Hum and tube glowing red on my Foreplay ll

[hron61]

My foreplay ll has been working fine for the past 3-4 months after sleeping for about 21 years.
In the past couple of weeks it has developed a hum on both channels.
Tonight I totally rearranged my stereo system rerouting cables thinking interference from the cables, separated signal cables from ac cables, hooked it back up and hum still there.
But this time when I turned it on still humming I noticed for the first time that my right channel tube is glowing red-hot on top, the left channel seems normal. SEE PICTURE.
I never noticed it before tonight.

Another thing I noticed is if I wave my fingers or hand over the top of the right channel tube without touching it the hum will get louder and when I move my hand away from it the hum goes lower again, weird.
Im not experienced with electronics even though I built it and a seduction and a pair of 300b mono blocks back in 2002-2003, and was a member here back then (same name) but I'm just now getting back into my tube gear.

I used my system for about 1.5 years before they got packed away and the system sounded amazing.
Im hoping it's a minor issue and would appreciate help with figuring out the issue. Thanks.

 

[Paul Joppa]

It's not unusual to have different brightness of one or even both section's cathodes like that. You can exchange the two tubes to see if the brightness follows the tube, which is likely. If the hum remains - I expect it will - then it's probably not a bad tube.

The hum may have many causes, but two likely ones are a failed ground connection, or a failed electrolytic capacitor in the power supply. For the former, it is actually pretty easy to re-solder every connection, and it resolves a great majority of problems. It goes faster than you'd think. (Don't re-solder the LEDs or the power switch, they are easily overheated and unlikely to be the problem.)

While you are in there, inspect each capacitor for swelling. And take some pictures of the build and post them. Then do the voltage checks near the end of the manual, and post them as well. That will give us much more information for diagnosis.

 

[Paul Birkeland]

A datapoint worth collecting is to listen to a 60Hz tone and a 120Hz tone, then let us know which one you're hearing out of your Foreplay. 

 

[hron61]

I don't have the tones to listen to just yet but I'll keep looking for some, I'm curious to hear them.
I do have some more pictures and voltages to share. The black strips are pieces of sound dampening.
Can the pictures be resized here before posting them?
I tested all the grounds with my continuity meter and they all beep, I did reflow terminal 14 though which is tied to 13.
I also did the chopstick test on all solder joints the other day while it was playing music and didn't hear any strange noises.
I haven't got around to reflowing all ground connections just yet, only terminal 14 so far.
Also i may add that lately ive noticed the sound has become muffled, like I cant even hear the high hats in the music any longer.


Terminal 2...171vdc,
Terminal 7...159vdc
10/11/12...147vdc,147vdc,147vdc
A1...49vdc
A3...2.09vdc
A4/A5...46vdc
A6...148vdc
A7...49vdc
A8...54vdc
A9...46vdc
B1...55vdc
B3...2.09vdc
B4/B5...45vdc
B6...148vdc
B7...55vdc
B8...58vdc
B9...46vdc

 

[Paul Birkeland]

I don't have the tones to listen to just yet but I'll keep looking for some, I'm curious to hear them.

https://letmegooglethat.com/?q=60hz+tone
https://letmegooglethat.com/?q=120hz+tone

 

[hron61]

Thanks Paul.
60hz sound is what im hearing.

 

[Paul Birkeland]

Are terminals 13 and 14 tied together?  Is the earth wire of the power cord connected to the chassis?

 

[hron61]

Earth ground from power cord is connected to terminal 13.
Terminal 13 and 14 are connected together.
Tonight i reflowed all the ground connections as well.
No changes noticed.
Also tonight i hooked up the adcom gfa5500 ss power amp (that i was using with the foreplay)
to my luxman ss R115 using the adcom as an external amp and had zero issues with the sound or hum. It sounded great. So that leads me to believe it seems to be a pre amp issue?

I did order the 3 nichicon snap in LGR2E221MELA25 caps that posted in my other thread.
S/b here in 2 days.
I forgot to mention that i tightened both tube sockets with a thin dental pic as well tonight.
No changes.
Did you notice any abnormalys with the voltages I posted?
I do appeciate your help very much.
Like i mentioned earlier when i built it it played very nicely, just very little hum and only if i put my ear up to the speaker a few inches away, but that seemed to be the norm from what ive read here without doing a snubber mod.
Ive done no mods other than the c4s, sweet whispers, panasonic caps and the auricaps, which were done as i was building it at the get go.
The ps caps have no swelling or leaking or melted wrappers, no external indicators of failure.
Maybe it is just a cap failure due to their age im guessing and hoping.

 

[Paul Joppa]

The tube socket voltages look right, just as they should be. For completeness you might do the resistance checks as well.

Normally, power supply hum is 120Hz, though failure of soldering of one of the HV rectifier might produce some 60Hz. The effect of your hand affecting  the hum suggests electrostatic pickup, so the level controls are a possible problem area.

There is a possibility that the 0.1uF cap in the power supply has become unsoldered, allowing some hum in the heater power.

That's all I've got right now.

 

[Paul Birkeland]

This feels like a missing earth reference to me.  This comes from the earth lug on your power cord and that is soldered to the chassis.  Back in the day, terminals 13 and 14 weren't connected, and you'd often get hum like this until they were jumpered together. 

The hand position influencing hum tends to suggest that you're a better earth than the chassis plate, so maybe use your meter to read DC resistance between the earth pin on the power cord and the chassis plate? (and double check the resistance between 13 and 14 just to be sure).

