6550 upgrades

[Revoli]

Originally Posted by Richard

Hi,

I've heard this amp at home quite a bit. I feel it's in the likeable and easy-going class, rather than sparky and up-front, and changes will really depend on how you find it.

Personally I'd want to liven it up a bit. There was a WAD supplement with upgrades Jan 2002 which was really just an upgrade kit of Alps pot, Jensen PIO coupling caps and BG cathode bypass caps for the 6500s. You could try that. I've used those parts in various amps and they do change the sound but not in the direction I'd take with this amp.

So, very much personal opinion but this would be my route,

Shunt pot volume control Alps 50k with 47k metal film series resistors see faq

C11/12/13/14 to Soniqs SAX 630v 0.47uF

C9/10 to Oscon 1000uF 16v RS 651 6056

C15/16/17/18 to Rifa 100v 100uF RS 226 7047

C3/4 to Rifa 450v 150uF RS 434 0964

I'd also add balancing resistors to the rectifier anodes; disconnect the wires at pins 4 and 6 of both rects and remake the connections with a 47R 3W ww series resistor in each, see the faq, and upgrade the ecf80 heater supply with schottkies and pi filter, again in the faq.

Valve-wise I recently heard a set of Russian Gold Lion KT88 against Svet 6550C (which I like very much) and was very impressed by them. Cleaner and more sparkling than the SV6550s, but not overly so, and more natural than the JJ KT88s which were a little too "hifi" for me. ECF80's would be worth changing to Mullards or another good nos type as the supplied EIs can be a little variable.

Richard

Am interested in the shunt pot upgrade as my current pot in Kit6550 is misbehaving. Was not obvious to me how to achieve and FAQ does not seem to have details. Can you or anyone else give more info on this please. I will take as much detail as poss as although built 6550 I am no subject matter expert! Thanks.

[Richard]

Hi,

Here;'s the FAQ article

http://www.world-designs.co.uk/forum...ead.php?t=5795

which gets a bit involved but really all you do is get a couple of metalfilm resistors of a similar value to the pot you're using (or a little less) and rewire the pot as shown.

For 50K pot use 47K, for 100K pot use 91K or 100K.

The FAQ also shows a practical way of doing this using a bit of Verostrip from Maplin as it is an easy mod, and most pots have similar layout of the terminals, but wiring pots is fiddly due to often big wire and small terminals!

[Revoli]

So that is literally a mod to existing pot? Had it in my head was a different pot. As I am replacing pot anyway are there any that have been popular/ better quality that people have used? Thanks for this.

[Revoli]

Sussed this now. I was thinking of the stepped attenuator approach but having read the forums on this topic will stick with the alps D wired config

[BOONDI]

Originally Posted by Revoli

So that is literally a mod to existing pot? Had it in my head was a different pot. As I am replacing pot anyway are there any that have been popular/ better quality that people have used? Thanks for this.

I believe this method can be used to improve almost any standard pot to decent quality levels.

Decent quality older pots can be salvaged from old amps, cleaned up and then used in shunt mode to give sound quality to rival Alps blue. Older Alps pots are very good for this. As used by many a far east manufacturer in the late 60's and 70's.....

DIY free parts.... Recycled is good....