Matchless spitfire el84 dissipation

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#22
If the tubes are upside down they have a tendency to fall off
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This comes from a personal email from Joe Rosen - he explains it better

"There is another problem with 9-pin power valves, one that nobody seems to talk about. The valves don't have as much glass to radiate the heat through like the bigger octal valves, and EL84's need substantial bias currents.
So the valve pins really heat up. What this does, apart from speeding oxidation/corrosion of the socket contacts (and 9-pin valves aren't this proper nickel material like the better octal sockets, but rather are this nasty cadmium-plated or worse, silver-plated ****), is that the heat seems to temper the metal alloy. After about a year, two at the most (call it 1000 hours), the sockets open up from the heat stress and mechanical forces on them to the point where they become so loose, that you can literally TURN THE AMPLIFIER UPSIDE DOWN AND THE OUTPUT VALVES WILL FALL OUT!!!!"

Of course in a Vox like amp you don't have to turn the amp upside down for this to happen.

I don't think your numbers are correct firechief (1 Watt), but not interested in discussing this.
 
#26
Cassiel said:
This comes from a personal email from Joe Rosen - he explains it better

"There is another problem with 9-pin power valves, one that nobody seems to talk about. The valves don't have as much glass to radiate the heat through like the bigger octal valves, and EL84's need substantial bias currents.
So the valve pins really heat up. What this does, apart from speeding oxidation/corrosion of the socket contacts (and 9-pin valves aren't this proper nickel material like the better octal sockets, but rather are this nasty cadmium-plated or worse, silver-plated ****), is that the heat seems to temper the metal alloy. After about a year, two at the most (call it 1000 hours), the sockets open up from the heat stress and mechanical forces on them to the point where they become so loose, that you can literally TURN THE AMPLIFIER UPSIDE DOWN AND THE OUTPUT VALVES WILL FALL OUT!!!!"

Of course in a Vox like amp you don't have to turn the amp upside down for this to happen.

I don't think your numbers are correct firechief (1 Watt), but not interested in discussing this.
Click to expand...

Cassiel, I have been on the road for nearly fouty years gigging with Fender blackface amps where the socket-clamps just kissed the 6L6's - and the stress from the G's in the road-cabs on the way to the next was intimidating. No problems!

Peter
 
#30
firechief said:
The current through the common cathode resistor is I=11.2/120 or 93.3 ma, devided by two is 46.7 ma per tube. I think thats not so bad. If p=.046 X 348 then each tube is disapating 16.0 W ---- I would like to hear from other on this because I have thoughts of trying a EL84 guitar amp.
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maximum ratings for the EL84 are 12watts plate dissipation and 300volts plate...if you stay outside this limits, expect short lived tubes...
 
#31
PeterDupont said:
Actually, real Class-A guitar amps are being very popular among jazz-guitarists with carved-top acoustic/electrics.
Peter
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classA means single ended topology, push-pulls always end up as classAB......

this is a single ended 5F1 clone is finished just the other day...

110510019.jpg
 
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#35
Can anyone tell me what the design concept is with the master 1M pot in the schematic in the first post? The pot is installed between the grids of the output devices. Does this not mean that one extreame setting its shorting the two grids together AC wise? I would think that this configuration stops working like a push pull amp at some point. Sure the volume is going to decrease, and there is no DC reason why it cant be done, but its either a clever idea, or just crazy.
 
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