I was doing some internet surfing (haven;t been on this board in a while ..was on an audio sabbatical...LOL) and I saw a thread talking down the Velleman K4040 (mostly down). As a proud owner I want to share some details that may give some folks HOPE who may have one laying around and not realize they are sitting on gold.
For the price and capabilities as a kit when these came out, it was really a steal. Maybe not so much straight out of the box as designed...where they could be a 10, they designed as a 7.
I actually purchased mine used about 10 years ago, pre-built for a very good price. That price was probably because one side crackled and the other had a hum. Not TOO bad but there and that would NOT do. So i did some research and enlisted the aid of a guy who could actually read schematics and teach me some things.
The first steps was donning an indiana jones hat and searching the WEB version of the amazon for details on what the heck. I stumbled upon some very detailed "fixes" that entailed mostly replacing certain caps, resistors and such with different values, a jumper wire at one location and some other mystical magical things. That worked really well but still had that subtle hum which after agonizing time turned out to be needing an additional ground. Now we had it clean.
Did that make it a 10 yet? Nope, the key to that was canning any thought of the stock type tubes (EL34's regardless of brand) and getting 6L6GC's. Bingo. In my case, I spent $90 EACH for 8 GE NOS form 1961. OMG. Amazing...there was the 10....but wait there is more
It uses 1 12AU7 and 2 12AX7's. The input tubes were another journey but well worth it. Tried Mullard, RCA, GE, Baldwin, you name it but the winner - a NOS matched pair of sylvania Black plates, square getter.
Now it went from 10 to 11 (like Spinal tap, its was 1 better ..lol)
So someone might ask, why got to all that trouble ? You could just buy one newer, etc. yada yada. NOTHING looks like this. Nothing evokes the sweetness from my vinyl than this. So if you have one lying around, dust it off. Pretend you are restoring a 66 Fastback mustang. It may look a bit rough, but when its done...WOW.
And just so you DONT have to play indiana jones, I have a step by step guide to upgrade and the original manual...shared on one drive. I would love to hear back - HEy this worked for me !!!
https://1drv.ms/u/s!AoQ15fY-JFvSpa1VIqlue-Qh60HRlA?e=O7s5SK
And also attached below
For the price and capabilities as a kit when these came out, it was really a steal. Maybe not so much straight out of the box as designed...where they could be a 10, they designed as a 7.
I actually purchased mine used about 10 years ago, pre-built for a very good price. That price was probably because one side crackled and the other had a hum. Not TOO bad but there and that would NOT do. So i did some research and enlisted the aid of a guy who could actually read schematics and teach me some things.
The first steps was donning an indiana jones hat and searching the WEB version of the amazon for details on what the heck. I stumbled upon some very detailed "fixes" that entailed mostly replacing certain caps, resistors and such with different values, a jumper wire at one location and some other mystical magical things. That worked really well but still had that subtle hum which after agonizing time turned out to be needing an additional ground. Now we had it clean.
Did that make it a 10 yet? Nope, the key to that was canning any thought of the stock type tubes (EL34's regardless of brand) and getting 6L6GC's. Bingo. In my case, I spent $90 EACH for 8 GE NOS form 1961. OMG. Amazing...there was the 10....but wait there is more
It uses 1 12AU7 and 2 12AX7's. The input tubes were another journey but well worth it. Tried Mullard, RCA, GE, Baldwin, you name it but the winner - a NOS matched pair of sylvania Black plates, square getter.
Now it went from 10 to 11 (like Spinal tap, its was 1 better ..lol)
So someone might ask, why got to all that trouble ? You could just buy one newer, etc. yada yada. NOTHING looks like this. Nothing evokes the sweetness from my vinyl than this. So if you have one lying around, dust it off. Pretend you are restoring a 66 Fastback mustang. It may look a bit rough, but when its done...WOW.
And just so you DONT have to play indiana jones, I have a step by step guide to upgrade and the original manual...shared on one drive. I would love to hear back - HEy this worked for me !!!
https://1drv.ms/u/s!AoQ15fY-JFvSpa1VIqlue-Qh60HRlA?e=O7s5SK
And also attached below
Attachments
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If I understand correctly, you had to spend $720 on output tubes, plus other expenses, to improve the sound quality of the amp. That seems a bit excessive to me.
Is this amp very sensitive to tubes that are mismatched at different operating points due to it parallel PP design? Could the toroid OPTs be more susceptible to imbalances?
