Tube Recommendations - 74 Fender Vibrolux

Discussion:

(too old to reply)

Eric Stahl

2007-02-11 23:11:47 UTC

Greetings all,

After listening online to the tones of various harp player's amps I'd
like to improve what I'm hearing on my 1974 Fender [silver face]
Vibrolux Reverb i.e. for a nicer distorted/overdriven sound when
playing harp.

What I'm playing on the harp-end is another story ;-)

If I crank the amp volume well up with the treble and brightness down
(and bass up) I get a decent enough sound until I hear some of the
really sweet recordings on line, and then realize that something's
lacking. I'd like to be able to get a better/sweeter distorted sound
and at lower volume - specifically for recording. What I get now is
mostly just louder, and not what I'm looking for when distorted.

My mic's include an old Shure 520 with volume control that lends
towards the best sound with it's volume well up, and the amp adjusted
as described above.

I've also got an old Turner 454X crystal mic that I use with the amp
(also with a volume control).

I've been reading through Usenet archives focusing on
alt.music.harmonica, and see that the recommendations for amps in
general are to replace any 12AX7 tubes with 12AU7's for a softer
overdriven tone, and possibly to change the first position (left to
right from the back) 6L6GC with a 5Y3GT to allow overdrive at a lower
volume.

The tube layout is shown on the manufacturer's original sticker as
follows (left to right from the back):

5U4GB 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025

The tube layout was as follows when I bought it used (again with one
12AX7)...

6L6GC 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025

Some questions I have are...

From reading Usenet archives, the first three tubes (left to right
from the back) seem to be called the "power tubes", and the next six
are the "preamp tubes". But I found conflicting info on this. Which is
correct?

Are the six smaller [preamp?] tubes divided into two sets, one for the
"Normal" and one for the "Vibrato" inputs? Or are they two sets with
one for each amp channel (labeled "1" and "2" under "Normal" and
"Vibrato"? And if two sets, then should the sets match? And why might
I want them to be different?

What tube configuration should I try starting with? Where and how many
12AU7's might I use? Is a 5Y3GT in the first tube position (left to
right) a good idea?

What am I missing - always a good catch-all question! :-)

I do appreciate the collective expertise of this group!

There are some folks in this newsgroup that I've never heard play -
Silk and keith Adams come to mind. It'd be nice to have some links to
what you're up to on harp.

Until recently (last couple months) I'd never really heard myself
play, and the experience is like hearing your voice for the first
time, like "damn, I won't do that any more!" :-) And other things
where I'm thinking "do more of that".

Two links I posted for this group were real simple and basic. I've
more recently (January 1st) started uploading to
http://www.harmonicaboogie.com and I'm having lots of fun with that.

The first eight tunes I uploaded are now gone from that site since the
new "Jam 12" started, but there are two there now at
http://www.harmonicaboogie.com/artist/ericstahl.php.

Thank you in advance for any advice short of "go to &%^#!" ;-)

Eric

Johnny

2007-02-12 02:25:45 UTC

Permalink

Eric,

Others on the NG are far more adept at this sort of thing than me (we've got
some actual EE's and other tube gurus here versus the "hope and poke" guys
like me), so wait to hear more input from them.

With that said, in general, I'd suggest putting the 5U4GB back in and then
swapping the 6L6's out in favor 6V6's. I'd also try swapping the two 12AT's
for 12AU's. Without benefit of a schematic, my guess is the 12AX runs the
vibrato, so you could try swapping that one too for a 12AU, but you might
lose the vibrato effect with that config.
--
Johnny

"No, we haven't failed. Now we know over 1,000 elements that will not work."
T.A. Edison

