Fender Blues Jr - Class A or A/B?
Axeman VR
A/B amp?
Seeing that it has only two EL84 tubes and is only 15 watts, I was thinking it
could be a Class A amp...
Anyone?
--
Axeman
davi...@mindspring.com
axem...@aol.com wrote on 6/26/01 11:27 AM:
I am not an authority on this, but I have read that it is class A/B.
David K
Billy Jr.
Just tube circutry powered amp.
b.w
If replying to this partictular address, take out the *REMOVE* from return
address;
Nick Dolling
To get 15W out of a pair of EL84s it would HAVE to be Class AB.
Nick
--
o--- Nick Dolling ------------------------------------------o
o--- Apexus Engineering Pty Ltd ----------------------------o
o--- ndol...@apexus.com.au --------------------------------o
o--- Ph : +618 8266 6222 Fax : +618 8266 6333 --------------o
Tony Hwang
Just looking at circuit and it's bias setting, plus there is PI
tube(half 12AX7), what do you think? I happen to own one as well.
Not A/B, AB which breakds down into AB1 and AB2.
Tony
Daniel
>Neither.
>Just tube circutry powered amp.
>b.w
>
How can it be neither? It's one or the other. Could you explain the classes for
us please?
Daniel
Daniel
JJman
I believe class A is possible in a push pull el84 amp if biased hot enough.
My guess is the BJ is AB.
SE vs PP refers to whether the tube(s) are working parallel to ea other (SE)
vs. configured like two guys using a double ended saw
simultaneously (PP: one pushes and the other pulls.)
One power tube=SE since there is no other tube to push while he is pulling
and vise versa. The saw has only one end being used.
Two power tubes could be either setup as parallel(SE) or PP. Two guys could
both grab the same end of a saw and work "parallel." This is SE.
This is also less efficient and rare (as with 2 guys on the same end
of a one handle saw.)
I think the Gibsonet is 2x 6v6 SE. 4 Power tubes is usually wired
as 2 paralleled pairs working in PP. This is a PP amp. 2 guys on each
end of the saw.
With the common PP 2 power tube setup (with phase inverter):
If each guy on the "saw" only works when the saw is closer to himself this would
be class B. If each guy is always pushing or pulling, this would be class A.
If each guy works while the saw is towards himself and part of the range while
the saw is towards the other guy, this is class AB. This is common and
efficient. The point where the saw is in the middle is the "crossover point."
In class B, this is the point where guy #1 starts to rest and guy #2 takes over
(in the middle.) If guy #1 stops pushing before the mid point and guy #2 hasn't
started pulling this causes "crossover distortion." This is bad. If the guys
are yelling as they work this is "overdrive" and is good :) If one guy is
stronger than the other they are not "matched."
JJman
brendo...@gmail.com
Les Cargill
You can get 25W out of a pair of EL84 @ 400V plate. An AC30 uses 4
EL84.
--
Les Cargill
Rick N. Backer
<lcarg...@comcast.com> wrote:
>brendo...@gmail.com wrote:
>> ???????, 26 ???? 2001 ?., 12:27:53 UTC-6 ???????????? Axeman VR ???????:
>>> A/B amp?
>>>
>>> Seeing that it has only two EL84 tubes and is only 15 watts, I was thinking it
>>> could be a Class A amp...
>>>
>>> Anyone?
>>>
>>> --
>>> Axeman
>>
>> Someone earlier said that getting 15 watts from two EL84s would have to make it class AB, but what about the Vox AC 15 and 30?
>>
>
>That posting was from 2001.
>
>You can get 25W out of a pair of EL84 @ 400V plate. An AC30 uses 4
>EL84.
Randall claims it runs class 'A' in all three modes (5/15/30W) using
1, 2 & 4 tubes progressively. He uses a tube rectifier for the first
two wattages and silicon diodes for the last. It might explain the
lower than otherwise expected output. Marshall was getting 18 to 20
out of a pair but definitely running them A/B.
Lord Valve
Fuck you.
