Pultec EQH-2

[warpboy]

Hello,
I'm trying to repair a pultec EQH-2. It works well for a couple of hours and after It starts to make some pop,crackle and other noises...and I have the same problem when the pultec is in bypass position. The 6X4 tube that is the rectifier tube (If I well understand) is ok, then I changed the two 22UF/450V caps, but nothing has changed....
I'm searching for a schematic and/or any helpfull information.


Thank you
Fabien

 

[okgb]

try some freeze spray on the large value resisters when it starts acting up

 

[drask]

Maybe try to change all tubes?

 

[lassoharp]

Try wiggling the tubes when it starts the crackling and popping and observe whether it makes the problem worse or better.  Sometimes you get excess noise from oxidized tube socket contacts.

As Greg alluded to, you could have out of spec resistors that are acting up as they get hot.  It would be a good idea to take some DCR measurements and see if any have gone way out of spec.  If they are using any large (1 or 2W) sizes anywhere, check those first.    Sometimes you can pinch a dying resistor with your fingers and they will crumble apart.

Could easily be a bad tube as well.

 

[warpboy]

thank you for your replies 
I've tried with new tubes but it is the same and I asked me if the sound goes in the two ecc tubes in bypass mode ?

For the rest I have to do all the tests that you're speaking about
definitively, there is no schematic (I did some search with google) ?

Thank you

 

[abechap024]

Maybe cold/dirty solder joint? Maybe clean wires pcb with alcohol...

 

[pucho812]

Your problem lies directly with the heat. Heat can cause things to expand or parts to go out of spec(resistors drift in value). Since it's popping and such when it gets hot, That would lead me to believe there is a faulty solder joint.  I would also check the tube sockets to make sure the tubes are fitting in properly and not loose.

 

[mjrippe]

Schematic posted in the Technical Documents section.

 

[lassoharp]

The 5W 18K resistor is a good candidate for a health check, as is the 2W 470r current limiting resistor between rectifier and 1st cap.

 

[warpboy]

Hello, thank you for all the infos 
I've downloaded the schematic (this is exactly what I need !) thanx Mjrippe

I've bought a new tube socket because the original seems to be bad, I can move the tube in the socket ...

As OKGB said, a freeze spray could help me to find the dead resistor, first I'll look at the 18K/5W & 470r/2W and do some measurement ( to see if I have the same values as in the schematic.

I'll give some news as soon as possible
Fabien

 

[warpboy]

Hello,
I've changed 18K/5w & 220R/3W resistors, but it doesn't change anything.
The 18k/5W is really hot after after a few minutes (the new one too)  and then the problem starts again...
Could it be a capacitor ? (for information, I've changed the two 22uf/450).
I can't see the 470R/2w. The first 1K/1w is directly connected to the 6X4 tube socket ....!!!!!

I really don't know what could be the problem  :-X

 

[lassoharp]

The first 1K/1w is directly connected to the 6X4 tube socket ....!!!!!

That is normal for P to P wiring.

Have you tried isolating where the noise is coming from?  Wait until noise starts then start by grounding grid of the 1st tube, then 2nd tube if needed.

The 18k/5W is really hot after after a few minutes

That amount of dissipation in a resistor will always get fairly  hot to touch.  If you suspect it's dissipating more than it should check the actual current passing through.  Should be around 2.5W or less based on stock rating of a 5W part.

 

[CJ]

sounds like the plate resistors, carbon comps get old and they were probably undersized to begin with,

 

[warpboy]

hello, another question : I've three tubes on my eqh2 : 6X4, ECC83 & ECC82. When I look at the schematic I see a 6AQ5( it's a 7 pins tube) instead of the ECC82.....is mine a different version of this eq?

sounds like the plate resistors, carbon comps get old and they were probably undersized to begin with,

CJ, do you mean it's a problem in the design of this eq? and do I change all the plate resistors

I'm not common with tube (as you certainly have already understood)....when you have transistors or opamps, I use my oscilloscope.....but with tubes, voltages are really higher and I can't use my scope.....

thank you again for your help

 

[CJ]

just build a voltage divider with a 1 meg/10k resistor and tape it to a bnc cable, no need for fancy probes at audio freqs, you can even use lamp cord at these voltages, we are so above the noise floor, 100 volts/10 mv = 10,000 to 1 s/n ratio,

where is the schematic?

 

[warpboy]

hello,
CJ, the Schematic has been posted in the Technical Documents section by Mjrippe.

 

[opacheco]

Hello,
I'm trying to repair a pultec EQH-2. It works well for a couple of hours and after It starts to make some pop,crackle and other noises...and I have the same problem when the pultec is in bypass position. The 6X4 tube that is the rectifier tube (If I well understand) is ok, then I changed the two 22UF/450V caps, but nothing has changed....
I'm searching for a schematic and/or any helpfull information.


Thank you
Fabien

Hi,
I have the same problems with my Pultec EQH-2!!!.....But my EQH-2 is very different to the Schematic from Mjrippe because it have a Solid State rectifier(2 Diodes for High Voltage rectifier instance 6X4 tube!!) and have a 6AQ5 and ECC 83. Do someone know how many version exist of this EQH-2 Pultec???....My unit is silver Face and look in a Original State inside!!.

How about the Filter seccion??? The Filter Section  look very different of the anothers Pultec EQ Units......Where I can find a schematic for that???

Thanks for comments
Opacheco.

 

[j.frad]

Hi guys,
I decided to write here and not make another EQH-2 fixing thread.
We have an original blue EQH-2 that stopped working.
All I hear coming out is a loud hum.

Tubes are 6X4 recifier, ECC82 (instead of 6aq5) and ECC83.
I tried swapping tubes with the other pultecs, it doesn't change.
The 6x4 rectifier seems fine, although voltages are low.
Power transformer outputs around 500VAC
Voltage after the first 470R 2W resistor is 250R
Voltage feeding the plate resistors is 233V

Heater voltage is 6,22VAC, heater elevation voltage is 80V instead ov 115.

I should still be working, right? What am I missing?

 

[lassoharp]

I should still be working, right? What am I missing?

How old are the filter caps?  That's what it sounds like

 

[j.frad]

In the power supply?
The large multicap is probably original...
I should probably look into finding a replacement, but the usual suspects that sell high voltage capacitors for tube gear usually don't stock this kind of capacitor, am I wrong?
I need to retain the original look of the unit...