I have a st70 modded with a vta board, upgraded cap board and power transformer …… It had the Sylvania el34’s in it and it sounded awesome! So I thought I would try a set of Gold Lion KT66’s. I installed them along with a new Sovtek 5AR4 and set the bias to .400mv per tube and had a listen…….Its awful! Even my girl friend noticed the difference…lol. The mid and top end is terrible! It sounds like a transistor radio with out sound stage compared to the el34’s? I’m new to tube amps, so maybe I’m doing something wrong? Now I understand the tubes need to break in but I can’t believe it makes that much of a difference, or does it? Also will the AC balance affect the sound? Because I’m not sure it’s adjusted correctly? Any suggestions?
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Dave_in_Va
j beede
musicgeorge11
xlr8
1MOR
kevco
bigmm79
GP49
Bob Latino
opti-mos pat
14 posters
I tried a set of Gold Lion KT66 tubes?????
opti-mos pat- Posts : 13
Join date : 2010-10-19
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
opti-mos pat wrote:I have a st70 modded with a vta board, upgraded cap board and power transformer …… It had the Sylvania el34’s in it and it sounded awesome! So I thought I would try a set of Gold Lion KT66’s. I installed them along with a new Sovtek 5AR4 and set the bias to .400mv per tube and had a listen…….Its awful! Even my girl friend noticed the difference…lol. The mid and top end is terrible! It sounds like a transistor radio with out sound stage compared to the el34’s? I’m new to tube amps, so maybe I’m doing something wrong? Now I understand the tubes need to break in but I can’t believe it makes that much of a difference, or does it? Also will the AC balance affect the sound? Because I’m not sure it’s adjusted correctly? Any suggestions?
Hi,
Try biasing the KT66's a little higher. You can go up to .450 VDC or even .500 VDC per tube on the GL KT66's.
Also, as you mentioned, all tubes nees a break in period. They should improve with 100 hours of run in .. Below is a post on the GL KT66's with another viewpoint ...
Comments on the GL KT66 tubes
Bob
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opti-mos pat- Posts : 13
Join date : 2010-10-19
Ok I'll try biasing a little higher ... Now do you need to play music to break in the new tubes? Or can i just leave it on? Also do they break in faster with loud music? Like I said this is all new to me....
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
Hi,
Play music through the amp .. It doesn't have to be loud ... Normal volume is fine.
Bob
Play music through the amp .. It doesn't have to be loud ... Normal volume is fine.
Bob
GP49- Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon
Recheck bias and readjust after the break-in, too.
bigmm79- Posts : 23
Join date : 2010-09-15
I have a quad of these GL KT66s and they really sound great to me. Surprised to hear your reaction, mine sounded great right off the bat. I ran them at around 43ma per tube for the first couple dozen hours and now at 48ma. I also have some Ruby EL34s and, recently, some Tung-Sol 6l6g. The GLs sound just as good as the EL34s to me, albeit different. I would say the KT66s sound a little bit more "solid state" like and the EL34s are a little less controlled and are a bit more flavored, but in a good way. How's that for some vague audio-speak? The 6l6g tubes seem to have a sound all their own as well, its still changing as they break in, but so far they sound the most "tubey" of the bunch, a liquid otherworldly flavor. I have found the El34s to have the strongest bass, which I didn't expect.
The GLs certainly are expensive, especially when great sound may be had from less expensive tubes like the Ruby el34s.
I'll probably try out the russian 6p5s-e tubes and maybe some other el 34s at some point. Won't be trying anything else priced as high as the GL KT66 though (like GL KT77).
The GLs certainly are expensive, especially when great sound may be had from less expensive tubes like the Ruby el34s.
