I do not think that the 5691 and the Tung Sol 6U7GTY are entirely the same thing, in fact I'm sure that they have different specs and as such I think the 6U7GTY will not correctly work to full efficiency with a 6SL7 only circuit, that is unless it's been tweaked to do so. This is my understanding, I could be wrong and would like to be corrected if I'm talking knackers. My Croft which was designed to run with 6SL7's it would run 5691's but not to full efficiency and needed an upgrade to get the 5691 heaters working to full capacity. I wonder if this is the same with the 6U7GTY???????
SS
CD Teac VRDS25X(Audiotuned) DECK 1210 Mat Crystal Audio Mods MN Base/Bearing/Platter+Ebony armboard Feet Isonoe PSU Paul Hynes SR7EHD-27XL/DCSXL Ag DC lead/3 Stage Regs/Recap PCB+No Pitch/Strobe/Light ARM SME V(Kondo Ag Rewire&Tags) MC Cadenza Black FGS CABLES Arm Yannis SPD-4 IC Yannis 222 Litz+Ag bullets Power WAR PRE ATC SCA2 SPEAKERS ATC 50ASL STANDS Atacama PHONO Sugden Masterclass PA4 SUT Ortofon ST80SE POWER PSAudio P10
VALVE
PRE Croft Epoch(Modded) AMP Sondex S100 (Modded) SPEAKERS Tannoy 15"MG+RFC Warwick cabs+ Ref XO + Batpure supertweeters DECK Garrard 301 Mat Teunto Bearings 401(Bastin) Plinth Bamboo Arms 3009/3012 PSU Eagle+Tachometer MC Ag Meister II/FGS + Ortofon SPU MONO CABLES Arm Yannis 420.5 Litz+ SpeakerPC Tripple C+WBT-0681 Ag IC Oyaide FTVS-510 AgWBT 0110Ag Phonostages Paradise(4 Box Mega-Modded) / Croft Musicmaker
MONO
Pre Croft Epoch Power Sondex S100 Deck Garrard 301 Tonearm SME 3009 Cartridge SPU MONO mk II Phonostage Croft Music Maker Speaker Quad ESL 57 Cables Tonearm SME IC - Duelund Realsound Speaker SEAC 850C