Post by Eric Stahl
Greetings all,
After listening online to the tones of various harp player's amps I'd
like to improve what I'm hearing on my 1974 Fender [silver face]
Vibrolux Reverb i.e. for a nicer distorted/overdriven sound when
playing harp.
What I'm playing on the harp-end is another story ;-)
If I crank the amp volume well up with the treble and brightness down
(and bass up) I get a decent enough sound until I hear some of the
really sweet recordings on line, and then realize that something's
lacking. I'd like to be able to get a better/sweeter distorted sound
and at lower volume - specifically for recording. What I get now is
mostly just louder, and not what I'm looking for when distorted.
My mic's include an old Shure 520 with volume control that lends
towards the best sound with it's volume well up, and the amp adjusted
as described above.
I've also got an old Turner 454X crystal mic that I use with the amp
(also with a volume control).
I've been reading through Usenet archives focusing on
alt.music.harmonica, and see that the recommendations for amps in
general are to replace any 12AX7 tubes with 12AU7's for a softer
overdriven tone, and possibly to change the first position (left to
right from the back) 6L6GC with a 5Y3GT to allow overdrive at a lower
volume.
The tube layout is shown on the manufacturer's original sticker as
5U4GB 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025
The tube layout was as follows when I bought it used (again with one
12AX7)...
6L6GC 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025
Some questions I have are...
From reading Usenet archives, the first three tubes (left to right
from the back) seem to be called the "power tubes", and the next six
are the "preamp tubes". But I found conflicting info on this. Which is
correct?
Are the six smaller [preamp?] tubes divided into two sets, one for the
"Normal" and one for the "Vibrato" inputs? Or are they two sets with
one for each amp channel (labeled "1" and "2" under "Normal" and
"Vibrato"? And if two sets, then should the sets match? And why might
I want them to be different?
What tube configuration should I try starting with? Where and how many
12AU7's might I use? Is a 5Y3GT in the first tube position (left to
right) a good idea?
What am I missing - always a good catch-all question! :-)
I do appreciate the collective expertise of this group!
There are some folks in this newsgroup that I've never heard play -
Silk and keith Adams come to mind. It'd be nice to have some links to
what you're up to on harp.
Until recently (last couple months) I'd never really heard myself
play, and the experience is like hearing your voice for the first
time, like "damn, I won't do that any more!" :-) And other things
where I'm thinking "do more of that".
Two links I posted for this group were real simple and basic. I've
more recently (January 1st) started uploading to
http://www.harmonicaboogie.com and I'm having lots of fun with that.
The first eight tunes I uploaded are now gone from that site since the
new "Jam 12" started, but there are two there now at
http://www.harmonicaboogie.com/artist/ericstahl.php.
Thank you in advance for any advice short of "go to &%^#!" ;-)
Eric

Robert Reynolds

2007-02-12 02:58:54 UTC

Permalink

I'm guessing that the amp does not work with the current set of tubes,
right? The 5U4 is a rectifier that turns AC into DC. The 6L6 amplifies
a signal and drives a loudspeaker. You can not put a 6L6 into a
socket intended for a 5U4 and get anything out of the amp.

From your description, it looks like you are suffering from "Big Fender
Syndrome", meaning that you have too much clean headroom. You can
usually get some satisfaction out of these amps by swapping tubes. The
best place to start is to figure out what you have. A 7025 is
essentially a 12AX7 with a different name, so assume that your amp has
four 12AX7 and two 12AT7. If you can get your hands on a few 12AU7s and
a few 12AY7s, you can swap them in and around until you start hearing
sounds you like. Another thing you might want to try is a 5V4 in place
of the 5U4.

My best cure for Big Fender Syndrome is to get a better harp amp. I
don't want to subject you to a soapbox speech, but that's essentially
what led me to build my own line of amps. You want the overdrive
threshold to be exactly between a soft note and a loud note. These big
Fenders just don't do that. Their threshold is just too high, and you
never get that perfect crunch on the note attack, unless you find a good
combination of preamp tubes that will make it happen.

