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  #1  
Old 2nd May 2021, 12:59 PM
tonyo tonyo is offline
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Default Kit 6550 refurbishment, guidance please. Help

Hi,
My first time finding this forum, hello everyone. (thank you to Matthew, I'm very pleased to have read though what I can find)

I have pulled my Kit 6550 out of retirement (13 years under a bed due to young hands damaging valves) alongside my Nkoe Tjoeb 4000. It will be driving PMC FB1's of the same retirement vintage.
This amp was built exactly to spec in 2002, and was used for probably a couple of years. It is going to need cosmetic work and electrical work.
For a start I have some corrosion in the ECF80 valve bases, that will need replacing.
I powered up the amplifier for the first time a couple of weeks ago and was gently reminded of one or two of the few probelms it had : rectifier valve flash over, and quite a physical hum from the power supply. Both of these points had been there since new.
So: I'm going to bite the bullet and refurbish, as a welcome therapeutic project.
All of my three tag boards are working as far as I can see. The laminations on the transformers need to be cleaned and repainted, along with the case. So the whole amplifier is going to be dismantled, and rebuilt from scratch. Orignal tagboards removed (kept safe)and replaced with a new builds.

Here are my plans: please feel free to point me in better direction
1.I have a complete set of Kiwame resistors purchased from Octave electrical in Malaysia in 2002 that I never got to trying out: are they worth building with , considering 20 years ago they were quite respected. Have they been superceded by a different philosophy?
2. PSU capactor upgades, to tackle the hum.
3. ECF80 heater supply: bridge to be replaced with fast diodes.
4. Consider 622S/EY500 recifiers, or at least series anode resistors to 5U4 if not changed.
5. Capacitor upgrades throughout. This is the can of worms I know. This is where your advice will be really appreciated, as I don't really want to spend a fortune if not rquired, but happy to buy right to start with. I was intending years ago to buy WAD upgrade capacitor kis of Jensen PIO and Blackgates, but did not get that far.
6. Alps volume pot (or what else?): possibly shunted through a metal film resistor. Again thoughts please on this resistor if I go this route.
7. I've quite a lot of silver wire (from 20 years ago): If I am rebuilding from scratch, is it really worth wiring the signal path with silver?

I'm not in a rush, so I expect my plans will alter daily until I actually do it, then as you know they can change again. I'm not over concerned with some expensive components if they justify the cost, but buying 'snake oil' audiophile named components for the sake of it is not on the agenda.
Valves: I appear to have quite a collection I don't remember purchasing.
I've various ecf80/e80cf NOS (mullard ecf80 were my first choice) and three sets of 6550. Ive a matched quad of Svetlana, and ElectroHarmonix. Were the originals Sovteck as supplied by WAD?
Thank for your thoughts
Tony
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  #2  
Old 3rd May 2021, 06:56 AM
bob orbell bob orbell is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Welcome Tony, what you are suggesting, will in my opinion change the sound of your amplifier dramatically and not for the better, I think if you do all these resistor/ capacitor/wire changes, the sound will be too much in your face and become very tiresome to listen to, I would suggest simply recommission and then attend to hum problems first. Bob
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Old 3rd May 2021, 10:56 AM
tonyo tonyo is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Hi Bob: on contemplating I think this is good advice thank you.
Itís been many years since I heard the amplifier in action at the moment Iíve no idea of itís sonic signature, although I was very enamoured with it except itís physical hum. The flash over problems I think need to be addressed at this point I think? Iíll rebuild it after cosmetic work as it is, except with maybe the PSU electrolytic capacitors replaced, and then go from there.
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Old 3rd May 2021, 02:13 PM
bob orbell bob orbell is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Tony, there is information in the FAQ about rectifier flash over, it is a simple fix. Bob Rectifier Flashover WAD Kits 34, 6550, 2A3
FAQ Team
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  #5  
Old 3rd May 2021, 07:23 PM
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Greg. Greg. is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Here’s the FAQ link Bob refers to.

http://www.world-designs.co.uk/forum...ead.php?t=3859

Last edited by Greg.; 4th May 2021 at 09:13 AM.
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Old 4th May 2021, 10:58 AM
tonyo tonyo is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Many thanks for the heads up. I hadnít seen the FAQ, phone browsing not great sometimes for the internet. Resistors on the way. eBay useful on occasion.
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Old 5th May 2021, 12:52 PM
John Caswell John Caswell is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

I put forward the 6D22S mod for the 5U4 as they are getting stupidly expensive.
I use the 6D22S in my GEC 88/50 and they are certainly bomb proof as well as cheap ( I like that) and run very well on 5Vac.
With regards to the rebuild I would build as standard and then change components one by one, that way at least you know what you like/what has gone wrong.

John
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Old 6th May 2021, 08:01 AM
Richard Richard is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Quote:
Originally Posted by John Caswell View Post
I put forward the 6D22S mod for the 5U4 as they are getting stupidly expensive.
I use the 6D22S in my GEC 88/50 and they are certainly bomb proof as well as cheap ( I like that) and run very well on 5Vac.
With regards to the rebuild I would build as standard and then change components one by one, that way at least you know what you like/what has gone wrong.

John

John's mod is in the FAQ here,


http://www.world-designs.co.uk/forum...ead.php?t=7971
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  #9  
Old 6th May 2021, 05:20 PM
John Caswell John Caswell is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Ta Richard,
I always forget to add the link to help others.

John
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  #10  
Old 7th May 2021, 03:37 AM
tonyo tonyo is offline
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Default Re: Kit 6550 refurbishment, guidance please. Help

Thanks gentlemen, first the rebuild as standard.👍
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