Hissing JJs (6v6s)

[proaudioguy]

12AD7.....Anyone used these?  Where would you use them?

Edit: the JJ stuff is later down the thread

[DummyLoad]

you can run the tube exactly as you would any 12AX7 or it's industrial variants.  the only difference is the heater current draw. i suspect this is due to the heater mechanical attributes, e.g., wind type / material / runs hotter allowing greater distance from cathode.

since the 12AD7 has guaranteed non-microphonics and maximum hum level specification, i wouldn't hesitate to use it any position in any amp that calls for a 12AX7 -  except for heater current, all ratings are identical to 12AX7 - 300V & 1W, 200V_h-k, etc..

stated simply, it's a plug and play 12AX7.

--DL

[HotBluePlates]

Unfortunately, you can't run this tube as hot as a 12ax7.   For example the 5f1 champ uses the 12ax7, and a 100K resistor in series feeding the anode, You might want to increase that 100K resistor to some larger. 

300v/100k = 3mA
3mA * 300v = 0.9w

So with a supply voltage of 300v and a 100k plate load, even if the tube becomes a short-circuit it is impossible to overheat a 12AD7 (or 12AX7).

Realistically, the way we use 12AX7's, you'll never bump into that dissipation limit. Note there is 2.1v at the cathode of the input tube on a Super Reverb. 2.1v/1500Ω = 1.4mA, and the schematic indicates 270v on the plate. 270v-2.1v = 267.9v*1.4mA = 0.38w. The 12AX7 is loafing. 12AD7 will work just as well.

Where would you use them?

Never seen one in person. But the Sylvania data sheet says it is "rigorously controlled to provide hum and microphonic free operation in low level audio preamplifier service."

I'd say there's your answer, like DL said. As scarce as these are, I'd tend to save it for the input tube position.

By comparison, the 7025 only claimed improved hum/noise over the 12AX7. Over the life of the 12AX7, its later variants often included shorter plates, partly to help reduce the tendancy to microphonics. Other variants used 3 mica spacers rather than two to stiffen the structure and reduce microphonics.

So you might make a sweeping generalization that the long-plate 12AX7's people go nutty for could actually have worse performance, from a microphonic standpoint. That said, the smoothplate Telefunken ECC83's tend to have excellent low microphonic performance, in spite of their longer plates.

But why the new tube number? A probably limited number of manufacturers made the 12AD7, and were trying to capitalize on improvements to the basic 12AX7 model, while attempting to steer replacement tube purchases their way with a different type number at the socket.

[PRR]

> even if the tube becomes a short-circuit

If tube is shorted, dissipation is Zero.

For steady supply voltage, series resistor, and variable/unknown device, device worst-case happens at half supply voltage.

For 300V, 100K, and a tube: worst-case is 150V across 100K resistor, 1.5mA. 150V across tube, times 1.5mA, is 0.225 Watts.

Or 410V, 100K, and a tube: 205V makes 2.05mA, times 205V is 0.42 Watts.

That's the worst it can be under those conditions.

As Fender ran it, 270V 1.4mA, as you say 0.378 Watts. Not much less than 0.42W max, but less.

If OTOH it were run slammed at 100V plate, 310V across 100K, 3.1mA, is 0.31 Watts. Also less.

[proaudioguy]

I bought 2 of them. Very pricey. Hoping to get a good sound with really low microphonics. My super champ and the other Rivera amps seem to be especially sensitive to microphonic tubes. I can tap on V1 and V2 when using the lead channel and they just ring right through the speaker. Some are better than others but all I have to try are cheap old sovtechs and old Chinese fender tubes. I'm really hoping this 12ad7 will get rid of the dissonant rattling sound you can barely hear when the amp is loud and the bass is heavy. Seems to be much less an issue when using an extension cab. Also plan to try it in V2 of the twin.

Super Champ schem says V2 is 12ax7. Tube chart inside amp says 12at7. Which one is right?  Mine is a very early example.  Btw amp sounds really good with the new correct Reverb tank. Wtb an EVM10L so I can get rid of the farty bass.

Thanks for the math guys.

[HotBluePlates]

For steady supply voltage, series resistor, and variable/unknown device, device worst-case happens at half supply voltage.

Thanks for pointing this out; yes, this would be the worst case. I forgot to include the fact that the resistor will be dropping the voltage as the current increases.

