Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?

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avahifi

Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #60 on: 3 Mar 2018, 07:24 pm »
The trick to access bias pot is to remove the 5 screws attaching back panel to main chassis on the bottom of chassis so you can tip back panel back.

Did new tubes deal with excess heat issue?

Frank

jeenam

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Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #61 on: 5 Mar 2018, 03:06 am »
Changing the tubes out did not have any effect on the temperature of the heatsinks. It is still extremely warm to the touch. I can only keep my fingers on the heatsink for 5 seconds or so.

Hydro

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Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #62 on: 5 Mar 2018, 03:25 pm »
I have a 350, 400and 600, the 350 runs much hotter than the new generation amps.

avahifi

Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #63 on: 5 Mar 2018, 03:42 pm »
The amps from the EXR series on have regulated output transistor power supplies.

In them, the bias current is adjusted from the regulated power supplies, not from the higher raw supplies.  Thus they produce less heat at the same bias current settings and run cooler.

Frank

avahifi

Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #64 on: 5 Mar 2018, 03:43 pm »
The amps from the EXR series on have regulated output transistor power supplies.

In them, the bias current is adjusted from the regulated power supplies, not from the higher raw supplies.  Thus they produce less heat at the same bias current settings and run cooler.

Your amplifier should not be running that hot.  The bias setting is probably way too high.

Frank

jeenam

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Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #65 on: 22 Jul 2018, 09:20 pm »
Following up on my earlier report...

It turns out the pair of Genalex Gold Lion 12AT7 that were purchased from Cryoset were no good. I've purchased a few sets from them and this pair just did not sound right even when tested in my Doge 8 preamp. They sounded very thin and were lacking in the low end. They've since been swapped out for a pair of NOS Sylvania JHS 12AT7 black triple mica and the sound is fantastic. In my experience, tube rolling changes are very apparent and dramatic. So far I've tested with the following:

Genalex Gold Lion 12AT7 (cryo)
Genalex Gold Lion 12AT7 (non-cryo) - Sounded like what you would expect from the Gold Lion series. Well balanced across the frequency spectrum. More hi-fi sounding than tube when compared to NOS tubes.
Sylvania 12ATWA (green label) - Very warm and lush midrange. Rolled off pretty severely on the high end giving a darker tone (this may be due to the tubes age as the previous owner did not specify how many hours were on these).
Sylvania JHS 12AT7 (green label) - These are supposedly similar to the Sylvania Gold Brand 6201 gold pin. I'd say they're about a 95% match for the sound of the 6201's. The Gold Brand 6201 are regarded as some of the best 12AT7's and these are no exception. Very good extension top to bottom, with a pronounced midrange that makes for great imaging and a wide soundstage. These and the 6201 are my favorite.

rollo

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Re: Best NOS 12AT7 tubes for Fet Valve 400R and 600R amp?
« Reply #66 on: 22 Jul 2018, 09:58 pm »
 Any 12AT7 with a rich warmish tone.  RCA, Mullard, Amperex in that order.


charles