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Any free online Cad programs for simulating vacuum tube circuits?

sdaudio2

New Member
Thank you for the info...I haven't used a cad program since 92'...they probably have a free one online somewhere...
 

billybob

Active Member
I've never done anything with tubes. They seem kind of daunting to me.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've never done anything with tubes. They seem kind of daunting to me.
Valve circuits are crude and simple, but it's very old obsolete technology and you struggle even buying decent valves these days, and there's very little choice.

So nothing daunting, other than the high voltages, and valves are actually even pretty easy to understand how they work.
 

sdaudio2

New Member
Not really...a tube can temporarily handle much higher voltages than their stated max with out damage...for use with a small triode (12ax7,12au7,ect;)use variable resistors for the plate and cathode ,use a resistor of appropriate value tied to grid and ground and allow the stated filament voltage to come up before applying B+ and use an appropriate rated metalized film cap to block DC(tied to the plate) ...hook up your genny between the output side of the film cap and ground ,then start having some fun...Depending which pins you use with a 12ax7 (you can use 6.3 or 12.6 VAC...consult a tube manual for pinout)...12ax7's have a gain of 100 with rather a high plate resistance...12au7's have lower gain and reduced plate resistance but can provide more current than a 12ax7...hope this helps...
 

sdaudio2

New Member
Actually...there are a few Russian valve manufacturers and they (russians) still have huge stock piles of superb sounding specimens and very cheap to purchase too....they have a much sought after 6bq5 substitute that uses heavier glass and are reputed to last 10,000 hours or more(6P14P,6P15P,SV83) Pinout may vary on some of these...the SV83 the screen is not tied to cathode,but ,apparently sounds better when a suitable film cap is used to tie to the cathode for single ended amplifier output....
 

sdaudio2

New Member
I meant to say that when using a genny you hook up between grid(triode grid) and ground and check output through an appropriatly rated blocking cap (tied to the plate)...sorry...my bad
 

sdaudio2

New Member
Hold the 12ax7 tube upside down ...where the space is between the pins start counting from the left clockwise 1,2,3,4,5,6,7,8,9...plate,grid cathode,heater,heater,plate,grid,cathode,htr center tap....Ty Nigel
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Actually...there are a few Russian valve manufacturers and they (russians) still have huge stock piles of superb sounding specimens and very cheap to purchase too...
As far as I was aware, the Russian valves have always been poor quality, both for their sound and their reliability, and the Chinese valves have been even worse.

But I suppose if you wanted quality, then you wouldn't be using valves :D
 

crutschow

Well-Known Member
Most Helpful Member
One device whose operation is not understandable using conventional current flow (positive charges being attracted to a hot filament?).
 

JimB

Super Moderator
Most Helpful Member
One device whose operation is not understandable using conventional current flow
That blew my mind when I was first starting out in radio at the age of 12 or 13.
Then I stumbled across the little snippet of information, that conventional current flow and electron flow are opposite to each other, only then did things start to make sense.

JimB
 

sdaudio2

New Member
England has produced some very beautiful sounding valves ,Chelmer,Mullard,et all...in a shoot out of 6dj8 variants on Head Fi Siemens gray shield (63' and 65') both came in 2nd and 3rd respectively compared to a Reflektor "Holy Grail" 75' silver shield 6N23P SWGP...I haven't heard those but did use the "Voshkod 6N23P gray shield (75') for many years and had a stash of highend Amperex,Mullard...you name it to compare with and they were not as neutral sounding as the Voshkod tubes I used in my Sonic Frontiers SFCD-1 CD player
 

sdaudio2

New Member
Its amazing people are so knowledgable about other peoples equipment...I 've been constructing/modifying tubed audio equipment for 40 yrs ...I don't claim to be to the nth degree in electronics,however having musicians in the family has given me exposure to and a deep appreciation for all music ...when I build and tweak circuits I use live unamplified instruments for my reference ....my past friendships with other DIY constructors has provided me with much information and have discovered there is no end to the modifications one can use on their equipment...as long as it is in service to the music (safety concerns do matter too of course)...
 

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