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

  • Jr. Member
  • Posts: 21
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

  • Jr. Member
  • Posts: 58
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