I'll probably try out the russian 6p5s-e tubes and maybe some other el 34s at some point. Won't be trying anything else priced as high as the GL KT66 though (like GL KT77).
opti-mos pat- Posts : 13
Join date : 2010-10-19
bigmm79 wrote:I have a quad of these GL KT66s and they really sound great to me. Surprised to hear your reaction, mine sounded great right off the bat. I ran them at around 43ma per tube for the first couple dozen hours and now at 48ma. I also have some Ruby EL34s and, recently, some Tung-Sol 6l6g. The GLs sound just as good as the EL34s to me, albeit different. I would say the KT66s sound a little bit more "solid state" like and the EL34s are a little less controlled and are a bit more flavored, but in a good way. How's that for some vague audio-speak? The 6l6g tubes seem to have a sound all their own as well, its still changing as they break in, but so far they sound the most "tubey" of the bunch, a liquid otherworldly flavor. I have found the El34s to have the strongest bass, which I didn't expect.
The GLs certainly are expensive, especially when great sound may be had from less expensive tubes like the Ruby el34s.
I'll probably try out the russian 6p5s-e tubes and maybe some other el 34s at some point. Won't be trying anything else priced as high as the GL KT66 though (like GL KT77).
I raised the bias up too 450mv and played it for about 5 hours last night… I find the midrange to be harsh to my ears. I wasn’t listening to it to loud but at the end, my ears felt like they were ringing….This never happened with the el34’s….like bigmm79 says; it does sound more “solid state”.
Now from your experience does increasing the bias make it sound tubbier or does decreasing it do that? Also, no one commented on the AC balance having an effect on sound……
I’m going to install the triode pentode switches this weekend if I have time….what mode are you guys running with these tubes in, pentode or triode? You think running it in triode mode would make it sound better? Tubbier? Thanks for the input….
kevco- Posts : 69
Join date : 2009-07-16
Location : Aldan, PA, USA
I've run every possible type of power tube in my ST70, my speakers are 99db/meter efficient so I hear everything in the signal chain. GL KT66's sound less "tubey" and more accurate to my ear than EL-34's. That said, they never sounded like a transistor radio and certainly never awful! I do not use a VTA driver board, but I am familiar with it and it is my understanding that AC balance on that board IS important. Do you have the VTA manual? Also running your amp in triode tends to make it sound "tubier" and perhaps less accurate if that's what your looking for.
opti-mos pat- Posts : 13
Join date : 2010-10-19
kevco wrote:I've run every possible type of power tube in my ST70, my speakers are 99db/meter efficient so I hear everything in the signal chain. GL KT66's sound less "tubey" and more accurate to my ear than EL-34's. That said, they never sounded like a transistor radio and certainly never awful! I do not use a VTA driver board, but I am familiar with it and it is my understanding that AC balance on that board IS important. Do you have the VTA manual? Also running your amp in triode tends to make it sound "tubier" and perhaps less accurate if that's what your looking for.
I just picked up this amp…..and not to sure what was do to it other then what the seller told me….I’m going to take a good look at it this weekend….I have been building SS amps by Randy Slone that are very accurate….
(System Bandwidth: 10Hz to 100kHz or wider
0.01% THD N or less across the entire audible Audio Bandwidth of 20Hz to 20kHz
0.1% THD N or less at an Ultrasonic frequency of 50kHz
0.01% THD N or less at a Subsonic frequency of 10Hz
0.01% THD N or less across the entire Power Bandwidth (from lowest level output to 0dB full power) 20Hz - 20kHz
THD N never rises above 0.01% levels at anytime or at any power level within the audible Audio Bandwidth of 20Hz to 20kHz
Ability to reproduce Subsonic and Ultrasonic frequencies with full power output (0dB) without ever exceeding 0.01% THD N at 10Hz Subsonic and 0.1% THD N at 50kHz Ultrasonic
Hum and Noise below -100dB
Symmetrical Soft Clipping. No hard clipping whatsoever when exceeding normal output levels)
Thats why I'm not lookin for accurate^^^^^^^and thats with 250W RMS per channel......
This is my first experience with a tube amp and when I listened to it, it sounded very pleasing to me that I had to have it….very smooth, especially the vocals…. Now when I installed these tubes it no longer sounds like a tube amp…..So that’s why I’m saying this. I like the tube amp to sound like a tube amp, if that makes sense. Now don’t get me wrong I understand your point, it is more accurate and its not awful, I shouldn’t of said it that way, it was just not sounding warm as it did before…..and its not accurate as I’m used to either…..
