K5881 Valve Amplifier

[RichW]

This is my first post so I would like firstly to say hello to all the forum members.
I work in electronics but I am ashamed to say that the use of valves were predominately over when I did my training many years ago.
So I decided to buy a WAD K5881 amplifier with the intention of learning something new or should I say old and use it to resurrect my interest in HiFi.
I believe the amplifier is a MK1 push pull.
Can anyone please provide me with a circuit diagram for the MK1 and MkII versions?

Thanks Richard

[FreddieT]

Hi Rich and welcome to the forum.

The K5881 is a great amp, I built mine 20 years ago and it is still just fine. If I was planning on using it in anger I might consider swapping the electrolytics in the PSU.

There is a quick way to tell if you have a MkI or MKII. If V1 is an EF86 pentode you have a MkI. If it is a 7025 (or equivalent) it is a MkII. The MkII is very sensitive. I'll have a hunt round for the circuits and the details and send them on unless someone gets there first.

It is worth considering a ground lift arrangement (to remove hum loops).

Enjoy!

F.

[bob orbell]

Hi Richard and welcome, sorry, I can't help you with this amp. but there are members who can, I think any of the moderators, Richard, Colin or John will help with a CD. BOB

[RichW]

Hello Freddie

Thanks for you reply.
The first stage is an EF86 so MKI and pretty much still original. There is hum on the right channel that I need to fix. I intend to go through the circuit with an audio signal generator and oscilloscope to make sure everything is how it should be.

Do you know whether a MKI to MKII upgrade has any advantages?

Need to get some suitable loud speakers to go with it also.

Rich

[colin.hepburn]

Originally Posted by RichW

Hello Freddie

Thanks for you reply.
The first stage is an EF86 so MKI and pretty much still original. There is hum on the right channel that I need to fix. I intend to go through the circuit with an audio signal generator and oscilloscope to make sure everything is how it should be.

Do you know whether a MKI to MKII upgrade has any advantages?

Need to get some suitable loud speakers to go with it also.

Rich

Hi rich
Welcome to the forum
I can help you out a bit with a tweak sheet for the amp plus schematic for the mk 1 and mk2 if you PM me with your email you may have to post up to ten post before you can PM me but don’t post your email on the forum for security reasons

[RichW]

Hello Colin

PM sent (fingers crossed)

Richard

[colin.hepburn]

hi Richard
email sent

[Richard]

Hi Rich and welcome. I've also sent some stuff so let us know if there's anything else you need and how it goes

[ZakB]

Hi Colin,

Could I possibly trouble you for a copy of your tweak sheet? Like Richard, I also have a K5881 mk1 that I've been looking to upgrade for years. I've finally got round to starting the job and would welcome any advice you have. I'm also looking for a copy of the original build instructions if you have any to see how the mk2 was laid out?

Any help would be much appreciated!

Kind regards,

Zak

[colin.hepburn]

Originally Posted by ZakB

Hi Colin,

Could I possibly trouble you for a copy of your tweak sheet? Like Richard, I also have a K5881 mk1 that I've been looking to upgrade for years. I've finally got round to starting the job and would welcome any advice you have. I'm also looking for a copy of the original build instructions if you have any to see how the mk2 was laid out?

Any help would be much appreciated!

Kind regards,

Zak

Sorry 5881 mk2 files no longer available Due to request from Mathew for info on WD/WAD mayj I sujjest contacting Mathew and checking out this link http://www.world-designs.co.uk/cd%20rom.htm