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deluxmon

arledgsc

Jim McShane

Dave_in_Va

Bob Latino

dougmon

10 posters

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variety of 6l6 tubes

dougmon: Posts : 65
Join date : 2013-11-04
Age : 67

Post n°1

variety of 6l6 tubes

by dougmon Thu Jan 30, 2014 1:36 pm

Hi:

The time has come once again to expose my ignorance of electronics Rolling Eyes

Rolling Eyes

I have a question, and instead of bugging Bob via email, I thought "why not tap into the vast knowledge of the community?"

Bob has told me that any 6L6 will work fine in the VTA ST-70, and I believe him. Who would know better?

But I've talked to a few people who tell me "Don't use a vintage 6L6GA - any modern amp will fry it" Obviously a blanket statement like that is bound to be wrong, but it does bring up a question in my mind.

If the VTA ST-70 will handle both the 6L6GA and the 6L6GC with their large differences in power handling (or max plate voltage as I understand it), is it running the 6L6GC at less than optimum? Does this question make sense?

Thanks for any info on this. The VTA ST-70 is the first amp I've owned that can handle a lot of different tubes, so questions like this haven't come up before.

By the way, I tried to search on 6L6 on this forum and got no results. But I'm sure I've seen posts talking about the 6L6 - or am I mistaken?

Bob Latino: Admin; Posts : 3262
Join date : 2008-11-26
Location : Massachusetts

Post n°2

Re: variety of 6l6 tubes

by Bob Latino Thu Jan 30, 2014 4:03 pm

Hi Doug,

The VTA ST-70 runs a plate voltage of 435 to 445 VDC. Check to see if that particular variety of 6L6 will handle that amount of voltage on the plates. Over the years I have run 6L6's a number of times in ST-70's and have never run into a problem.

Bob

dougmon: Posts : 65
Join date : 2013-11-04
Age : 67

Post n°3

Re: variety of 6l6 tubes

by dougmon Thu Jan 30, 2014 4:27 pm

Talked with a guy who has 40 billion tube manuals (ok, I'm exaggerating a bit) and he says it looks like the 6L6GA has a max of 360 VDC. He also said they'll run in the ST-70, but there might be reliability problems. Looks like I'm stuck with the 6L6GC or EL34 for now. Not that I can really complain about that - Laughing

Laughing

Dave_in_Va: Posts : 443
Join date : 2013-04-02
Location : Mid. VA

Post n°4

Re: variety of 6l6 tubes

by Dave_in_Va Thu Jan 30, 2014 5:24 pm

I've got KT 88s in my VTA ST 70. I can't tell if I like them better than the stock EL 34's or not. They sure look cool, though........

dougmon: Posts : 65
Join date : 2013-11-04
Age : 67

Post n°5

Re: variety of 6l6 tubes

by dougmon Thu Jan 30, 2014 5:40 pm

Dave_in_Va wrote:I've got KT 88s in my VTA ST 70. I can't tell if I like them better than the stock EL 34's or not. They sure look cool, though........

I used to have an amp that was built for 6550/KT-88 tubes, but would take EL34s if you rebiased. I liked the KT-88s for some things, and the EL34s for other things. I thought the KT-88s were clean and detailed, but that the EL34s had a better midrange presentation. For either tube, I liked the SED =C=. If you can find a quad of the SED =C= KT-88s, though, they'll cost you quite a lot. You can still get the =C= EL34s, though -- they're expensive, but really very good.

For now, though, it's the 6L6GCs for me. Of the less expensive modern 6L6 tubes, I like the Tung-Sol 6L6G (thank you, Jim McShane, for the recommendation) -- they're really just 6L6GC tubes in a big bottle.

What KT-88s are you using? Can you give your impressions?

Dave_in_Va: Posts : 443
Join date : 2013-04-02
Location : Mid. VA

Post n°6

Re: variety of 6l6 tubes

by Dave_in_Va Thu Jan 30, 2014 6:03 pm

Genelex Gold Lions from Jim also. I'm afraid I'm not much good at objectively describing how things sound.
I had some Chinese Psvanes that I THINK I liked better but one tube in the quad was kind of troublesome..it wouldn't bias properly.
The Genelex biased up perfectly and are stable.
I may just go back to the original Valve Art EL 34's and sell the Genelex quad here. It's a tough call.