One more thing….Coming from a hardcore SS guy I’m starting to love these tubbie things…
And my girl friend loves the heat 
Last edited by opti-mos pat on Fri Oct 29, 2010 11:14 am; edited 1 time in total (Reason for editing : added more info)
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1MOR- Posts : 19
Join date : 2010-02-04
WOW! I have a ST-70 that I put together from one of Bob's kits. Per recommendations from this board, I purchased a matched quad of the GL KT66 reissue tubes from Jim McShane. I had been using the Ruby EL34s that Bob supplied. The GL KT66s are outstanding, right from the get go. Over the years, I have owned everything from ARC to Krell. So I do have a frame of reference as to what sounds great and what does not.
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xlr8- Posts : 68
Join date : 2010-02-09
my speakers are 99db/meter efficient so I hear everything in the signal chain. GL KT66's sound less "tubey" and more accurate to my ear than EL-34's. That said, they never sounded like a transistor radio and certainly never awful!
I'll second that. All eight of mine sound fantastic together.
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opti-mos pat- Posts : 13
Join date : 2010-10-19
OK, I got about 50 hours on them now and they seemed to sound a little better but I still didn’t like it as much as the el34’s….
I installed the triode/pentode switches in it this weekend and WOW! I can’t believe that not one person recommended trying these tubes in triode mode, it sounds so much better to me…It sounds more like that “tube amp sound” I was looking for, that it had with the el34’s but more defined. Very nice! I’m glade I tried this….. Before going back to the el34’s
If anyone tries these tubes and finds them not as warm as they like, try them in the triode mode and you will be happy…..
I installed the triode/pentode switches in it this weekend and WOW! I can’t believe that not one person recommended trying these tubes in triode mode, it sounds so much better to me…It sounds more like that “tube amp sound” I was looking for, that it had with the el34’s but more defined. Very nice! I’m glade I tried this….. Before going back to the el34’s
If anyone tries these tubes and finds them not as warm as they like, try them in the triode mode and you will be happy…..
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
Not every tube sounds "just right" in every music system. The original ST-70 with a stock driver board did not have the top end extension that modern tube amps have. A KT66 in a stock ST-70 usually brings out a little more top end that was missing with the stock EL34 tubes. Some people like this effect and possibly some don't.
Your associated equipment like your preamp, CD player, cables and speakers also influence the type of sound you get from your system. Speakers a little on the bright side won't be helped by KT66 output tubes. The extra top end extension on such speakers can make the sound (with KT66 tubes) sound even worse.
Your analysis of the triode mode on any Dynaco amp is spot on. Smoother, mellower and a "tubier" sound are in store for you when you switch to the triode mode. Yes - you do lose a little power in the triode mode. It is possible, however, that you may not even notice (or miss) the slight loss of power when you go from pentode (ultralinear) to triode mode. Rock fans usually like pentode mode. Vocals and acoustic jazz sound really nice in triode.
Bob
Your associated equipment like your preamp, CD player, cables and speakers also influence the type of sound you get from your system. Speakers a little on the bright side won't be helped by KT66 output tubes. The extra top end extension on such speakers can make the sound (with KT66 tubes) sound even worse.
Your analysis of the triode mode on any Dynaco amp is spot on. Smoother, mellower and a "tubier" sound are in store for you when you switch to the triode mode. Yes - you do lose a little power in the triode mode. It is possible, however, that you may not even notice (or miss) the slight loss of power when you go from pentode (ultralinear) to triode mode. Rock fans usually like pentode mode. Vocals and acoustic jazz sound really nice in triode.
Bob
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opti-mos pat- Posts : 13
Join date : 2010-10-19
Bob Latino wrote:Not every tube sounds "just right" in every music system. The original ST-70 with a stock driver board did not have the top end extension that modern tube amps have. A KT66 in a stock ST-70 usually brings out a little more top end that was missing with the stock EL34 tubes. Some people like this effect and possibly some don't.
