montesquieu
28-03-2016, 20:16
DHT preamps are a fascinating topic, almost a holy grail of preamps - a single gain stage, one directly heated triode in the audio circuit, dead simple, all the juiciness of a single ended triode circuit, in a preamp rather than a power amp. The trouble is that they tend to be microphonic and are quite difficult to implement - I had a DIY Audio Supplies Tram2 for a bit (which used 45s or 2A3s in the gain circuit) and it was in turns both glorious and maddening.
While I was waiting for Will of Radford Revival to do my preamp build, I picked up this DHT pre, and fairly quickly sent it off to Ampregen (Valvebloke) for checking over and for attention to microphonics. He made various mods to it, including ensuring it ran at UK voltage, met CE requirements for earthing, and he also replaced/upgraded a few components along the way.
The result is quite a lovely thing for the money, with quite a lot of character.
The original listing is here:
http://www.ebay.co.uk/itm/Sheer-Audio-DHT-01A-Direct-Heat-Triode-Preamplifier-/252307058580
I spent £290 on the amp, another £55 on postage, £60 on VAT, and another £60 or so on spare tubes (I have a spare set of 12As, and three spare rectifiers - the tubes are available it seems despite being from the late 20s/early 30s - though the power tubes run quite cool so I'd expect them to last a very long time), plus tube dampers - the rubber rings are cheap but I’ll include a pair of the remarkably effective Herbies tube dampers as they damp out any last traces of microphony. So including the time spent by Valvebloke, it owes me altogether well over £500. I’ll let it go for £300 collected, or courier at cost (though I’d much rather go collection).
BTW I did report on this before:
http://theartofsound.net/forum/showthread.php?42136-Sheer-Audio-DHT-01A-preamp-bit-of-fun-from-Taiwan
http://i1181.photobucket.com/albums/x440/montesquieu61/pre1_zpsxv76o9wd.jpg
http://i1181.photobucket.com/albums/x440/montesquieu61/pre2_zpsc6wbgnvb.jpg
http://i1181.photobucket.com/albums/x440/montesquieu61/pre3_zpsm3abilop.jpg
While I was waiting for Will of Radford Revival to do my preamp build, I picked up this DHT pre, and fairly quickly sent it off to Ampregen (Valvebloke) for checking over and for attention to microphonics. He made various mods to it, including ensuring it ran at UK voltage, met CE requirements for earthing, and he also replaced/upgraded a few components along the way.
The result is quite a lovely thing for the money, with quite a lot of character.
The original listing is here:
http://www.ebay.co.uk/itm/Sheer-Audio-DHT-01A-Direct-Heat-Triode-Preamplifier-/252307058580
I spent £290 on the amp, another £55 on postage, £60 on VAT, and another £60 or so on spare tubes (I have a spare set of 12As, and three spare rectifiers - the tubes are available it seems despite being from the late 20s/early 30s - though the power tubes run quite cool so I'd expect them to last a very long time), plus tube dampers - the rubber rings are cheap but I’ll include a pair of the remarkably effective Herbies tube dampers as they damp out any last traces of microphony. So including the time spent by Valvebloke, it owes me altogether well over £500. I’ll let it go for £300 collected, or courier at cost (though I’d much rather go collection).
BTW I did report on this before:
http://theartofsound.net/forum/showthread.php?42136-Sheer-Audio-DHT-01A-preamp-bit-of-fun-from-Taiwan
http://i1181.photobucket.com/albums/x440/montesquieu61/pre1_zpsxv76o9wd.jpg
http://i1181.photobucket.com/albums/x440/montesquieu61/pre2_zpsc6wbgnvb.jpg
http://i1181.photobucket.com/albums/x440/montesquieu61/pre3_zpsm3abilop.jpg