Supratek Owners Thread

Ah, I see,.. I’m pretty sure (without seeing a schematic) that cap is feeding a regulator used to increase the cathode voltage of the DHT. It has nothing to do with the filament V if this is the case. The circuit is direct/DC coupled between the 2 stages (sn7/DHT) and the DHT cathode has to be raised beyond what is naturally generated through the cathode resistor/current alone. That cap is not in the audio path at all and should have no noticeable effect on the sound (provided it is installed correctly and working as intended). Obviously in your case, with it being blown, it was effecting the reg that was helping raise the cathode V so yes, it would have thrown the circuit out of spec.
In regards to the transformers, Mick has been using them a long time and found they sounded more ’real’ than most anything else he has tried and lived with. I had the same misgivings as you at first when I realized what they were, very much wanting to see some ’boutique’ brand like lundhal, etc... I have listened to both and others at this point in my Cortese lcr as I couldn’t resist ’knowing’ for myself and being a constant tinkerer the swaps were pretty easy for me. If it makes you feel any better I ended up with the Blue Talema’s back in there at the end of it all. I felt they really provided a more natural presentation of the music. Everyone hears different though. You very well may like a slightly different sound/presentation that swapping them will provide. I do think that if you make the change you will realize with a little time that the Talema’s are really spot on and excellent when used with Mick’s specific circuits. Best,

Thanks @jslateiv for your feedback. Indeed the electrolytic caps are not on the sound path as they are coming from the 5V DC regulator. These are the Panasonic 10000uf. My guess is they are used for smoothing the DC from regulator. Nonetheless I replaced them with similar equivalent.

Very interesting that you tried different set of transformers. What did you try and was it a drop in replacementm? I might try a set of Hashimoto with similar ratio.

DC after the reg is already smooth. (that's what the reg does, ;-)) those 10Kuf help knock the ripple down before the reg so it doesn't work as hard and produce as much heat.   Again,.  I suspect it is tied into the supplemental V circuit used to boost the cathode V,.   Anywho,  sounds like you got it sorted and working.

I try all kinds of different configs, including messing with and adjusting the feedback..  can't help myself.   Lundhal,  Jensen, some hammond are what I've tried,  some with air gaps, and some without (purpose built for parafeed).   4:1 and 8:1 ratios are what you need to look for. I  prefer the 8:1 as the circuit already has alot of gain.   Keep in mind that these are configured as parafeed (no DC current) so you don't have to worry about any dc current spec on the tranx.   Unfortunately don't have any of the really nice trans like hashimoto, tango, etc..  laying around to try.  Honestly though i doubt I would like them enough more to justify the cost but ya never really know till ya try,.  plus most of those are all big units with air gaps which are not needed..   Anywho,.  feel free to PM if you have any specific questions about the circuit,  I'll try to help the best I can.  Don't want to continue to junk up this thread with repair related posts..  Best,

Thanks @jslateiv. This indeed matches my guess. Let's talk separately with mod ideas. :)

Well Mick sent me a new power supply and it still hums. I tried without umbilical cord and a new tube and it still hums. I am so disappointed because I love the sound of the preamp but the hum is driving me crazy. I can hear it in the speakers and I hear it if real close to the power supply. Any suggestions what I should do?