Heathkit S-99
 

Yes another Heathkit. I’ve had this ecl86 amp based on the Williamson circuit (so the manual tells me) for over 10 years being one of the first vintage audio things I picked up. As purchased it was cosmetically nice but a non runner on one channel. This was eventually sorted by me with some help (I can't recall the exact problem) and the amp sounded good and soldiered on a few years before developing a lot of hum and generally sounding tired. It was then put in the loft well wrapped and boxed for a rest for a few years. When I picked up a set of Heathkit Cotswold speakers locally for £30 it was always in my mind to get the S-99 back in action so I could “party” like it’s 1965. This time I did a full chassis strip down, I’d already replaced some of the caps when I got it so did all the rest bar the ceramics. The resistors were all individually measured (only 3 carbon comps were in tolerance) and replacements fitted. The pots were cleaned and the rotting foam behind the Perspex faceplate (which had turned to dust) replaced with pieces of stiff grey and black card from a local art shop. I can’t see a way to remove the marks left by the foam's glue as the paint is on the rear of the Perspex. There is a lot of desoldering in this project and the early PCB needs care not to overheat it as the tracks will lift. De-bugging the voltages were finally all good and within the tolerance set out in the manual. My one mistake was a couple of bad joints on a couple of the RCA input terminal resistors which had caused one channel to keep crackling and again go low output. The paint is original as are the valves...one of the reasons I didn’t want to strip this down for the transformers as so many of these are. Now it’s done it sounds really nice and better than when I first got it, no hum on the phono input until the volume pot reaches 12 o clock then it’s quite low. I’ve run CD's through the aux input to test and it sounds excellent but needs attenuating so that’s the next job. I have a soft spot for these green era Heathkit although this model really packs in the circuitry in a very small space particularly the preamp section.

Re: Heathkit S-99
 

A few more pics.

Re: Heathkit S-99
 

Nice one Mike
regards Trev

Re: Heathkit S-99
 

Well done. I've a couple of those amplifiers, one has been my main amp for a few years now.

Re: Heathkit S-99
 

Congratulations, nice work. Quite a rare amp these days I guess. Do you think it was originally built professionally by Heathkit, or from a kit by a previous owner?

Re: Heathkit S-99
 

Hi Phil
Definitely kit built as I got it with the manual many years ago complete with the original owners scribbles! It does sound really nice and fingers x’d since the last (hopefully final) rebuild it’s been 100% reliable and “quiet”. Since taking the pics I went back and swapped the polyester caps in the power amp section for paper in oil as it was sounding just a tad clinical. Changing those caps seems to have returned the tone I remember. I like listening to a lot of 60’s stuff and it just sounds right on this.
Best
Mike

Re: Heathkit S-99
 

Hi Phil
Definitely kit built as I got it with the manual many years ago complete with the original owners scribbles! It does sound really nice and fingers x’d since the last (hopefully final) rebuild it’s been 100% reliable and “quiet”. Since taking the pics I went back and swapped the polyester caps in the power amp section for paper in oil as it was sounding just a tad clinical. Changing those caps seems to have returned the tone I remember. I like listening to a lot of 60’s stuff and it just sounds right on this.
Best
Mike

Re: Heathkit S-99
 

I doubt my ears could tell the difference! Do you know what type of capacitor was originally supplied for those positions?

Re: Heathkit S-99
 

Hunts mouldseal paper types....I replaced the 600v polyester I’d originally used in these positions with some Hunts NOS “military grade” metal cased paper caps ...I tested these at working voltage beforehand for capacitance and leakage. I’m not into all the voodoo but it did seem to subjectively improve the mid range, can’t really explain it.
Mike