Is this amp very sensitive to tubes that are mismatched at different operating points due to it parallel PP design? Could the toroid OPTs be more susceptible to imbalances?
No. The $720 in tubes was my choice. Other 6l6gc’s sounded awesome. I went beyond awesome. And considering I bought a $2000 amp for under 500, I was ahead of the game. Also, my post was about longevity, this thing does not break down and one of the coolest bias setting I have seen.
so go price tubes. Then price the finest ever made. (1960’s the peak of tube production). Modern tubes are like nails on a chalkboard in comparison
so go price tubes. Then price the finest ever made. (1960’s the peak of tube production). Modern tubes are like nails on a chalkboard in comparison
Let us assume perfectly matched tube DC currents, and perfectly matched dynamic parameters for the 4 EL34 tubes;
And perfectly matched tube DC currents, and perfectly matched dynamic parameters for the 4 6L6GC tubes.
What major difference remains?
The greatest differences of a 6L6GC versus an EL34 is:
Transconductance: 6000 micro-mhos for a 6L6GC versus 11000 micro-mhos for an EL34).
And: u g2/g1 of the 6L6 is about 8; and for the EL34 u g2/g1 is about 11.
The amplifier uses Ultra Linear mode. u g2/g1 counts for a lot.
The amplifier uses global negative feedback.
The ratio of open loop gain to closed loop gain, is far less for the 6L6GC than it is for the EL34.
Too much of a good thing with the EL34, versus the 6L6GC?
Is that possible?
. . . Just food for thought.
YOMV (Your Opinion May Vary)
And perfectly matched tube DC currents, and perfectly matched dynamic parameters for the 4 6L6GC tubes.
What major difference remains?
The greatest differences of a 6L6GC versus an EL34 is:
Transconductance: 6000 micro-mhos for a 6L6GC versus 11000 micro-mhos for an EL34).
And: u g2/g1 of the 6L6 is about 8; and for the EL34 u g2/g1 is about 11.
The amplifier uses Ultra Linear mode. u g2/g1 counts for a lot.
The amplifier uses global negative feedback.
The ratio of open loop gain to closed loop gain, is far less for the 6L6GC than it is for the EL34.
Too much of a good thing with the EL34, versus the 6L6GC?
Is that possible?
. . . Just food for thought.
YOMV (Your Opinion May Vary)
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Would you please elaborate on this? Thank you! In addition, if B+ changes, mostly due to mains voltage changes, grid bias also changes, hence compensates more or less.
Best regards!
I lost my reply so I will keep it short. 8 tubes not 4. You theory means very little to me because that was all done in the quest. I have forgotten most of it. Each tube has its own bias setting and are perfectly matched and set … I almost never have to readjust ( one every couple of years ?). The el34’s were notorious for blowouts. The gc’s don’t. So after much research, 6 months work, burned fingers from a soldering iron, it’s one of the sweetest sounding tube amps I ever heard
I don’t have your expertise in the linguistics but I know how to build a bridge 😎
I don’t have your expertise in the linguistics but I know how to build a bridge 😎
By the way, I didn’t mean that in a bad way. Just saying, I have forgotten 10x more than I remember. Every step had a reason. The only one I remember is the tubes and the extra ground needed inside. The rest is lost in the dust of my memory
Most good tubes do not blow out, unless:
Their maximum ratings are exceeded, or they are not good tubes.
EL34 plate max dissipation 25 Watts (I hope the designer of Velleman did not exceed this).
6L6GC plate max dissipation 30 Watts
I thought your complaint was that the EL34 tubes did not sound good.
I thought you said the 6L6GC tubes sounded good.
I guess I was wrong about what you said.
That leaves us with some possible sound differences . . .
6L6GC: g2/g1 8; Gm 6000 micro-mhos
EL34: g2/g1 11; Gm 11000 micro-mhos
(Totally different open loop gain in Ultra Linear)
If there is enough open loop gain for both of those tube types, than the closed loop gains will be almost the same.
Just my opinion
Their maximum ratings are exceeded, or they are not good tubes.
EL34 plate max dissipation 25 Watts (I hope the designer of Velleman did not exceed this).
6L6GC plate max dissipation 30 Watts
I thought your complaint was that the EL34 tubes did not sound good.
I thought you said the 6L6GC tubes sounded good.
I guess I was wrong about what you said.
That leaves us with some possible sound differences . . .