[proaudioguy]

Hey guys I like this tube.  I have very little to compare it to.  Compared to the Sovtechs I bought in the 1990s, a couple of chinese, and a few really old probably well used american made 12AX7s (probably 12AX7A), these area really really good.  The improvement over the Sovtech (I want to stress these are not recently made sovtechs) tubes I purchased form Mojo back in the 90s is quite large.  I really want to try some good old RCA, GE, Tung Sol, Silvania, etc.  The JAN Phillips 12AT7s I have (NOS) are kind of sterile compared to these, but also don't seem to add a sound of their own which is OK.  I'm now very curious about the 5751.

I wish there was a sticky here with very detailed descriptions (based on a general consensus) of the NOS tubes and where we like to use them (style of music the reviewer likes to play too).  I don't know the difference in sound between a long grey plate with 3 micas and a short black plate with 2 micas (220 221 whatever it takes), and these things can be very expensive to just try out.  I think I'm going to lurk some HIFI sites because I think a good HIFI tube would be a great guitar amp tube (but I might be wrong).

[HotBluePlates]

I wish there was a sticky here with very detailed descriptions (based on a general consensus) of the NOS tubes and where we like to use them (style of music the reviewer likes to play too).  I don't know the difference in sound between a long grey plate with 3 micas and a short black plate with 2 micas (220 221 whatever it takes), and these things can be very expensive to just try out.

You can find those kinds of descriptions all over the net. I suspect that as yesterday's "gotta have" tube becomes too scarce to find, vendors begin talking up the virtues of what they have left.

The one good piece of advice I can offer is the closest the tube is to the input jack, the more obvious the change will be. I can't honestly claim to hear any real difference changing output tubes, except for the nature of the distortion.

Second piece of advice: if the tube is under a lot of negative feedback, you probably won't hear much difference from a tube swap. This also speaks to my comment about output tubes. However, you can say the same for cathode followers (100% negative feedback) and probably tube stages which don't use a cathode bypass cap. Feedback helps linearize the tube's characteristics, and also masks variation of stage operation with differences between tubes (or as the same tube ages).

I really want to try some good old RCA, GE, Tung Sol, Silvania, etc.  ... these things can be very expensive to just try out.

I got lucky and acquired most of my tubes for relatively little money. If you buy from individuals you run the risk of getting a noisy/humming tube, but you'll also likely pay a lot less. Relative deals are probably out there if you look long enough.

[proaudioguy]

I was not aware of that.  12at7 for current. Good to know.

I had a chance to crank it up a bit today. The new V1 sounds good and makes a noticeable improvement.  Enough better that I immediately noticed 2 other issues. One is the hissing on certain notes.  I traced this to the almost ran new JJ 6V6 pair. If I put gloves on and grab the two output tubes the hissing goes away.  I knew to try this because my pro jr suffers from the same issue and causes me not to use that amp. I have 2 pairs of EH 6V6s with one tube from each pair being bad.  I installed the 2 unmatched good tubes and the hissing was gone but these EH tubes dont sound nearly as good.  Might need to bias them. I am convinced more than eer I need some good old RCAs. Please recomend the best sounding NOS 6V6 tubes you would use in your prized deluxe reverb (since that is the clean I'm looking for) with the least microphonics. And no glass rattling.

The other issue is above a certain SPL (drive loudness etc) the speaker buzzes.  I mentioned this a while back.  I'm looking for an EV Force 10 or an EVM-10M to try.  I know they won't buzz.

Btw anyone that wants to know the true story of the EVM-10L pm me.  My friend at EV (retired after 40 years) researched it for me.

[HotBluePlates]

... I am convinced more than ever I need some good old RCAs. Please recomend the best sounding NOS 6V6 tubes you would use in your prized deluxe reverb (since that is the clean I'm looking for) with the least microphonics. ...

Any tube can be microphonic; you'll have to rely on a vendor that tests the tubes or allows returns.

You could buy old RCA tubes; they'll cost you, unless you get the old metal 6V6's (but then you need to ground pin 1, and ensure nothing is using it as a tie point).

Or, you could use just about any American-made 6V6GT (or 6V6GTA).

I've used a bunch of different 6V6's. I've used RCA (gray and blackplate, with and without smoked glass, and metal varieties), G.E., Sylvania, KenRad, Westinghouse, Tung Sol, CBS, even some Raytheon 6V6's (I'm not sure Raytheon even produced those). I've also tried Brimar and Mazda 6V6's (though I think the Brimar were russkie fakes).

With a good amp and speaker, all of them sounded good to me. Maybe a very slight difference, but I honestly can't rule out that wasn't just me wanting to hear a difference.

Just know there were microphonic American tubes too. Sometimes a 6V6 might be used as a series-pass tube in a low-wattage regulated power supply. In this case, the microphonics don't really impact the performance. You can buy 6V6 variants that guarantee low-no microphonics, but people already beat you to that punch a couple decades ago. Now those ultra-heavy-duty Bendix tubes have all been snatched up and cost $$$$ when you can find them.

