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Post by kettlechips on Jan 31, 2017 9:11:14 GMT
I acquired the amplifier from Martin T of this parish on Monday the 23rd of Jan 2017. KEL34 was a high quality integrated valve amplifier kit first launched in October 1998 by World Audio Designs (WAD). It was designed by Gary Devon, and uses two pairs of 6CA7 valves (an EL34 equivalent) in push-pull configuration. It was based on the famous Mullard 5-20 circuit design. Stated power output is 40W into 8 ohms. WAD no longer exists, but their successors; World Designs Ltd. are still trading, and similar kits can be bought from them www.world-designs.co.ukThe kit build had been started by Martin T several years ago, and he had populated the main board, and fitted the transformers to the chassis. My initial inclination was to complete the build as ‘standard’, and then later on perhaps install a few sensible modifications, upgraded capacitors etc. However, on inspection I noted that Martin had already replaced several capacitors, added some film bypass capacitors to four of the electrolytics, and had embarked on conversion to a power amp specification. Martin had also alerted me to patches of corrosion on the chassis in a couple of places, and the powder coating was bubbling in some other areas. It looks like this could turn out to be a little more work than initially anticipated. Oh well, I like a project! |
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Post by Greg on Jan 31, 2017 11:44:29 GMT
The designer was actually Andy Groves, AKA Gary Devon which is an anagram of his real name. He used this alias when he was moonlighting for WAD when at the time was in full time employment with Audionote.
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Post by MartinT on Jan 31, 2017 12:27:16 GMT
Sorry about the state of the chassis, Graeme. It had been in storage in three garages for around 20 years and suffered accordingly. I was hoping that with your access to spray painting it would be no problem for you.
It's a nice kit and my reason for abandoning it has nothing to do with the amp at all. My life changed at that point and I took a different (solid state) path to later success. I hope you have fun bringing the KEL34 to life!
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Post by kettlechips on Jan 31, 2017 14:01:10 GMT
Absolutely nothing to apologise for Martin! It is just my writing style - I was trying to create an interesting narrative. I have several more posts to come in a similar style...
I do indeed have access to spraying facilities, and the chassis are in the shop now getting their first coats of etch primer as I type. They will have to be painted around other jobs, but we are making progress :-) |
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Post by kettlechips on Jan 31, 2017 14:02:28 GMT
The designer was actually Andy Groves, AKA Gary Devon which is an anagram of his real name. He used this alias when he was moonlighting for WAD when at the time was in full time employment with Audionote. Thanks for that bit of info I did not know that! It just goes to show what knowledge there is out there. |
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Post by Sovereign on Jan 31, 2017 17:02:34 GMT
What a thoroughly decent thread.
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Post by MartinT on Jan 31, 2017 18:05:53 GMT
I think they need pictures - warts and all  |
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myles
Rank: Trio
Posts: 153 
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Post by myles on Jan 31, 2017 19:21:03 GMT
I think they need pictures - warts and all Agreed. An after picture is nothing without the before. Looking forward to this thread unfolding. |
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Post by kettlechips on Feb 7, 2017 11:20:43 GMT
Sorry, I've been struggling with putting pictures into the board. Seems like I had to join some photo sharing site in order to do this.... Anyway here's the picture that should have gone with the first post in this thread: |
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Post by kettlechips on Feb 7, 2017 11:25:26 GMT
Since Martin had already fitted some improved components, I now feel that I may as well continue down that route. It’s generally agreed the best practice is to build a kit in ‘standard’ form and get it working correctly, before doing any modifications. However, that does also bring a risk of potentially damaging the components, or the circuit board when making the changes. I have built several kits before, and have modified commercial equipment, so I feel I know the sorts of modifications and components that will work for me. I did some research, and WAD themselves issued an upgrade kit which could be added to KEL34. They even printed a review of the upgrade kit in HiFi World Supplement, June 1999 pp101-105. A full list of the component parts was published, so I think that largely following that route would be a good place to start. The upgrade kit involved replacing all the standard bridge rectifiers with Schottky or ultra-fast diodes, replacing four of the .47μF film capacitors with Ampohm paper in oil caps, replacing the cathode bypass caps with low esr Elna Starget’s, and replacing the standard 100k ohm pot with a Panasonic one. Unfortunately, some of the upgrade components that they used back in 1999 are no longer in production; the Ampohm and Elna Starget capacitors being examples, even one of the types of diode is now obsolete. If I build the kit as a power amp, then I won’t need the pot anyway, and the capacitors and diodes can be replaced by even better modern equivalents. My first step was to disconnect the board from the chassis, and remove all the hardware that Martin had installed. Sorry Martin :-) The chassis was then carefully cleaned and inspected. As this will be a power amplifier, I need to change the values of R28 and R29 from 1M to 100k. This takes into account the removal of the 100k pot from the circuit. WAD themselves made this change in several of their later kits, where essentially the same circuit was used for both integrated and power amplifier variants. e.g. KiT34/KaT34 and KiT88/KaT88. To aid channel balance, I will use 1% tolerance resistors for this job. For those interested, a copy of the circuit diagram for KEL34 can be found here. |
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Post by MartinT on Feb 7, 2017 12:05:54 GMT
I remember with the Leak Stereo 20 that Sanyo Os-Cons were very effective in the cathode bypass positions for lifting sound quality. Watch the voltage rating, though, as they really don't like over-volts.
EDIT: I understand that Os-Cons are now made by Panasonic. Also (but not quite as good) are Elna Cerafine.
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Post by kettlechips on Feb 7, 2017 12:16:32 GMT
Thanks Martin, I'm toying with Elna Silmic II's in that place, or Nichicon Muse. The chassis painting is coming along nicely, first couple of colour coats are on, and I hope to have that element completed by the end of the week.
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Post by MartinT on Feb 7, 2017 12:22:01 GMT
Yep, used both of those to good effect, too.
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Post by ChrisB on May 2, 2017 6:04:40 GMT
Is there any news on this project?
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