12ax7 tube rolling Fisher 500b

[Sam08861]

I'd restored the 500B some time ago. Jim McShane Kit with PIO K40Ys and Matched Tung Sol quad from him also + IBBA.

Decided to order a set of the Sovtek 12AX7LPS and got here this afternoon.

After taking out the 7 12AX7s in the chassis, I found they all measured ~56 on my Eico 625.

The New Sovteks measures ~58. Hmm.... Not much difference. Wondering if these are harder to measure, or they are in fact, almost as good.

Decided to look up what the original tubes were. 4 are Mullards and 3 are Telefunkens. The Mullards are the short plate, ribbed variety and the Telefunkens are long plate and smooth with the diamonds on the bottom with a number in the center. Mullards say 'THE FISHER' in all caps, while the Telefunkens are smaller font and leading capitals only and have 'Made in Germany' on the label.

The pulled tubes, teles on the bottom.





And the bottom of a tele...



Swapping in the Sovteks now.

Any advice on how to better test the tubes or what positions to put which types in?

 

[thornev]

I put a 12AX7 and 12AX7LPS, both Tung-Sol, in the preamp transformer section. Noticed an improvement in fullness of total frequency range especially in the upper frequencies that seemed more bright. I forget what was in there. Dialing in 80% of max plate dissipation will also improve your sound. I built and installed IBAM to dial in those values.

 

[Sam08861]

thornev,

I am hearing pretty much the same thing and these are clearly audible differences.

The sovteks are 'fuller' across the board. Had to dial back the bass a good bit as the sound is punchier down low, and the added 'sparkle' on the top end was also welcome.

The old tubes, sounded a bit more rolled off on top and mid heavier. Seems the new tubes also present a bit more detail. Liking the changes as it seems more balanced from low to high frequencies now.

I built/installed the IBBA instead of IBAM on my fisher, and are dialed in at ~79% across the board and were a matched quad to begin with.

 

[Sam08861]

After a day of critical listening and perhaps burn in, these Sovtek LPSs have come into their own. It's a bigger difference than I originally thought, as I can now put the unit out of loudness mode and they sound almost as good as the old ones with loudness off. I was actually feeling fatigued after listening and realized there was just too much low end. Clicked the loudness off and I'm listening to my albums in a new light. Did have to dial up the bass and treble to the 1pm positions. (flat is 12 noon)

Previously felt that I had to have loudness on for a fuller sound.

So I'm guessing while the Eico 625 (emission type tester) told me there were no faults with the old tubes, it really doesn't tell condition as a mutual inductance type tester might.

 

[thornev]

Interesting. So one can make judgements about how tubes sound by studying the differences in their parameters and perhaps graphing which parameters and their values contribute to "good-sounding" tubes. Of course "good-sounding" is completely subjective. I don't want to start THAT war !

 

[thornev]

It's interesting that we get to play sound engineers with these great-sounding machines. How much bass did the creators of the recordings want their fans to hear versus how much bass we like to hear. Flat frequencies versus (de)attenuated bass frequencies. It's one of the many things I love about listening to music. I want to be able to hear each individual instrument so that I can choose to focus on what each individual player contributed to the music. And we have all these tubes (and EQ devices) that can aid in achieving those goals. My 500-C has brought back my love for FM radio (though I can do without the political talking heads and shock jocks) that I started in the late 60's. I do miss the likes of Allison Steele, Tom Donahue and Pete Fornatelle. It's great to have these pieces of music and electronic history to help bring back those memories and provide us with ways into new hobbies. Rock n Roll ! Thorne

 

[Sam08861]

In addition to tubes we can play with capacitance and crossover networks! Not to mention delay, and of course signal processing and active crossovers for those souls that are farm more adventurous than myself.

To your point seems there's the camp that likes the studio monitor sound, those who like the live performance sound as well as niches for those crazy about voices or detail or PRaT, rocking out or any combination of the above plus more.

The FM section in the Fishers is astounding. Reminds me of the sound I used to hear growing up, but all grown up, lol. No need for HD radio or lossless audio files for me. Sure, there's a bit of FM stereo hiss, but all is forgiven when those sweet sounds come out or one remembers these were the very first of the FM stereo integrated units as evidenced by the add on module looking plates for the FM section on the chassis. It's clear that they were just developing this capability and weren't sure if they would be ready or a competing standard might have come to bear.

The tuning is nowhere as crisp as my buddy's Sony 6065 that seems to almost burst into tune with stations with a loud crackle or bark and near dead silence between stations, but rather a visceral exercise in watching the stereo beam and confirming by ear that you got it just right. There's a great station here, WXPN which bills themselves as 'all vinyl all the time' and I've found myself listening to FM again after years of only doing so in the car.