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Old 12th November 2016, 12:19 PM
snowman_al snowman_al is offline
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Default Another WAD KEL84 Rebuild

Hi everyone. New to this forum, but I have been a frequent visitor before.

Very recently acquired a 'pre-loved' kit built WAD KEL84 that dates from about 2003 I guess (transformer codes 01/03). It has had the Jensen and Black Gate capacitor and Alps pot upgrades at sometime too.
It is working and actually sounds pretty good. Surprisingly quiet, solid bass, sweet mid, but a touch of shrillness to the very top end.

So one or two problems to sort out.
First - The input wiring, is thin grey screened stuff. Several of the RCA end connections have fractured and are floating free. Then there has been 56k resistors added to the pot (ground to wiper so not an attempt at a shunt mod)? and is generally a bit un-tidy.
Second - There is a track to one of the cathode bypass resistors lifting, but is repairable. 3 or 4 resistors have drifted in value, so will need repacement.
Third - The mains transformer humzzz. Even unloaded I can hear it 20 feet away... It does not have much clearance from the chassis, certainly less then 1/2mm, so something else to play with.

My intentions are to get used to it as it is for a while, and fix the immediate problems, input wires, pot etc.
The PWBA will have to come out at some stage to replace the 270 ohm cathode and 100K anode resistors. So I will probably replace the rectifiers for Schottky and fast recovery types too.

So a few questions to all of you who have already been on this path:
What it current the flavour for input wiring types, are the Black Gates and Jensens still liked or should I replace them with something else? Nice smooth treble if possible
I can fix the PWBA, but is there any benefit in the new version 3(?) one or is it even available as a spare? Transformer hum fixes?

That's enough for now, thanks in advance, Alan
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Old 12th November 2016, 04:51 PM
bob orbell bob orbell is offline
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Default Re: Another WAD KEL84 Rebuild

Hi Alan and welcome, the thin grey cable is what was supplied with the kit, it is OK but some like silver plated cable, I don't, too bright sounding, Van Dame do some nice cables, you can get from Maplin, but don't go over board, the resistors on the pot wiper suggest it may not be a logarithmic pot, they are there to achive law facking. Under the power transformer, there should be 4 small plastic washers, to insulate the transformer from the chassis, are they present?, if they are then you have a noisy transformer, . The PCB is available from our admin, Matthew, and is much better than the old WAD one, I recommend it as you have the option of individual diodes or bridge packages, and the copper tracks are much larger. There is a post on one that I rebuilt, using a new board. BOB
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Old 12th November 2016, 08:28 PM
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Phil Y Phil Y is offline
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Default Re: Another WAD KEL84 Rebuild

Hello Alan,

I think quite a few people, me included, had mains transformer buzz with this amp. Basically, you need to isolate the Tx from the chassis. It makes the chassis shake and this in turn makes the shelf the amp is sat on behave like a sound board. I ended up mounting mine with grommets in the chassis, with nuts keeping the Tx stack tight, sat on the grommets and then a set of nyloc nuts inside the chassis holding it all in place. Like this, mine is quiet and can only be heard from very close range.
I believe that WD changed the kits at some point to include some sort of isolation so it may be worth talking to Matthew at WD HQ.

If you do this be sure to include an earth connection to one of the bolts as the Tx will no longer be connected to the chassis otherwise.

For coax I used some Shark Wire from Maplin which sounded a lot better than the standard stuff but was fairly cheap. I don't have the number handy but it was single core with clear insulation.

Black Gates are still highly regarded. Are the Jensen caps "paper in oil" ? If so, keep an eye on them as this type can be unreliable, going (electrically)leaky with age and causing problems.

If you decided to upgrade resistors, and you like a warmer sound, stick with good carbon types like Kiwame or Takman. In my opinion, Tantalum film and metal film have a bright, rather forward sound which I don't like but this is personal taste and you will find those who say otherwise.

I'm not sure what is causing your shrillness as the amp certainly does not have a reputation for that sort of sound.

Phil.
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Old 13th November 2016, 11:13 PM
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Shane Shane is offline
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Default Re: Another WAD KEL84 Rebuild

Having just been down the same route as yourself, I would strongly recommend getting a new PCB from Matthew. It's not expensive, and if you approach it logically it's pretty straightforward. The new board has a slightly different layout to improve the earthing arrangements but the components are the same so it's a direct swap. The main reason for doing it it that the current board is of far higher quality than the old one and is much less likely to suffer from track failures.

