Rexton's Valve System - Upgrade Blog

[Wakefield Turntables]

Its been a while since I updated this. My mine power amp is a Sondex S100 which is basically the last iteration of the Radford STA 100 power amp. I bought this quite some time ago but have never really got around to spend much time or money on upgrading the old beast until now. I've always had a slight hum in the background and have discovered that the amps left channel is suffering from a loose connection causing a hum. The right channel is perfectly quite so I decided to have a look under the hood of the amp to discover some pretty poor wiring the RCA sockets. Mainly very ancient tinned copper wiring. I don't usually subscribe to FOO but tonight I decided I better order a few parts as I think the S100 with the correct fettling is probably going to be as good as anything out there using a KT88 valve. At this moment in time I'm not really bothered moving upto the bigger KT120's or 150's, maybe at some point in the future but I'm happy with what I'm hearing through my Tannoy's at the moment (apart from the hum)! I decided to order top range kit for the amp so I went for some of these.

Pure copper FURUTECH IEC with 24K gold plating. Sure I could have had a pure silver one from IEGO but couldn't quite justify that much FOO!

iec2.jpg

WBT binding posts and RCA's, these are a known tried and tested entity which I have installed on my CROFT preamp.


BINDINGS POSTS.jpgWBT RCA.jpg

I intend to rewire the RCA's with solid silver in teflon and shortening the signal path bewteen the RCA the PCB. The RCA's on the S100 are hopeless and quite loose, probably where the hum is being generated. I also tightened up the screw holding all the star earthing in place and also reattached the left channel RCA, the hum, whilst still present is slightly better I can notice a little difference in the clarity of the Jazz I'm currently listening to. I'm going to be having a serious think about having the amp overhauled at some point in the new year. In the mean time I'm going to be pulling the trigger on a quad of these :-

GL-KT88_Genalex-GoldLion-KT88-1.jpg

Supposedly the best sounding KT88 kicking around at the moment. The S100 has had SOVTEK, and TAD which were ok but not as good as the current JJ KT88's. This sure beats fettling a Lenco!

[brian2957]

This sure beats fettling a Lenco!

Sacrilege young Andrew Lencos are the holy grail of fettling . Not that I've ever done mine you understand

[Wakefield Turntables]

This sure beats fettling a Lenco!

Sacrilege young Andrew Lencos are the holy grail of fettling . Not that I've ever done mine you understand

Well I am on a "break" from the Lenco. It's getting near Xmas and I like to usally hunker down with a project until the weather turns or the days get a little longer!

[brian2957]

Aye , know what you mean mate . In the last few years I've really grown to hate the short days and the Scottish winters

[Wakefield Turntables]

I've had a little time to myself so I decided to get the Sondex fettled.

Firstly I removed the hopeless RCA's that Sondex installed and fitted something that WBT produce .

rca.jpg

Here's a picture of the new RCA's installed. These work really well with my MG cables.

back2.jpg

I changed the RCA's tinned copy multi-strand wire for solider silver in Teflon. I also took the opportunity to try and shorten the signal path.


rca.jpg

Finally and true to my word a Quad of matched Gold Lion Genalex KT88's. I have also removed the horrid cage from around the amp, I'm not a very big fan of excessive components and can't bare to think of all the excess vibration rattling around in that thing.

amo2.jpg

I'm now looking into getting the terrible binding posts removed. They are a horrible design which relies on several nuts to keep both the binding post and speaker termination attached together. The speaker cable inside the sondex is quite heavily oxidised tinned multi-strand copper. The binding posts can be easily improved upon and I'm looking into getting some WBT jobbies

BINDINGS POSTS.jpg

I'll also be replacing the tinned copper wire with solid core 2mm silver in teflon, again looking to try and shorten the signal path if possible. I'm now in the process of researching components for a complete recap and rebuild of the PCB's.

The RCA mods have worked quite well and I'm already finding more detail coming through the Tannoys, the WBT RCA's also offer betting earthing than the Sondex offerings so I'm hearing less transformer hum through the Tannoys. So all in all quite a decent afternoons work.

Stay tuned...

[Jimbo]

Andy could you pop a picture up of your mega modded Croft with internal pics? Would be a Christmas treat for me.

[Wakefield Turntables]

Andy could you pop a picture up of your mega modded Croft with internal pics? Would be a Christmas treat for me.

There is a link here https://theartofsound.net/forum/show...ht=croft+epoch

I intend taking both the Sondex and the Croft to Alan (Firebottle) for even further modification. I'm think Dual mono power supply and valve regulation and any additional mods for the Croft. The Sondex will need a lot of work. I've noticed some very very old caps some with tolerances of 50% . It looks like someone did a little work recapping the two main channel boards some time ago with cheap RS component caps and resistors. I've already decided which valve bases I want and I'm currently researching resistor types, I've seen several brands at offering various tolerances ranging from 0.01%, 0.5% and 1%. Interesting times!

[brian2957]

Nice work Andy

[Jimbo]

There is a link here https://theartofsound.net/forum/show...ht=croft+epoch

I intend taking both the Sondex and the Croft to Alan (Firebottle) for even further modification. I'm think Dual mono power supply and valve regulation and any additional mods for the Croft. The Sondex will need a lot of work. I've noticed some very very old caps some with tolerances of 50% . It looks like someone did a little work recapping the two main channel boards some time ago with cheap RS component caps and resistors. I've already decided which valve bases I want and I'm currently researching resistor types, I've seen several brands at offering various tolerances ranging from 0.01%, 0.5% and 1%. Interesting times!

Thanks Andy, dual mono sounds good plan.

[Wakefield Turntables]

Nice work Andy

Thanks mate!

Thanks Andy, dual mono sounds good plan.

Well that's what Glenn seems to suggest.