Fisher 400 tube rolling

[pich]

Experimenting with some different tubes in my 400 this morning. I replaced the Tele 12AX7 driver tubes with a pair of NEC 12AD7s. Hard to tell if the receiver sounds any different but still sounds fine.

Any thoughts if I would notice a bigger difference swapping the tone control tubes?

I also have a bunch of other AT7s and AU7s. Any advice on favorite brand, type, and rolling suggestions welcomed.

Thanks
Bruce

 

[Jailtime]

Just use a strong matched pair of tubes in the phase inverter positions. No need for good vintage tubes there, they don't really impact the sound of the amplifier. You will notice a difference in the phono and tone control tubes. The Fisher receivers respond quite well to tube rolling.

 

[pich]

I assume the tone control tubes are just behind the front panel. I use an external phono preamp so I'll experiment with those. Thanks for the advice.

 

[Jailtime]

V10 and V9 are your tone and voltage amps. V7 and V8 are your phono amp tubes.

 

[sgmlaw]

Just use a strong matched pair of tubes in the phase inverter positions. No need for good vintage tubes there, they don't really impact the sound of the amplifier. You will notice a difference in the phono and tone control tubes. The Fisher receivers respond quite well to tube rolling.

PIs do make a difference in the sound on these, albeit not as profound as the upstream small signal bottles.

Still, I will not burn up really good old production in the PIs in these any more. You want a tough, rugged, but still good sounding tube there that doesn't cost an arm and a leg. I won't use new production. Right now, relatively tight matched Japanese Philips (Matsushita) or similar off-shore Raytheon production works well. Very good sound and very durable tubes for this application. I believe Matsushita may have made the OP's NEC, so he's on the the right track, generally speaking.

A 12AD7 might be overkill in a PI. Uber low noise and microphonics are not as critical there. That's a tube type better suited in the earlier stages, where its design strengths shine a little better. But if the price was right, who am I to argue?

 

[pich]

Thanks for all the advice.

I put the original Telefunken smooth plates back in the phase inverter positions and listening to the NEC 12AD7 in the tone circuit. I have the following tubes and will try them in the tone circuit.

Fisher branded 12AX7 ribbed, made in W. Germany but not Telefunken (no <> on bottom).

Fisher branded 12AX7 ribbed, Telefunken.

EICO by Mullard 12AU7A.

Motorola (made in Great Britain \ Mullard?) 12AX7A

Not sure how matched the tubes are but each pair test strong with equal emission readings on my cheap Sencore tester.

So far I think the 12AD7s seem to have a little less bass then the Telefunken 12AX7 smooth plates. My guess is that I'll end up sticking with the original Telefunkens but will have fun experimenting.

 

[audiodon]

12AU7s are not used in the 400.

 

[pich]

The 12AU7 has less gain and more current draw. I tried them and didn't notice much difference. I won't use them since I have no idea the what the impact is of the added current draw. Thanks for the warning.

 

[audiodon]

I tried them for the heck of it once myself. Didn't sound terrible, but didn't add anything.