 

[hron61]

I measured DC resistance between the earth pin on the power cord and the chassis plate and got 27.3 ohms.
Terminal 13-14 is 3.8 ohms.

One thing i forgot to mention and post and it may be very important is the fact that my outlets are NOT grounded but its plugged into GFCI recepticle. I rent a house built in 1926.
Ive read a gfci outlet should give protection should a fault happen.

One other thing is my power cord is wired with both ends of the cord connected to the ground pins on both ends. Maybe disconnect one end of the ground wire in the cord?
Im not up to speed on on my electrical knowledge but i know a little bit about the safety aspect enough to not get shocked while inside of an amp. I make sure ALL CAPS are discharged prior to parts changing. And keeping a steady hand while testing when energized. And to go slow.
My solid state gear has zero hum, its just the foreplay.

I do have a pair of wl laurel 300b mono blocks that im going recap sometime but im now having second thoughts about using them in this house due to the lack of grounding.
When i built my system back in 2002-3 i was in a house that was properly grounded and everything played well together and sounded great with a tiny bit of hum which seemed normal
without the mods to totally eliminate it.

 

[Paul Birkeland]

Is there anything metal close by in the room you're in or under it?  You could probably grab a proper ground through a water pipe or maybe even a radiator.  This is very likely to be the issue you're up against unless all of this was working in that room previously.

 

[hron61]

Nope, nothing like that nearby unfortunately.
I do have an idea though, I have buddy that owns a record store in town and sells new and used audio also, I'll call him tomorrow and see if I can bring my foreplay, my ss amp, cd player, my cables and some speakers and hook it up in the shop and see if the hum is still present.

I'm curious to see if it works correctly (no hum) with a proper grounding like when it was first built.
If it does then that should solve the issue unless ive caused damage to it by not having it properly grounded in the first place, which i hope is not the case.

I'll be sure to wave my hand over the tubes as well to see if it makes it hum...maybe im just an
human with special powers I dont know about... Yet.  Lol

Paul Joppa mention the following as well... Thanks Paul  for your help also, much appreciated.
Electrostatic pickup,..Level controls are a possible problem area.
There is a possibility that the 0.1uF cap in the power supply has become unsoldered, allowing some hum in the heater power. I'll check that cap also but I dont know how to check the level controls for problems.
EDIT, i didnt see the 0.1uf cap in there, was it installed in the completely stock unit? Mine is an extended foreplay with no other mods except what was ordered thru Bottlehead.


I do appreciate your time, patience, and expertise in helping me get to the bottom of this issue.
One last thing, the way the treble started to get muffled as well has me baffled as well.
I did read that lowered voltages can have a muffling effect on the sound also, have you heard of that?
Do my voltages seem acceptable?

 

[Paul Birkeland]

I can see your 0.1uF cap in your build. 

Muffled treble could be worn down tubes, though your voltages don't exactly indicate that. 

 

[Paul Joppa]

The 0.1uF capacitor is located between the right-hand volume control and the adjacent B tube socket - I apologize, I was working from the circuit diagram instead of the physical layout (too lazy to go downstairs and pull out the manual ...).

For the volume control, I was just thinking it might have a bad ground connection or  switch contact. There were two different volume control switches over the years, called "Sweet Whispers" and the later "Sweetest Whispers" - I think you have the first one?

Your voltages are only 7% low, well within normal tolerances.

 

[hron61]

I see that cap now, i thought it was a type of resistor. Just used to seeing a standard shaped cap.
I'll reflow that one also as i only checked for a loose connection on it earlier.
I'm curious now about the sweet or sweetest whispers, since i dont have my original paperwork from when i purchased the foreplay, i'll research it further for external indentifiers of each. I'll post a seperate thread for that info.

 

[hron61]

The 3 power supply caps arrived today and got them installed.
Will power up tomrw and check voltages and resistance and if all goes well i'll fire it up and see if anything changes and report back. I'll order that .1uf cap that I overlooked asap too.

 

[hron61]

The 0.1uF capacitor is located between the right-hand volume control and the adjacent B tube socket - I apologize, I was working from the circuit diagram instead of the physical layout (too lazy to go downstairs and pull out the manual ...).

For the volume control, I was just thinking it might have a bad ground connection or  switch contact. There were two different volume control switches over the years, called "Sweet Whispers" and the later "Sweetest Whispers" - I think you have the first one?

Your voltages are only 7% low, well within normal tolerances.

I'm pretty sure i have the Sweet Whispers. I bought the fp in 2003 but i do remember the manual said rev2. All my paperwork and manuals were lost back in 2004
I found an old post that said the Sweetest Whispers were used in Foreplay lll.

Btw, would you have replacement recommendation for the 0.1 cap? I've been searching and so many choices and i just want to make sure i get a correct replacement. Much appreciated.

 

[Paul Joppa]

The 0.1uF cap should be rated for at least 100 volts. (The original is "400v, metal film"s. It, along with the two resistors to which it is connected, raises the filament power bias voltage to around 45-50 volts. It is NOT in the audio circuit, so nothing critical. It is unlikely to be a problem unless it is incompletely soldered, so re-soldering it probably sufficient. It and the two resistors are all crammed into the pin 9 solder lug of the B tube - it's a tight fit, which is a risk factor in making good solder joints.

 

[Paul Birkeland]

Btw, would you have replacement recommendation for the 0.1 cap?

Leave the one you have in place.  Those things are extremely long lived.