Questions about valves...

RichT · 17th October 2003, 03:45 PM

One of the valves in our TL Audio 5021 Valve Compressor has died. Poop.

Currently the compressor uses two Sovtek 12AX7WA's. It's very transparent and doesn't really sound 'valve' at all.

Anyway this means I gotta replace 'em, before I do I was wondering if anyone had any recommendations on 'alternative' valves to use for a certain sound.

Secondly, biasing. I know in amps when you change the valves you have to rebias them, any ideas on compressors or this compressor in particular?

Cheers,
Rich

jbuntz · 17th October 2003, 03:52 PM

You don't need to rebias with preamp tubes. You only have to adjust bias on power tubes in class A/B amps. Improper bias will give you intermodulation distortion. In the guitar amp world,

12AX7A = American spec, a little bright, clean

ECC83 = British spec, linear response, dirty, fuzzy breakup

12AX7C = Chinese spec, dirtier brighter than the ecc83

12AX7R = Russian Spec, somewhere between A and C. Good for all around guitar amp tube. Not sure about mic pres.

12AT7 = lower gain, brightest

12AY7 = also lower gain...tone?

12AU7 = not sure. they put these in Ampegs and those DBX pres. They invert phase.

7025 = Brighter than 12AX7's and higher gain

If you try something lower gain, you are going to have to drive it harder to get your proper line level which means you'll get more 'valve' coloration.

Midlandmorgan · 17th October 2003, 04:12 PM

This whole tube thing is a mess... I've always agreed with jbuntz in that 7025s are a bit different that 12AX7s, but every manual I've seen shows them to be the exact tube...

Be advised though, that there are only a few tube manufacturing plants left, and almost everything comes out of those is checked, spec'd, kept or rejected, badged, and sold...the rejected ones go to cheaper brand or generic placements....

I honestly think your best bet is to grab hold of some NOS JAN 12AX7...In English, this is new old stock (pretty old but never used) joint Army/Navy (built to military specs)...

And, you know that the same tubes from various sellers can sound radically different...so if possible, audition as many as you can...

Ken

jbuntz · 17th October 2003, 04:46 PM

You can use 7025's and 12ax7's interchangably. I think 7025's are military spec 12ax7's. Just like 5881's aren't like regular 6L6's.

RichT · 17th October 2003, 05:06 PM

Thanks JBuntz and MidlandMorgan for your suggestions.

I think it's gonna be a case of 'suck it and see'...

Good to know about the re-biasing (or not as it seems).

Cheers,
Rich

Drumsound · 17th October 2003, 05:47 PM

Check out Lord Valve He's got all kids of stock and knowledge. He's in Colorado.

Saucyjack · 17th October 2003, 07:20 PM

You shouldn't have to worry about rebiasing...I would recomend getting a few different tubes...some different 12ax7s and a few 7025 and experiment.
I would start with some NOS(New old stock)12ax7s tubes...check out Ei,GE,Philips,Mullard/Telefunken(pricey).Except for the Mullard/Telefunken tubes the rest are not that expensive and will often have a big effect on the sound,and likely be somewhat of a upgrade from the Sovtek.

RichT · 18th October 2003, 12:20 AM

Thanks again Guys,

I'm gonna see what I can pick up cheap off of ebay

and experiment...

Jay Kahrs · 18th October 2003, 12:36 AM

Putting different tubes into a TL Audio piece probably won't yeild the same results as putting different tubes into something like a DW Fern or Tube Tech piece. There are too many IC's in there, the tubes are part of an input or output stage. Given that, I wouldn't spend the money on high dollar tubes, get something decent (GT, Ruby, ElectroHarmonix) but spending money on Telefunken, Mullard, GE etc. is going to be a waste.

RichT · 18th October 2003, 02:43 PM

Ended up buying a pair of Phillips 12AX7WA Military Grade Valves at £12.00 each from www.watfordvalves.com

Also picked up a couple of matched Svetlana EL34s for my Ampeg VL503.

