Isotek Substation ?

Hi i have just got hold of a used isotek substation. I have found an improvement in the sound stage.

After a week or so of use my amp has started humming (WAD Kat 6550 - with EH KT88s)

I am using it plugged into the 600 output but then when plugging back into direct mains outlet it still hums. Its not loud and doesn't increase with volume but still when listening at low levels i can pick it up.

Any ideas some damage maybe ?

 

What is the '600 output'?

The WAD will draw a lot of current - big tubes including valve rectifiers and it runs in class A. Perhaps it exceeds the current limit of the Isotek. Stick up a link to the Isotek if you can and lets see the spec.

 

http://cgi.ebay.co.uk/ISOTEK-SUBSTA...in_3?hash=item3eed195a30&_trksid=p3286.c0.m14

Thats the same station

ISOTECH SUBSTATION MAINS FILTER
WITH 6 INPUTS

2 ARE SHARED ISO 150
1 ISO150
1 ISO 300
2 FILTERED 6.3AMP

 

Hmm i guess i should try an earth spike grounding the chassis to it.

I know the sparky said our earth ohms are 100 should be 1 apparently

 

Chris, something else to check would be the condition of caps C1 & C2 that sit in the HT supply. These take a hammering in that particular circuit due to he high ripple from the 5U4G rectifiers and can start to hum after a couple of years.
C3 & C4 can also be replaced but come after the choke so benefit from lower ripple on the line, and last a good bit longer.
Gets hot inside that amp which doesn't help cap life either.

My humming 6550 fell near silent with a couple of Mundorf caps in there.

If the amp hums even when directly connected to he mains you've eliminated the Isotek.

 

Ok Rob will do need to find a circuit diag for the amp. I know its had several upgrades mundorf black gate and audyn. I might just replace the lot and start a fresh

Thanks for your kind help Rob

 

No problem - but start with C1&2 first as that is very likely the problem:

Schematics:

PSU:



Channel:

 

Cheers Rob

Do you still own your Kat6550 ?

 

I do Chris but don't use it at the moment.

Completely recapped it about six months ago when it started to hum like yours. Lots of AN & Jensen PIOs in there, plus Mundorfs for the PSU. Don't think it sounded any better for it, but it did stop humming

 

Rob

I was thinking (dodgy thing to do but hey)

Maybe i should take the PSU/transformers off the main chassis and locate them on a separate rosewood box type arrangement all correctly wired shielded and safely done. Wondering if this would help a good deal with heat and valve rattle also improving sound quality. What do you think ?

 

That could work Chris - sort of DIY BP

Something else to try is a layer of cork floor tile under the mains TX and possibly the choke.
The choke can buzz and get quite noisy but this is also a symptom that C1 & C2 are failing. Those caps form the initial filter before the choke smoothing, so if they deteriorate you get more ripple going through the choke, and it vibrates.

 

Ok Cheers Rob

I will order said caps on monday then draw up plans for moving the power plant over. Mean time i have fitted an earth spike and earth star then dropped the earth going to the mains.

Again thanks for the help !