Old Pro Junior Weird Noise

[Travis8]

Hi

My old Pro Junior have a weird Noise, like an ugly distorted sound on every volume.

I check the circuit, changue filter caps (one was out of Range) and try new valves and the problem still there.

Also I replace C13, C14, C11 and C10.

Some ideas or Help?

Thanks...

[Travis8]

https://drive.google.com/drive/folders/1W-DInbzcLAMrbwoLeAOBITj30HR07leR

[PRR]

Are there any voltages in there?

[Travis8]

All caps have good voltages

[tubeswell]

All caps have good voltages

And these would be??

[PRR]

I was thinking the tubes. Does V13 G2 have 111 Volts, or whatever the service data says? If any of the readings is way-wrong, that is a CLUE.

[Travis8]

Preamp tubes:

V1:
9- 3.3v
5- 3.3v
4- 3.3v

V2:
9- 3.3v
5- 3.3v
4- 3.3v

[PRR]

.

[Travis8]

TP4 : 1.9VDC
TP2 : 122VDC
TP6 : 125VDC
TP8 : 1.8VDC

TP15 : 27.7VDC
TP12 : 176.9VDC
TP10 : 177VDC

[tubeswell]

Those look okay


What about the idle voltages on the output tubes' grids, screens and plates? (and do any of the screen grid resistors measure open?)

[Travis8]

I look at + lug on c13 and c14 and I get 0 volts.

let me see screen grid resistors

[sluckey]

I look at + lug on c13 and c14 and I get 0 volts.

That's right. But what do you measure on the negative lug of those caps?

[Travis8]

Those look okay


What about the idle voltages on the output tubes' grids, screens and plates? (and do any of the screen grid resistors measure open?)

Plate: around 350vdc bouth valves

Screen grid: 322,8vdc bouth valves

Control grid (TP13 and TP14): v4: 0,8vac  v3: 0,8vac

[Travis8]

r20 and r23 are ok, 1,5kohm

[Travis8]

TP23: 12,8vdc

[Travis8]

TP2 : 122VDC
TP4 : 1.9VDC
TP6 : 125VDC
TP8 : 1.8VDC
TP10 : 177VDC
TP12 : 176.9VDC
TP15 : 27.7VDC
TP23: 12.8VDC

Plate: around 350vdc bouth valves

Screen grid: 322,8vdc bouth valves


TP13: 0.8VAC 
TP14: 0.8VAC

[sluckey]

TP23 should be a negative DC voltage. TP13 and TP14 should also be a negative DC voltage and should be about the same as TP23. Please check these three points again.

Any AC voltage you see at those test points are meaningless unless you have injected the proper test signal into the input jack. We don't need those at this time.

[Travis8]

TP23 should be a negative DC voltage. TP13 and TP14 should also be a negative DC voltage and should be about the same as TP23. Please check these three points again.

Any AC voltage you see at those test points are meaningless unless you have injected the proper test signal into the input jack. We don't need those at this time.

Yes.

TP23: -12.8VDC

I assume TP13 and TP14 is pin 2 on bouth EL84.

I got 0 VDC and around 0,8VAC on bouth

[Travis8]

If I touch R20 and R23 i get -12,8VDC but if I test on pìn 2 I get 0 VDC

I check continuity between R20 and pin 2 of v3 and between R23 and pin 2 of v4. It´s correct

[sluckey]

So you have -12v on one side of R20 and R23, but you have zero volts on pin 2 of the EL84s. Not much between those points. Ensure that R20 and R23 both measure 1.5KΩ and are not open circuit. Then measure resistance between V3 pin 2 and chassis. Repeat for V4 pin 2 and chassis. Should be approx 270K and definitely not zero ohms. Report

[Travis8]

So you have -12v on one side of R20 and R23, but you have zero volts on pin 2 of the EL84s. Not much between those points. Ensure that R20 and R23 both measure 1.5KΩ and are not open circuit. Then measure resistance between V3 pin 2 and chassis. Repeat for V4 pin 2 and chassis. Should be approx 270K and definitely not zero ohms. Report

Bouth around 270kohm. R20 and R23 are ok, not open.

I clean the pin 2 and now I get the correct vdc (-12,8) so it's correct

[Travis8]

Some new ideas?