Thanks for the suggestions everybody!

subspace · 18th October 2003, 03:28 PM

I put a pair of Amperex "Bugle Boys" in my TL Audio pre, which didn't affect the mic pre's sound quality greatly, but did improve the DI's tone a bit. The DI bypasses the monolithic mic pre IC and goes directly into the first tube stage.
Both were improved by yanking out the TL074 output driver and dropping in a Burr-Brown OPA4134. Bigger improvement than the tube swap, stiffened up the outputs nicely.
Both of those are pretty straight forward swaps, but if you want to get really tweeky you could pull the SSM2017 mic pre IC and try an INA103, but it may require some additional tweaking. Haven't got around to trying it yet...
HTH

RichT · 18th October 2003, 03:36 PM

Quote:

Originally posted by subspace
I put a pair of Amperex "Bugle Boys" in my TL Audio pre, which didn't affect the mic pre's sound quality greatly, but did improve the DI's tone a bit. The DI bypasses the monolithic mic pre IC and goes directly into the first tube stage.
Both were improved by yanking out the TL074 output driver and dropping in a Burr-Brown OPA4134. Bigger improvement than the tube swap, stiffened up the outputs nicely.
Both of those are pretty straight forward swaps, but if you want to get really tweeky you could pull the SSM2017 mic pre IC and try an INA103, but it may require some additional tweaking. Haven't got around to trying it yet...
HTH

Yikes, that sounds like a job for another day

Burr-Browns do sound nice though, we have two channels of them in our Sytek MPX-4A that sound great.

Cheers,
Rich

subspace · 18th October 2003, 03:48 PM

Quote:

Originally posted by RichT
Yikes, that sounds like a job for another day

Burr-Browns do sound nice though, we have two channels of them in our Sytek MPX-4A that sound great.

Cheers,
Rich

Just look to see if it has a pair of socketed TL074s on the board. If so, exchanging them with OPA4134s is as simple as a tube swap. Oh, and TI.com will ship you the chip "samples" for free...
HTH

RichT · 18th October 2003, 03:52 PM

Quote:

Originally posted by subspace
Just look to see if it has a pair of socketed TL074s on the board. If so, exchanging them with OPA4134s is as simple as a tube swap. Oh, and TI.com will ship you the chip "samples" for free...
HTH

Oooooooooh, someone said the word....FREE

I'll definitely check that out then.

Thanks!

Rich

RichT · 18th October 2003, 04:13 PM

Right, have a pair of OPA4134s on their way to me too.

I may have to pay some VAT / Import tax when they arrive but I should imagine that will be minimal.

Coolio.

Cheers,
Rich

RichT · 18th October 2003, 07:27 PM

Quote:

Originally posted by subspace
Just look to see if it has a pair of socketed TL074s on the board. If so, exchanging them with OPA4134s is as simple as a tube swap. Oh, and TI.com will ship you the chip "samples" for free...
HTH

Hmmm, just got to the studio and opened 'er up. No socketed chips and no less than 10 (!) TL074 chips inside.

Guess I'm gonna have to get the schematics to see which pair will benefit most, if at all.

Damn cheap boxes...

subspace · 19th October 2003, 02:48 AM

Quote:

Originally posted by RichT
Hmmm, just got to the studio and opened 'er up. No socketed chips and no less than 10 (!) TL074 chips inside.

Guess I'm gonna have to get the schematics to see which pair will benefit most, if at all.

Damn cheap boxes...

Jesus, guess the mic pre unit has a wee bit shorter signal path...
No matter, TL07Xs can be fine in lotsa places, my Trident is filled with them, but they suck at driving wire. So for stiffening up the outputs while driving low impedence loads, the output drivers are the pair you want to upgrade. Find the traces leading to the output jacks, they should come from a big electrolytic cap, say 100MF - 220MF, and before that the output buffer TL074 to be upgraded.
You'll have to solder in sockets for the Burr-Browns, but at least you'll be able to swap chips then to compare...
Out of curiousity, are there SSM2017 mic pre ICs in there as well as all those TL0s?

RichT · 19th October 2003, 01:12 PM

Quote:

Originally posted by subspace
Jesus, guess the mic pre unit has a wee bit shorter signal path...
No matter, TL07Xs can be fine in lotsa places, my Trident is filled with them, but they suck at driving wire. So for stiffening up the outputs while driving low impedence loads, the output drivers are the pair you want to upgrade. Find the traces leading to the output jacks, they should come from a big electrolytic cap, say 100MF - 220MF, and before that the output buffer TL074 to be upgraded.
You'll have to solder in sockets for the Burr-Browns, but at least you'll be able to swap chips then to compare...
Out of curiousity, are there SSM2017 mic pre ICs in there as well as all those TL0s?

