Jansen 4/TWELVE SPECIAL
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Re: Jansen 4/TWELVE SPECIAL
I just noticed the photo haha
The v1 cathodes arent linked that I can see, all pins look disconnected.
I thought the PI was all messed up then realised it's a cathodine circuit and another gain stage driving it.
The v1 cathodes arent linked that I can see, all pins look disconnected.
I thought the PI was all messed up then realised it's a cathodine circuit and another gain stage driving it.
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Re: Jansen 4/TWELVE SPECIAL
Burnt yourself again ?GrantB wrote:I made some toast this morning.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...
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Re: Jansen 4/TWELVE SPECIAL
My toaster actually has more technology than this amp doesGrantB wrote:I made some toast this morning.
Slowy wrote: That's the problem; everything rewarding is just such hard work. Regret takes much less effort.
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Re: Jansen 4/TWELVE SPECIAL
I think you guys should start making those changes on Slowy's amp, just to make sure you like the sound before you make yours! I'm sure Slowy won't mind
Slowy wrote: To Danny, everyone is either a supplier, customer or a courier.
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Re: Jansen 4/TWELVE SPECIAL
Danny...........I know where you live.AiRdAd wrote:I think you guys should start making those changes on Slowy's amp, just to make sure you like the sound before you make yours! I'm sure Slowy won't mind
Beyond a critical point within a finite space, freedom diminishes as numbers increase. This is as true of humans as it is of gas molecules in a sealed flask. The human question is not how many can possibly survive within the system, but what kind of existence is possible for those who so survive.
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Re: Jansen 4/TWELVE SPECIAL
Yes I can hear you Clem Fandango !GrantB wrote:I made some toast this morning.
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Re: Jansen 4/TWELVE SPECIAL
YES, YEESSSS.StrummersOfThunder wrote:Yes I can hear you Clem Fandango !GrantB wrote:I made some toast this morning.
If anyone has watched Legion (Netflix - the mutant power one, not the other one) Oliver is super cool. Reminds me of Steven.
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Re: Jansen 4/TWELVE SPECIAL
Thanks for drawing up the schematic!
I wonder if the drifted R7 value is what is giving this amp so much mojo? If R7 is measuring >1M then it would give a pretty big gain boost while rendering the tone controls more or less transparent, as Optical points out. Do the tone controls do much?
Also, the 1st half of V2 is a bit different - the 47k anode resistor would mean this stage wouldn't be swinging as much voltage as traditional stages (ie. lower gain), which may be by design so that the following cathodyne phase splitter doesn't get overloaded as much, which can produce nasty overtones.
I wonder if all this amounts to most (all?) of the distortion character being generated in the power amp, not the preamp? The use of a 12AY7 is a bit unconventional too - could this be a mod, with the original as a 12AX7? The 12AY7 would keep the preamp cleaner as well but it's not a typical preamp tube for any vintage kiwi amp as far as I've seen. 12AX7s, 12AT7s and 12AU7s seem to be the usual choices.
I wonder if the drifted R7 value is what is giving this amp so much mojo? If R7 is measuring >1M then it would give a pretty big gain boost while rendering the tone controls more or less transparent, as Optical points out. Do the tone controls do much?
Also, the 1st half of V2 is a bit different - the 47k anode resistor would mean this stage wouldn't be swinging as much voltage as traditional stages (ie. lower gain), which may be by design so that the following cathodyne phase splitter doesn't get overloaded as much, which can produce nasty overtones.
I wonder if all this amounts to most (all?) of the distortion character being generated in the power amp, not the preamp? The use of a 12AY7 is a bit unconventional too - could this be a mod, with the original as a 12AX7? The 12AY7 would keep the preamp cleaner as well but it's not a typical preamp tube for any vintage kiwi amp as far as I've seen. 12AX7s, 12AT7s and 12AU7s seem to be the usual choices.
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Re: Jansen 4/TWELVE SPECIAL
The 12AY7 is my modification. I prefer the sound. And you are correct; power amp distortion is what this does.RectifiedAmps wrote:Thanks for drawing up the schematic!
I wonder if the drifted R7 value is what is giving this amp so much mojo? If R7 is measuring >1M then it would give a pretty big gain boost while rendering the tone controls more or less transparent, as Optical points out. Do the tone controls do much?
Also, the 1st half of V2 is a bit different - the 47k anode resistor would mean this stage wouldn't be swinging as much voltage as traditional stages (ie. lower gain), which may be by design so that the following cathodyne phase splitter doesn't get overloaded as much, which can produce nasty overtones.
I wonder if all this amounts to most (all?) of the distortion character being generated in the power amp, not the preamp? The use of a 12AY7 is a bit unconventional too - could this be a mod, with the original as a 12AX7? The 12AY7 would keep the preamp cleaner as well but it's not a typical preamp tube for any vintage kiwi amp as far as I've seen. 12AX7s, 12AT7s and 12AU7s seem to be the usual choices.
Beyond a critical point within a finite space, freedom diminishes as numbers increase. This is as true of humans as it is of gas molecules in a sealed flask. The human question is not how many can possibly survive within the system, but what kind of existence is possible for those who so survive.
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Re: Jansen 4/TWELVE SPECIAL
I have always wanted a Harvard!
"Man is the most insane species. He worships an invisible god and destroys a visible nature. Unaware that this nature he's destroying is this god he's worshipping." - Hubert Reeves
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Re: Jansen 4/TWELVE SPECIAL
Thanks Optical, SizzlingBadger and RectifiedAmps for your feedback.
R17 and R18 are indeed going to ground, just had not noticed the soldering pin was actually used as mounting pin to the chassis as well.
C5 - I have chosen a value in between what you suggested, so going with 120pF.
R1 - Yes, colour code says 1M, but I accidentally used the drifted value which is 1M6.
R7 - great spotting Optical - it is actually 6K9 on my hand drawn circuit but obviously when entering in Digi-Key I forgot to enter the correct value. And yes, the tone controls work fine.
V1 second triode - correct SB, is not biased.
SB - what do you mean with C6 being wrong? And what value would you recommend for the capacitor in the input circuit?
The updated circuit diagram will be posted later today.
R17 and R18 are indeed going to ground, just had not noticed the soldering pin was actually used as mounting pin to the chassis as well.
C5 - I have chosen a value in between what you suggested, so going with 120pF.
R1 - Yes, colour code says 1M, but I accidentally used the drifted value which is 1M6.
R7 - great spotting Optical - it is actually 6K9 on my hand drawn circuit but obviously when entering in Digi-Key I forgot to enter the correct value. And yes, the tone controls work fine.
V1 second triode - correct SB, is not biased.
SB - what do you mean with C6 being wrong? And what value would you recommend for the capacitor in the input circuit?
The updated circuit diagram will be posted later today.
When faced with quality, I recognise it every time.
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Re: Jansen 4/TWELVE SPECIAL
I also don't have a Harvard - so perhaps you would like to elaborate?Optical wrote:I just noticed the photo haha
I thought the PI was all messed up then realised it's a cathodine circuit and another gain stage driving it.
Long live the Valve Wizard
http://www.valvewizard.co.uk/cathodyne.html
So if I understand the Valve Wizard correctly, then R16 has a dual purpose: 1) creates the required cathode bias, 2) is the large gridstopper which avoids anode 'frequency doubling' in case the cathodyne is being overdriven. Yes? No?
Last edited by Jay on Fri Nov 09, 2018 3:35 pm, edited 1 time in total.
When faced with quality, I recognise it every time.
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Re: Jansen 4/TWELVE SPECIAL
C6 is fine, I too was thinking it was long tailed pair PI at first.
0.1uF should be ok on the input make sure R1 is on the tube (grid) side of the cap though so it can drain the DC.
0.1uF should be ok on the input make sure R1 is on the tube (grid) side of the cap though so it can drain the DC.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...
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Re: Jansen 4/TWELVE SPECIAL
Circuit Diagram Revision 1 courtesy of Optical, SizzlingBadger and RectifiedAmps.
What is the impact of R17 and R18 actually being 390K?
Close up of C5 pipe capacitor:
What is the impact of R17 and R18 actually being 390K?
Close up of C5 pipe capacitor:
When faced with quality, I recognise it every time.