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Best production EL34?

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#21
Thanks Jim, it is all so confusing.. I have mostly avoided the issue by buying other brands or by getting them overseas.

OT: Any recommendations for a current production KT88 or 6550 that will be reliable at voltages slightly in excess of 500V? I have not had good luck with JJ KT88 in this particular amplifier and need to find something else.
 
#22
kevinkr said:
Thanks Jim, it is all so confusing.. I have mostly avoided the issue by buying other brands or by getting them overseas.

OT: Any recommendations for a current production KT88 or 6550 that will be reliable at voltages slightly in excess of 500V? I have not had good luck with JJ KT88 in this particular amplifier and need to find something else.
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I've had very good luck with the EH. I've handled a few of the Genalex reissue as well, but far too few to have any worthwhile feedback for you.

The EHs are my current recommendation in the Citation II, they can take a pounding. Do be aware they have a lighter tonal balance than the JJ. Excellent bass, very well controlled - just not as much of it as some others.

JJ? Far too many quality issues for me to deal with, I stopped carrying almost all their stuff.
 
#24
kstagger said:


I have an old 60s era '70 I rebuilt a few years ago with the SDS Power supply board and the Triode Electronics input board.

The Svetlana version of the 6L6GC is pretty tough - 30W plate/500V max
http://www.drtube.com/datasheets/6l6gcsvet1996.pdf

- so (this was in a pinch!) I biased them up like the EL34. Treble seemed a little softer than the Matsushita EL34, but otherwise an excellent sounding tube. They also served duty when I was testing a pair of rebuilt Mark IIIs and they took the abuse (biased for lower than 6550 current though).
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Oh I did not know that you could just pop them in and they would be close enough to work. What did you bias them at?
I bias the 6L6GC's at 0.410 in the St-70 and they sound great. I did have some cheap Chinese tubes and they would start to glow nicely at that but they sounded terrible so they are in a box now somewhere. I have tried many 6L6GC's and currently are torn between a quad of RCA black plate clear tops and a quad of Rodgers black plates. They are both called black plates but the clear tops are really not that black.
 
#25
#26
tubelab.com said:


I have always had good luck with old Svetlana / Winged C tubes, but not this time. One of the Winged C tubes had a clearly mis alligned screen grid which glowed brightly at 325 volts. It distorted badly and I did not want to try it at higher voltages. Another tube exhibits a glowing grid wire (only one) at voltages over 350 volts. The other two work fine and can handle everything that I throw at them. 2 out of 4 is not good odds, maybe this is an anomaly.
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tubelab.com said:


The Electro Harmonix EL34's are the smallest EL34 tubes. They can handle about 30 watts before glowing. No grid wire glow in 8 tubes at max voltage. The sound is similar to the Shuguangs, maybe a little brighter.

I have one of the fat bottle EH 6CA7 tubes. Be aware that this tube is actually a beam tetrode so it is not exactly identical to an EL34. I tested it with good results. I could crank 35 watts through it without glow and it rocked. It is the loudest and has the best bass of all of the tubes tested. I only tested one tube, but it draws more current than the other types.
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tubelab.com offered his knowledgeable opinions of these earlier. Those are the same ones that I was looking at on ebay. At that price you can afford to play around with a few different sets.
 
#28
OT: Any recommendations for a current production KT88 or 6550 that will be reliable at voltages slightly in excess of 500V? I have not had good luck with JJ KT88 in this particular amplifier and need to find something else.
Click to expand...

I second the reccomendation for EH. These tubes have added heat radiating fins welded to the plates at the spot where the red glow usually happens. I have run them in triode mode in my SE amps with 490 volts of B+ and 100 mA of current. Since the amp uses cathode bias the actual voltage across the tube is about 430 volts.

I tested an amp with a monster Antek toroid (800 VCT 400 VA) and SS rectification yielding about 525 volts of B+. I ran all 8 tubes that I have through this amp and no issues were seen. I didn't run them long for fear that my 500 volt electrolytics would soon depart from the planet once the amp got hot. I plan to build a monster SE amp using this power transformer and 4 of these tubes (2 per channel). This test was mainly to select two matched pairs of tubes for this amp and set them aside.

tubelab.com offered his knowledgeable opinions of these earlier. Those are the same ones that I was looking at on ebay. At that price you can afford to play around with a few different sets.
Click to expand...

There are reports that factory reject Shuguang, New Sensor , and SED tubes are being sold on Ebay. I bought several Shuguang "coke bottle" 6L6GC tubes on Ebay, 4 tubes for $12 (that vendor now charges $15 for 4 tubes). This is below the price that most tube dealers pay. I don't know where these tubes are coming from, but I have tortured them severely and none have blown up yet. When I buy $3 or $4 tubes from Ebay, I expect some of them to be junk. Sometimes they are, sometimes they work well.

