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6L6 - 12AT7 SE UL 1944 JAN metal tube power amp MKII
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Author:  mwhouston [ 30 Jul 2017, 01:17 ]
Post subject:  6L6 - 12AT7 SE UL 1944 JAN metal tube power amp MKII

Ok you have seen it before and above the bonnet it is exactly the same. In the engine room most components are different. This was the prototype for "Silver Supreme" SE UL amp with the JJ 6L6GC tubes and Mundorf Silver Supreme inter-stage caps. That amp I absolutely love and has not moved out of my main system for some months. 
 
This amp (the original prototype) was a real rough build, had a hum and sounded too similar to the Supreme. So I tore it down and rebuilt almost from scratch. Only the initial stage of the PS remains even the ceramic tube sockets got swapped out. I want this amp with the 1944 JAN 6L6 metal tubes to have its own character. For that all resistors are 1W carbon film (and not metal film), inter-stage caps are the original Solens. No silver solder here just Jaycar off the shelf but I did use twisted pairs of Cat5 solid core as hookup. The PS has 475uf of electros and the final filter cap to the driver tube (a well used (tests 98) 12AT7 and not a high end Psvane "T" series) is a Russian 4uf PIO snubbed with a 220nf poly. All other eletros in the PS are snubbed with 0.1uf polies. I didn't split the HT feed to the 12AT7 this time as in the Supreme, again to endow a different image presentation. All filaments (AC) are cap snubbed. I upped the HTs to 300V and 290V.
 
After chasing down a horrid buzz it is all is now quiet but not absolutely dead silent as the Supreme but it passes the 1M test. Sound is warmer which is strange as the driver tube has no bypass cap which not only reduces gain slightly but drops a lot of the second harmonic. I did this once more to give this amp its own personality. On a short listen (wifes home) it sounded more mellow than the super fast Supreme and as above, warmer. Very different 6L6 tubes and not the ruggedized GCs in the Supreme.
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Author:  mwhouston [ 30 Jul 2017, 20:06 ]
Post subject:  Re: 6L6 - 12AT7 SE UL 1944 JAN metal tube power amp MKII

To help reduce even the hum which remained I increased one of the limiting resistors to 330ohms. This dropped the HT to 280V and total current draw to 87mA. Hum is less but not gone. Hard with 99db efficient speakers. Also the old 12AT7 I was using went noisy and now I'm using a NOS JAN GE 12AU7. Need a big listen to see if I like it a lot or a little. So far I'm happy.

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