Bottlehead Forum
General Category => General Discussion => Topic started by: robertod on June 02, 2020, 09:48:40 AM
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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
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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.
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Thanks Doc. I will ask PB. I appreciate your help. Very sad to hear about Roger.
I'll pm PB.
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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).
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More Sovteks.
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Thanks PB.
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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.
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Do the amps have hum pots?
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I'm not sure. Attached a pic.
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There's no hum pot and AC heating, you have to live with it, or you have to add hum pots.
-PB
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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.
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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.
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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?
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As I recall, Georgfe Wright eventually added hum pots to his 2A3 amps. He was somewhat (in)famous for making frequent undocumented changes.
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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.
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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 (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:
- 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 (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 (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.
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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
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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.
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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.
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That's a 1uF 250V cap.
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To summarize;
Items;
1. More ventilation,
2. Cap from Mouser(link sent)
3. Blue coupling cap 1uf 250v cap.(I could get from Mouser?)
4. Cap from Mouser(link sent)
5. Two resistors 1) 100k resistor Vishay PR-3 Metal films. 2) 30k resistor (I could also get from Mouser the type would be my choice, right?
I have summarized your recommendations is it fair to say I can go ahead with the upgrades.
Thanks PB
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Yeah, that's what I would do! You also have heatshrink right? If you wanted to get some from Mouser, I would get this:
https://www.mouser.com/ProductDetail/TE-Connectivity-Raychem/SCL-3-16-0-STK?qs=pUKx8fyJudD1JeC4dGRpiw%3D%3D (https://www.mouser.com/ProductDetail/TE-Connectivity-Raychem/SCL-3-16-0-STK?qs=pUKx8fyJudD1JeC4dGRpiw%3D%3D)
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Any recommendations;
Replacement on blue coupling cap
And 30k resistor.
I will get everything from mouser.
Thanks
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I'm sure there's a 30K PR-03.
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P.B.
Thanks for your help.
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Having trouble locating 16-18 AWG buss wire. I've checked with local audio dealers, and electrical distributors. Any suggestions, recommendations.
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If you e-mail me your address I can mail you some in a postal envelope. pb(at)bottlehead(dot)com
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PB,
Thank you.
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PB,
Thanks for all your help and patience's on all my questions!
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PB
I'm getting ready to install hum pots and upgrades ( caps and resistors) I have a few questions;
I received the buss wire, I don't know if it is enough. (could I use 16-19awg stranded and tin the ends, or solid 18 gauge copper wire?
The caps have neg-pos symbols, these caps are directional do they flow from pos---neg--> ?,
The 250v 1uf film cap does not have a - or + , is it safe to say this is not directional?
The resistors are they directional?
RESISTORS ( added pic to verify location)
Resistor- 3watts 30kohms
Resistor- 3wats 100kohms
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On the hum pots, you could also glue them just behind the grommet where the blue/red wires poke through from the OT. I like black RTV for that job, which is available at the autoparts store.
I would not use stranded wire anywhere in those amps. I would not use bare copper wire anywhere in those amps either. You should only need a few inches of that wire; it's just to connect the outer lugs of the pot to the filament lugs on the sockets. You'll need some solid core tinned hookup wire to go from the center lug of the pot over to the rest of the circuit. I would've sent you some if I'd thought about it, but that didn't cross my mind when I mailed your envelope.
On axial capacitors, there will either be a bunch of + symbols indicating the positive side, or a big fat black stripe that looks like a continuous arrow that points to the negative section. Another way to triple check is that most of these caps have a crimp on one end of the tubular body, and that is on the positive end.
The film caps and the resistors are non directional parts.
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Also, it goes without saying, do one amp at a time!!! Been there, done that! Don't want to do that again!
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I understand the negative and positive sides of the cap.
Yes, for sure one amp at a time. Thanks for answering all my questions. I never worked on amp(s), replaced/upgrade de-solder/solder.
That is why soooo many questions.
Thanks!!!!
Congrats on the Moreplay pre-amp!!! Another solid build from Bottlehead!
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As I work on the mono blocks, I have noticed a goldish color around the different connections.
Can this be cleaned or should I leave alone. Also I noticed the new capacitors (silver) have a plastic wrap on them. Should I remove it?
Thanks
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The goldish color on the connections would be flux from the solder. I would just leave it there, as it isn't all that easy to clean off, and when you do it will just migrate down into that chassis.
The plastic wrap on the connectors insulates the metal body of the caps (which is also the negative connection of the cap) from coming into contact with anything. I would not remove the plastic wrap under any circumstances.
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Thank you for the response. I'm learning every day.
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George's vintage surplus solder. ;)
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Re: George Wright WPL-20
« Reply #17 on: August 09, 2020, 04:19:14 PM »
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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.
I copied your post that I did not answer. I have attached a pic showing the resistor your referenced that needs to be grounded. I hope the pic helps.
The hook up wire is on its way, then I can continue the mods.
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On the 4 pin side of the blue cap, there will be a resistor to ground.
That would be this resistor. You could probably just call it good with the hum pots and some fresh caps.
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Ok, so I'm good to go with the other mods, thanks for clearing that up.
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Picking up hookup wire tomorrow. This will allow me to finish the hum pot. The caps have beeen upgraded. The two new resistors have to be installed. If I install the two resistors should the resistor you mentioned in the above post, need to be grounded? And how do you ground the resistor?
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If you are going to replace any resistors, you pull the one out you'd like to replace, then put the new one in exactly where the old one was (connected to the same terminals).
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Ok gotcha, I do not have to ground the the resistor you mentioned earlier.
Thanks.
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Ok gotcha, I do not have to ground the the resistor you mentioned earlier.
Thanks.
The resistor I mentioned earlier would go between the grid of the output tube and ground.
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Could you send pic how it should be done.
Thanks
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You have multiple photos of that resistor. It is where it is, either you leave the one there that came with the amp or you pull it out and put a different one in there.
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ok, thanks.
Completed one amp, after re-soldering a few connections and adjusting hum pot can't hear the hum from listening chair. Will work on second amp after I get a few things done at work. Will update status soon.
Thanks,
PB
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PB,
Upgrade/mods. on the Wright Sound 3.5, 2A3's complete. The hum is gone, can't hear it from listening chair. The music, I can hear the difference and I know only with time (100hrs) the caps will break in and even sound better.
Thanks PB for all your help.
Roberto
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I'm glad you got it all sorted out and the hum is gone.
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Hi There,
I just picked up a WPL20 but it's missing its external power supply. I'm looking for specs, circuit diagram, etc, anything that can help me build another one.
I found a website that allegedly has the circuit diagram (contact for access), but appears to be defunct. (audiocircuit . com)
So, I thought I'd ask here. I can't image the layout for the PS is that complex, maybe just some detailed pics of the circuit and components might allow a deduction of the design.
Any help greatly appreciated
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You'd be best off buying another WPL-20 and cloning its power supply for yours.
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I'd be open to that, if it was even possible to find one...
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sent you pm