Nope, no SSM2017s in there - guess that's extra expense considering it's just a compressor.

Can't easily see which TL074s are linked to the output jacks - Time to ask our studio tech what he thinks.

Thanks for your help Subspace.

Cheers,
Rich

Jay Kahrs · 20th October 2003, 01:56 AM

Quote:

Originally posted by RichT
Can't easily see which TL074s are linked to the output jacks - Time to ask our studio tech what he thinks.

If you have the schematic for it you can look to see which IC's are on the output. Either that or look at the circuit board. Chances are pretty damn good that the highest numbered IC's are the ones driving the outputs.

One thing to be careful of is that the Burr Browns and most other IC's pull more current then a TL07X. Swapping a pair or two shouldn't be a problem but you might want to see how much reserve current you have before swapping everything inside the box.

RichT · 20th October 2003, 08:18 AM

Quote:

Originally posted by Jay Kahrs
If you have the schematic for it you can look to see which IC's are on the output. Either that or look at the circuit board. Chances are pretty damn good that the highest numbered IC's are the ones driving the outputs.

One thing to be careful of is that the Burr Browns and most other IC's pull more current then a TL07X. Swapping a pair or two shouldn't be a problem but you might want to see how much reserve current you have before swapping everything inside the box.

Hi Jay,

I've scoured the net for a schematic, nothing so far but I'm fairly confident I've found the pair to replace but there's nothing like a local second opinion - I don't really want to screw the compressor up considering all it needs is a tube change

Thanks for the tip on the power, will mention it to our tech and see what we've got to play with.

Cheers,
Rich

RichT · 1st November 2003, 09:18 PM

Just to finish the story, turned out there was nothing wrong with the valves - there was a leaky diode on the board which meant the heaters weren't working either.

All fixed now and running with some new Phillips 12AX7WAs, quite nice.

Cheers,
Rich

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
New Valves for TLA indigo compresser	krisstoff	Geekslutz forum	0	10th January 2006 10:34 PM
replacing valves on drawmer 1968?	baikonour	So much gear, so little time!	12	20th December 2005 09:45 PM
Has anyone ever changed the valves in an SPL Kultube?	TSM	Geekslutz forum	0	16th October 2005 01:45 PM
Microphonic valves ?	espasonico	So much gear, so little time!	5	13th June 2005 05:18 AM
Tubes and Valves?	HeveyMetil	Geekslutz forum	1	22nd October 2003 03:54 PM

17th October 2003, 03:45 PM	#1
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Questions about valves... One of the valves in our TL Audio 5021 Valve Compressor has died. Poop. Currently the compressor uses two Sovtek 12AX7WA's. It's very transparent and doesn't really sound 'valve' at all. Anyway this means I gotta replace 'em, before I do I was wondering if anyone had any recommendations on 'alternative' valves to use for a certain sound. Secondly, biasing. I know in amps when you change the valves you have to rebias them, any ideas on compressors or this compressor in particular? Cheers, Rich __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

17th October 2003, 04:12 PM	#3
Midlandmorgan Lives for gear Join Date: Jun 2002 Location: Midland TX Posts: 1,078	This whole tube thing is a mess... I've always agreed with jbuntz in that 7025s are a bit different that 12AX7s, but every manual I've seen shows them to be the exact tube... Be advised though, that there are only a few tube manufacturing plants left, and almost everything comes out of those is checked, spec'd, kept or rejected, badged, and sold...the rejected ones go to cheaper brand or generic placements.... I honestly think your best bet is to grab hold of some NOS JAN 12AX7...In English, this is new old stock (pretty old but never used) joint Army/Navy (built to military specs)... And, you know that the same tubes from various sellers can sound radically different...so if possible, audition as many as you can... Ken __________________ Ken Morgan Wireline Studio Midland, TX Don't Blame Me, I Just Recorded What You Played

17th October 2003, 05:06 PM	#5
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Thanks JBuntz and MidlandMorgan for your suggestions. I think it's gonna be a case of 'suck it and see'... Good to know about the re-biasing (or not as it seems). Cheers, Rich __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

