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Old 16th September 2011, 12:23 PM   #171
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ok.. so being normal as it is, will IT(glow) not shorten the lifespan of the heater?
undervolting or overvolting is bad for any tube...a tube rated for 6.3 can work with voltages 5.9 to 6.9 volts with out problems.......

if your filament supply is higher even under full load, you can always add a resistor in series wit the the filaments to trim off excess voltage. it is a simple appplication of ohms' law...
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Old 16th September 2011, 09:07 PM   #172
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Default Heater Voltage

This is an interesting problem. Higher voltage increases the output/gain, but shortens life. Lower voltage does the opposite. However, we must remember that line voltages varied by up to 20% around the nation for a good part of the period of tube manufacturing--and tubes had to take this variance. Very seldom was the filter supply regulated.

I have done quite a bit of testing on varying voltages and my general recommendation is to keep power tubes at the rated voltage--this seems to give the best average performance. Small signal tubes are more forgiving, and so I like to run that at the rated value, or up to 5% under to save life. You can run them hot, but that will shorten life.

There are a few exceptions to the rule. 5687, for example, like to run hot as do 12B4s, at least with my testing of lots to date.
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Old 1st November 2011, 02:58 PM   #173
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Anyone who has built Fred Nachbauers Miniblok set? Or his Miniblok PP amp? If 13em7's are hard to come by in sunny SA, will 12ax7's work or maybe the new JJ ecc832/12dm7's? or perhaps 7025's which are listed as available here? If I understand Fred's schematic & write up correctly, the hi-gain half is used as a preamp and the low gain hi current half as the output. The miniblok 2 is a pp amp using 2 of these tubes, the 2nd tube high gain stage is used as a phase inverter for pp. The project appeals to me to cut my teeth with a kit, or can anyone recommend a better set project. It needs to be simple. I'm a blockhead at this stage.
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Old 2nd November 2011, 11:34 AM   #174
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Originally Posted by BHD View Post
This is a great idea for a thread.

This is one of the best beginner sites I've found, it walks you step by step through the design and construction of a simple single ended amp:

http://boozhoundlabs.com/howto/

I am afraid that this site is not reachabe now. I have seen it 3 days ago and it was a good site for beginners.
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Old 2nd November 2011, 12:39 PM   #175
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That's what the wayback machine is for Boozhound Laboratories

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Old 2nd November 2011, 12:54 PM   #176
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Thank you nthere, tried boozhound in spite of what you said (just in case) always being hopeful, I have visited Hans Niejbaum's 6C33C OTL site as well as Tom Mellow's OTL site. OTL is the way I will eventually go, as Philips OTL's were marketed under the Novosonic brand in my teenage days.Ist encounter with Hi-Fi, still mono in those days, stereo came a bit later. Novosonic's had a kick like a proverbial Mississippi mule. Could feel drums against your chest if u were listening to a percussion band. Handled classical music equally well; a pity this avenue of sound reproduction wasn't followed thru, though some were more in love the the lush, mellow Dynaco sound. Sound of transformer windings? Vere nice though. But otl's aside for the moment, I need to familiarise myself with an easy inexpensive project that works. Then...OTL's. Yum, Yum. I understand the principle of the late Fred Nachbauers topology very well, I am just not sure I can substite the 13em7's with other tubes (i.e dissimilar dual trodes) but I'll get there. Don
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Old 3rd November 2011, 10:27 AM   #177
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I perhaps should have mentioned that you need to wait for about 10 seconds for the boozhound page to load when you click on the wayback machine link I posted above

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Old 4th November 2011, 10:57 AM   #178
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Smile donerlank

Thanks,Wintermute, successfully accessed Boozehound and perhaps you will be pleased to know that the lights have started flickering for me. Isnt knowledge wonderful? Knowledge gives power, power gives enablement, enablement brings satisfaction. Dunno who said that. Perhaps it was Confucious, could even be Julius Ceasar or Shakespeare, does it matter?, or better still:Mr Tube. I will now be able to choose a tube, do some maths to determine if it will work in a given circuit, even modify the circuit to suit the tube and later on design my own circuit. I must remember to thank Boozhound also.
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Old 14th November 2011, 04:53 AM   #179
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Effusive thanks to all of the posters and their references
Wonderful dissemination of knowlege
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Old 14th November 2011, 09:08 AM   #180
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Originally Posted by RX5 View Post
ok.. so being normal as it is, will IT(glow) not shorten the lifespan of the heater?
i can buy it back from you if you can bring it to the house....

you can buy JJ 12ax7 tubes here: http://www.epektos.com/catalog/90270...03444af81.aspx
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Last edited by AJT; 14th November 2011 at 09:22 AM.
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