Looks like a good kit for a starting point. neat looking chassis with good transformers.
I'm looking for people's impressions of the difference in sound / tone / flavour / smell / texture or whatever between the EL34, the 6550 and the KT88 in this style of manual bias p-p amp topology.
I've done a lot of searching and the kt88 seems harsh, the el34 mellow and the 6550 something in between. That's about all I could find. A lot of the discussion is about their use in guitar amps which is not much help to me.
Please share your experiences with currently available (not NOS) versions of these tubes. I know there are a lot of dodgy kt88 copies out there. I'm mainly interested in differences between the el34 and the 6550. A transparent, detailed amp is my primary aim but I admit I like the look of the old fashioned bulbous glass envelopes given a choice between two otherwise equal tubes.
I'm looking for people's impressions of the difference in sound / tone / flavour / smell / texture or whatever between the EL34, the 6550 and the KT88 in this style of manual bias p-p amp topology.
I've done a lot of searching and the kt88 seems harsh, the el34 mellow and the 6550 something in between. That's about all I could find. A lot of the discussion is about their use in guitar amps which is not much help to me.
Please share your experiences with currently available (not NOS) versions of these tubes. I know there are a lot of dodgy kt88 copies out there. I'm mainly interested in differences between the el34 and the 6550. A transparent, detailed amp is my primary aim but I admit I like the look of the old fashioned bulbous glass envelopes given a choice between two otherwise equal tubes.
OzMikeH said:
Unless you intend to eat the tubes, I wouldn’t worry too much about the last three. With respect to the first two, the tubes are only one part of an amplifier and subjective reports generally (if anything) are much more a reflection of a person’s competence at amplifier building than a true gauge of “tube-type sound”.
Also, I really doubt that the KT88 is the only of the three tubes you mention plagued by nasty remakes of questionable reliability.
The 6550 is virtually a drop-in substitute to the KT88. As for the EL34, that’s a lower power tube with a significantly lower cathode current and plate dissipation rating, so a choice between it and the 6550/KT88 really depends on how much power you want.
Then agian, if you only need as much power as, say a pair of EL34’s can provide, then a pair of 6550/KT88’s could arguably do a better job running well below their maximum ratings.
Hi Mike,
I have built and modified an Ella from DIYHifi Supply - great amp, great supplier.
It is a mistake to generalise about the sound of these tube types as so much is dependant on the application and the listeners prejudices.
In my Ella, with my speakers, I prefer the sound of EL34's. They have greater clarity and finesse. I've tried ElectroHarmonix 6CA7, JJ E34L and Valve Art EL34, the EH's are my fave. I wanted to love the KT88's 'cos they look so cool, but they sound relatively boomy and muddled in the mid-bass. Not horribly so but noticeable. These were EH KT88's. Also tried Valve Art 6550 which had the same character but worse.
With EL34's being about half the price, or less, I'd recommend starting with the standard Valve Art EL34 and spending any spare bucks on coupling or power supply caps.
Also running the circiut in triode mode as opposed to the standard ultralinear gives a big improvement in quality. Output power drops by half so your speakers probably need to be on the more sensitive side of average.
Rod
I have built and modified an Ella from DIYHifi Supply - great amp, great supplier.
It is a mistake to generalise about the sound of these tube types as so much is dependant on the application and the listeners prejudices.
In my Ella, with my speakers, I prefer the sound of EL34's. They have greater clarity and finesse. I've tried ElectroHarmonix 6CA7, JJ E34L and Valve Art EL34, the EH's are my fave. I wanted to love the KT88's 'cos they look so cool, but they sound relatively boomy and muddled in the mid-bass. Not horribly so but noticeable. These were EH KT88's. Also tried Valve Art 6550 which had the same character but worse.
With EL34's being about half the price, or less, I'd recommend starting with the standard Valve Art EL34 and spending any spare bucks on coupling or power supply caps.
Also running the circiut in triode mode as opposed to the standard ultralinear gives a big improvement in quality. Output power drops by half so your speakers probably need to be on the more sensitive side of average.
Rod
thanks Rod and G.Kleinschmidt.
There are some rather strange words people use to describe sound, I had been reading too many of them at the time.
Exactly the sort of answers I was looking for.
Did you try the kt88 or 6550 in triode mode?
Good to know about the valve art 6550s, I was leaning that way as a starting point because all tubes are a bit expensive around here. around $75 for a GD 6550, $30 for an EH EL34.
My speakers are 95dB fullrangers in a MLTL/TQWT type cabinet. The room is rather big (100m3 and Z shaped). I borrowed a Mr Liang EL34 PP and occasionally found myself running out of power.
I'm looking at the level 3 kit. mainly for long life, reliable tube sockets.
There are some rather strange words people use to describe sound, I had been reading too many of them at the time.
Exactly the sort of answers I was looking for.
Did you try the kt88 or 6550 in triode mode?