17th October 2003, 05:47 PM	#6
Drumsound Lives for gear Join Date: Jun 2002 Location: Bloomington Il Posts: 3,585	Check out Lord Valve He's got all kids of stock and knowledge. He's in Colorado. __________________ Tony Oxide Lounge Recording See the Oxide Lounge! WWJMD? Come see me on the Tape Op boards! "If I have to flip flop more than three times in an A/B test to figure out what the difference is, I lose interest in that difference.'--Tchad Blake

17th October 2003, 03:52 PM	#2
jbuntz Lives for gear Join Date: Jul 2003 Posts: 1,651	You don't need to rebias with preamp tubes. You only have to adjust bias on power tubes in class A/B amps. Improper bias will give you intermodulation distortion. In the guitar amp world, 12AX7A = American spec, a little bright, clean ECC83 = British spec, linear response, dirty, fuzzy breakup 12AX7C = Chinese spec, dirtier brighter than the ecc83 12AX7R = Russian Spec, somewhere between A and C. Good for all around guitar amp tube. Not sure about mic pres. 12AT7 = lower gain, brightest 12AY7 = also lower gain...tone? 12AU7 = not sure. they put these in Ampegs and those DBX pres. They invert phase. 7025 = Brighter than 12AX7's and higher gain If you try something lower gain, you are going to have to drive it harder to get your proper line level which means you'll get more 'valve' coloration.

17th October 2003, 04:46 PM	#4
jbuntz Lives for gear Join Date: Jul 2003 Posts: 1,651	You can use 7025's and 12ax7's interchangably. I think 7025's are military spec 12ax7's. Just like 5881's aren't like regular 6L6's.

17th October 2003, 07:20 PM	#7
Saucyjack Lives for gear Join Date: Jan 2003 Location: Knoxville,Tn Posts: 569	You shouldn't have to worry about rebiasing...I would recomend getting a few different tubes...some different 12ax7s and a few 7025 and experiment. I would start with some NOS(New old stock)12ax7s tubes...check out Ei,GE,Philips,Mullard/Telefunken(pricey).Except for the Mullard/Telefunken tubes the rest are not that expensive and will often have a big effect on the sound,and likely be somewhat of a upgrade from the Sovtek. __________________ If you really want to make orginal results,work fast and cheap,because there's more of a chance that you'll get somewhere that nobody else did. Brian Eno

18th October 2003, 12:20 AM	#8
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Thanks again Guys, I'm gonna see what I can pick up cheap off of ebay and experiment... __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

18th October 2003, 02:43 PM	#10
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Ended up buying a pair of Phillips 12AX7WA Military Grade Valves at £12.00 each from www.watfordvalves.com Also picked up a couple of matched Svetlana EL34s for my Ampeg VL503. Thanks for the suggestions everybody! __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

18th October 2003, 03:28 PM	#11
subspace Lives for gear Join Date: Jun 2002 Location: Too sun Posts: 556	I put a pair of Amperex "Bugle Boys" in my TL Audio pre, which didn't affect the mic pre's sound quality greatly, but did improve the DI's tone a bit. The DI bypasses the monolithic mic pre IC and goes directly into the first tube stage. Both were improved by yanking out the TL074 output driver and dropping in a Burr-Brown OPA4134. Bigger improvement than the tube swap, stiffened up the outputs nicely. Both of those are pretty straight forward swaps, but if you want to get really tweeky you could pull the SSM2017 mic pre IC and try an INA103, but it may require some additional tweaking. Haven't got around to trying it yet... HTH __________________ "If you never did, you should. These things are fun and fun is good."

18th October 2003, 04:13 PM	#15
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Right, have a pair of OPA4134s on their way to me too. I may have to pay some VAT / Import tax when they arrive but I should imagine that will be minimal. Coolio. Cheers, Rich __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

1st November 2003, 09:18 PM	#21
RichT Lives for gear Join Date: Jul 2003 Location: Portsmouth, UK Posts: 1,454	Just to finish the story, turned out there was nothing wrong with the valves - there was a leaky diode on the board which meant the heaters weren't working either. All fixed now and running with some new Phillips 12AX7WAs, quite nice. Cheers, Rich __________________ www.oldblacksmiths.com www.myspace.com/theoldblacksmiths

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread: