Lowering feedback, KiT/KaT88 and KeL 34

[Greg.]

Please could someone (Richard/Neal?) refresh my memory. I am currently doing some work on a pair of KaT88's. The owner has asked me to introduce the reduced feedback mod. I remember I didn't do this on mine because I did not upgrade to the Sowter O/P Tx's which I think at the time was part of the mod consideration. Is this still a mod worth doing if the standard WAD Tx's are used?

Best wishes,

Greg

[John Caswell]

Hi Greg,
Look in the FAQ where there is a heading for lowering feedback on KiT88 etc etc.

John aka Dr John

[Greg.]

Hi John,

Exactly. Read the FAQ and references are to outcome with Sowter Tx's and I'm not clear if this is Sowter exclusive or also applies to amps retaining the original stock Tx's. It doesn't alter my question. if using the original Tx's, is reducing feedback a worthwhile mod?

Best wishes,

Greg

[prince of darkness]

The FAQ section actually gives details for the standard transformers, with capacator values for Sowters in brackets.

[John Caswell]

Hi Prince and Greg,
That's how I read it, component changes for both standard and Sowter txs.

Regards

John aka Dr John

[Greg.]

Hi John (picked up your phone message, thanks) et al,

I've now read thoroughly. My oversight, although I have this nagging recollection that when I had the KaT88, I made a specific decision not to introduce the feedback mod, but for the life of me I can't recall what my reasoning was at the time and I was wondering if anyone can remember the old discussions we had on the WAD site and drop a hint to restore my memory.

Best wishes,

Greg

[Richard]

Hi Greg

This one was my choice after trying the ones listed (and no fb at all),

"680R at R38/39 with 680R cathode to ground and 2n2 cap Kit88/KEL34 (2n7 Sowters) gives 17dB fb"

Downsides to the mod are less bass control and f bandwidth, and an increase in noise, distortion and sensitivity by the same dB amount as the reduction in fb. Upside is an increase in stability margin.

Perhaps it was the bass control issue?

Rich

[Greg.]

Hi Rich,

Yes, that's it It was the bass control issue which at the time troubled me because my KLS3's were inclined to be bass heavy. I've done stuff to them since and now wouldn't hesitate to try the mod. Good news. Thanks Richard for bringing it all back to me. Actually, the whole thing is a rediscovery experience. I've not looked at KaT88 for a few years and now I'm confronted with a pair that need a little fettling. I'm enjoying re-aquainting myself with the design and also a read of all the printed copies I made from the original WAD threads. What a value that has turned out to be.......you seem to feature in most of it

Best wishes,

Greg

[Richard]

Hah, yes, spent a few hours on those didn't we all! Be interesting to hear what you make of them after fettling compared with your 300BPP Greg. Can be good to re-visit. I find things often snap into place aurally - like standing back to look at a picture rather than eyeing it very close as you might if you were working on it, or too familiar, - err.... pretentious - moi??!!

Rich

[Black Stuart]

Never Richard,
good insight I say.

Black Stuart