|
Page 1 of 1
|
[ 10 posts ] |
|
Author |
Message |
mstamper
|
Post subject: Intractable hum problem solved Posted: Oct Sat 15, 2016 5:27 pm |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 308 Location: Windsor, CT USA
|
After restoring my Grommes 61pg 6L6-based mono integrated amp, I had a hum problem with the volume at minimum. Not a loud hum, but irritating nonetheless. I finally traced it to an unexpected source. The Grommes uses PECs underneath the bass, treble, and loudness controls. My other Grommes 61pg uses discrete capacitors and resistors. Anyway, the twisted pair of wires leading to the on-off switch passed directly over one of the PECs. I happened to move the wires, and the hum level changed! Apparently, the PEC was acting like an inductive pickup which absorbed 60 cycle AC waves from the twisted pair. Moving the PEC and wires away from each other gradually reduced the hum. I eventually added wire to the twisted pair and completely rerouted the wires away from the PECs. Result: hum completely eliminated.
I guess I'm just going to have to replace the PECs with discrete components. No telling how off-spec the PECs are by now.
|
|
Top |
|
 |
dberman51
|
Post subject: Re: Intractable hum problem solved Posted: Oct Sat 15, 2016 6:45 pm |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 4278 Location: Boston, MA USA
|
I think PECs have indefinite life as long as they are not exposed to excessive light, which can burn them.
-David
|
|
Top |
|
 |
Jim Mueller
|
Post subject: Re: Intractable hum problem solved Posted: Oct Sun 16, 2016 1:57 am |
|
Member |
 |
Joined: Sep Mon 16, 2013 2:42 am Posts: 3547 Location: Tucson, Arizona U.S.A.
|
dberman51 wrote: I think PECs have indefinite life as long as they are not exposed to excessive light, which can burn them.
-David ? I have never seen a "burned" one but I have seen several that have failed. How would it get exposed to excessive light under the chassis?
_________________ Jim Mueller
|
|
Top |
|
 |
dberman51
|
Post subject: Re: Intractable hum problem solved Posted: Oct Sun 16, 2016 6:53 pm |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 4278 Location: Boston, MA USA
|
They don't -- they get burned from careless handling when exposed.
-David
|
|
Top |
|
 |
tube42
|
Post subject: Re: Intractable hum problem solved Posted: Oct Mon 17, 2016 10:09 pm |
|
Member |
 |
Joined: Jan Tue 23, 2007 10:23 pm Posts: 5388 Location: Chicago IL
|
Anyone chime me in as to what a PEC is?
_________________ -Carlos
|
|
Top |
|
 |
JerryHawthorne
|
Post subject: Re: Intractable hum problem solved Posted: Oct Mon 17, 2016 11:30 pm |
|
Joined: Feb Sun 24, 2008 4:21 am Posts: 4661 Location: Sedona, AZ/ Placentia CA
|
I'm with you Carlos??????????????????? 
_________________ A friend in need is a pest. Bill Slee ca 1972
|
|
Top |
|
 |
Jim Mueller
|
Post subject: Re: Intractable hum problem solved Posted: Oct Tue 18, 2016 12:13 am |
|
Member |
 |
Joined: Sep Mon 16, 2013 2:42 am Posts: 3547 Location: Tucson, Arizona U.S.A.
|
PEC is a brand name that means Packaged Electronic Circuit. Another brand name is Couplate. It is a ceramic wafer with resistors and capacitors screened on and then conformal coated. They're pretty reliable but they have been known to fail. If you know what is inside, you can replace it with discrete components.
_________________ Jim Mueller
|
|
Top |
|
 |
dberman51
|
Post subject: Re: Intractable hum problem solved Posted: Oct Tue 18, 2016 5:44 pm |
|
Joined: Jan Thu 01, 1970 1:00 am Posts: 4278 Location: Boston, MA USA
|
Oops, I assumed incorrectly that this amplifier had some sort of lamp-driven audio controls using Photo Electric Cells (known as PECs).
The other usage for PEC is Packaged Electronic Circuit as was noted.
Never mind.....
-David
|
|
Top |
|
 |
postman56
|
Post subject: Re: Intractable hum problem solved Posted: Mar Fri 15, 2019 11:34 pm |
|
Joined: Mar Mon 26, 2018 9:20 pm Posts: 6 Location: Calgary,Alberta T2R0S9
|
Hello Mstamper, could you get back in touch with me in regards to restoration of the Grommes 61PG, I'd appreciate any help you could offer in doing this resto? Ken gold@nucleus.com
|
|
Top |
|
 |
jmsent
|
Post subject: Re: Intractable hum problem solved Posted: Mar Sat 16, 2019 3:13 pm |
|
Joined: Aug Sat 01, 2009 2:23 pm Posts: 1709
|
You find PEC's in a lot of hi fi audio equipment, some of it considered quite "high end". For example, McIntosh used them as well as Fisher and quite a few others. My last restoration of a Fisher 800 series receiver presented me with a PEC related problem. Measuring the phono section I found a huge difference between left and right channels. The problem was the PEC in the feedback loop of the phono preamp. Thankfully it only required 4 parts to replace it.
_________________ John Stone Antique Radio Club of Illinois
|
|
Top |
|
 |
|
Page 1 of 1
|
[ 10 posts ] |
|
Who is online |
Users browsing this forum: No registered users and 5 guests |
|
|