Matchless spitfire el84 dissipation

[Cassiel]

Hi,

I'm building the Spitfire for a friend. I am worried about El 84's dissipation limit. According to the schematic in this amp they're about melting point.

Does someone knows what's the sturdiest el 84 in production?

[Tony]

hi,

i used lower plate bias for the EL84's, i used 250ohms instead or 120 ohms....

[firechief]

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.

[Cassiel]

I smiled reading that old post, I was a noob back then. Well, Firechief - what do you want to know? I didn't finish that amp, my friend didn't have a good finish - toxic ways. Spitfire is sort of a Vox clone, not much gain in front though . I love PP el84's amps- hifi and guitar amps. There's the Vox and the Marshall 18 watt.

http://www.ampwares.com/schematics/m...watt_schem.pdf

Both would be good choices, I like the Vox 15.

I don't think there's much difference in sound with a colder bias, my cathode resistor is 150 Ohms.

[firechief]

Cassiel- I honestly didtent read the date on that first post That just goes to show not much has changed. Here is my latest project. Quad El84 amp. Let your friend's story be a lesson to us all.

[PeterDupont]

Having several Matchless amps, the trick of the trade is to know how to run the amp (with high bias). It has to sweat - but never to be leaved with no signal and plate on for longer than ten minutes. Unless you use unarticulate speakers it's clear to hear loss of the typical "shimmer" when you dial down the bias. The nearest comparison-device is a Celestion Gold.

Peter

[firechief]

note taken

[PeterDupont]

Originally Posted by firechief

note taken

It wasn't to sound rude FC, but there's so much hype around these amps. They call them "Class-A" - and all they are is high-bias'ed AB's.
Around tube choice, go for the Winged-C Svetlanas or the JJ's that Phil stick in before they leave for customers.
They will last some 200-300 hours before they need a switch, but that is the downforce of running hot.
Of utmost importance for that "sound" is the input-tube! A NOS Mullard will maybe empty your pocket but will last nearly forever.

Peter

[firechief]

Not rude at all. I know that class A guitar amps is are a myth. Why would you even want a super clean, distornless amp anyway? Here is a link to my earlier efforts
http://www.diyaudio.com/forums/music...uitar-amp.html
and thanks for posting . Tube coice is kinda limited, I need to stick with current production output devices, So for now JJ's are my tube of choice.
Bob

[PeterDupont]

Originally Posted by firechief

Not rude at all. I know that class A guitar amps is are a myth. Why would you even want a super clean, distornless amp anyway? Here is a link to my earlier efforts
http://www.diyaudio.com/forums/music...uitar-amp.html
and thanks for posting . Tube coice is kinda limited, I need to stick with current production output devices, So for now JJ's are my tube of choice.
Bob

Hey Bob,

The guitar-amp scenario are as complicated as the hi-fi ditto. Do you want the British Brown-Sound or the American Fender Surf! 6L6's, EL34/EL84? Open back or semi-vented, one/two/four speakers... And what kind of music do you play, single-coil or humbuckers, miked cabs on the scene or "direct-in-your-face" stacks?.

And then comes the fairy with another problem: effects! Currently I'm running a Matchless Phoenix with EL34's and am trying to implement a stage-mounted effects-unit in the loop. Six isolation-transformers needed to get grip of ground-level hum.

There's no free lunches...