[tubeswell]

Time to do a VAC test on your OT

[Travis8]

Time to do a VAC test on your OT

This is the sound of the amp at any level

https://drive.google.com/file/d/1WkZa7RMnWxanWrzv7hGmpBUcMGcZ-G5H/view?usp=drivesdk

[tubeswell]

Time to do a VAC test on your OT

This is the sound of the amp at any level

https://drive.google.com/file/d/1WkZa7RMnWxanWrzv7hGmpBUcMGcZ-G5H/view?usp=drivesdk

That’s not doing a VAC test. Unhook the OT primary centre tap, pull the output tubes, and disconnect the OT secondary from the speaker output Jack. Then put a lowish VAC source across the secondary (5 or 6 VAC will work) and measure the resulting VAC between the Primary CT and each output tube socket plate pins. You should get a highish VAC that corresponds with the expected Sec:Pr VAC ratio given whatever voltage your source VAC is on the secondary. What’s more, the VAC across each half of the Primary should be the same. If you don’t get these results, the OT is haddit.

[Travis8]

Time to do a VAC test on your OT

This is the sound of the amp at any level

https://drive.google.com/file/d/1WkZa7RMnWxanWrzv7hGmpBUcMGcZ-G5H/view?usp=drivesdk

That’s not doing a VAC test. Unhook the OT primary centre tap, pull the output tubes, and disconnect the OT secondary from the speaker output Jack. Then put a lowish VAC source across the secondary (5 or 6 VAC will work) and measure the resulting VAC between the Primary CT and each output tube socket plate pins. You should get a highish VAC that corresponds with the expected Sec:Pr VAC ratio given whatever voltage your source VAC is on the secondary. What’s more, the VAC across each half of the Primary should be the same. If you don’t get these results, the OT is haddit.

Nice, I'm learning a lot. I dont have a VAC supply, wich one could I use/buy?

[tubeswell]

Time to do a VAC test on your OT

This is the sound of the amp at any level

https://drive.google.com/file/d/1WkZa7RMnWxanWrzv7hGmpBUcMGcZ-G5H/view?usp=drivesdk

That’s not doing a VAC test. Unhook the OT primary centre tap, pull the output tubes, and disconnect the OT secondary from the speaker output Jack. Then put a lowish VAC source across the secondary (5 or 6 VAC will work) and measure the resulting VAC between the Primary CT and each output tube socket plate pins. You should get a highish VAC that corresponds with the expected Sec:Pr VAC ratio given whatever voltage your source VAC is on the secondary. What’s more, the VAC across each half of the Primary should be the same. If you don’t get these results, the OT is haddit.

Nice, I'm learning a lot. I dont have a VAC supply, wich one could I use/buy?

Poor man’s VAC source. Disconnect your PT secondaries and use the 6.3VAC winding

[tubeswell]

BTW, it should go without saying, but don't let the loose/bare ends of any windings come into contact with the chassis or you or any other part of the circuit

[Travis8]

The OT is working correctly.

I can order two el84, maybe the problem is there. Becouse I check all the circuit and try new preamp tubes.

[Travis8]

Also If I turn on the amp and wait a lot (around 30 min) it's work perfectly.

Some ideas?

[tubeswell]

The OT is working correctly.

What VAC did you get on each 1/2 of the primary? (assuming you put 6.3VAC across the secondary?)

[Travis8]

Wait, I think I did bad. I will repeat it this week.

Check If I´m doing it correctly:

1- Unhook the OT primary centre tap (Red Cable of OT)

2- Pull the output tubes, disconnect the OT secondary from the speaker output Jack.

3- Disconnect PT secondaries and use the 6.3VAC winding (Green Cables of PT)

3- Connect the Green Cable of PT to the Red Cable of OT

4- Measure the resulting VAC between the Primary CT (Red Cable of OT) and each output tube socket plate pins (Pin 7).

Of course I don't let the bare ends of any windings come into contact with the chassis etc

[Travis8]

Thanks guys, I´m learning more and more every day in this forum

[tubeswell]

3- Connect the Green Cable of PT to the Red Cable of OT

No. Each end of the PT 6.3VAC winding (after disconnecting from heater circuit) gets connected to each end of the OT secondary winding. You are supplying the OT secondary winding with a 6.3VAC source voltage (so you can determine the resulting VAC on each half of the OT primary).


If you don’t understand this, you probably should take your amp to a tech.

[Travis8]

Ok, that was what I mean, I understand it thanks!

Let me do it this week, thanks again

[Travis8]

I write it again:

1- Unhook the OT primary centre tap (Red Cable of OT)

2- Pull the output tubes, disconnect the OT secondary from the speaker output Jack.

3- Disconnect PT secondaries and use the 6.3VAC winding (Green Cables of PT)

3- Connect the Green Cables of PT to the secondary cables of OT.

4- Measure the resulting VAC between the Primary Center Tap (Red Cable of OT) and each output tube socket plate pins (Pin 7).

Of course I don't let the bare ends of any windings come into contact with the chassis etc