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Bias

Started by Pundan, January 21, 2012, 06:20:35 PM

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Pundan

Hey, would this be good enough to use when changing tubes? I've never done a bias adjustment myself before, but I have a friend that knows what he's doing.

http://www.ebay.com/itm/Quad-Tube-Audio-Amp-Bias-Probe-Tester-6L6-EL34-KT88-6V6-/300602047839?pt=Vintage_Electronics_R2&hash=item45fd473d5f#ht_1532wt_1396

RAGER

No Focus Pocus

neighbor664

Would you like a biased or non-biased opinion?

Hemisaurus

Long as it's wired up right. If the instructions are as engrish as the eBay post, it will help to know what you are doing.

Watch the eurotubes vid.

http://eurotubes.com/euro-Generic-Bias.htm


Mr. Foxen

Kept intending to buy one of these then being annoyed because half my amps run 6 EL34. Putting in shunt resistors and not putting them somewhere stupid enough that stuff arcs.

Hemisaurus

Looking, eurotubes sells one for $25 and for another $10 they throw in the multimeter.

VOLVO)))

I dig the multi-unit...
"I like a dolphin who gets down on a first date."  - Don G


CHUB CUB 4 LYFE.

Ayek


Hemisaurus

#8
Quote from: SunnO))) on January 21, 2012, 11:28:28 PM
I dig the multi-unit...
With meters being so cheap, it's almost worth running multiple meters at once rather than jumping back an forth. Course if  you were doing a Mesa or a Peavey VB then it might start getting a bit expensive ;D

I can see you with a little meter shelf, with a lip on it to hold them up, the four identical meters side by side, and the four tubes all jigged up as you tweak ;)

Damn, I'm starting to convince myself now.

Yeah, especially on those units with one damn bias control for 4 tubes :)

dunwichamps

Quote from: Mr. Foxen on January 21, 2012, 08:06:37 PM
Kept intending to buy one of these then being annoyed because half my amps run 6 EL34. Putting in shunt resistors and not putting them somewhere stupid enough that stuff arcs.

1 ohm 1% 2W cathode resistors no good?

Mr. Foxen

That should have ended 'will do'.

dunwichamps

those SC run a high plate voltage?

Hemisaurus

Define high? I never saw one with more than 520 on the plate, MusicMan's on the other hand had 720 :o

dunwichamps

Quote from: Hemisaurus on January 22, 2012, 05:27:14 PM
Define high? I never saw one with more than 520 on the plate, MusicMan's on the other hand had 720 :o

i was thinking 600+ is high for a generic tube amp.


Mr. Foxen

Think the SC200 with KT88 has stacked HT giving 700 or so. Gonna have to be a bit more careful there, but that is 4 valves.

From memory I think I got 540v in the SC120 without valves loaded. Drops with valves so 520 sounds about right. Some of the Laneys and Carlsbros ran pretty high.

FullCustom

Quote from: Hemisaurus on January 22, 2012, 05:27:14 PM
Define high? I never saw one with more than 520 on the plate, MusicMan's on the other hand had 720 :o
Yes, but the screen voltage is only 350.  Screen current and voltage is one of the most overlooked things in tube amp design.  Even with 700 Volts on the plates a Musicman amp is by no means running at it's limits.

Hemisaurus

Quote from: FullCustom on January 25, 2012, 10:40:47 AM
Quote from: Hemisaurus on January 22, 2012, 05:27:14 PM
Define high? I never saw one with more than 520 on the plate, MusicMan's on the other hand had 720 :o
Yes, but the screen voltage is only 350.  Screen current and voltage is one of the most overlooked things in tube amp design.  Even with 700 Volts on the plates a Musicman amp is by no means running at it's limits.
Yep, the plate limits on an EL-34 are 800V, a pair at 800V running with I think (without checking the datasheet) a 11Kohm impedance can push 100W, I seem to recall the rating on the MM output is 5.5Kohm, so if it could handle the extra wattage you could use it to pull 200W out of the quad, big if though, I doubt it could handle the extra power long-term.

FullCustom


[/quote]
Yes, but the screen voltage is only 350.  Screen current and voltage is one of the most overlooked things in tube amp design.  Even with 700 Volts on the plates a Musicman amp is by no means running at it's limits.
[/quote]Yep, the plate limits on an EL-34 are 800V, a pair at 800V running with I think (without checking the datasheet) a 11Kohm impedance can push 100W, I seem to recall the rating on the MM output is 5.5Kohm, so if it could handle the extra wattage you could use it to pull 200W out of the quad, big if though, I doubt it could handle the extra power long-term.
[/quote]
Correct, I've worked on a few Bogner amps that were 185 Watts RMS with just four EL34's.  My Traynor is 150 Watts and only useds four EL34's also. 

Hemisaurus

Good to have my long term memory confirmed ;D

I tend to check the datasheets anyway, before doing anything in the real world, better safe than sorry.

VOLVO)))

I wish my T was a little hotter sometimes. The 800 is TOO hot, I need something inbetween. A bassman or something. I really dig the "falling to pieces" pushed as fuck tone you get from Bassman/Twins.
"I like a dolphin who gets down on a first date."  - Don G


CHUB CUB 4 LYFE.

Hemisaurus

You cut the wire on the master vol didn't you? Did you do the other suggested mods? Gaining up sections is a fairly easy thing, within limits.

VOLVO)))

#22
Yup, Did that all that. It sounds great. I still haven't gotten around to recapping it, I'm sensing it needs it real bad. The 800 makes it sound like a toy in terms of volume.


This is Sim's old T, and mine sounds NOTHING like that. I need to get into some decent cabs, I think.
"I like a dolphin who gets down on a first date."  - Don G


CHUB CUB 4 LYFE.

Hemisaurus

Why not use the T on the cabs you use the 800 with then?

VOLVO)))

I do, I switched them last week, and it was better, but still not even remotely like that. I need to come into some extra money, I'll build a couple and have decent cabs.
"I like a dolphin who gets down on a first date."  - Don G


CHUB CUB 4 LYFE.