12au7 Tubes

scubalab · October 2020

Full disclosure here - I’m fairly inexperienced when it comes to tubes!

I have a Triode TRV-88ser integrated that I purchased from Skip about a year or so ago. Unfortunately it hasn’t seen much use in the time I’ve had it. A few months ago, I switched speakers back and forth comparing two different pairs and noticed that the sound was muddy in one speaker. I did the usual - reconnect cables, swap L/R speakers, etc., and could not resolve. So, I reached out to Skip and he said it’s likely a bad tube or two. I finally got around to trying some of his suggestions. At first the music sounded pretty good, but as things warmed up, I definitely noticed the sound was more pronounced from the right speaker. The first thing I did was switch the preamp tubes and sure enough, the problem followed the tubes - now the left speaker is louder.

This amp has the original stock tubes. So, I’d like to upgrade while addressing the issue. Looking for a recommendation on a matched pair of 12au7 tubes. I could also use a single 12ax7 for the input. Eventually, I’ll be looking to upgrade the Quad set of KT88 tubes, but can’t swing that right now.

I know there are some tubes in the FM. Any other options? Anyone have some good tubes they’re willing to part with that you think would be a good choice to try? Or, I’m open to recommendations on what to look for.

Thanks - Al

Clipdat · October 2020

New production Tung Sol a safe bet.

audioluvr · October 2020

I have a few good sets I'm not using.

mhardy6647 · October 2020

The nice thing about 12AU7s is that there are still reasonably priced vintage Amurrican variants on the open market. There are, of course, boutique variants, too, but there are good old meat and potatoes tubes that won't break the bank.

http://www.audiotubes.com/12au7.htm
https://www.tubesandmore.com/search/node/12au7 (some NOS variants down at the bottom of the page)

pitdogg2 · October 2020

The tall bottle 6085's are worth looking into Al. They are not cheap but they are rated at 10,000 hours. They are either made in Holland (amperex) or Hungary (tungsram). Only two plants made them so no matter the name on the side 6085 gold pins Holland, regular pins Hungary

scubalab · October 2020

Thanks for all the advice thus far! I'll do a little research and post back with any questions.

@audioluvr shoot me a PM with what you have!

Ivan @pitdogg2 , other than long life, do the 6085's generally increase the gain of a 12au7?

mhardy6647 · October 2020

scubalab wrote: »

Thanks for all the advice thus far! I'll do a little research and post back with any questions.

@audioluvr shoot me a PM with what you have!

Ivan @pitdogg2 , other than long life, do the 6085's generally increase the gain of a 12au7?

I'm not @pitdogg2, but I play him on television in some of @Hermitism's mashups

I was gonna say "no, the gain's the same"... but I looked 'em up @ TDSL
http://tdsl.duncanamps.com/tubesearch.php

6085 has an amplification factor (each triode) of 30 per
https://frank.pocnet.net/sheets/201/6/6085.pdf

12AU7A has amplification factors of 19.5 and 17 (triode 1 and triode 2, respectively) per http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/12AU7-A.PDF

So... yeah, a wee bit, apparently.

pitdogg2 · October 2020

here you go AL I find them to be very 3d'ish

Since this tube has a much higher Gm and Mu factor than a 12AU7, the gain is going to be greater and this tube will give a more forward presentation. Awesome in phase splitter applications. If in doubt, check with your amp or preamp manufacturer to see if this tube will work OK in your application. This tube is also about twice as tall as a 12AU7, so installation space in your chassis is a consideration as well.

https://www.effectrode.com/knowledge-base/the-12au7-tube/

scubalab · October 2020

Mark - as always, thanks for the comprehensive (educational) advice!

Drew - I looked a bit into the Tung Sol's. Any particular ones you'd recommend for best bang for the buck?

Rob - Let me know what you've got (or are willing to let go)!

Ivan - The 6085's sound interesting. Height shouldn't be an issue as I keep the 'cage' off the amp; plus with the size of the KT88 tubes, I'd think clearance will be maintained even if I do put the cage back on. Do I really need to "check with your amp or preamp manufacturer"? I know that came from the article and not necessarily you. I don't think Triode Corporation is very responsive... It's a cool amp, but literature and support is slim to none.

Here's a little more detail on my setup:

Integrated - Triode Corporation TRV-88ser. I think it's rated at 45 WPC which makes sense with the KT88 tubes. (purchased from Skip.)
Turntable - Fluance RT85 with the Ortofon Blue cart (purchased new from Fluance).
Phono pre - Lounge LCR MkIII (purchased from Zach @stangman67).
Speakers (Primary) - Polk Monitor 11 (RTA-11) (purchased from Jesse @F1nut)
Speakers (Secondary) - Polk LSiM703 (purchased new from Adorama)
Power Center - Monster HTS-2600 (karma from Joe @joecoulson )
Speaker Cables - Zu Audio Libtec (purchased new from Zu)
ICs - Wireworld Oasis and BJC LC1 (purchased from Zach @stangman67).

Forgot to mention the "karma" rack from Zach @stangman67 for being a 'repeat' customer of his

Photos:

pitdogg2 · October 2020

I didn't check, I also tried 12at7's in the AU spot I knew right away they would not work. I do not get the SHHHHH with the 6085's like I got with the AT's. The 6085's are dead quite in my pre-amp.

