Valve amplifier service

If they glow, this is the place to be
Post Reply
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#1 Valve amplifier service

Post by bostod »

Hi guys. I have a world audio design 5881 valve amplifier that has developed a noticeable hum coming out of both speakers. Not noticeable when music is playing but very noticeable with no music or between tracks.
I have no technical experience myself so I am looking for someone or a company to service, bias and rectify the problem.
I live in Doncaster and I am looking for someone in this area. My preference would be to get there within the hour so a 50 mile radius.
I would travel further if no one in my area.
Do you guys have any recommendations
simon
Thermionic Monk Status
Posts: 5643
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#2 Re: Valve amplifier service

Post by simon »

I'm not really the best person for this (understatement!) but if you don't find anyone else I could have a look at it - I'm in Donny too.

I've a feeling the WAD5881 was PP? I have no experience of PP but might be able to navigate if someone has a circuit diagram?
User avatar
Nick
Site Admin
Posts: 15740
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#3 Re: Valve amplifier service

Post by Nick »

Yep I think so, I am not sure there is much in there to actually "service" other than looking for burnt bits. I think its auto bias. If both channels are getting hummy it may just be a case of needing new valves. How old are the valves currently in it?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#4 Re: Valve amplifier service

Post by IslandPink »

There were both PP and SE. I think the SE was a parallel SE.
http://world-designs.co.uk/forum/showthread.php?t=7445
"Once you find out ... the Circumstances ; then you can go out"
simon
Thermionic Monk Status
Posts: 5643
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#5 Re: Valve amplifier service

Post by simon »

Burnt bits was my thought too. Or possibly a blown cap though not sure why that would necessarily make it hummy unless it's a filter cap. Worn valves was my other thought as you say.
simon
Thermionic Monk Status
Posts: 5643
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#6 Re: Valve amplifier service

Post by simon »

IslandPink wrote: Sun Apr 02, 2023 7:39 pm There were both PP and SE. I think the SE was a parallel SE.
http://world-designs.co.uk/forum/showthread.php?t=7445
I saw that, also that it was PSE though I wonder if that was mistaken I'd.
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#7 Re: Valve amplifier service

Post by IslandPink »

Take your pick -
5881 I.jpeg
5881 I.jpeg (141.17 KiB) Viewed 16114 times
K5881 2.JPG
K5881 2.JPG (112.12 KiB) Viewed 16114 times
wadpse5881.jpg
wadpse5881.jpg (112.1 KiB) Viewed 16114 times
"Once you find out ... the Circumstances ; then you can go out"
simon
Thermionic Monk Status
Posts: 5643
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#8 Re: Valve amplifier service

Post by simon »

Ah right...
User avatar
andrew Ivimey
Social Sevices have been notified
Posts: 8315
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#9 Re: Valve amplifier service

Post by andrew Ivimey »

I was going to say what Mark said but I'm a bit busy and the schematics say all. Still the problem could be the same ( and fairly easy to get to the bottom...) but I dont live near Donkers!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
User avatar
pre65
Amstrad Tower of Power
Posts: 21397
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#10 Re: Valve amplifier service

Post by pre65 »

I did something similar a few years ago for a chap from Norwich. I got the build sheets from Greg, and gleaned a few upgrades and mods from the World Designs forum.

Upgrading the wire wound resistors to a higher wattage was one, from memory.
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Greg
Social outcast
Posts: 3201
Joined: Wed May 23, 2007 11:14 am
Location: Bristol, UK

#11 Re: Valve amplifier service

Post by Greg »

Yes, I can supply the full build instructions with schematics for all the three versions of the WAD5881 kits. Worth having as the diagrams posted by Mark above come from the DIY Supplement articles which were often based on the prototype build and sometimes changed when the kit was finally released.
Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?
Douglas Adams (HHGTTG)
simon
Thermionic Monk Status
Posts: 5643
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#12 Re: Valve amplifier service

Post by simon »

Thanks Greg, good to know.Let's see what bostod comes back with.
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#13 Re: Valve amplifier service

Post by bostod »

Here is an update based on the above advice and my skill level, or lack of it.
I have replaced all the valves both the small preamp and large power valves. This made no difference to the hum. To clarify the hum. When I switch on the amp it is very quiet. After about 15 seconds the hum gradually gets louder until it becomes consistent, that process taking a couple of seconds.
I've taken the bottom off and took a look. While I dont understand it at all, there was nothing obviously burnt out.
I have 2 sets of power valves. The new set that are in have had maybe 100 hours use so like new I guess

https://www.dropbox.com/s/nqkkyjo0izel5 ... 8.jpg?dl=0

https://www.dropbox.com/s/48c89rw4z0gvd ... 4.jpg?dl=0
User avatar
Greg
Social outcast
Posts: 3201
Joined: Wed May 23, 2007 11:14 am
Location: Bristol, UK

#14 Re: Valve amplifier service

Post by Greg »

It would help,to identify which version of K5881 you have. Easiest way is to check the small valves.
Mk1 has Valve 1, EF86. Valve 2, ECC83.
Mk2 has V1, 7025. V2, ECC83.
PSE has V1, 7025. V2, 6922.

It looks like the kit has the standard WAD upgrade components of Audionote Paper in Oil caps and Blackgate caps. Considering the kit’s age, the Audionote caps have got to be suspect.
Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?
Douglas Adams (HHGTTG)
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#15 Re: Valve amplifier service

Post by bostod »

Well mine currently has ecc83 in all 4 positions. Could that be the problem.
Post Reply