Tube SE power amp , which one??

[gaborbela]

Hello

As a last project I would like to build a SE tube amplifier.
I built several Solid S. amplifiers over the last 20 years.. So I would like to finish all my project and enjoy listening music.
I need some advise which amplifier to choose between the two project.
The KT88 has PC board lay out, I can make the PC board, I have only one question can I drive with a half ECC83 these amplifier
These project from a Germany website..The owner of the amp wrote he more than happy with the result!
KT88SE Roehrenverstaerker, von Michael Dieckmann
Also I think I can use here 6550 and other tubes??
The another project from a Japanese Website
These is a Super triode mode also half 12AX7 driver stage and 6L6GC power tube.
Also I don't know if the power tube can be replaced by EL34 or KT88 with out any modification on the circuit to get more power.
I would like to get 7 to 10W power but most important the quality of those watts..
Any advise welcome.
I just star collecting the parts . When I have to choose the irons I want to buy something good quality like these..
2 SE Tube Output Transformers 300B 6L6 EL34 KT88 6550A on eBay.ca (item 370354427846 end time 17-May-11 16:03:48 EDT)
It is $400 + shipping import tax etc..
So I have to know which one I choose . Once I purchase the Irons I have to stick with that design..
The 6L6GC use 5K primary
The KT88 use 2.5K primary
Any pro and contra from tube experts welcome!!
Thank you very much
Greetings gabor

 

[Wavebourn]

If you want quality of watts 6L6 clones are not the right choice. For 7 to 10 watt of output pair I would prefer something like 4 of 6P15P in parallel, in triode mode.

 

[singa]

Hi, If you are going to spend serious money on iron, might as well get
Tango U808 or SE20 don't know if I got the last one right .Both with multiple
taps then you would not be restricted by choice of tubes.

 

[rvrazvan]

If you want quality of watts 6L6 clones are not the right choice. For 7 to 10 watt of output pair I would prefer something like 4 of 6P15P in parallel, in triode mode.

I'm with him.
Triode mode is the real deal.
6p15p are cheap.

 

[gaborbela]

Hello

Thank you for the replies and advise!
Only problem with 4 parallel tube they have to be matched I think.
I do not own tube tester.
My speaker is 90db probably 7W is enough. What about the KT88??
Or if I use 6550 instead KT88 tubes..
Thank one more time
Greetings

 

[gaborbela]

I forget to me very important to have a working schematic to build something!
With out schematic I'm lost in a tube world..
Greetings gabor

 

[the_manta]

Like the 6L6 and all of its higher Pa-max clones, the EL84 weren't designed for triode SE use either. The best triode curves has IMHO the KT66. But today people even use line-output-switching tubes as linear amplifiers (as people use IRF530 switching MOSFETS) or transmitting tubes etc. Paralleling tubes will add distortion, too just because of different dynamical parameters of each valve.
I don't want to discuss about "sound", but you can certainly build a excellent sounding KT88 SE amp for example.
Getting 10W out of in SE is as pentode is easy, as triode it isn't that easy.
You just have to know what you want. Why not EL34 SE. they're very cheap, reliable and everywhere available.

 

[gaborbela]

Hello
From EL34 I can get max. 5-7W..
I had a Revox mono block amplifier with EL34 PP and ECC83 driver. The sounded awful.
OK these was a old design from 60s..
Also I had a DIY PP EL34 , I do not want to comment.
Many EL34 tube sound cheap.
Like Tesla, Tungsram,EI so on. A pair Siemens or RFT not cheap either $$$..
Yes you right I want to use one power tube to avoid distortion and other complication .
I only can build if I have schematic..I don't know about PP, I'm still open for both..
Even to PP the power tubes good to be matched.
What about the KT88 I posted??
Greetings

 

[tomchr]

Getting 10W out of in SE is as pentode is easy, as triode it isn't that easy.

Depends. I get 13 W out of my JJ 300B's using something akin to George/tubelab's PowerDrive. 400 V on the anode of the 300B, 90~95 mA quiescent current, 5 kOhm primary impedance on the OPT. Yes. 95 mA, 400 V is hot but within the original WE spec. With current production tubes, I have no issues.

