HELP!!!...no sound from left monoblock

[steamer]

Hello,

Took delivery a few days ago of a pair of Electriprint 300b DRD monos.After unpacking and setting them up for the first time I powered them up.I had no sound from the left mono.I checked all connections and everything looked good.Next I swaped out the Sofia 300 tube with TJ 300.I now had sound from the amp.A couple hrs later the sound stopped in that chhannel again.WTH another tube?I thought I lost one in the shipping.I powered down the amp and tried to investigate,for some reason I pulled the output tube and reinstalled,now I had sound again.This has happened several times over the last few days.It happens at anytime whether the amp is warm or cold.The problem is always corrected by pulling and reinstalling the output tube.

My best guess is a bad tube socket.I dont know enough about the circuit to troubleshoot further.I do know not to stick my hands in the amp untill I discharge the caps.I havent opened it up yet but pulled the amps from the system for my 2a3 monos.I will look under the hood tomorrow when I get more time.Does anyone have ideas what to look for?I am attaching a circuit diagram,maybe you can see other possible issues.

Thank you for your help,

Greg

[mikebse2a3]

Greg said:

I pulled the output tube and reinstalled,now I had sound again.This has happened several times over the last few days.It happens at anytime whether the amp is warm or cold.The problem is always corrected by pulling and reinstalling the output tube.

------------------------------------------------------

Hi Greg

I don't see a diagram but anyway;

Have you noticed if the filament of the 300B is still working when you have no sound?

If not then look for a bad connection as you said in the socket or any solder connections at the tube socket or anywhere in the filament circuit itself. Most of the time if the amp was working and then lost sound due to a bad filament connection the sound would just fade out as the filament cooled off.

If your sound goes away abruptly then look for problems in the Plate connection of the tube socket as well as the solder connections involved in the Plate B+ Supply circuit all the way back to the B+ power supply. Also look for bad connections where the filament makes connection to ground through a couple of low value resistors(approx. 20 ohms) if Fixed Biased or if Self Biased through a resistor(s) of Several Hundred Ohms to ground.

Pin (1) and (4) are the filament pins of the 300B

Pin (2) is the Plate

Pin (3) is the Grid

If you can get the schematic posted I might can give more specific suggestions or maybe someone familiar with the Amp will comment.

mike[]

[steamer]

Mike,

Have you noticed if the filament of the 300B is still working when you have no sound?

Yes the filiments in both the 300b's tried are working when it happens

If your sound goes away abruptly then look for problems in the Plate connection of the tube socket as well as the solder connections involved in the Plate B+ Supply circuit all the way back to the B+ power supply. Also look for bad connections where the filament makes connection to ground through a couple of low value resistors(approx. 20 ohms) if Fixed Biased or if Self Biased through a resistor(s) of Several Hundred Ohms to ground

The sound goes away abrubtly,not a fading as the filiment cools.And also after the sound is gone the 300b filiment is working(the tube looks like the functioning tube on the right amp)

I'm not sure what happened to the schematic I attached but here it is again.

Thanks Mike

6AN4_DRD.pdf

6AN4_DRD.pdf

6AN4_DRD.pdf

[mikebse2a3]

Greg

Interesting design here!

Since pluging and unpluging the 300B seems to temporarily clear up your problem you definitly want to inspect the sockets Pin Connections for good contact with the 300B's Pins.

If you haven't done this yet you might want to swap the 6AN4 with the good amps 6AN4 just to rule it out as a possible problem.

The most likely problem would be a bad solder connection/wiring so you will want to look at all the solder connections in the PWR Supply starting with the 47 ohm (5 watt) coming off the 5R4 Rectifier Tubes working your way through the circuit till you get to the 300B's socket.

Also look for bad connections/wiring from the filament connections pins of the 300B socket, 10 ohm (5 watt), 5K (30 watt) Variable Resistor which connects to ground. Also look at the connections/wiring of the 70uf OIL Capacitor from the 300B's Socket's filament connection to it's connection to the Output Transformer.

Another possible problem area could be where the 6AN4's Plate Voltage(220v) is supplied through the 70H Choke Coil from the 5K ohm (30 Watt) Control. I would assume this Variable Resistor is a Variable Wire Wound Resistor which could have developed a dirty connection between the wiper and wire of the Resistor and could easily act intermitent. You could work(ie: move this terminal slightly back and forth) this Resistor's Variable Terminal being very careful to adjust it back to it's orginal location but you should really measure for the 220V and set it for that reading.

Greg if you continue to have problems and are comfortable taking some Voltage Measurements of the Amplifier or we could also take some resistance measurements (if the problem gets to where the Amp stays out).

Your welcome to E-mail me through the forum (just indicate Greg/Klipsh Forum in the subject line) your Phone Number and I will call you on my cell phone and maybe can help you more.

mike[]

[steamer]

Mike,

Thanks for the direction.I have been at work this weekend so tomorrow I will look closer at everything.Hopefully it is something ovious.If not I will send mail and proceed from there.I have a multimeter and can get some measurements if need be.

Greg

[mikebse2a3]

Nice looking AMP Greg.

Hopefully the problem is located at the socket and is simple to find. The good thing is these circuits are so simple it shouldn't be very hard to find the problem.

Again let me know if I can be of any help.

mike[]

[NOSValves]

Mike,

Thanks for the direction.I have been at work this weekend so tomorrow I will look closer at everything.Hopefully it is something ovious.If not I will send mail and proceed from there.I have a multimeter and can get some measurements if need be.