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°7

Re: variety of 6l6 tubes

by Jim McShane Thu Jan 30, 2014 8:43 pm

Bob Latino wrote:Hi Doug,

The VTA ST-70 runs a plate voltage of 435 to 445 VDC. Check to see if that particular variety of 6L6 will handle that amount of voltage on the plates. Over the years I have run 6L6's a number of times in ST-70's and have never run into a problem.

Bob

A question Bob - what happens to the heater voltages when you plug 6L6 tubes into the amp. The current draw drops by about 2.4 amps which certainly could allow the heater voltage to rise. Have you got any info you can share on that?

THANKS!!

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°8

Re: variety of 6l6 tubes

by Jim McShane Thu Jan 30, 2014 8:50 pm

Dave_in_Va wrote:For now, though, it's the 6L6GCs for me. Of the less expensive modern 6L6 tubes, I like the Tung-Sol 6L6G (thank you, Jim McShane, for the recommendation) -- they're really just 6L6GC tubes in a big bottle.

Other than some differences in interelectrode capacitances the 6L6G is rated pretty much identically to the 6L6GC. But don't make the same assumptions about the old stock tubes - 'cause it isn't correct.

Thank YOU Dave - for the kind words. That tube has started to catch on more now, and a lot of guys really like it. I'm one of them!!

Last edited by Jim McShane on Fri Feb 07, 2014 5:12 pm; edited 2 times in total (Reason for editing : Typo repair!)

Bob Latino: Admin; Posts : 3262
Join date : 2008-11-26
Location : Massachusetts

Post n°9

Re: variety of 6l6 tubes

by Bob Latino Fri Jan 31, 2014 9:46 am

Jim McShane wrote:

Bob Latino wrote:Hi Doug,

The VTA ST-70 runs a plate voltage of 435 to 445 VDC. Check to see if that particular variety of 6L6 will handle that amount of voltage on the plates. Over the years I have run 6L6's a number of times in ST-70's and have never run into a problem.

Bob

A question Bob - what happens to the heater voltages when you plug 6L6 tubes into the amp. The current draw drops by about 2.4 amps which certainly could allow the heater voltage to rise. Have you got any info you can share on that?

THANKS!!

I don't have any info on heater voltage rise when using 6L6 type tubes in an ST-70. I have many years ago used 6L6 tubes in an ST-70 with no issues but I honestly never checked the heater voltages when the 6L6's were in the amp. Customers have mentioned to me about using the Russian 6P3S-E in their VTA ST-70 amps with success. I personally have not used these Russian military 6L6 type tubes.

Jim - Are you saying that you don't recommend the use of 6L6 type tubes in an ST-70 ?

Bob

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°10

Re: variety of 6l6 tubes

by Jim McShane Fri Jan 31, 2014 10:26 am

Bob Latino wrote:

Jim McShane wrote:

Bob Latino wrote:Hi Doug,

The VTA ST-70 runs a plate voltage of 435 to 445 VDC. Check to see if that particular variety of 6L6 will handle that amount of voltage on the plates. Over the years I have run 6L6's a number of times in ST-70's and have never run into a problem.

Bob

A question Bob - what happens to the heater voltages when you plug 6L6 tubes into the amp. The current draw drops by about 2.4 amps which certainly could allow the heater voltage to rise. Have you got any info you can share on that?

THANKS!!

I don't have any info on heater voltage rise when using 6L6 type tubes in an ST-70. I have many years ago used 6L6 tubes in an ST-70 with no issues but I honestly never checked the heater voltages when the 6L6's were in the amp. Customers have mentioned to me about using the Russian 6P3S-E in their VTA ST-70 amps with success. I personally have not used these Russian military 6L6 type tubes.

Jim - Are you saying that you don't recommend the use of 6L6 type tubes in an ST-70 ?

Bob

Hi Bob,

If the heater voltage rises too much it can shorten tube life, but there would be no immediate indication of any issues. The amp will work and play well. So I was hoping somebody would measure the voltages and tell us what they find with EL34 family tubes in there and again with 6L6 family tubes. I am concerned, so I'd like to know what actually occurs rather than just speculate about it. I'd be happy to measure them myself but I don't have access to an ST-70.