~Tom

 

[the_manta]

Hi,
The actual sound of a Tube amplifier is very complex thing. I can tell you one thing for sure: In a strong feedback pentode amplifier, the output Pentode does very little to the sound. It's mostly the preamp/driver and the OPT (because of its phase shift and bandwith in the feedback loop) which affect what is called sound. When I swap in my EL38 between EL34, 6L6 etc. The difference is hardly noticable and mostly cause of wrong bias. Or can you hear the difference between a Toshiba and Motorola MOSFET ? (Of course connected as Drainfollower). With less feedback and Triode connected the difference will become significant. Moreover I don't understand the argument with the EL34 brand. I have lots of european EL34, most of them in linear power supplies. My Altec 1568a's play great with JJ EL34. They're cheap and come in matched pairs. About 35$ for a pair, when you pay more, you got duped It's unimportant whether it is labeled JJ, Siemens, SED, RFT or herpyderpy.

The KT88 amplifier from german site has a few flaws. The main problem is, that driving a KT88 to full output and using a good amount of feedback, requires lots of signal amplitude, thus gain from the driver. A single small signal triode is on its limit with this purpose. Especially in this circuit, where the ECC83 has no cathode bypass capacitor which means current-feedback and reduced gain in the driver stage I would rather suggest this amplifier: KT 88 SE-Amp, von Franz Wichlas. The cascode stage gives plenty of gain. But the Power stage is IMHO driven by too low voltage. I would give a KT88 at least 350-400V to gain max. output power.

At first you need to know what you want, How much Power, SE or PP, triode or Pentode. As tomchr pointed out, for triode SE you will need big tubes to get some power.
Regards, simon

 

[Wavebourn]

Hello

Thank you for the replies and advise!
Only problem with 4 parallel tube they have to be matched I think.
I do not own tube tester.

You can easily select them using power supply, tube socket, and one cathode resistor. Swap them and write down voltage you measured on the cathode resistor when screen grid and anode connected to B+, control grid to ground.

Another alternative is to use huge and linear tubes like GK-71, GM-70, GU-13.

If you want smaller tubes you may use GU-50 in pentode mode with local feedback around it. But be prepared to pay more attention to the driver stage.

It is up to you. Even 6L6 clones like KT-66 or KT-88 can sound well, but with significant local feedback around them, in pentode mode. In triode mode, oor pentode mode without feedback, their linear mode means such power dissipation they would melt down, or driver would be needed too good, to drive them in triode mode with local feedback. You can use nested feedbacks (local and global) to ease requirements to the driver stage, but people believe it is not kosher.

 

[gaborbela]

Thanks Wavebourn

I try to avoid to use 3-4 or more power tubes in parallel! Simple because mostly every tube behave different.
If I go with 2 power tube ad rather chose PP.. I read PP not need to be matched so well like parallel tubes.
Yes you right one large linear tube it would be useful. 7-8W in triode mode it would be nice!
I have to search for schematic, I'm unable to design or modify tube staff with out help.
GU-50 nice tube, I don't know soundwise I never heard one..

JJ Tesla to me not a tube for audio. Sorry, my friend when I had my Revox amplifier measured the brand new orig Tesla factory matched.
One word he said. Garbage. Waste of money!Also he measured the RFT and has much better characteristic.
He measured the curve, distortion etc , not the tube strength..
Greetings

 

[Wavebourn]

GU-50 nice tube, I don't know soundwise I never heard one..

Here is the thread where we discussed several variations:

GU-50 Single Ended Amplifier Design

Here is one particular version that I like:

 

[pieter t]

JJ Tesla to me not a tube for audio. Sorry, my friend when I had my Revox amplifier measured the brand new orig Tesla factory matched.
One word he said. Garbage. Waste of money!Also he measured the RFT and has much better characteristic.
He measured the curve, distortion etc , not the tube strength..
Greetings

You cannot judge a brand of tubes based on one unlucky incident.
I have no experience with all types JJ tubes, but I am sure there are good types among them.
For instance I have some older production 300B's which have proven to be excellent in terms of sound, life expectancy and specifications.

 

[tomchr]

At first you need to know what you want, How much Power, SE or PP, triode or Pentode. As tomchr pointed out, for triode SE you will need big tubes to get some power.