Your associated equipment like your preamp, CD player, cables and speakers also influence the type of sound you get from your system. Speakers a little on the bright side won't be helped by KT66 output tubes. The extra top end extension on such speakers can make the sound (with KT66 tubes) sound even worse.
Your analysis of the triode mode on any Dynaco amp is spot on. Smoother, mellower and a "tubier" sound are in store for you when you switch to the triode mode. Yes - you do lose a little power in the triode mode. It is possible, however, that you may not even notice (or miss) the slight loss of power when you go from pentode (ultralinear) to triode mode. Rock fans usually like pentode mode. Vocals and acoustic jazz sound really nice in triode.
Bob
I don’t play it to loud so I didn’t notice any power loss.... And your right I listen to music with good vocals and classical guitar and it sounds awesome in triode mode... If I were to have a party and listened to different music I would use them in pentode mode... But for easy listening this works for me.....
musicgeorge11- Posts : 4
Join date : 2017-06-24
Age : 53
Location : Calexico, California
Hi everyone,
New to the forum. Have a couple of Dynaco ST70's, finally came time to modify and work on one, the other I want to leave stock. So for the modified version, I purchased a kit from tubes4hifi, thanks Roy's help I finally decided on purchasing: a) VTA70 octal driver, PCB and parts kit; and b) a capacitance upgrade, and c) the quad cap. So I will be running 6sn7 tubes now, but here is my question: I'm still undecided as to which output tube to use: (listen mainly to jazz, classic rock and b¡ts of classical). Should I go for the KT 66 Golden Lion's or KT 77's? or stay with the el34's?. What reissue brand? and regardind the other tubes, i.e., rectifier and the 6sn7, What do you guys use and recommend? Should add that the amp will be used with a McIntosh c22 and Klipsch Heresy and sometimes KEF LS50 speakers.
Thanks!!!!
New to the forum. Have a couple of Dynaco ST70's, finally came time to modify and work on one, the other I want to leave stock. So for the modified version, I purchased a kit from tubes4hifi, thanks Roy's help I finally decided on purchasing: a) VTA70 octal driver, PCB and parts kit; and b) a capacitance upgrade, and c) the quad cap. So I will be running 6sn7 tubes now, but here is my question: I'm still undecided as to which output tube to use: (listen mainly to jazz, classic rock and b¡ts of classical). Should I go for the KT 66 Golden Lion's or KT 77's? or stay with the el34's?. What reissue brand? and regardind the other tubes, i.e., rectifier and the 6sn7, What do you guys use and recommend? Should add that the amp will be used with a McIntosh c22 and Klipsch Heresy and sometimes KEF LS50 speakers.
Thanks!!!!
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j beede- Posts : 473
Join date : 2011-02-07
Location : California
A couple suggestions based on my experiences:
-Keep the number of variables small as you experiment
-Consider using socket savers if you will be doing many tube swaps
-Let your amp run for at least 30 minutes after swapping tubes before you make any observations. 30 days of cycling would be even better.
-If you haven't already done so, and if you plan on using tube rectification, pre-rectify your B+ via the "yellow sheet" modification
-I am pleased with the Sovtek 5AR4 rectifiers that I buy from Guitar Center
-What are you trying to achieve by replacing EL-34 with KT-66? The GL KT-66 look cool--that's why I use them ;-)
-Keep the number of variables small as you experiment
-Consider using socket savers if you will be doing many tube swaps
-Let your amp run for at least 30 minutes after swapping tubes before you make any observations. 30 days of cycling would be even better.
-If you haven't already done so, and if you plan on using tube rectification, pre-rectify your B+ via the "yellow sheet" modification
-I am pleased with the Sovtek 5AR4 rectifiers that I buy from Guitar Center
-What are you trying to achieve by replacing EL-34 with KT-66? The GL KT-66 look cool--that's why I use them ;-)
Dave_in_Va- Posts : 443
Join date : 2013-04-02
Location : Mid. VA
This is just my limited experience with power tubes in my VTA ST70.
