WHOA !!! super hot deville bias

[dreadzeppelin]

Checked out eurotubes.com website and they have a biasing video section and one video is biasing a hot rod deville. Bob from eurotubes was doing the video and set the deville 91 mv!!! Has anybody done this with decent results? Fender recommends 60 mv I think. Would this high setting fry this puppy?

[JAM]

Isn't he in the business of selling tubes?

[GearHeadFred]

Yeah, you have to consider the source!!

I think the "conventional" thinking is that the 60mv that Fender specs is too cold. Since they have to warranty the amps, that makes a lot of sense.

70% idle dissipation equates to around 68mv. I think that's where most people tent to bias them. That's where mine is.

[hawkeye2u]

That bias setting would sound HOT, BUT your tubes will NOT last long
68-70mV would be my setting ( as it is now)

[²Thom]

Bob uses JJ 6L6 GC.
They didn't start getting red at even 150 mV. I tried it and couldnt beleave it.
I biased while playing guitar:

somewhat above 20mV the amp startet to work
between 40 and 55 mV the sound getting better, but sterile and flat
68 mV ist the bottom value and sounds like solid state
then, when I pass the 80 mV going straight to the 90mV the Amp opens and getting a great fundamental bass


I think fender uses low biases Sovtecs because its better for the PCB and Transformers.

[dreadzeppelin]

I run mine at 68.4 I think , I have to check. If it's tube life, I don't mind that much. If it's pcb life, well...........
You know, if we start talking about about it alot and making a commotion, i bet somebody will make replacement pcb boards!!!

[rudutch]

can you confirm the accuracy of your meter?
I have 3, none of them read the same at that level.
(the one I think is most accurate is a clamp-on amp meter - VOM)

I had similar results with my digital VOM...

[²Thom]

Yes rudutch my meter works accurate its a 4 1/2 digit yellow Metex which costs about 300 DM 20 Years ago.

In another experiment I went further with the current (you have to change the value of a Resistor).
Slightly above 250mV I saw one tube begins getting red. That is 125 mA at 430V means 53.75 W Heat on the Plates of each Tube!!!

Now I biased my HRDx at 88mV at 410V means 18W on each Tube that is full OK for Sound and lifetime.

[NTBluesGuitar]

So anyone know what percentage of maximum plate dissipation their bias numbers are?

[²Thom]

Bob at Eurotubesis going 70+ % of maximum plate dissapation but it depends on the Amp.

I think everything above 60 % sounds good.

[NTBluesGuitar]

Sorry for being a smartass.

But the 70% plate dissipation depends more on the tube than the amp, generally.

Just wanted to make sure that folks didn't just start throwing out bias voltages all willy-nilly with no frame of reference.

[²Thom]

So anyone know what percentage of maximum plate dissipation their bias numbers are?

Yes: You and me and Bob.




the mathematics behind isn't that tough even for 24-hours-drunken-musicians

[yankeerob]

I agree with NTBluesGuitar re: depends on tubes - I have my Deville biased as standard with TAD 6L6WGC STR's - but I regularly run it pretty wide open - with clean gain and MV at around 9-10 - so I'm getting plenty of rich harmonics out of the power tubes...

I've also taken to using short plate BVA's (British made Mullard, Brimar, Mazda ECC83's - they're used - NOS ones fetch too much dough but they test fine - I buy them on ebay off of tube geeks who go to yard sales etc looking for old tube radios and tape decks...) because they have plenty of rich but clean gain, a very low noise floor and great frequency response...

All this hot bias stuff is fine if you're gonna sit around your bedroom or garage, play at lower levels and never move it around much - it'll just begin to sound dull and muddy quicker in the life cycle of whatever 6L6 you've chosen to use...

But if you start gigging with a hot bias then you are almost certainly going to have reliability issues - one night you're going to want to throw your axe back in the case, chuck that baby in the trunk or the back of the van and get the hell out of Dodge; not allowing your amp to cool down enough to transport it - then the next time you power up you'll curse that hot bias

When I first got my Deville it had all the original GT's still in it and the bias had never been checked - I put the TAD's in (and was using JJ ECC83s's until my BVA revelation) and had the bias done to spec - all my peers started asking how I got such a good tone out of a Deville - I just looked at my mate John who'd done the work for me, smiled and told 'em that it was a stock amp, made in the USA and here's the guy who set the bias for me - end of story.

The Celestions play a part too - apologies to everyone sick me ranting about them - G12T-100's - one of their least expensive spkrs - go figure - from what I can gather they're hard to come by over there - apparently Fender are using a 65W version of the GT12T in CyberTwins(?) - but I digress and will start a thread re: Hot 100's as they are known here...

Having now done a few mods on it (audio pot on MV, removed hi-pass on reverb, cap upgrades) - I'm just fine tuning what is already a great sounding amp and bolstering up a few key components to give me reliability for gigging at high power - that's not to say that you need to do them to get a great sound out of the Deville - although the audio pot in the MV is a pretty good one to have done for better control of the Drive channel at lower levels...

Keep the faith brother - you've bought a great amp - keep rockin the free world