[Bub]

I have to post my 2 cents on this one. I have boxes of RCA, GE, Amperex, Brimar, Tung-Sol, Marconi, etc, long plate, short plate, black plate, grey plate, 12a_7,  7025, 5751, 6681. I had to enter the world of tube rolling. Plugged every tube in my KOC 5F6a. V2 and V3 came down to RCA 7025s. After trying every tube I own in V1 it came down to 3 tubes. 1950s RCA 12ax7 long black plate. After 6 of those I  found two that had no hiss or noise. There is no question if you find a good one they sound incredible. #2 is the Amperex 7025. I tried 8 of these and everyone sounded awsome, but there not cheap either.  #3 is the under valued Amperex 12ax7 made by Matsushita on Mullard equipment. I tried 5 of these and could not tell the difference between these and the Holland 7025s. The Amperex by far gave me that piano like tone on my bass I was looking for. For the price it's worth trying the Matsushita 12ax7. For the same price you can find these NOS as new 12ax7s.

Thanks

Bub    

[proaudioguy]

Thanks I definitely feel the need to stock up on some preamp tubes (I have 4 amps as it is).  My current issue is the 6V6s.  No doubt the hissing glass issue is not country of origin specific.  I guess the question is what tubes DON'T have this problem and of those, what are the best sounding?  Seems to me if the glass on these JJ tubes was a lot thicker I would not be posting this.  They actually sound really good, certainly good enough for me not to bitch if it weren't for the hissing.

Thoughts on stuff like this?
http://www.audiotubes.com/damper.htm
http://www.positive-feedback.com/Issue25/tube_dampers.htm
http://herbiesaudiolab.net/tube.htm (fender recommended these)
http://www.needledoctor.com/EAT-Tube-Cool-Dampers?sc=2&category=774
http://www.eurotubes.com/eurotubes-EuroDamper-Tube-Damper-Rings.htm (these actually look promising and ironically they have them on the JJs)

Or maybe I can just get a 99 cent roll of tef tape and wrap the tubes nice and thick with it?

BTW I doped up the speaker edge (it's days are numbered for this amp anyway) and it's made a rather large difference in the BUZZING at higher volume.  I can actually drive it harder without the buzz and when it does start to lose it, it's a little less annoying.  I have read a few folks using EVs and an Eminence Legend iirc, could turn both the volume and master all the way up with no speaker distortion at all.  I have now confirmed the optional EV was a Force 10 so I am looking for a Force 10 or an EVM-10M to use in this amp.  If I don't find one of these at a reasonable price soon, I'll have a cabinet built just a tiny bit taller and an inch or two deeper and stick one of my EVM12Ls in there, problem solved.

[HotBluePlates]

My current issue is the 6V6s.  No doubt the hissing glass issue is not country of origin specific. 

Seems like you could apply some high-temp RTV sealant to the area where the base meets the glass to try to combat this. Buy it from an auto parts store.

Or maybe I can just get a 99 cent roll of tef tape and wrap the tubes nice and thick with it?

Don't do that because it will inhibit the tube's ability to dissipate heat, and will definitely kill output tubes faster.

Tubenit had made some homemade versions of those tube dampers. Hopefully he'll chime in and link back to where he explained how he did it.

[proaudioguy]

Funny you should say that.  I did just that today.  I spent a lot of time looking at the tube dampers and decided to try just spooging the tubes.  I used Permatex Ultra Copper 700 degree Silicone RTV gasket maker.  My output tubes look pretty ugly with the 3 large beads of redish goo, but they sound a lot better.  I put one in the middle and one at each mica.  There is a large gap in between each bead and at the base and the end.  Hopefully that's enough to dissipate the heat.

Without the goop the JJ 6V6S stays cool enough to touch on the end.  The base stays very cool too.  The middle gets too hot to touch.  OTOH the EH tubes are too hot to touch anywhere on the tube for several minutes after shutting down and even melted a piece of carpet the end was touching when I had the amp out and had a bias probe attached which made the tube stick out past the cap can.  It's OK the carpet in this case was trashed long before that, but I still had no business working on it.  I am not too concerned about the heat dissipation issue with the JJs but in general some tubes get very hot and covering them with goop will make it worse as you said.  I was thinking for the EH tubes a copper pipe a little larger with some thermal grease filling the void, then a small bead of the silicone on top and bottom to hold it together.  That would add enough mass and maybe get the heat out.  I won't bother trying it since the EH tubes don't sound as good and they also don't hiss.

