Valves, I think I'm starting to understand what the fuss is about.

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Originally Posted by tubehunter

Hi Dave


No I didn't build this one, but have built this model before.
The amp is fairly old and I just replaced the psu caps.Think I upgraded them and increased the capacity.

Yes valves are the only valid way of enjoying music.

http://i514.photobucket.com/albums/t...0/IMG_5602.jpg

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Hi Duncan, thanks for the info. That's a lovely photo. I love the blue glow, very sexy.

I've had a look inside and I can see that it's the original spec with the exception of the power caps. I'm starting to make a list of tweaks starting with the power amp conversion. I'll then probably try new coupling caps.

I noticed that the ECF80's have a non-regulated DC heater supply and the EL84's an AC heater supply. Does anyone think upgrading either of these to regulated DC might provide any benefits? Other than that I've read that the cathode caps can be upgraded along with a few of the other caps. Feedback can also be reduced but I don't know what difference that will make. Then of course I could try upgrading the valves but as the current ones a new I'll probably leave that for a while.

I think I'll just gradually try a few of the above and see what improvements can be made. It should be a good learning process.

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Originally Posted by Ali Tait

I found it very worthwhile changing the coupling caps im my KEL. Easy to do and makes a big difference IMHO. I put ClarityCaps in mine when I had it, and I found them a big improvement. Not expensive either.

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Thanks Ali,

I've heard ClarityCaps are supposed to be good. Mundorf Supreme's (non silver) are also supposed to be good vallue and I've seen some Russian Teflon caps on ebay that aren't too expensive. I know Teflon caps are theoretically the best but I don't know if they'll be any better than polyprop's in this application. :scratch:

Beware, badly done DC heating can do more harm than good.

DC heaters should only realy be necesary when the gain of a paticular stage is so high[ phono stages etc] where the AC heater noise/hum can be a problem, beware though as standard DC heating ie; with no means of reversing the voltage polarity can cause premature loss of emision.
output valves in a push-pull design rarely need their heaters DC'd due to natural cancelation of hum within the push-pull operation.
as for coupling caps, if the circuit has been designed properly then polyprop caps should be all thats needed.
Good power supply caps are a must, rectifier diodes can also have quite an impact on sonics.
Anthony,TD...

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beware though as standard DC heating ie; with no means of reversing the voltage polarity can cause premature loss of emision.

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Not saying you are wrong, but how does that occur with an indirectly heated valve?

6.3v was originally the heater voltage for DC heated valves after all (3 Lead Acid cells 2.1 * 3 = 6.3v)

Thanks chaps. Very interesting stuff.
I understood most of what you said Anthony with the exception of this bits about polarity. I knew there was difference in the way some valve needed to be heated from the point of view of direct vs indirect, current source vs voltage source but I don't understand how polarity comes into this. My knowledge on this subject is quite limited. Would you be able to explain a bit further?

I think all the valves in the KEL84 are indirectly heated. It has 2x ECF80 and 4x EL84. What heating method would you use with these valves?

Here's the schematic (page 6): http://www.world-designs.co.uk/acatalog/kel84.pdf

Cheers. :cool:

What valves are in it Dave?

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Originally Posted by Ali Tait

What valves are in it Dave?

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See my last post, second paragraph. ;)

I know what valves are in it, I used to have one!

I meant what make. :lol:

jj el84, mullard ecf80

Doh. :doh: Sorry.

ECF80's are Mullards. I'm not sure when they were made.
EL84's are the standard JJ's.

What makes did you find gave the best results?

I fancy trying some E80CF's and maybe some Shuguang Psvane EL84's but they're all a bit pricey. Which I don't mind if they're quite a bit better but that's the bit I don't know. :scratch:

Cheers.