Clipdat · October 2020

scubalab wrote: »

Drew - I looked a bit into the Tung Sol's. Any particular ones you'd recommend for best bang for the buck?

https://www.thetubestore.com/tung-sol-12au7w-6189?quantity=1&additional_options=3

This is what I was thinking. I realize it won't have the performance of the nicer NOS options, but it could be a quick and easy way to get back up and running with a minimal expenditure.

audioluvr · October 2020

These are what I'm using in my pre. I've bought 3 matched pairs because I like them so much and surprisingly they all sound the same.
https://www.ebay.com/itm/163533485479

scubalab · October 2020

Thanks to everyone who reached out in this thread and via PM. Very early on, Bruce (@Faustin) reached out to me with some suggestions including the Raytheon (made for Baldwin) tubes. I decided to give them a try. I got them today and had a couple minutes at lunch to try them out. I’m thrilled to say I’m back in business!

I’m not one who can hear the improvements some things (like cables) can bring, but these tubes... WOW! I’ve now got a soundstage that expands not only from speaker TO speaker, but beyond them (left, right, front, and back). I also immediately noticed fuller bass, more balanced, warmer mids, and pleasant highs. Next to adding a separate amp on my home theater, these tubes (over the stock tubes) have been the most impressive audio improvement I’ve experienced.

Both sets of speakers (the Monitor 11s and the LSiM703s) sound incredible. Maybe the 703s are finally breaking in, but these little speakers present way bigger than they are!

Thank you Bruce for reaching out and for the great tubes.

Rob, I’m still considering giving the RCA clear tops you have a try as well. I’ll keep you posted.

Thanks again everyone

Clipdat · October 2020

Very nice.

Faustin · October 2020

@scubalab

My pleasure!

Clipdat · January 24

audioluvr wrote: »

These are what I'm using in my pre. I've bought 3 matched pairs because I like them so much and surprisingly they all sound the same.
https://www.ebay.com/itm/163533485479

@audioluvr The link doesn't load anymore. What kind were these?

pitdogg2 · January 24

Knowing Rob I'm guessing some Raytheon black plate 12au7 organ tubes. In the past he has mentioned he really liked them.

Clipdat · January 24

Oh ok interesting. I was trying to look into some balanced triode 12au7 tube pairs for my new ST-70.

Supposedly rolling the rectifier can also improve things. Not in a big hurry though it still only has 3hrs play time.

Edit: Also for anyone reading that's interested, this is the for sale ad where I purchased it: https://www.usaudiomart.com/details/650058317-dynaco-st-70-brand-new-custom-build-beautiful/

Highly recommend this seller. Class act all the way.

pitdogg2 · January 24

https://www.ebay.com/itm/265322627696?

Keep an eye open for some RFT 12au7 tubes. They can have many names on them and still be made by RFT. Earlier the better some very nice tubes. Hard to get, can be very pricey, boy will your ears thank you.
5AR4 rectifier? Fat bottle Sylvania's and Mullard are the best.

Clipdat · January 24

Just link me Ivan, I'm ready to buy! TELL ME WHAT TO DO!

pitdogg2 · January 24

I gave you a link

Clipdat · January 24

MOAR LINKS!

bcwsrt · January 24

The man knows his tubes!!

Clipdat · January 24

I'm stupid. On the link you provided it states:

"Matched tested NOS pair of RFT 12AU7 tubes

Tester mutual conductance: 2200/2200

Tubes tested: 2350/2500, 2350/2200"

Which of these number sets refer to the triode balance?

pitdogg2 · January 24

Clipdat wrote: »

I'm stupid. On the link you provided it states:

"Matched tested NOS pair of RFT 12AU7 tubes

Tester mutual conductance: 2200/2200

Tubes tested: 2350/2500, 2350/2200"

Which of these number sets refer to the triode balance?

Tester mutual conductance: 2200/2200 < NOS would be this

These tubes tested above NOS with the exception of one triode that tested AT NOS, tubes tested: 2350/2500, 2350/2200.

They are very strong tubes. I have them in my watch list and If you do not I will buy them.

pitdogg2 · January 24

https://www.ebay.com/itm/235221863064?

https://www.ebay.com/itm/285653553623?

https://www.ebay.com/itm/175837062765?

https://www.ebay.com/itm/256388124281?

https://www.ebay.com/itm/116048987511?

Clipdat · January 24

pitdogg2 wrote: »

They are very strong tubes. I have them in my watch list and If you do not I will buy them.

Ok ok I bought them!

marvda1 · January 24

I was going to show you these, nice sounding tubes.
https://upscaleaudio.com/products/ge-12au7-6189w?variant=37476278304952

Clipdat · January 24

Nice, I'd be down to get them from somewhere other than Upscale.

Kex · January 25

I thought Upscale were a reputable outfit. Is this not the case?

Viking64 · January 25

Kex wrote: »

I thought Upscale were a reputable outfit. Is this not the case?

I took a wild guess and checked to see if this is the company with the guy some people tend to strongly dislike. Mind you, this memory was from something I briefly read/saw here maybe 5 years ago.

Sure enough, I search for "upscale audio" and who do I see but Kevin Deal. I have no personal experience with this guy, but I recall him to be rather . . . polarizing.

12au7 Tubes

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