I have a small lathe.  I was thinking about a way to make a channel in a piece of aluminum to fill with silicone to make dampers like the eurotubes ones I linked.  I have not figured out a way to get the silicone back out after it cures (perhaps spray silicone lube on the surface).  Of course it would take 24 hours to make each one.  Not a very productive way to work, but I wouldn't be selling them.  The inner part of the donut would be just a bit smaller than the diameter of the tube.

I'm not sure gooping the EL84s would work.  When I had the Pro Jr (son has it now) I had to really grab those things to get it to stop.  These JJs just needed a gentle touch.

[proaudioguy]

So I pretty much have the entire glass covered in goop.  Problem is mostly gone but still there to some extent on some notes.  Really bugs me.  I guess the only way to get rid of it with these JJs is to use an extension cabinet.  Defeats the purpose of a smallish portable amp.

The goop (permatex gold RTV gasket maker type of stuff) gets too hot to grab.  You can touch it but you can't really grab it.  Not sure if holding that much heat inside the tube is a good idea.  I've played it for no more than 20-30 minutes at a time and had it idle for a couple of hours.  No sign of anything burning but the heat can't be good for the tubes (not that tubes that go SSSSSSS on certain notes are worth anything).  Clearly some of the "noise" is internal and not simply the glass.

Any suggestions?

[sluckey]

These may give you some ideas...

http://www.ebay.com/itm/TOMS-TUBE-TAMER-For-Peavey-Delta-Blues-Classic-30-/251133840499?pt=LH_DefaultDomain_0&hash=item3a78be4c73

http://www.ebay.com/itm/4-SoniKLEER-TUBE-AMP-DAMPERS-FOR-12AX7-12AU7-12AT7-12BH7-EL84-6922-5687-EL84-/370633042480?pt=Vintage_Electronics_R2&hash=item564b736a30

http://www.ebay.com/itm/Tube-Dampers-Silicone-Ring-fit-12AX7-12AU7-12AT7-12BH7-EL84-10pcs-for-tube-amp-/160750248480?pt=Vintage_Electronics_R2&hash=item256d762220

[HotBluePlates]

So I pretty much have the entire glass covered in goop. 

I was not intending you to apply the RTV sealant to the glass, but if the base was loose from the glass, at the point where they meet.

If you have the glass covered, and it still rattles, then the problem is likely with the internal structure, which you can't do anything about.

I would also be concerned about the tube's ability to dissipate heat with the glass covered. The tube may not die right away, but the excess heat could shorten tube life (by how much is unknowable until the tube finally gives up).

[proaudioguy]

Steve imagine taking those sonicklear giant o rings and lining them up from the top to the bottom.


Hbp i had not considered the glass was loose from the base.  Seems tight.  Ill look into it.  I was wondering if taking the screws out of the tube sockets on the amp and devising a way to insulate the tube from the chassis vibration. Perhaps the chassis itself is rattling the tube.  The way to check I guess would. E to pull the chassis out and hold it so the tubes are very close to the speaker and see if it's still doing it.  First I'll remove the goop. Going to work today so it might be a while before I get to it.

[HotBluePlates]

I was wondering if taking the screws out of the tube sockets on the amp and devising a way to insulate the tube from the chassis vibration.

You can try. You'll need some tiny o-rings, with a hole just big enough to fit the, probably #4, screws that attach the sockets to the chassis. The trick is to also have top-mount tube sockets, so that the o-rings aren't bumping into a part of the socket and preventing a good free fit.

Matchless did that to mount their tube sockets.

[sluckey]

Fender used grommets back in the '50s.

[proaudioguy]

Is it necessary to have the tube brackets grounded?  I'm assuming that was done for a reason on the amp in that picture.
So I could get longer than normal screws and use a flat washer, then O ring, then tube socket flange, then O ring, then chassis, right?  Well I'm in Bradenton now so it'll have to wait.  It's certainly worth trying.

[jojokeo]

Is it necessary to have the tube brackets grounded?  I'm assuming that was done for a reason on the amp in that picture.

Only to ground the shielding tubes if they're used on the preamp tubes. Not for the ocatals unless something like a grounding lug is used on the screws from the underside maybe?

[HotBluePlates]

I think that's a good guess.

Shields for the preamp tubes.

Chance of using metal 6V6's for the output tubes. The metal envelope is considered a shield, connected to pin 1 and grounded (see the Deluxe 5D3 schematic).

Not on the 5Y3 rectifier socket. Don't want to invite arc-over...

[tubenit]

This worked well for me and was inexpensive.

Tubenit