The Winged C tubes that I have were purchased from a reputable supplier, are only marked with the =C= logo, came in white boxes with a =C= sticker on them. 2 out of 4 are defective. These days you take your chances with any tube in current production. I think every manufacturer makes a bad batch of tubes now and then. What happens to them is another matter. Some are obviously marked up to resemble first quality tubes and sold as such.

Thanks for the info. I might go for the EH Fat Bottles but tubelab.com mentioned it draws more current. I wonder if that would be an issue with the Dynaco ST-70? My other question would be since the tube the Fat Bottle EL34's are not an exact copy of the real EL34, what tube is it a direct replacement for?
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All of the EL34's and 6CA7's made in the 70's and before were true pentodes. There have been some beam tetrodes labled 6CA7 and even EL34 produced since then. The EH 6CA7 is one of these. New Sensor has been rather liberal with the type numbers that they use on some of their tubes. The Electro Harmonix brand was used on guitar effects boxes in the 70's, and is now owned by New Sensor. It seems that they have been offering tubes with improved power handling capabilities for the guitar amp market. Guitar amplifiers are typically tough on tubes, and some of the EH tubes seem to be modified for better life in a guitar amp. The 6CA7, KT88EH, 6550EH, and EH6L6GC fall into this category. They bear little resemblance to the originat tube type, but all seem to do a good job in the "stress test" department. I don't know if any of these are a "direct replacement" for any particular tube type. The one 6CA7 that I have does draw about 72 mA when plugged into my amp (cathode bias) where all of the other EL34's draw 60 to 65 mA. The tube seems to work well at this current, KT88EH's and 6550EH's draw over 100mA in the same amp where GE 6550's draw about 85 mA.
 
#29
tubelab.com said:


The 6CA7, KT88EH, 6550EH, and EH6L6GC fall into this category. They bear little resemblance to the originat tube type, but all seem to do a good job in the "stress test" department. I don't know if any of these are a "direct replacement" for any particular tube type.
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I'ds be curious as to why you would think they weren't direct replacements. If it is because the current drawn varied from the old stock tube's draw then I would beg to differ with you in using that as a criterion.


tubelab.com said:

The one 6CA7 that I have does draw about 72 mA when plugged into my amp (cathode bias) where all of the other EL34's draw 60 to 65 mA. The tube seems to work well at this current, KT88EH's and 6550EH's draw over 100mA in the same amp where GE 6550's draw about 85 mA.
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Well, I'm sure you know that there is a significant difference between tubes of any given make/number in terms of how much current they pass. For instance, the GE 6550As I've tested and matched (over 500 of them) will pass anywhere from about 55 to about 110 ma at my setup of 465 volts plate and screen with -50 at the grid. The 6CA7 EHs fall in the same category in terms of variance. That variance is 100% normal. That's why matching of tubes is done - to put together sets of tubes with identical characteristics.

The 6CA7s bias different than the KT88 and 6550. That's why you found a difference there.
 
#30
I am aware of the huge variances from tube to tube of the exact same type and make. These variances are much greater with fixed bias set at a constant value (say 50 volts) than cathode bias with a fixed resistor value, 560 ohms in my case. As I stated, I am making assumptions based on one tube which may or may not be valid. I don't have any more of those tubes to try.

I bought a large box of "pre auditioned" Russian tubes for $10 each. They all have TubeStore.com stickers on them, and I suspect that they were probably returns that tested OK. Even so, all of the EL34 variants that I have run through the amp draw 60 to 65 mA with no changes to the amp. I think that there were a few slightly outside this range, but I am at work now so I don't have my data. The EH6CA7 drew 72 mA in the same amp. This is not a big deal in a cathode biased amp, and it won't be in a fixed bias amp that has provisions for adjustment. I liked the sound of that tube, and I will get some more sooner or later. Yes, bias current alone is not a criteria to call a tube "different". The EH 6CA7 did however sound different than all of the other EL34's, it was louder and had more bass. The internal construction is also completely different from an EL34, it is a beam tetrode, where all of the EL34's are true pentodes. Any data that I can find on 6CA7's show them as true pentodes.

I also got 8 KT88EH's and 2 EH 6550's (these appear to be the same tube). I selected my matched pairs from these 10 tubes based on bias current at the intended operating voltage (520 volts), and transconductance (change in curent for a 1 volt step in grid voltage) at the intended operating voltage. One pair turned out to be a KT88 paired with a 6550 (both EH). These tubes can run calmly at 45 watts dissipation showing no color on the plate in a dark room. None of my other KT88's or 6550's can do this, and none of them come anywhere near matching the EH tubes. The EH tubes have far better bass and just flat rock better than any of the other KT88 or 6550 tubes. Same goes for the EH 6L6GC and the Sovtek 6L6WXT. They appear to be the same, but don't look or sound like any other 6L6GC in HiFi applications.

