Hum and tube glowing red on my Foreplay ll

[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.

[hron61]

Thanks for the info on what the 0.1 cap is for.
And solid advice from both of you about it, thanks for that.

It is very tight in there and i do have continuity in the connections of it and the solder doesnt look cold, so i'll just let it be. Dont want to create an issue if its not an issue.

[hron61]

I thought i would post a quick update on the situation and to thank you for trying to help figure this out for/with me.

I havent tried hooking the system up to a grounded electrical outlet just yet, i ordered resistors to make a shorting plug for the fp outputs and waiting for those. I would like to check the hum level.

A quick history note...when first built back in 2003 with the extended version installed at the get go
it was hooked up to my WL Laurel 300b mb with Klipsch Forte's and a Thornes turntable with diy cables of belden 89259 ic and belden 89364 for the pc and the hum was barely noticeable and only and only if i put me ear within a couple of inches from the speaker BUT it was plugged into a properly grounded electrical system. Everything played very well with each other and sounded amazing, then packed away.
Fast forward to today 22 years later and just the foreplay is being used Without a grounded outlet.
Its hooked to a solid state adcom gfa5500.

I did hook it to another adcom amp i own, a ss gfa535 and got the same hum as the with the 5500 amp.
Another thing i did was used my Luxman ss R115 receiver as a pre and hooked it up the 5500 and got Zero hum, quiet as a mouse.

I installed new power supply caps in the foreplay, reflowed all ground connections, did the chop stick testing., and tried multiple tubes and hum is still there.
Im not into electronics like alot of members here but i can follow directions in laymans terms and can solder very well.

Im still waiting to bring the system to my buddy's store to hook it up to a grounded outlet, im hoping that it just needs to be grounded.
For safety sake the Foreplay and the Adcom are plugged into a GFCI ext cord while im using it.
I'll post back after the hum is measured and i hook it to ground which should be soon i hope.
In the meantime feel free to toss anything else out there, im all ears and appreciate the help.

[Paul Joppa]

This is a real puzzler!

I still suspect a ground problem, but a grounded outlet could easily be a red herring. It's not much help, but as I recall those copper ground wires were a real bear to solder - the insulation was extremely hard to get through or burn off. And terminal 14 seems to have a bunch of them, which makes it even harder. It would not surprise me if a connection failed there.

[hron61]

Yes, it sure is.

Thats funny that you mentioned terminal 14 ground.
Late last night i was thinking the same thing.
I will put great effort in totally reworking all connections on that area.
Last night i watched some soldering videos on this sight that doc(thanks doc) had posted years back and it got me thinking about a good mechanical connection before the solder is applied and proper wire stripping, how very important that combination is.
One of the videos showed just how important flux is for the metal. A very eye opening matter to say the least. Oxidation of the metal must be eliminated.
I also use the Cardas Quad Eutectic Solder and have a container of their flux that I will make sure to use on that area as well.

[Doc B.]

There is plenty of flux in the core of the Cardas solder. Don't add extra. That will make things worse.

[hron61]

Hi Doc,
Thanks for the tip.
Definitely don't want to make it worse. 

[hron61]

Heres an update on the hum issue ive been trying to locate.

Took the advice from Paul to fully check over all my solder joints including terminal 14 which is very busy indeed. I completely desoldered term 14 and made sure all wire ends had no varnish on them, i rescraped all the ends with an exacto knife also.
Before i resoldered the wires i moved a couple to the eyelet below the top hole of same 14 terminal and that took away the clump of wires, and made for a better connection for ground.
While searching for questionable solder joints i found one on a right channel rca center pin and repaired that. Still hums but very slightly less but nothing to write home about.

I still havent tried hooking up system to another location with a grounded electrical system just yet
but will do that soon.
The main amp is an Adcom gfa 5500 and i also have an Adcom gfa 535mkl which i hooked up also and it hums too. I did check bias and dc offset and adjusted to factory specs on both also.
I must say, the little Adcom gfa535mkl is one sweet sounding little amp and was worth every penny of 49.99. Lol

Ok so now heres where it gets weird, i also have a Luxman R115 ss receiver in mint condition and sounds wonderful. On a whim i connected the foreplay to the tape in of the luxman to use it as the pre, then i hooked up the gfa535 to the pre outs of the luxman to use that as the power amp.
So basically the luxman is just the middleman AND it has a remote (nice).
When i turned everything on i have very very little hum. Weird huh? And that motley crew acually sounds pretty good together.

So im thinking it must some sort of ground loop issue afterall because when i first built it back in 2003
i didnt have a hum whatsoever, (and with a properly grounded wiring system)... just a deep dark silence. Even the seduction i built with it had zero hum.
Its strange that by hooking everthing up to the Luxman thats what took the hum away.
Since this home has no ground in the wiring the pre, receiver amd main amp are plugged into a GFCI heavy duty cord. The rest of the stuff all plugs into an older monster cable 2500 power station component.
Man as im in my mid sixtees now,i do love that remote, lol.
I still want to measure the hum since i got a couple of output shorting jacks with resistors made up finally.
So what do you think about this?

[Paul Joppa]

I think you are right, it's a "ground loop." (I put that in quotes because most ground-current issues are noise capacitivly coupled from power transformer windings, rather than magnetic fields.)

I haven't had my coffee yet this morning, so I 'll have to think this through before I have any advice to offer.

[Paul Birkeland]

Do you have any water pipes or gas pipes near your system?  Is your gear plugged into an outlet on an exterior wall? 

While it is a tremendous pain in the butt to add grounds to all the outlet in a house, it can be very easy to add a ground to just one outlet. 

[hron61]

Sorry for the delay in response, i just havent had anything positive to add unfortunately.
Been reading many many posts going back years and trying to gather info from others to print out and research. There are so many possibilities and I've tried many but no luck so far.
Have gone over all the solder joints with my magnifying glass, refrowing all joints,qmaking sure the wires are routed correctly, etc.
My next step is to measure the hum then to bring the system to a friends house with proper grounding. I do believe that to be the problem because I have not touched the underside at all since it was built in 2003 and it was in a home with a proper ground and it was quiet then.
I built a Seduction pre and a pair of 300b's around the same time and they was quiet as well.

I know that when turn off the amplifier the hum goes away, does that sound like a grounding problem? Or an impedance issue? It does it with all 3 amps I've tried.

No luck on the wall, its an interior directly in center of house.