6L6GC: g2/g1 8; Gm 6000 micro-mhos
EL34: g2/g1 11; Gm 11000 micro-mhos
(Totally different open loop gain in Ultra Linear)
If there is enough open loop gain for both of those tube types, than the closed loop gains will be almost the same.
Just my opinion
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Well, I think it's somewhat comparing apples with oranges, in terms of replacing EL34's of more recent production with good old NOS GE 6L6GC's or 7581A's. Probably the same would have been experienced with good old NOS EL34's, made somewhere by the Philips company or Telefunken.
Best regards!
Best regards!
Hello … let me be clear
1 - el34’s we’re known to blow on the vellemans
2 - new or old, the 34’s did not sound that great
3 - based on feedback from others with a similar journey, I tried the 6l6gc’s and they sounded great
4 - as I am persistent, I sought the best variations similar to what I did with the input tubes
5 - one tweak I did not make was someone e didn’t like the phase splitter design ( 12au7
1 - el34’s we’re known to blow on the vellemans
2 - new or old, the 34’s did not sound that great
3 - based on feedback from others with a similar journey, I tried the 6l6gc’s and they sounded great
4 - as I am persistent, I sought the best variations similar to what I did with the input tubes
5 - one tweak I did not make was someone e didn’t like the phase splitter design ( 12au7
I had one, it's HF performance was quite slew rate limited mainly in the phase splitter. If used to pop EL34's so I stuck some 6550's in. KT77 may have been easier. I quite liked the chrome very art deco.
What exactly is failing in the EL34's? If the correct bias, correct value components, and the correct transformers are used, they won't fail.
And, operated under the correct conditions EL34's can sound great. They certainly do in my Tubelab SSE.
So, it doesn't look like a tube problem to me. But rather, a problem with the design and operation of the amp. As Kay Pirinha stated, Marshall - and countless others - figured out how to use EL34's to great effect.
And, operated under the correct conditions EL34's can sound great. They certainly do in my Tubelab SSE.
So, it doesn't look like a tube problem to me. But rather, a problem with the design and operation of the amp. As Kay Pirinha stated, Marshall - and countless others - figured out how to use EL34's to great effect.
It is a problem with the K4040. I think they are at the edge of their rating partially on the screen voltage in UL. They do go up like light bulbs and burn out the cathode resistor in the process.
Yes and no. Two or decades ago EL34's from then current production were well known for their unreliablility, especially with screen voltages >400 V. Even Marshall swapped for 6550's in their amplifiers then. Not so with good ole NOS tubes which could cope with moderate screen voltage abuse.
Best regards!
Best regards!
My reply is that for hi-fi is not ok , for a guitar amplifier maybe that is part of the "sound" , you can't contest this
Probably the Velleman kit is intended for hi-fi ...
Okay, I see no good deed goes unpunished here. - Alot of hypotheticals from some who have not used it, been through it , etc and really dont know that their are varied opinions across the web on what sound people like better (EL34 or 6L6's). I have seen each one touted as being clearer than the other , each said to clip worse than the other ..LOL. So everything I have read is pretty much opinions. One thing to note and no one can deny is EL34's run hotter than 6L6's which may have been why earlier reports of tube malfunction (which may have actually been amp malfunction)
I know this and will leave it at this. I provided the attachment of fixes and the manual for use by someone who may work on one of these. It came from painstaking research of others who went before me, trial, error, help from an engineer with an oscilloscope, etc, And it sounds amazing. If you dont like the design, that's fine, it doesn;t change the result. Zero hum. Zero noise. Plenty of power. Sounds very crystal clear without and hint of harshness. Great soundstage.
Oh and BY the way, I believe there was some version with the KT77's from velleman ..I believe in dim memory I tried them from Golden Lion....didnt like them as they sounded harsh....Be well all....I am done with this thread
I know this and will leave it at this. I provided the attachment of fixes and the manual for use by someone who may work on one of these. It came from painstaking research of others who went before me, trial, error, help from an engineer with an oscilloscope, etc, And it sounds amazing. If you dont like the design, that's fine, it doesn;t change the result. Zero hum. Zero noise. Plenty of power. Sounds very crystal clear without and hint of harshness. Great soundstage.
Oh and BY the way, I believe there was some version with the KT77's from velleman ..I believe in dim memory I tried them from Golden Lion....didnt like them as they sounded harsh....Be well all....I am done with this thread