Does this make them not a "direct replacement"? I don't know. I am sure that you could put any of the EH tubes in place of any of the original types in most amps with only a bias adjustment. Some of them will sound quite different than the original. I am not saying this is a bad thing, just different. This goes for many tubes being manufactured today. Many new production 7189's, EL84's, and 7591's will melt in some old amps that violate the published plate and screen voltage specs. They are definitely not "direct replacements" for the original tubes.

I sold my Dynaco ST70 years ago and don't remember if it had adjustable bias or not. There are a few HiFi amplifiers and some guitar amps that have non adjustable fixed bias. These tend to operate on the verge of meltdown already due to todays high line voltage. I would hesitate to just pop a pair of these tubes into one without carefully checking things out. If you know what you are doing, they can be made to work.

The 6CA7s bias different than the KT88 and 6550. That's why you found a difference there.
Click to expand...

I know this. I picked an operating point that seems to work with 6L6's, EL34's, 6550's and KT88's. The 6L6's run hot, about 28 watts dissipation, only the strong will survive. The EH 6L6GC and Sovtek 6L6WXT work well here and sound the best of all the 6L6 types that I tried. The older Shuguang "coke bottle" tubes show a little color but play amazingly well and have lived for almost 2 years. EL34's all bias up at about 24 watts and work well. Most 6550 and KT88 tubes bias up at around 30 to 35 watts, except for the EH tubes which draw a lot more current and run at 40 to 45 watts. They are not bothered by this and sound the best of all tubes tested if you want to play it loud.

The picture shows a pair being tested at 45 watts dissipation.
 

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#31
MAybe a little off subject but tonight I blew the dust off one of my ST.70's and tried a quad of Sylvania 6L6CG's that I used to beat to death in my old Bassman. I am surprised that the 6L6 sound as good or better than ANY of my EL34's!😱
 
#32
Thats interesting I have 3 brand new quads of the Russian 6L6WXT's in my stock and would love to try a set in my Dynaco ST-70. Looking at the data sheet for the 6CA7 and 6L6 (see attachment) the basing is different as the 6L6 has G3 and K tied to pin 8 and the 6CA7 has G3 on pin1 and K on pin 8.

The good thing is G3 and K are tied together on the Dynaco ST-70.

Pyre mentioned he set the bias at 0.410 volts. How did you arrive at that number? Even though I played with tube audio and never designed a tube amp to figure the bias out.

The heater requirements for the 6L6 is .9amps and the 6CA7 is 1.5 amps so that should ease the pain on the power transformer.

Regards,
Sal Brisindi
 

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#33
Pyre said:
Hello,

I have a unmodified ST-70 that came with no tubes. I plan on modifying the ST70 and getting some better tubes for it later but would like to pick up a quad of current production tubes to run it with so that I know all the tubes are good and in case I blow some stuff up I am not tossing out a good vintage tube. From what I have seen for choices under $100.00 bucks a quad I have seen:

EL-34 Mullard Reissues quad 70$
Shuguang EL34B quad 45$
EL34 SED SVETLANA winged quad 80$
Quad 6CA7 ELECTRO HARMONIX EH EL34 Fat bottle 55$
Quad EL34 ELECTRO HARMONIX EL34EH 6CA7 50$

Is there any EL34's under 100 bucks a quad new that are worth buying or does anyone have any good things to say about the tubes in this list. The Fat bottle electro's sure look pretty but that does not mean they sound ok.

Thanks for your constructive opinions in advance.
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Give JJ-electronics a try. Good price to durability and sound ratio IMHO. They are pretty much my default when i am not going to plunk NOS into a circuit. Some of the current Russian fat bottles are not bad, but they have suffered horribly premature failures in some of my stuff where JJ's and NOS keep going and going.
 
#34
Sal Brisindi said:

Pyre mentioned he set the bias at 0.410 volts. How did you arrive at that number? Even though I played with tube audio and never designed a tube amp to figure the bias out.
Click to expand...

The 0.410 volt bias is the amount of current between pin 8 and the chassis as set by the bias pot. This is the recommended voltage from Audio Research. I have tried it a bit lower and higher but it sounds best at 0.410
 
#36
I've just finished a modified (has a 2 x 6au6 + 1 x 12AU7 upgrade board) ST-70 restoration. The owner is the Head of Percussion at the State Universty School of Music. He has been tube rolling since I completed the restoration for him. If you are willing to take the advise of a drummer - he settled on JJ KT77.

As for me - frankly I didn't like the ST-70 with any of the tubes tried. Sterile and boring with no stereo image to speak of.

Cheers,
Ian
 
#37
KT77 being good, that will interest tubelab, if his empty pockets will - and the many that will build his amp

A long time ago I put a KT88 in place of a KT66, and the poor amp played ok, but didnt last long
If the KT77 is a combination of the two, I am sure its the one to choose, with the finesse of the KT66 and the power of the KT88, but maybe only in my dreams

UPS, sorry.....topic, EL34
 
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