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Old 17th October 2007, 02:59 AM   #1
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Default learning design but need help

So I built el cheapo and used it to drive a REALLY old speaker from a tube radio I found in my basement (my parents were surprised as they thought it got tossed the last time the basement flooded). I was surprised the old speaker worked after being submerged for about three days not to mention not being used since before my grandparents got married.

While building el cheapo was educational it didn't really teach me much about how tube amplifiers are designed. So I when searching on google and came across the howto on boozhoundlabs. The page was the most helpful I found so far as it didn't go off on tangents. Unfortunately it left some things unexplained and the amp I plan on building doesn't use the same output tubes (I picked up some 6C33C tubes at a flea market... I was there to buy some surplus 7.62X54R for my mosin but they were just so ugly they were cute ...like little chibi ogres...I had to buy them too).

How do you determine what tube(s) to use in the driver stage?
If the tubes you chose for the driver don't have a nice little table to uses for the circuit how to you design it and find the values to use?
Say you don't want to couple the tubes with a capacitor how do you chose an interstage transformer?

I also had a question concerning mercury vapor rectifiers (ie type 82 and 83). Is it ok to use a separate transformer for the filament? I'm asking as all of the schematics that I've seen have it coming off of another winding on the main transformer.
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Old 17th October 2007, 03:17 AM   #2
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Designing tube amplifiers is a broad subject and you're right, you won't learn much about it by building someone else's design. I tend to think that DiY ought to stand for Design it Yourself.

Rather than asking only the questions that occur to you and gaining incomplete information, I suggest you consider investing in a book that was written for the purpose. The book that I've found helpful is 'Valve Amplifiers' by Morgan Jones. It's very readable and, though it doesn't cover every aspect of tube audio design, it does gives you a sound foundation on which to search for answers that it doesn't provide.
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Old 17th October 2007, 03:19 AM   #3
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I will leave explaining the driver stage to someone that knows the correct way to do it.

Interstage transformers are pretty standard, they do start to get a bit more complicated in more powerful amps due to much more powerful driver tubes and power tubes with low input independence running in class a2.

It's ok to use a separate transformer for rectifiers but keep in mind it must have a center tap for the negative of the b+ if it is a directly heated rectifier.
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Old 17th October 2007, 04:38 AM   #4
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I think I might order that book (local barns and nobel doesn't have it in stock...wonders of the internets).

For the transformer would it be ok to wire one with dual secondaries in series to make my own "center tap". I saw it in a schematic before for something entirely different but never bothered to find out if it works as I never needed to for the way I wired my gainclones.
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Old 17th October 2007, 07:28 AM   #5
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Default Re: learning design but need help

Quote:
Originally posted by lochness
I also had a question concerning mercury vapor rectifiers (ie type 82 and 83). Is it ok to use a separate transformer for the filament? I'm asking as all of the schematics that I've seen have it coming off of another winding on the main transformer.
For Hg rectifiers, it's not only OK, but essential! These require preheating before you hit 'em with the HV in order to vapourize the mercury. That's usually at least 30 secs of preheat. 30 minutes if you disturb the mercury to insure that there aren't any droplets shorting the plate to cathode. If you don't preheat, these won't last too long.
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Old 17th October 2007, 07:46 AM   #6
Colt45 is offline Colt45  Serbia
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I wouldn't bother with those quicksilver lamps... they look cool, but they're a pain in the ***.


What are you planning on doing with 6S33S? OTL?
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Old 17th October 2007, 08:39 AM   #7
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I already knew about the time delay needed for the hg tubes. was going to set up a time delay with a relay if it needed to be off of the same transformer. Might set up a time delay anyways so there is only one on switch and because I want an excuse to use tube shaped amprite delay relay. Not gonna lie though I'm only using type 83 tubes because I want the blue glow.

For the 6C33C's I plan on using a simple SET setup. Why? Theres a lot of information of SET and for a first time design I wanted to keep the overall design simple.
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Old 17th October 2007, 10:13 AM   #8
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83's don't glow a whole lot. Use 866's if you want real glow.


I'm kind of worried that the glass will pass the UV light and burn your retinas though.
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Old 17th October 2007, 08:26 PM   #9
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I think a 866 needs at least 1000 volts with a decent amount of current to glow.
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Old 17th October 2007, 08:58 PM   #10
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Quote:
Originally posted by Colt45
I'm kind of worried that the glass will pass the UV light and burn your retinas though.
They won't since glass is obaque to UV. All the Hg vapour UV sources are made from quartz, which will transmit UV. If you're really worried about it, you can always include a plexiglass shield. That, too, is obaque to UV.
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