Yep. GM-70 is another option. As well as 845, 211 and other big tubes. But to get significant output power with a single-ended triode, you need gobs of B+. Most people seem to get 20+ W with their GM-70's running at a bit over 1 kV. In fact, that I didn't have to mess with too high voltages is one of the reasons I chose the 300B.

~Tom

 

[gaborbela]

Hello pieter t

Please read what I wrote, it is about the EL34 tubes.
Out of four two was so so one leak (gas) one bad!
We tested 8PC RFT and all RFT were great! The guy told me before I purchased the tubes do not buy them. I didn't listen on his advise because they were factory matched.
I have same experience with EL84 Tesla, Tungsram,EI far behind RFT, Siemens , Telefunken , AEG , even Russian tubes sounded better and the can take the heat!
I used them B-415V most of them after 2-3 min were red like a furnace. Not the RFT, Telefunken or the Russian tubes.. I switched the tube rectifier to diode! That gave me higher voltage.
After I sow the difference Tesla curve and the RFT nobody sell to me Tesla EL34 not even for $10!
JJ is not Tesla.
They purchased the licence and some machine that does not make them orig Tesla.
Can be better to.
EI purchased some Philips licence that does not make Philips.
Russian Gold Lion not the same as British..
All do they can be great! I never try them , just ECC83...

Wavebourn thank you, I will check the site. I cant see your picture.
Greetings

 

[singa]

Posted by garbobela
My speaker is 90db probably 7W is enough. What about the KT88??
Or if I use 6550 instead KT88 tubes..

Hi, If you really want to experience or hear SE triode and this is going to be
your last build then all the talk about using pentodes wired in triode is...
well a non issue.You might as well go the full distance and then tell yourself
you have no regrets. Use DHT triodes like 2A3(only 3watts),300B and the big brothers transmitting tube 211,845,805 etc.

Your speakers being 90db may look sensitive but I think you need all the headroom you can get.SE directly heated triodes are not cheap to being with
because they don't have economies of scale in production because the tube
business supports the guitar amplifier market which uses pentodes predominantly.

So a big transmitting tube like 845 or 211 is to go for but bear in mind that to
bulid a good DHT amp the driver is paramount meaning it's got to have sufficient driving power and good linearity or else you will essentially be hearing driver distortion more than the power tube itself.Choose a circuit wisely and do the homework. The project is most likely to be costly relatively but well worth it.

 

[gaborbela]

Hello
Thank you for the advise
What I read if I want SE triode I have to use large (exotic-expensive) tubes.
Even with that will not guaranteed I can get the sound I wish.
What if I give up the SE idea.
Do you think PP can easier deliver 6-8W with out spend a fortune on the tubes.
I want to buy good iron which is not cheap. And to spend on the tubes an arm and a leg I think is not the way were I want to go..
The problem I never heard SE in triode mode..
Another think I had a Philips Class A tube amp with EL95 about 2-3W SE. I rebuilt with better parts.
Very often I listening Classical , the problem it easily reach the max output and got distorted.
So I sold it..
To me SE a bit deliver better , cleaner mids (please correct me if I'm wrong)..
Here is a PP in triode , uses cheap (not expensive) Russian tubes (I have good experience with those power tubes)
To tell the truth I will have several great sounding SS amp.
Sometimes I would like to listening good tube sound!
If it sound bad com pare to the Pass amps and Krell ,Musical F. I would never turn it on. Or if I get only 2-3W I will have the same problem I had with the Philips.
I want to spend that money wisely or better not to spend it if I cant get the result..
Greetings

 

[singa]

Hi Gaborela,
I hear you ,cheap and good then try a SE using pentodes
with optional triode switch ,6L6,KT88 etc.Regarding other peoples opinions
it's your right to take it or leave it.You can use Hammond's cheap SE outputs for guitars without the end covers.If you are buying Hammond's covered
HiFi outputs ,you might as well go for Tango U808.6L6 SE in pentode mode
can get you easily between 10-14 Watts.Plenty for you right? To put this
in perspective ,you don't know if you don't try.

 

[nomiconxp]

why not try a GM70 tube with a D3A tube in the driver stage?? i have build an amplifier with this tubes.. and i am very happy with the results. i got 20W-25W in pure class A!
GM70 runs with 900V B+ i and the D3A with 200V B+ about 24mA i don't recommend running it above 1kv.. cause you are going in to another region..