Good to know about the valve art 6550s, I was leaning that way as a starting point because all tubes are a bit expensive around here. around $75 for a GD 6550, $30 for an EH EL34.
My speakers are 95dB fullrangers in a MLTL/TQWT type cabinet. The room is rather big (100m3 and Z shaped). I borrowed a Mr Liang EL34 PP and occasionally found myself running out of power.
I'm looking at the level 3 kit. mainly for long life, reliable tube sockets.
I ordered the Ella. I was going to get a kit but they had a preassembled one with a minor scratch for less than the kit.
I'll start with the Valve Art EL34s that come with it, study the circuit and decide from there if I'll go with some better EL34s or maybe optimise the circuit for the KT88, triode or pentonde, feedback, who knows. It'll keep me busy researching and tinkering for a while.
I'll start with the Valve Art EL34s that come with it, study the circuit and decide from there if I'll go with some better EL34s or maybe optimise the circuit for the KT88, triode or pentonde, feedback, who knows. It'll keep me busy researching and tinkering for a while.
OzMikeH said:
I actually didn't do much tube swapping with mine -- but any good 6SN7 will be an improvement (RCA 6SN7GTB or Sylvania 6SN7GTB are a great bet -- I personally used GE in mine). And for 6922s, I like Tungsram for being rugged and affordable. I think I used some old Sylvania 6922s, nothing fancy. Tesla, EH, or JJ should also be better than Chinese tubes (which likely come with it). I don't recall the voltage, so can't say if 6922 type is needed, or if ECC88/6DJ8 is "enough".
Frankly, I owned mine for about a year, and had to sell it to fund a vintage amp project that was running me out of money
My Ella came with the Chinese military tubes that Brian at DIYHifi Supply stocks and are meant to be a cut above the standard Chinese stuff. Amp certainly sounded good with them.
Problem with trying NOS tubes is that the Ella uses the two of the most popular and therefore expensive types. Prices of the "right" types of 6922 and 6SN7 are just stupid - way to the right on the curve of diminishing returns.
Upgrading to Russian military or EH tubes may be worthwhile but don't expect massive changes if you try the lower end NOS types.
Playing with the feedback and triode mode are excellent ideas - learn more about the amp, improve the sound and costs zip.
Rod
Problem with trying NOS tubes is that the Ella uses the two of the most popular and therefore expensive types. Prices of the "right" types of 6922 and 6SN7 are just stupid - way to the right on the curve of diminishing returns.
Upgrading to Russian military or EH tubes may be worthwhile but don't expect massive changes if you try the lower end NOS types.
Playing with the feedback and triode mode are excellent ideas - learn more about the amp, improve the sound and costs zip.
Rod
rhone said:
You should be able to get excellent 6922s and 6SN7s for cheap, with some patience on eBay. I usually pay less than EH prices for RCA, Sylvania, and Tung Sol 6SN7GTBs, new in box. I find lots of good pairs for ~$20 (There were recently two pairs of old TS 6SN7GTBs in-box for $17.99 each!). Good 6922s shouldn't cost much either -- no need for overrated (and noise-prone) Amperex PQ tubes. Tungsrams are fantastic, and you can get them for about $10-20 each. You can also find lots of good tubes labeled as GE/RCA -- either top-notch American tubes, or often British relabels (some Japanese, too, and those aren't bad either!).
I've just read, (but not completely understood) Lynn Olson's article: The Hidden Harmonics behind THD
It's prompted me to start thinking about Push-Pull class-A Triode mode. Then there is the negative feedback to consider. Less is better but it means everything needs to be working nicely in the first place.
Theres a few things I'm considering here which will cost power. So I'm looking at 6550, KT88 and similar.
With this amp there a few things I can not change:
The first thing is the 5k primary impedance on the output transformer. I suppose it could be driven using the ultralinear tap but for all I know this is a completely daft idea or may be of no benefit. Let's just say it's fixed at 5k because smarter people than me have made it that way.
The second thing is the B+ which from what I can gather is something like 405 to 475V, Of course it could be reduced if that is of any benefit but people often run the kt88 with more than this.
Given these constraints, how would you bias it and what would the circuit around it look like.
It's prompted me to start thinking about Push-Pull class-A Triode mode. Then there is the negative feedback to consider. Less is better but it means everything needs to be working nicely in the first place.
Theres a few things I'm considering here which will cost power. So I'm looking at 6550, KT88 and similar.
With this amp there a few things I can not change:
The first thing is the 5k primary impedance on the output transformer. I suppose it could be driven using the ultralinear tap but for all I know this is a completely daft idea or may be of no benefit. Let's just say it's fixed at 5k because smarter people than me have made it that way.
The second thing is the B+ which from what I can gather is something like 405 to 475V, Of course it could be reduced if that is of any benefit but people often run the kt88 with more than this.
Given these constraints, how would you bias it and what would the circuit around it look like.
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