I tried a quad of Gold Lion KT 88's and I thought the stock Valve Arts EL 34's sounded better. I also tried EH, ANOS set of Siemans and a NOS set of Mullards from about 1969-'70. The Mullards sound the best, Valve Art second.
I am not set up for octals in my ST70.
I've used several rectifiers and I think there's a JJ or Ruby in there now. Remember to re-tension your sockets. It's super important. I think I lost a Mullard EL34 and both a NOS Mullard and Sylvania 5AR4 rectifier because I wasn't careful about re-tensioning when messing around with the tubes.
I tried a quad of Gold Lion KT 88's and I thought the stock Valve Arts EL 34's sounded better. I also tried EH, ANOS set of Siemans and a NOS set of Mullards from about 1969-'70. The Mullards sound the best, Valve Art second.
I am not set up for octals in my ST70.
I've used several rectifiers and I think there's a JJ or Ruby in there now. Remember to re-tension your sockets. It's super important. I think I lost a Mullard EL34 and both a NOS Mullard and Sylvania 5AR4 rectifier because I wasn't careful about re-tensioning when messing around with the tubes.
musicgeorge11- Posts : 4
Join date : 2017-06-24
Age : 53
Location : Calexico, California
Many thanks guys. J beede: my aim using the KT66 is also partly esthetics, but I was mostly driven by Bob Latino's comments in a different thread, and I imagine these are better with rock music and the Klipsch's. Thanks Dave_in_Va, will search for those tubes also before buying and deciding. Thanks for the advice!
knotscott- Posts : 58
Join date : 2019-12-28
Location : Rochester, NY
I had been using the ElectroHarmonix EL34s on my Dyna/VTA 70s for about a year, and found them very pleasant. I switched to the GL KT66 and didn't like them quite as much at first. Lower mids sounded a little bloated, and treble emphasized sibilance at first. However, the midrange was lush, and showed a lot of promise, so I stuck with them. Now that they've got some 60+ hours or so on them, and the bias has been increased slightly, they're starting to sound wonderful from top to bottom....it just takes quite a bit of time.
Update 10/26/2022: It took every bit of Bob's suggested 100 hour burn-in time for these to come around. Almost a year and a half later I really love the GL KT66s on the Dyna/VTA 70s, and am getting phenomenal sound. I'm currently running two Dyna/VTA 70s as single channel monoblocks in triode, along with SS diode rectifiers.
Update 10/26/2022: It took every bit of Bob's suggested 100 hour burn-in time for these to come around. Almost a year and a half later I really love the GL KT66s on the Dyna/VTA 70s, and am getting phenomenal sound. I'm currently running two Dyna/VTA 70s as single channel monoblocks in triode, along with SS diode rectifiers.
Last edited by knotscott on Wed Oct 26, 2022 10:55 am; edited 1 time in total
Brap- Posts : 229
Join date : 2013-11-28
Age : 68
Location : Plainfield, illinois
Been running GL 66's for 6+ years in my VTA-ST70 and love them. Would get them again. I agree - 60+ hours and the sound opens up.
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itrfguy- Posts : 22
Join date : 2020-10-26
Location : Lehigh Acres, FL
Love the KT66 tubes in triode mode.
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peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
Unless you have reduced the grid resistor ( 270k in this amp) to 100k you could experience
current avalance aka redplating in the future.
https://frank.pocnet.net/sheets/086/k/KT66.pdf
current avalance aka redplating in the future.
https://frank.pocnet.net/sheets/086/k/KT66.pdf
Brap- Posts : 229
Join date : 2013-11-28
Age : 68
Location : Plainfield, illinois
Over the Holidays, I replaced my GL KT-66's with new ones since the originals have 8 years on them. The sound "opened" up again - amazing. In discussing this with Bob, he mentioned that over time, there is sound degradation -- very subtle so it really is not noticeable until you get new tubes. Making this change and re-biasing to 0.450 VDC, the amp came back to a more detailed open soundstage. Highly recommen GL KT-66's from vacuumtubevalues.com
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