George Wright WPL-20

[robertod]

Needs some thoughts on a problem.  I have a GW WPL-20 sounds good one problem a hum coming through speakers.  I have narrowed the problem to the power supply.  I changed out tubes, hum still there. The hum is constant, changing from phono to line.  Increasing the volume does nothing, hum still there.
Any ideas?  Thanks. Roberto

 

[Doc B]

Well, you have narrowed down the problem to not being the tubes. Might be the power supply, might be a ground issue, might be an issue with the heater bypass cap if it is floated, might just be the way the preamp was made. Could be that a recap of the power supply filter would solve the problem. Hard to say without having the amp on the bench. Roger Hug was working on George's stuff a few years ago, but unfortunately Roger passed away in 2018. Don't know if PB might be willing and able to fit it in, you would have to ask him.

 

[robertod]

Thanks Doc.  I will ask PB. I appreciate your help.  Very sad to hear about Roger.
I'll pm PB.

 

[robertod]

The George Wright WPL-20 has been repaired, thanks PB.  The detail and separation of the music is great and also the sound stage.  It's funny how you hear something new, like a slight hum.  I checked all connections, tubes, TT level and cart seated correctly and checked for ground loop.  Then a couple of days ago the hum is almost gone.  You have to hold your ear up to the speaker to hear it.  It got me thinking the tubes settled in IDK.  After reading a post here about tube life, I think it's time to replace my 2A3's (18years old).  I only say this as the hum did come back only on the right channel so I reseated the 2A3 and hum gone. Idea's on some 2A3's (currently using Sovtek).

 

[Paul Birkeland]

More Sovteks.

 

[robertod]

Thanks PB.

 

[robertod]

I could tell the difference in the music with the new sovteks 2A3's.  But the hum is still there.  Could it come from the Mono Blocks?  I ask this because I disconnected the interconnects coming from the pre amp., turned on the mono blocks on and hum coming through speakers. 
When everything is connected;  On the pre amp there is a switch on right side with 3 different settings 0, -10 and mute. When I set the knob at 0 the hum is a little louder and at -10 it is faint but noticeable.
The hum does not increase with volume so when listening to Lp's cannot notice hum.
Maybe upgrade power cord its only a two prong no ground.....
Thanks for your thoughts, ideas and or recommendations.

 

[Paul Birkeland]

Do the amps have hum pots?

 

[robertod]

I'm not sure.  Attached a pic.

 

[Paul Birkeland]

There's no hum pot and AC heating, you have to live with it, or you have to add hum pots.

-PB

 

[robertod]

I would like to cure the hum problem.  Is it very difficult to do? Add hum pot and AC heating.  I have never dealt with soldering audio equipment ie., amps, pre amps.  I did put together the Jager speakers.  Not sure or confident I could pull this off.

 

[Paul Birkeland]

It's not that hard.  The hum pot will have to live on the inside, so it will be a bit tedious to adjust, but once adjusted you can leave it till you get new tubes.  I would buy some 16-18 AWG buss wire to use to attach the outer pot lugs to pins 1 and 4 on the socket.  That will help immobilize the hum pot inside the amp physically.

Beyond just adding the hum pot, you need to pop off the green/yellow stripe wire and cap it with heatshrink so it doesn't touch anything, then run a wire from the center lug of the hum pot to where the green/yellow wire connected.

 

[robertod]

Straight forward directions. Unfortunate hum pot in chassis there is just no room to mount I understand that.  What hum pots do you recommend? 
Since I have the mono blocks open, see anything I should upgrade? 

 

[Paul Joppa]

As I recall, Georgfe Wright eventually added hum pots to his 2A3 amps. He was somewhat (in)famous for making frequent undocumented changes.

 

[robertod]

I understand that from George.  I did buy the 3.5 mono blocks from George unfortunately before he added the hum pots. 
There has always been a slight hum (ear to speaker) but now I purchased George wpl-20 and the hum is little more noticeable but not to bad.
I just would like it to be a (little) more quiet.

 

[Paul Birkeland]

Straight forward directions. Unfortunate hum pot in chassis there is just no room to mount I understand that.  What hum pots do you recommend? 
Since I have the mono blocks open, see anything I should upgrade?

What I recommend... not buying 10 turn pots!!!

These are OK:https://www.mouser.com/ProductDetail/CTS-Electronic-Components/026TB32R500B1A1?qs=%2Fha2pyFaduj4XvYIjXDDp0se3jA0cGcd9%2FjCnKWc9EhzbKyEB7d6lQ%3D%3D

I think you have enough space to drill a hole in the side of each chassis and add them there.  That also makes them more accessible.

You definitely have Magnequest output transformers, so it's worth keeping these going as they are worth some good money and should sound quite nice.  The things that I see are:

[list type=decimal]
[*]There's no ventilation (we had this conversation about your preamp already didn't we!).  I would space up the bottom plate with some washers to get some air moving through there. You could also just run them with no bottom plates and put some rubber feet around the edge. 
[*]The 100uF/100V cap by the cathode resistor has likely lived a rough life.  I would favor these as replacements:
https://www.mouser.com/ProductDetail/KEMET/PEG124PF310VQL1?qs=DqLQsTv2bi4z4%2FmyDhxewA%3D%3D
[*]The blue coupling cap is probably an inexpensive mylar type, you could replace it with whatever makes you happy. 
[*]The Nichicon VX power supply caps are definitely not bad, but depending on their age you may want to toss them while you are in there.  These are what I would replace them with:
https://www.mouser.com/ProductDetail/KEMET/PEG124YH2220QL1?qs=DqLQsTv2bi6qw6e9LF%2Fn1Q%3D%3D 
[*]The 100K 2-3W resistor that goes to pins 1/5 on the octal driver socket looks like an inexpensive metal oxide.  I'm sure you could find a nice replacement at Parts Connexion.  The same goes for the 30K cathode resistor going to pin 3.
[/list]

 

[robertod]

1)  I agree on mounting on the side.

2)  Ok

3)  Blue coupling cap?  Is it solid blue no lettering on it? I would like a recommendation not familiar with a replacement.

4)  Ok

5)  100k 2-3w resistor center bottom. Parts connexion, Holco resistor brand? Not sure where 30k cathode resistor pin 3 is.(is this resistor under blue cap(no lettering) in photo.

Thanks

 

[Paul Birkeland]

On the 4 pin side of the blue cap, there will be a resistor to ground.  I can't see it in the photo, but if you provide the value I could give an educated guess as to what value it might be.

Yes, the 30K resistor goes to pin 3.

Holco would do just fine.  If you're ordering from Mouser, you could also just get Vishay PR-03 metal films while you are there.

 

[robertod]

Attached a few more pics including blue cap.
The Vishay PR-3 metal films would be the other resistor I need to purchase.  Under #5 item.

 

[Paul Birkeland]

That's a 1uF 250V cap.