I am less concerned about using KT-66 Genalex reissues or any other "real" KT-66. They draw more current than a standard 6L6 (1.2 amps per tube vs. .9 amps) so the loading on the heater windings is closer to the stock tube draw of 1.5 amps per EL34 tube.

The bottom line is that I'd like people to know what they are getting into when they make that swap. They can then decide what they'd like to do.

arledgsc: Posts : 495
Join date : 2012-11-30
Age : 70
Location : Santa Rosa CA

Post n°11

Re: variety of 6l6 tubes

by arledgsc Fri Jan 31, 2014 10:46 am

I used Gold Lion KT-77s in a Marshall clone guitar amp for some of that 6L6 type goodness with a Fender strat. Not as gritty and smoother low end response versus EL34s. If you shop around they are not all that expensive for a quad.

Bob Latino: Admin; Posts : 3262
Join date : 2008-11-26
Location : Massachusetts

Post n°12

Re: variety of 6l6 tubes

by Bob Latino Fri Jan 31, 2014 11:55 am

Ok - Jim McShane has 6L6's and no ST-70. I have an ST-70 here but I don't have any 6L6's ... If one of the forum members has BOTH an ST-70 and 6L6 output tubes, could you drop the 6L6's in, rebias the amp and measure the heater voltage. If you also have EL34's, maybe you could also measure the heater voltage with EL34's also so we could see how much the heater voltage rises when switching from EL34 output tubes to 6L6's ? I am glad that Jim brought this up. I had never even considered the rise in heater voltage when you use 6L6's in an ST-70 and its affect on tube life ...

Bob

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°13

Re: variety of 6l6 tubes

by Jim McShane Fri Jan 31, 2014 1:09 pm

arledgsc wrote:I used Gold Lion KT-77s in a Marshall clone guitar amp for some of that 6L6 type goodness with a Fender strat. Not as gritty and smoother low end response versus EL34s. If you shop around they are not all that expensive for a quad.

Good advice! The KT-77 Genalex has been described as a "cross" between an EL34 and a 6L6. It does have more top end energy than an EL34 - much like a 6L6!

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°14

Re: variety of 6l6 tubes

by Jim McShane Sat Feb 01, 2014 2:42 pm

Bob Latino wrote:Ok - Jim McShane has 6L6's and no ST-70. I have an ST-70 here but I don't have any 6L6's ... If one of the forum members has BOTH an ST-70 and 6L6 output tubes, could you drop the 6L6's in, rebias the amp and measure the heater voltage. If you also have EL34's, maybe you could also measure the heater voltage with EL34's also so we could see how much the heater voltage rises when switching from EL34 output tubes to 6L6's ? I am glad that Jim brought this up. I had never even considered the rise in heater voltage when you use 6L6's in an ST-70 and its affect on tube life ...

Bob

Bob,

If no one volunteers I'll send you a quad of new 6L6GCs to allow you to test the voltages. It's an important issue, and I know how much making quality products and giving good advice means to you (me too!). So let me know if you want/need them and I'll get them off to you - on me, of course.

Last edited by Jim McShane on Sat Feb 01, 2014 2:43 pm; edited 1 time in total (Reason for editing : Fix typo)

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°15

Re: variety of 6l6 tubes

by Jim McShane Fri Feb 07, 2014 5:09 pm

I shipped a matched quad of 6L6GC-STR Tung-Sols to Bob today - he volunteered to do the testing of heater voltages. He should have them by next Tuesday or so, so sometime after that he will be able to share his findings with us.

A big thanks to Bob!! This is VERY useful information he's developing for us all.

Last edited by Jim McShane on Sat Feb 08, 2014 4:19 pm; edited 1 time in total (Reason for editing : Typo (what else?))

Bob Latino: Admin; Posts : 3262
Join date : 2008-11-26
Location : Massachusetts

Post n°16

Re: variety of 6l6 tubes

by Bob Latino Mon Feb 10, 2014 4:09 pm

A quad of Tung-Sol 6L6GC STR's arrived today in the mail from Jim McShane (thanks Jim!) to compare to the Ruby EL34's that I had in the stock ST-70 that I have here ..