Post by Eric Stahl
The tube layout is shown on the manufacturer's original sticker as
5U4GB 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025
The tube layout was as follows when I bought it used (again with one
12AX7)...
6L6GC 6L6GC 6L6GC 12AT7 12AX7A 7025 12AT7
7025 7025

Eric Stahl

2007-02-12 04:40:30 UTC

Permalink

Post by Robert Reynolds
I'm guessing that the amp does not work with the current set of tubes,
right? The 5U4 is a rectifier that turns AC into DC. The 6L6 amplifies
a signal and drives a loudspeaker. You can not put a 6L6 into a
socket intended for a 5U4 and get anything out of the amp.
From your description, it looks like you are suffering from "Big Fender
Syndrome", meaning that you have too much clean headroom. You can
usually get some satisfaction out of these amps by swapping tubes. The
best place to start is to figure out what you have. A 7025 is
essentially a 12AX7 with a different name, so assume that your amp has
four 12AX7 and two 12AT7. If you can get your hands on a few 12AU7s and
a few 12AY7s, you can swap them in and around until you start hearing
sounds you like. Another thing you might want to try is a 5V4 in place
of the 5U4.
My best cure for Big Fender Syndrome is to get a better harp amp. I
don't want to subject you to a soapbox speech, but that's essentially
what led me to build my own line of amps. You want the overdrive
threshold to be exactly between a soft note and a loud note. These big
Fenders just don't do that. Their threshold is just too high, and you
never get that perfect crunch on the note attack, unless you find a good
combination of preamp tubes that will make it happen.

Thank you for the replies Johnny and Robert.

It sounds like a starting point might be swapping out (counting
the nine tubes from left to right and from the back) The 6L6GC
in socket one with either a 5Y3GT or 5V4 (which 5V4?); and the
12AX7 and 7025's in sockets five, six, eight and nine with 12AU7's
or 12AY7's. Looking online five such tubes might cost me $30 to
$75 or more (http://www.tubesandmore.com/). I'll go with "less is
better" until I find a sound I generally like.

Robert, you said "5V4", and online I see 5V4G's, 5V4GA's, and
5V4GT's. Which were you refering to? One site
(http://www.members.optusnet.com.au/~valventube/5V-Rectifiers.html)
stated: "5V4G = GZ32 .. 5V4GA .. 5V4GT". I'm wondering if these are
"essentially" the same ;-) or really the same?

Any idea what "Long plate" tube versions are? I see those
referenced as well.

The amp works in as much as what goes in, comes out amplified ;-)
it's just not the smoothe distorted sound that at times I want to
hear.

You said "a 7025 is essentially the 12AX7 with a different name".
Wondering why the original Fender sticker inside the amp specifies
the one 12AX7 and three 7025's I looked further online and found
e.g. from "Rick Plays the Blues" in Germany on Dec 21st 2006...

"12AX7 is the same as ECC83
12AT7 is the same as ECC81
12AU7 is the same as ECC82

12AX7, 12AT7, 12AU7, 5751, 12AY7, 7025 are all
interchangeable - but will deliver different
sounds and different amount of gain.
12AX7, 7025, 5751 and 12AY7 and more euqal to
each other - they feature compareable impedances
and can always be replaced by each other. The
12AX7 has the highest gain, usually. The 7025 is
kind of a high quality version of the 12AX7
(used by Fender in their combos especially for
V1)
5751 has only roughly 70% of the gain and
basically a rounder, sweeter sound. 12AY7 has
only 40% of the gain of a 12AX7 and comparable
sound.
12AT7 and 12AU7 are a little different regarding
impedances and likely don't work as V1
(exceptions are just there to confirm the
rule :^) being too dark ..... 12AT7 is roughly
60% of the 12AX7 gain, 12AU7 is 20%. Both tubes
are suited very well for high current delivery,
as you need it as reverb driver or phase inverter
tube."

Thank you for the information!

Eric

Robert Reynolds

2007-02-12 05:55:39 UTC

Permalink

Post by Eric Stahl
The amp works in as much as what goes in, comes out amplified ;-)
it's just not the smoothe distorted sound that at times I want to
hear.
Eric

It does? Do you still have a 6L6 in socket #1 where the 5U4 is supposed
to be, or did you put a 5U4 in? If this amp works with a 6L6 where the
rectifier is supposed to be, then the rectifier tube has probably been
cut out of the circuit and replaced with a solid state rectifier inside
the chassis.

