Kat6550

[Dave999]

Just a quick note
A Have a KAT6550 that i have owned since 2007. it was purchased off a gent called Stuart A who used to frequent this parrish.

it is an Ex WAD build service device. all standard parts apart from Mullard ECFs russian black plate rectifiers and Shuguang KT88s

as such apart from mechanical buzzing through the base plate from time to time it is and has been perfect..... I like it.

however the capacitors in the power supply have been there since day one and as i find myself at home all day every day at the moment, with time on my hands i thought they were due a refresh. Even just for piece of mind when valves and transformers cost a fair bit.
needless to say i'm not the type to spend £20 per capacitor...as such ebay turned up 4 decent, branded, low ESR 110*C capable capacitors for the main supply and i'm waiting for one for the heater circuit.

bit of fiddling, wrestled the old big electrolytics out, 2 over and 2 under the central tag board and they were replaced with the slightly longer but smaller diameter new ebay-fodder capacitors.

which i believe will be much the same quality or perhaps a smidge better than originals...

i'm not one for waxing lyrical about sound quality, poetry was never a strong point, but i can report that there is a noticeable improvement.. having spent my youth in a wind band backed by (literally in my case) full drum kit, percussion section and electric bass and guitar...drums are sounding pretty real to me....strummed strings stand out with their own melody or rhythm easily picked out and the bass lines are easily discernible. I like it and i am listening more. i would not have thought that the power supply had much influence on this amp...but one that works just a little better seems to have some benefit. its been a week now so i assume the aura of successful modification/restoration making me assume it is better becasue it didn't end in fireworks has worn off....

one thing to note my WAD built example doesn't follow the instructions for the main power amp tag boards in respect to spacing and positioning. everything is 1 tag out and on one board connections from the top side are made on the bottom..... beautifully mechanically connected and soldered but not exactly as pictured in the instructions....

so if you own a 6550 or similar that is getting on a bit..all of them i'd suggest. It might be worth spending a few quid on new capacitors for places where heat and high voltage could have degraded them a bit over the years.

i'm off to check ebay for bits of russian military 1960s tech, for my phono II.
ecc83s are too expensive, £40 per black nasty looking tube and some of the nice looking NOS must be faked, so some socket savers from china and some voskhod rocket tubes 6N2P-EV in manky old boxes might arrive. I plan an experiment with a slightly reconfigured pin out for the heater supply. i'll have to work out what to do with the in built shield.
It would be good to know if anyone has tried these, the guitar amp fraternity love them but i think what is hailed as good for a guitar amp is usually not that good for hifi.


Dave

[John Caswell]

Hi Dave,
There are some good ECC803s form J and the likes at reasonable prices that might be worth a look.

John