With the EL34's in there and biased to about 40 milliamps per each output tube (about 1.25 VDC per each PAIR) of tubes
B+ voltage was 441 VDC, heater voltage was 6.15 VAC with an incoming line voltage of 119.7 VAC

I then pulled the EL34's and plugged in the Tung-Sol 6L6's. First off I could not get the bias voltage down to the 1.25 volts that would be about 40 milliamps per each output tube. About the lowest that either channel would go down to was about 1.47 volts which equates to about 47 milliamps per each output tube. To get these tubes down further will require an adjustment on the two bias resistors on the 7 lug terminal strip. I later played both sets of tubes for about 1/2 hour each. Both sets of tubes sounded fine with maybe a slight advantage to the 6L6's BUT - the Ruby EL34's that came with this amp have unnkown hours on them so any comparison would be an "apples and oranges" comparison.

The filament voltage on the 6L6's only rose marginally to 6.3 VAC, the B+ went down one volt to 440 VDC with a 119.6 VAC incoming line voltage. Interestingly enough, both sets of tubes used the same amount of power on idle > 155 watts

Bob

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°17

Re: variety of 6l6 tubes

by Jim McShane Mon Feb 10, 2014 9:08 pm

Bob,

Thank you VERY much for your effort! That's great to have accurate and reliable data to go on.

deluxmon: Posts : 17
Join date : 2013-03-20
Age : 69
Location : DENVER

Post n°18

Re: variety of 6l6 tubes

by deluxmon Sat Apr 12, 2014 9:45 am

Has anyone tried 5881's - which I believe to be a military version of the 6l6 in one of Bob's ST-70's?

GP49: Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon

Post n°19

Re: variety of 6l6 tubes

by GP49 Sat Apr 12, 2014 10:39 am

I have a set of metal 1614 tubes that are a 6L6 type. Never have heard them. Others were the 1622 and 7581.

Jim McShane: Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago

Post n°20

Re: variety of 6l6 tubes

by Jim McShane Sat Apr 12, 2014 1:34 pm

GP49 wrote:I have a set of metal 1614 tubes that are a 6L6 type. Never have heard them. Others were the 1622 and 7581.

IIRC some early Macs (among others) used the 1614. They aren't a bad tube at all, but they were never common so they are hard to find in matched sets now.

corndog71: Posts : 840
Join date : 2013-03-19
Location : It can get windy here

Post n°21

Re: variety of 6l6 tubes

by corndog71 Sat Apr 12, 2014 10:11 pm

There's a new American company called RCH Labs set to release two versions of 6L6 at the end of the year. The standard version will be $40 but they'll also have a premium version made with a proprietary metal called "Supernal". Both will be cryo-treated as well.

I heard they got a hold of RCA's tube-making gear. Eventually they plan to release more tubes such as the KT88, 12AU7, 12AX7, and 12AT7. Possibly more.

Guest: Guest

Post n°22

Re: variety of 6l6 tubes

by Guest Sat Apr 12, 2014 10:22 pm

corndog71 wrote:There's a new American company called RCH Labs set to release two versions of 6L6 at the end of the year. The standard version will be $40 but they'll also have a premium version made with a proprietary metal called "Supernal". Both will be cryo-treated as well.

I heard they got a hold of RCA's tube-making gear. Eventually they plan to release more tubes such as the KT88, 12AU7, 12AX7, and 12AT7. Possibly more.

a link to their web site, not a lot of info on it as yet.
I just hope their tube prices will be reasonable!
http://www.rchlabs.com

corndog71: Posts : 840
Join date : 2013-03-19
Location : It can get windy here

Post n°23

Re: variety of 6l6 tubes

by corndog71 Sat Apr 12, 2014 10:36 pm

I forgot to add that their premium tubes will cost $120 each! Shocked

Shocked

Guest: Guest

Post n°24

Re: variety of 6l6 tubes

by Guest Sun Apr 13, 2014 10:13 am

corndog71 wrote:I forgot to add that their premium tubes will cost $120 each!

guess I won't be buying from them in a hurry!

skriefal: Posts : 135
Join date : 2011-09-20
Location : Utah, USA

Post n°25

Re: variety of 6l6 tubes

by skriefal Sun Apr 13, 2014 4:08 pm

$40 each for the standard grade 6L6 isn't bad. A pair of those in a single-ended amp would be a nice bedroom setup...

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Re: variety of 6l6 tubes

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