Building a Jansen 4/TWELVE SPECIAL copy (COMPLETE)

Amp tinkerers and people who aren't afraid of 700 volts or so in here....

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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Slowy »

jeremyb wrote:Pretty excited by how close this is to completion!!
Mate, you and me both. It's like someone cloning your kid!
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Slowy »

jvpp wrote:
Optical wrote:Your node voltages will come down once you have tubes in - there's no current drawn without tubes in, so you get no voltage drop. i.e. it'll read high now and lower with the tubes in.
Also if you want to match the original node voltages, it's likely you'll need to play with your psu dropper resistor values. That doesnt matter for a first test though.
Thanks, powered it up with valves in. So far so good. Proud Mary coming through loud and clear. Couple of issues I note though... The EL84 valves are getting really hot, can't touch them, not sure if that is okay or not. Voltages are 358V on OT, 338V on next stage (EL84 V3&V4), 317V (V2) on next and 305V (V1) on last one. Are these too high? Is the EL84 biasing causing them to run too hot?

Also have a bothersome hum but that can wait until I sorted out the hot EL84s.

Any advice welcome.
For what it's worth, my valves don't get hotter than I'd expect. No hotter than my 6L6 and 6V6 amps.
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

Slowy wrote:
jeremyb wrote:Pretty excited by how close this is to completion!!
Mate, you and me both. It's like someone cloning your kid!
Me too, although the DNA has several mutations which yet need to be classified as beneficial or detrimental.

So far, at low volume and in its current configuration, all I can say is that the cleans are very good with ample bass and treble if required. Particularly impressed with the bass on a humbucker. Did Jansen design this amp for a bass guitar?
Haven't tried single coils yet.
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Slowy »

jvpp wrote:Did Jansen design this amp for a bass guitar?
Look up Lucid3's albums. This was the bass amp on all of them.

When used for guitar, the previous owner dimed everything and put a Rangemaster in front. But he's that kind of guy.

I like its clean tones and ability to take Klon and Dumble style drive pedals.
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

Slowy wrote:
jvpp wrote:Did Jansen design this amp for a bass guitar?
Look up Lucid3's albums. This was the bass amp on all of them.

When used for guitar, the previous owner dimed everything and put a Rangemaster in front. But he's that kind of guy.

I like its clean tones and ability to take Klon and Dumble style drive pedals.
Cool, I will find some videos on the tube hopefully. Anyone any ideas what speaker would do for both bass and guitar playing for this amp?
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Slowy »

jvpp wrote: Anyone any ideas what speaker would do for both bass and guitar playing for this amp?
No, It doesn't work like that.
Plenty of Lucid3 on Utoob.
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by jeremyb »

What's it owe you so far if you don't mind me asking?
#gayerformayer
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Slowy »

jeremyb wrote:What's it owe you so far if you don't mind me asking?
Mine or JVVP's?
What mine owes me is criminal. I found it buried in a corner of the band's studio, dug it out and said, " You don't deserve this anymore, I'm taking it home. Here's some cash."

And to my amazement, they said, "Er, OK". :rofl:
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by jeremyb »

Slowy wrote:
jeremyb wrote:What's it owe you so far if you don't mind me asking?
Mine or JVVP's?
What mine owes me is criminal. I found it buried in a corner of the band's studio, dug it out and said, " You don't deserve this anymore, I'm taking it home. Here's some cash."

And to my amazement, they said, "Er, OK". :rofl:
:lol: JVVP's, was wondering what the parts cost to put it together was, its probably still > Katana head, there needs to be a cheaper way to make toob amps!!
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

jeremyb wrote:
Slowy wrote:
jeremyb wrote:What's it owe you so far if you don't mind me asking?
Mine or JVVP's?
What mine owes me is criminal. I found it buried in a corner of the band's studio, dug it out and said, " You don't deserve this anymore, I'm taking it home. Here's some cash."

And to my amazement, they said, "Er, OK". :rofl:
:lol: JVVP's, was wondering what the parts cost to put it together was, its probably still > Katana head, there needs to be a cheaper way to make toob amps!!
It's double PP not double VV. I'll do a tally of the parts costs to date, labour hours are huge too. There are absolutely no economies of scale at work for this stuff.
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Cdog »

One certainly doesn't build tube amps to save money. All of my builds easily cost more than a used 'real' one in parts alone! :)

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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

jeremyb wrote:What's it owe you so far if you don't mind me asking?
Parts only for the chassis..... a couple of dollars short of NZD500

It is supposed to be called a hobby but sometimes it feels like a form of self flagellation :crazy:
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by tubeswell »

jvpp wrote:
Cdog wrote:Congrats on getting this far... it's looking rather grand.
RE: EL84 heat - Check your heater voltages?
Yes, straight from the transformer, 6.7vac
Try a pair of anti-parallel 6A diodes in series with one side of the heater winding. This should drop the heater winding voltage by 0.6VAC
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

Optical wrote:
jvpp wrote:
Optical wrote:EL84s do run very very hot, hotter than you might expect. You could increase the cathode resistor by 10R if you are concerned about the bias, but your bias resistor looked in spec for 340V on the plates. Measure the bias current to be sure though!
Q: what is the voltage across your cathode resistor?

6.7V is also a bit high - likely because your transformer is spec'd to power several more tubes. You could load up the heater rail with an appropriate resistor to drop it down a bit, or convert to a regulated supply.
Thanks chaps,
EL84 voltage across the 130ohm/ 5W resistor is 11.6 VDC.
Re heater voltage, yes i will work out a resistor value to force a voltage drop of about 0.4volt.
Ok, you're at max plate dissipation, i.e.running the tubes as hot as you'd ever want to. I run my 84s here, but you could try dropping the bias a bit and see if you still like how it sounds. The tubes will last longer if you do as well. Try a 140R and 150R, or just insert one/some 10R in series with the 130R and see
Added 820 Ohm in series with the 1K Ohm resistor and that dropped the the first stage by about 16VDC to 322VDC and dropped the EL94 cathode resistor voltage to 11.3V. Could not detect any sound differences, so all good there.

This 130 Ohm gets hot though.... According to Ohm's law the DC current should be 11.3 / 130 which is about 87mA. The power consumption should then be V squared / R which is about 1W, way lower than the 5W max. I am clearly missing something... I have an 150 Ohm one, so will try that.

Sorted the hum issue but would like to receive confirmation what I am doing is okay. I think it was Alan who showed the earthing connections in different colours for each section of the circuit. There was a yellow line drawn from the middle of the heater winding to the plus of the EL84 cathode capacitor. There is no middle tap on my transformer so I grounded one of the heater winding ends to earth via a 150 Ohm resistor. Since there was no voltage drop over the resistor, I can directly connect one of the heater winding ends to earth. Doing so removes all the hum, so is this safe to do?
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Re: Building a Jansen 4/TWELVE SPECIAL copy (slowly)

Post by Jay »

Reading the valve wizard :thumbup: .... so I am going to answer my question above...
I will use the bottom circuit to get rid of the hum.

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