Dynaco PAS 4 Phono stage is almost so low it's inaudible

I have a 90s model PAS 4 and the phono section is extremely low/quiet. I checked the tubes for the phono sockets in an SCA 35 and the record player produced the regular level volume you'd expect. The other inputs for cd etc produce regular volume. If the tubes work in an alternate integrated with phono stage fine enough, and the other inputs work... any ideas what the problem could be? Its a early 80s Denon deck with a MM bronze Ortofon cart. Also, I plugged my phone into the phono stage using TRS headphone to stereo RCA and the volume from it is also extremely low. I would have figured a line level signal would be extra loud through phono. Ive triple verified that I am using the correct 12ax7 tubes and recently bought some pretty nice NOS testing Raytheon Baldwin tubes for this application. Any ideas would be appreciated.

You also have a 6DJ8 tube at each channel (V2 and V5). But as both channels are affected it's
not a likely cause.

They both are biased by an odd mechanism  ( D6 throug D11 ). If on or several of these are
shorted the bias would be wrong.
Measured at the negative side of C207 it should be -3.3 Volt   Start by examine this !



/PS
If you scrap it i will happily pay for shipping to sweden where it can be scrapped
environmentally friendly

/DS

peterh wrote:You also have a 6DJ8 tube at each channel (V2 and V5). But as both channels are affected it's
not a likely cause.

They both are biased by an odd mechanism  ( D6 throug D11 ). If on or several of these are
shorted the bias would be wrong.
Measured at the negative side of C207 it should be -3.3 Volt   Start by examine this !



/PS
If you scrap it i will happily pay for shipping to sweden where it can be scrapped
environmentally friendly

/DS

Hey I recognize your cool emblem thing from when I was here before. I will get it off the rack later and get a read. Thanks for the reply.

peterh wrote:You also have a 6DJ8 tube at each channel (V2 and V5). But as both channels are affected it's
not a likely cause.

They both are biased by an odd mechanism  ( D6 throug D11 ). If on or several of these are
shorted the bias would be wrong.
Measured at the negative side of C207 it should be -3.3 Volt   Start by examine this !



/PS
If you scrap it i will happily pay for shipping to sweden where it can be scrapped
environmentally friendly

/DS

Okay I got it to a workspace and it reads -2.93

Check your input select switch for continuity. I had to recently replace mine in my PAS-4 due to horrendous connectivity issues.
What happens if you wiggle it while playing a record?

45scratches wrote:

peterh wrote:You also have a 6DJ8 tube at each channel (V2 and V5). But as both channels are affected it's
not a likely cause.

They both are biased by an odd mechanism  ( D6 throug D11 ). If on or several of these are
shorted the bias would be wrong.
Measured at the negative side of C207 it should be -3.3 Volt   Start by examine this !



/PS
If you scrap it i will happily pay for shipping to sweden where it can be scrapped
environmentally friendly

/DS

Okay I got it to a workspace and it reads -2.93

That is less then ideal but it should not cause your problems.
How is the B+ voltages ( on pin 6 on V2 and V5) should be 300V

[/quote]
That is less then ideal but it should not cause your problems.
How is the B+ voltages ( on pin 6 on V2 and V5) should be 300V
[/quote]

Both read 350 on the nose

StereoGaryo wrote:Check your input select switch for continuity. I had to recently replace mine in my PAS-4 due to horrendous connectivity issues.
What happens if you wiggle it while playing a record?

I plugged my phone back into phono as the work space is cramped to have a record player up by the PAS 4. I hear only the faintest of sound from the phono section when both the PAS 4 and a class d 300 wpc desk amp is connected. On the cd input its very loud and clear. Wiggling the selector switch causes no changes on either input.

peterh wrote:

45scratches wrote:

peterh wrote:You also have a 6DJ8 tube at each channel (V2 and V5). But as both channels are affected it's
not a likely cause.

They both are biased by an odd mechanism  ( D6 throug D11 ). If on or several of these are
shorted the bias would be wrong.
Measured at the negative side of C207 it should be -3.3 Volt   Start by examine this !



/PS
If you scrap it i will happily pay for shipping to sweden where it can be scrapped
environmentally friendly

/DS

Okay I got it to a workspace and it reads -2.93

That is less then ideal but it should not cause your problems.
How is the B+ voltages ( on pin 6 on V2 and V5) should be 300V

Both read 350. I tried to delete part of the previous text and realized i did soemthing wrong. Only replied twice to make sure youd get alert.

Then it's time for a instrumental session using a signal source ( sine 1khz 4mV) and an oscilloscope.
Follow the signal, see if the AC after the ECC83 is some 100 mV then examine the my-followers behaviour

( and yes the voltage on 'A' and 'D' should be about 300Volt too. If not the ECC83 wont work ok)

peterh wrote:Then it's time for a instrumental session using a signal source ( sine 1khz 4mV) and an oscilloscope.
Follow the signal, see if the AC after the ECC83 is some 100 mV then examine the my-followers behaviour

( and yes the voltage on 'A' and 'D' should be about 300Volt too. If not the ECC83 wont work ok)

Yep. You beat me to it.

peterh wrote:Then it's time for a instrumental session using a signal source ( sine 1khz 4mV) and an oscilloscope.
Follow the signal, see if the AC after the ECC83 is some 100 mV then examine the my-followers behaviour

( and yes the voltage on 'A' and 'D' should be about 300Volt too. If not the ECC83 wont work ok)

Any lead on a inexpensive and slightly decent digital scope?

Maybe you should start with the bias. There is 7 inexpensive diodes in series ( D6 - D11) if one
is shorted you will get the reduced value you measured. See if you can identify the shorted one
( or change all with new 1N4007 )
The reduced bias you have will affect the tube V2 and V5 , they _might_ have got overheated.

peterh wrote:Maybe you should start with the bias. There is 7 inexpensive diodes in series ( D6 - D11) if one
is shorted you will get the reduced value you measured. See if you can identify the shorted one
( or change all with new 1N4007 )  
The reduced bias you have will affect the tube V2 and V5 , they _might_ have got overheated.

Okay, ordered. Thanks for the tips. I will have them in a few days and this is a very cheap and easy fix if it works. Cant wait!

45scratches wrote:

peterh wrote:Then it's time for a instrumental session using a signal source ( sine 1khz 4mV) and an oscilloscope.
Follow the signal, see if the AC after the ECC83 is some 100 mV then examine the my-followers behaviour

( and yes the voltage on 'A' and 'D' should be about 300Volt too. If not the ECC83 wont work ok)

Any lead on a inexpensive and slightly decent digital scope?

There are public domain programs that will turn you computer into both a signal generator and an o'scope. Worth a try.