Greg

Greg,

Nice looking amp. I don't see the dual 5R4 rectifier on that chasses are they behind one of the transformers in the picture or on another chassis?

As far as your problem. I would clean and tension then tube sockets for the 300B and re-solder all the wire and components attached to this socket sound like an intermittent. connection to the grid of the 300B stopping the signal from entering the 300B.

Craig

[steamer]

Mike,

Thanks for the direction.I have been at work this weekend so tomorrow I will look closer at everything.Hopefully it is something ovious.If not I will send mail and proceed from there.I have a multimeter and can get some measurements if need be.

Greg

Greg,

Nice looking amp. I don't see the dual 5R4 rectifier on that chasses are they behind one of the transformers in the picture or on another chassis?

As far as your problem. I would clean and tension then tube sockets for the 300B and re-solder all the wire and components attached to this socket sound like an intermittent. connection to the grid of the 300B stopping the signal from entering the 300B.

Craig

Craig,

I noticed that the rectifiers are missing also as shown in the schematic.I believe they are using SS now like the Welbourne designs.

I retensioned and cleaned the contacts on the socket in question.The solder joints looked ok,nothing loose and they appeared shinny so I didnt feel any need to resolder.

The tube was definately loose and I could see the pin losing contact when moved.That was viewing from the bottom side of the socket.

The result is quite dramatic.Everthing is clearer and the images that were shifted to the right are now back where they should be.I have a different impression of the amps now,before sounds were veiled and somewhat distorted.It had me worried,I coudnt believe the sound could be that BAD!!!.I bought these amps because I wanted to hear the 300b tube and this cicuit interpetation by Jack Eliano.I can now say WOW!!! It is very good.

Only one thing that bothers me is when after doing the maint. and powering up I still had the problem.I did the remove/reinsert trick and had sound.They have been on for 5 hrs now with no issues and like I said the sound is noticably better.Time will tell I guess.

Thanks,Greg

[steamer]

Thanks to both Mike and Craig!

Greg

[mikebse2a3]

Greg said:

Only one thing that bothers me is when after doing the maint. and powering up I still had the problem.I did the remove/reinsert trick and had sound.They have been on for 5 hrs now with no issues and like I said the sound is noticably better.Time will tell I guess.

------------------------------------------------------------

Intermittent Problems[6]

Usually simple when you find it but it can sure be a devil to find!!!

Anyway let us know what you think about the Amps after you've spent some time with them and if it gives you more trouble.

mike[]

[steamer]

Greg said:

Only one thing that bothers me is when after doing the maint. and powering up I still had the problem.I did the remove/reinsert trick and had sound.They have been on for 5 hrs now with no issues and like I said the sound is noticably better.Time will tell I guess.

------------------------------------------------------------

Intermittent Problems[6]

Usually simple when you find it but it can sure be a devil to find!!!

Anyway let us know what you think about the Amps after you've spent some time with them and if it gives you more trouble.

mike[]

Will do Mike,

I hope to do a comparison of my Wavelentgh Gemini 45/2a3 monos and these amps,kind of a 300b vs.2a3.

I shut them down to get a bite to eat and 2hrs later it powered up ok.I will be more comfortable after a few days of run time.

Greg

[NOSValves]

Sounds like your dealing with some serious oxidization caused by loose intermittent long term connection tube to socket. Try some pipe cleaners or small brushes with Cage deoxit and clean inside the sockets and the tube pins of the 300B's. The metal contacts inside the socket need to seriously grab the tube pins and be clean to properly conduct. Some times its just best to replace the sockets or the problem will just keep haunting you.

Craig

[DRBILL]

I just skimmed the posts, so somebody else may have suggested this. I would re-heat the tube pins. They are hollow and the wires that pass through the glass are soldered to them. On more than one occasion I have found "cold" solder joints in tube pins. Just heat the pin with your iron and flow a little new solder into the pin interior.

It costs no more and what could it hurt.

DRBILL

[steamer]

Sounds like your dealing with some serious oxidization caused by loose intermittent long term connection tube to socket. Try some pipe cleaners or small brushes with Cage deoxit and clean inside the sockets and the tube pins of the 300B's. The metal contacts inside the socket need to seriously grab the tube pins and be clean to properly conduct. Some times its just best to replace the sockets or the problem will just keep haunting you.

Craig

Well guys it's back lol,with a twist...kind of.

The system has been on since last night and about 6 this morning I was checking the amps out.I was curious how warm they get and was pressing lightly on the top plate in the area of that extra switch next to the signal tube(see note below)

The sound was lost in that amp.I pressed down on the same area and it came back.That is the same area or close to both tubes.I believe I have had my hand there each time I do the tube reinstall trick.

It has been fine since,and I am not gonna touch it anymore today.I will open the amp back up and look there.Seems like a possible problem in the signal circuit and that switch is in the same circuit.Lots to look at.When I open it up I will take a pic and post.

Craig

I did as you said about cleaning that socket.Also I am planning on replacing all 4 sockets sometime soon.Any recommendations on quality sockets?In addition I might have to resolder some other joints like you talked about earlier.

NOTE:The switch by the signal tube is a 70hz cut requested by the previous owner and installed by Electriprint.Originally there was a volume pot there.I would like to take the switch out of the circuit and put the volume control back in.Ideally I dont want anything in the circuit but dont want a hole in the chassis either.I cross the signal the amp sees at 400hz with my Rane active so a 70hz cut is useless and just more in the signal path.

Thanks,Greg