Best ROI for rolling in tube tuners?

[Jacob Bucci]

Hello AK!

I'm starting to roll tubes on a suhweeet McIntosh MR67 scored a few weeks ago, and it has me pondering where the best bang-for-buck is in tube tuners: audio amps? RF amps/demux? IF filter? Stereo amp/demux?

So far it's been:
1) Left audio 6BL8 was a no-diamond Telefunken that flared during power-on, probably because the right was a McIntosh-branded Amperex. Both are now Philips, and the flare is gone.

2) MPX amp was 6EA6 Sylvania, replaced with GE 6GH8A

3) 19kHz MPX demux oscillator was Elektro-Harmonix 12AU7, replaced with the GE from my Bottlehead Crack.

4) RF front-end was McIntosh-branded 6DS4, now it's RCA 6CW4.

This tuner sounded great before, but now the sound is simply holographic at all listening levels, and the background is completely dark. I did not spend much time listening between individual swaps, but I suspect the biggest gains are from the matched audio tubes and the new front end. Next up will be the 12AT7 RF amp/mixer, as I know there's a lot of nice options to be had.

Thanks for your thoughts!

 

[gadget73]

unless the tubes are bad, there is no point at all in messing with tubes before the audio section. If you're getting improvements with anything before the detector, pretty good chance you are replacing tired tubes with not-tired tubes.

 

[peterh]

Best bang-for-the bucks is with solid state gear.

 

[Jacob Bucci]

unless the tubes are bad, there is no point at all in messing with tubes before the audio section. If you're getting improvements with anything before the detector, pretty good chance you are replacing tired tubes with not-tired tubes.

Thanks, this is close to my thinking. Other than matching audio outputs I want to approximate the original BOM and get the old McIntosh labels in glass on a shelf. I'm also pleasantly surprised by how cheap radio tubes are, even rare ones.

1) Philips/Amperex supposedly provided the original audio tubes. I understand wanting to keep the McIntosh label in the lineup, but matching outputs are kinda crucial.
2) Richard Modaferri recommends the 6GH8 for MPX demux, runs a bit hotter than the original 6U8
3) My opportunism to have an all-GE MPX decoder.. running a beautiful Genalex Gold Lion in my Crack
4) RCA allegedly provided the 6DS4 replacements, probably providing "the darkness" over the original

I actually have yet to remove the shields on the RF and IF tubes, if something goes awry I'll can get them tested. Although I've read the IF stage is basically immortal, so it might be a while.

 

[we421a]

You can try substitute 6bl8 with 6gh8 and 6u8a. I tried telefunken and Amprex Holland and I didn’t hear much difference in MR71. For other tubes, I tried tube rolling as well and draw similar conclusion. I had my modified/upgrade by Richard Modafferi from audioclassics. Hope this helps.

 

[Jacob Bucci]

You can try substitute 6bl8 with 6gh8 and 6u8a. I tried telefunken and Amprex Holland and I didn’t hear much difference in MR71. For other tubes, I tried tube rolling as well and draw similar conclusion. I had my modified/upgrade by Richard Modafferi from audioclassics. Hope this helps.

Good to know, I'll spring for the Modaferri mods if I start to hear things degrade but for now this thing blows me away as is.