[millerdog]

Hey guys, I just rolled the two center tubes with some conspicous 7025 amperex'...lost some signal in the left side. Changed them to sylvy green label JANS..okay back to normal.
Will I find the same set up with my Fisher 400?
md

 

[mkmelt]

I don't know a thing about the tube layout of your integrated amp. On the 400, the voltage amplifier tube is towards the front center. The tone control amplifier tube is to the right of this one, again at the front of the chassis.

The two driver/inverter tubes are mounted just in front of the output transformers, shortest path to the left and right 7868 pairs I guess. If your amp is arranged differently, then removing the bottom plate will make it easy to see which tubes are driving the 7868s. Just be careful, look but don't touch anything. There are 425 volts lurking inside some of those caps.

You'll definitely want to keep the two driver tubes the same type and vintage. The voltage amplifier tube definitely has an audible affect on the sound, not as sure about the tone control tube though. Unless you modify the unit, the tone controls circuit is always in the signal path, so this tube has the potential to affect the sound you hear even if the control is centered. It's worth a test to see if changing this tube makes an audible difference. In the past, I've placed a known strong ribbed Telefunken 12AX7 in the tone circuit and just left it alone. I've also stuffed as many as 9 GE USA made 12AX7s inside a 400 and been happy with the sound.

My 400 originally came with the Fisher Doctor restoration already installed and Westinghouse 5751s with the windmill getter (rebranded Raytheons) for the voltage, tone, and driver tubes. It has HP branded 12AX7s that appear to be by Amperex in the FM section in the phono section. I replaced the Amperex tube in the FM audio section with a Mullard - Great Brittain made 12AX7 because I think that this tube is warmer and fuller than the Amperex tubes, which sound a little thin to me.

 

[millerdog]

Thanks mkmelt,
I think I'll just pull the bottom plate and see what under there!
md

 

[Dan H]

Here I go again off topic…
Have you replaced the power cord yet Jeff? That thing is nearly 40 years old. Its the first thing I do to all my old stuff. You'll hear much better bass.

 

[millerdog]

Dan, the power cord end is not stock. To tell you the truth, I have been listening to this thing and enjoying it too much to even think about the cord. I will check it out tomorrow.
Keep your 500c...if you sell it, you know you'll regret it.
md

 

[millerdog]

Update:
I think the two center tubes make the most difference. I tried some GE 5 stars and some RCA triple mica blackplates. I think the GEs have a tighter bass. I tried some JAN 5751 sylvy green labels and the bass got huge and muddy. Right now the sylvies are on the far right. Didn't notice a difference when those sets.
I pulled the bottom cover and gave up trying to trace the signals. They go in and out of the high filter and loudness thing. I guess I should go find a schematic.
I been playing with these "cheap" tubes for now. I am afraid of plugging in the Rays for I may like them and will have to get more.
I still can't believe the sound I'm getting out of this puppy! I liked my Grados before, but now they are like 100% better.
md

(edit) anyone try those sovtek 12AX7LPS?

 

[Tuberoller]

Quote:

Originally posted by millerdog Update: I think the two center tubes make the most difference. I tried some GE 5 stars and some RCA triple mica blackplates. I think the GEs have a tighter bass. I tried some JAN 5751 sylvy green labels and the bass got huge and muddy. Right now the sylvies are on the far right. Didn't notice a difference when those sets. I pulled the bottom cover and gave up trying to trace the signals. They go in and out of the high filter and loudness thing. I guess I should go find a schematic. I been playing with these "cheap" tubes for now. I am afraid of plugging in the Rays for I may like them and will have to get more. I still can't believe the sound I'm getting out of this puppy! I liked my Grados before, but now they are like 100% better. md (edit) anyone try those sovtek 12AX7LPS?

The Sovteks are great!!! Try them in the gain stages.

 

[millerdog]

thanks Tuberoller,
Based upon my original intentions I only bought one. I guess I'll seek out a couple more.
md

 

[millerdog]

update:
I like the RCA triple mica BP in the gain stages. The bass just seems more controlled. I haven't heard any high end differences though that is probably due to my source.
I couldn't do the Raytheon cause I got a bad tube. I want to try the GE Commands but I only got one so am searching for another.
I spent like a couple of hun on tubes and am realizing that that's nothing! the 400 is on it's way with a stock front end so am looking forward to rolling some TKFs in there. Man I need to sell some pots so I can pay for all these tubes

md