As for the input wiring, unfortunately you can't use the current relay switching board since your amp has more sockets, with different spacing between them, being fitted with tape inputs and outputs to allow off tape monitoring. You could rewire with better quality cable although space is limited, our you could do what I did and try building your own relay board with vero-board. Took a bit of head-scratching, but ultimately worked a treat!
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Old 14th November 2016, 06:53 PM
snowman_al snowman_al is offline
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Default Re: Another WAD KEL84 Rebuild

Hi guys,
Thanks for your input.

Spent an hour or so over the weekend experimenting with the buzzy mains transformer and have made good progress here.
First it has the hard white plastic locating washers installed, but they are crushed near flat. I guess in an attempt to clamp the laminations? So I tried to raise it off the chassis onto various thicknesses of rubber grommets and that made it even worse!

Next I took all 4 bolts out and the end cap off to see if the laminations or bobbin was loose. No, they are well impregnated and totally solid.
Just resting the naked transformer on the chassis results in near silence (you cannot hear it at 12 inches away anyway) and the very slight mechanical vibration had totally gone. Excellent, at least the transformer itself is quiet.

Placing the end cap back on though, even clamped tight, immediately brought the mechanical vibration back and half the noise. So now I've made a thin oblong plastic washer to fit between the core and end cap. Not sure if this provides a mechanical isolation or a magnetic one, either way, it works.

If I rest it on the thin grommets now, it is silent, but as soon as I put all the bolts back through the chassis some noise returns depending greatly on how each one is tightened... The bolts are a tight fit in the chassis though, so I intend to open the holes up and maybe fit the grommets into the chassis when I have it stripped down.

Yes I agree, best to replace the PWBA, I've sent Matthew a PM.
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Old 15th November 2016, 01:05 PM
John Caswell John Caswell is offline
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Default Re: Another WAD KEL84 Rebuild

Hi,
Absolutely no reason why you cannot use the Pre 3 relay input PCB, just mount it on short 20SWG wires soldered to the phono sockets. This reduces the wiring "mess" drasticallyAlso mount the relays in standard DIL IC sockets.

John
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Old 15th November 2016, 08:36 PM
snowman_al snowman_al is offline
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Default Re: Another WAD KEL84 Rebuild

Investigated the volume pot this morning.
Found not just the one resistor in there (56K ground to wiper) but another 42K from wiper to R4/5. So looks like an attenuator, but the with the 56K resistor the wrong side of the 42K. Anyway they are gone.
Tried it as 'normal' and then tried the 'shunt' mod. That's a keeper.
The volume pot is pretty battle scared (100K) is there any benefit in using a 50K pot, with 47K resistor? Or even 20K pot 18K resistor. This is never going to be driven by a high impedance pre-amp. (Just CD player, transistor phono stage or Squeezebox.)

I've ordered some longer bolts (55mm M5) so I can mount the transformer on grommets and also contacted Matthew. Looks like a new PWBA and Relay Board then...

Again thanks everyone for the advice, Alan
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Old 15th November 2016, 11:35 PM
John Caswell John Caswell is offline
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Default Re: Another WAD KEL84 Rebuild

Hi Alan,
Stick with a 50K pot and a 47K series R, that will give you a fighting chance being medium-ish impedance.
When rebuilding on the new PCB, do not bend the component wires more than 10 just enough to hold them in place, space the power type resistors at least 10mm away from the PCB, use enough solder to fill the joint but don't overdo it.
Any problems ask back here.

John
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Old 16th November 2016, 12:50 AM
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Phil Y Phil Y is offline
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Default Re: Another WAD KEL84 Rebuild

Just a quick one, what does PWBA stand for?
(I know Alan is referring to the PCB)

Phil.
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Old 16th November 2016, 08:04 AM
snowman_al snowman_al is offline
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Default Re: Another WAD KEL84 Rebuild

Printed Wiring Board Assembly. (Sorry I worked for two American companies for over 35 years...)

And as it's a bare board it should be just PWB. Alan
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