Les Cargill
> On Thu, 8 Oct 2015 00:11:26 -0500, Les Cargill
> <lcarg...@comcast.com> wrote:
>
>> brendo...@gmail.com wrote:
>>> ???????, 26 ???? 2001 ?., 12:27:53 UTC-6 ???????????? Axeman VR ???????:
>>>> Does anyone happen to know whether the Fender Blues Jr is a Class A or a Class
>>>> A/B amp?
>>>>
>>>> Seeing that it has only two EL84 tubes and is only 15 watts, I was thinking it
>>>> could be a Class A amp...
>>>>
>>>> Anyone?
>>>>
>>>> --
>>>> Axeman
>>>
>>> Someone earlier said that getting 15 watts from two EL84s would have to make it class AB, but what about the Vox AC 15 and 30?
>>>
>>
>> That posting was from 2001.
>>
>> You can get 25W out of a pair of EL84 @ 400V plate. An AC30 uses 4
>> EL84.
>
> I wonder how that applies to Mesa's Lonestar Special. I believe
> Randall claims it runs class 'A' in all three modes (5/15/30W) using
> 1, 2 & 4 tubes progressively.
tubes ) and 30 watts ( both pair ).
Seems ordinary enough.
> He uses a tube rectifier for the first
> two wattages and silicon diodes for the last.
> It might explain the
> lower than otherwise expected output.
although I dunno how much B+ they'll take. So 15W per pair
says "AB" to me.
It's the same levels you get from an AC15 and an AC30. Hardly
seems substandard.
> Marshall was getting 18 to 20
> out of a pair but definitely running them A/B.
>
.79 or 1.78 dB :) Wikipedia says Traynor got 25W a pair from EL84s
with 400V B+.
--
Les Cargill
Pt
It is giggable.
Pt
Les Cargill
be that there are 11 watt amps that outrun a 22 watt amp. Mike Adam
had a Budda Superdrive that you could hardly stand next to when
he turned it up.
--
Les Cargill
jh
is the question good for?
Of course you CAN build an EL84 amp in "pure class A"
Jochen
jh
> Am 08.10.2015 um 05:29 schrieb brendo...@gmail.com:
>> вторник, 26 июня 2001 г., 12:27:53 UTC-6 пользователь Axeman VR написал:
>>> Does anyone happen to know whether the Fender Blues Jr is a Class A
>>> or a Class
>>> A/B amp?
>>>
>>> Seeing that it has only two EL84 tubes and is only 15 watts, I was
>>> thinking it
>>> could be a Class A amp...
>>>
>>> Anyone?
>>>
>>> --
>>> Axeman
>>
>> Someone earlier said that getting 15 watts from two EL84s would have
>> to make it class AB, but what about the Vox AC 15 and 30?
>>
>
>
> Of course you CAN build an EL84 amp in "pure class A"
>
>
> Jochen
fred...@gmail.com
Lord Valve
> On Tuesday, June 26, 2001 at 1:27:53 PM UTC-5, Axeman VR wrote:
> > Does anyone happen to know whether the Fender Blues Jr is a Class A or a Class
> > A/B amp?
> >
> > Seeing that it has only two EL84 tubes and is only 15 watts, I was thinking it
> > could be a Class A amp...
> >
> > Anyone?
> >
> > --
> > Axeman
>
> Axeman is correct. The Fender Blues Jr is a 15 watt "class A" amp
and it only requires you to pop in and play with your choice of output tube....I would stay with EL84s although there are other tubes depending on the tone you are looking for out there.
The is considered a Cathode-biased amp, no re-bias.
http://support.fender.com/schematics/guitar_amplifiers/BluesJuniorIII_schematic_Rev-D.pdf
Hey - you didn't use to call yourself RS, didja?
Lord Valve, ThD
Expert (fuck you)
palli...@gmail.com
>
>
>
> Axeman is correct.
> The Fender Blues Jr is a 15 watt "class A" amp and it only requires
> you to pop in and play with your choice of output tube....
>
The schem shows grid bias of only -10.6 volts with screen and plate voltages of 305V and 329V respectively. With most new EL84s, this results in a plate current of 50 to 60mA per tube - well over the maximum continuous rating.
R52 is a 22k resistor in the bias supply that can be increased to 47k to give -15V which stops the overheating with no bad effects. The amp is then operating in class AB.
> The is considered a Cathode-biased amp, no re-bias.
.... Phil