one is correct?

Hi, coupling capacitors besides avoiding direct current act as a filter for the signal, that is, 4 uF filter from 40Hz, 2 uF from 20Hz and so on.

Cana you post a picture of you pre amp?

Regards.

[Dr.Greenthumb]

FWIW, here’s an early review.

https://www.stereophile.com/content/con ... eamplifier

I am pretty sure the PV11 was not a hybrid, and not buffered, so I’m not clear on the reference to SS devices having been replaced.

Is this a Backert (or other) “improved” version?

The line stage gain is 18 dB … much less than the 25ish of more recent CJ preamps.

I replaced every diode and transistor in the power supply, along with every capacitor. I started going through checking the diodes and there were so many bad, I just replaced everything. The MPSU60 and MPSU10 were replaced with KSA1381 and KSC3503, respectfully. The replacements needed the pins (ECB) to be bent to be in the correct order as the original parts (EBC). I need the test point voltages to see how far off I am after the rebuild.

[AnotherJohnson]

Great project!

[Dr.Greenthumb]

The relays are for prevent any odd noise while the tubes are warming up. Also the timer built in is the right time to have all the voltage stages to be stabilised, then they click and the preamp sends the signal to the amp. On later models, the power on LED flashes, and with the click, stays on.

I pulled the relays out and there was a substantial improvement. The relays just pop out and the signal still makes its way through, no addition monkey business to get the signal out. Hiss was eliminated, however I still have the 60hertz to deal with. The sound stage expanded and the bottom end tightened up. With these gone, I've had to power up the PV11 the old fashioned way by tuning the pre-amp on about 45 seconds before turning on the amps. I forgot this the first time powering up and it was like "accidentally" closing the door on a cat's tail. So if anyone else tries this, REMEMBER to power up pre-amp 60 seconds before the amps come on.

[Dr.Greenthumb]

Has the unit had any modifications? You can lower the gain by adding a resistor at the output connectors.

Not sure what relays you are referring to, but relays typically control on and off states. For example, disconnecting the audio path until tubes warm up.

The unit has had repairs, but as far as I can tell, there hasn't been any modifications. All replaced resistors are the correct values.

I increased resistor 40, 47.5 ohm, to 75 ohm. This didn't make any real difference.

[admin]

I pulled the relays out and there was a substantial improvement. The relays just pop out and the signal still makes its way through, no addition monkey business to get the signal out. Hiss was eliminated, however I still have the 60hertz to deal with. The sound stage expanded and the bottom end tightened up. With these gone, I've had to power up the PV11 the old fashioned way by tuning the pre-amp on about 45 seconds before turning on the amps. I forgot this the first time powering up and it was like "accidentally" closing the door on a cat's tail. So if anyone else tries this, REMEMBER to power up pre-amp 60 seconds before the amps come on.

The 60hz hum is most likely a ground loop.

You can remove the relays but as you gained from experience, there are going to be some major transients with startup that are fed directly into the outputs. You will have to be real careful with that.

[Dr.Greenthumb]

I pulled the relays out and there was a substantial improvement. The relays just pop out and the signal still makes its way through, no addition monkey business to get the signal out. Hiss was eliminated, however I still have the 60hertz to deal with. The sound stage expanded and the bottom end tightened up. With these gone, I've had to power up the PV11 the old fashioned way by tuning the pre-amp on about 45 seconds before turning on the amps. I forgot this the first time powering up and it was like "accidentally" closing the door on a cat's tail. So if anyone else tries this, REMEMBER to power up pre-amp 60 seconds before the amps come on.

The 60hz hum is most likely a ground loop.

In the pics you can see a green wire that isn't connected to anything. It's soldered to a stand-off with a purple and blue wire from the transformer. None of those wires are connected, nor do they go to ground . The other pic shows a couple of caps going to ground. I haven't seen that before so I'm not sure of their purpose. Could either one of these contribute to the ground loop?

[Dr.Greenthumb]

Schematic shows couplings caps as 2uF, but they are 4uF on the board. Which one is correct?

Hi, coupling capacitors besides avoiding direct current act as a filter for the signal, that is, 4 uF filter from 40Hz, 2 uF from 20Hz and so on.

Cana you post a picture of you pre amp?

Regards.

Pic of pre-amp before restoration.

[AnotherJohnson]

If I remember correctly, the PV 11 still had a two prong hard wired plug. Did someone modify it to take aftermarket power cords? If they did, they might have gotten into ground loop issues and disconnected the green wire.