To answer your other question, you could use any version of a 5V4.
You're just experimenting anyway. And regarding the interchangeability
of 12AX7, 7025, etc, you can assume that these tubes have similar
ratings but may have slight differences that you wouldn't notice anyway.
For tube data, check out this site:
http://www.nj7p.org/Tube.php

In particular, check out the description of the 7025:
http://www.nj7p.org/Tube4.php?tube=7025

This is a nifty site because you can get the data sheet on any tube, and
then you can check for tubes with the same characteristics or the same
base. Same base comparisons will give you all tubes that will plug into
the same socket. It doesn't mean that it will do what you want it to,
it just means that the tubes are compatible because they have the same
parts assigned to the same pins. So, type in 12AX7 and check for tubes
with the same base, and you will see all the tubes with direct plug-in
compatibility. If you try comparing tubes this way, don't forget to
note the heater ratings, usually denoted by the first number in the
tube's name.

Eric Stahl

2007-02-12 06:33:33 UTC

Permalink

Post by Robert Reynolds

Post by Eric Stahl
The amp works in as much as what goes in, comes out amplified ;-)
it's just not the smoothe distorted sound that at times I want to
hear.
Eric

It does? Do you still have a 6L6 in socket #1 where the 5U4 is supposed
to be, or did you put a 5U4 in? If this amp works with a 6L6 where the
rectifier is supposed to be, then the rectifier tube has probably been
cut out of the circuit and replaced with a solid state rectifier inside
the chassis.
To answer your other question, you could use any version of a 5V4.
You're just experimenting anyway. And regarding the interchangeability
of 12AX7, 7025, etc, you can assume that these tubes have similar
ratings but may have slight differences that you wouldn't notice anyway.
http://www.nj7p.org/Tube.php
http://www.nj7p.org/Tube4.php?tube=7025
This is a nifty site because you can get the data sheet on any tube, and
then you can check for tubes with the same characteristics or the same
base. Same base comparisons will give you all tubes that will plug into
the same socket. It doesn't mean that it will do what you want it to,
it just means that the tubes are compatible because they have the same
parts assigned to the same pins. So, type in 12AX7 and check for tubes
with the same base, and you will see all the tubes with direct plug-in
compatibility. If you try comparing tubes this way, don't forget to
note the heater ratings, usually denoted by the first number in the
tube's name.

Robert,

Thank you for your help.

Eric

Keith Adams

2007-02-13 06:51:57 UTC

Permalink

Damn Eric. Theres been some strange modifications to your amp if you've got
a 6L6 in the rectifier socket?
I cant think why that would be because amps dont generally use an odd
number of power tubes. Robbies right though. Unless its a tweed amp the
larger Fenders are known for their clean chimey sounds. Especially the
Silverfaces. Its a good harp amp but for clean tones only.
You might run some kind of overdrive pedal in front of the amp and get
where you want with it?

Eric Stahl

2007-02-23 06:50:47 UTC

Permalink

On Mon, 12 Feb 2007 22:51:57 -0800, "Keith Adams"

Post by Keith Adams
Damn Eric. Theres been some strange modifications to your amp if you've got
a 6L6 in the rectifier socket?
I cant think why that would be because amps dont generally use an odd
number of power tubes. Robbies right though. Unless its a tweed amp the
larger Fenders are known for their clean chimey sounds. Especially the
Silverfaces. Its a good harp amp but for clean tones only.
You might run some kind of overdrive pedal in front of the amp and get
where you want with it?

Short of physically pulling the tube I would have needed a small
mirror and flashlight to see exactly what the tube was. My mistake -
it was the original Fender rectifier tube.

I sure do appreciate the wealth of harp and amp knowledge in this
group.

Haven't decided what to try next - either getting hold of a pile of
tubes and swapping them into the Vibrolux (it holds nine); or locating
a preamp/amp-emulator as my present playing is limited to home
recording and internet uploading.

There's some fascinating equipment out there, with sound clips
available online for some of it. Less expensive are some of the IC
emulators, but even the Harp Commander doesn't sound as nice as some
of the tube amps. That Marble Max amp that Ben's talked about sounds
real nice - at a price that's multiples of the emulators - and can be
configured to run right into a sound card for late night home
recording. The Hughes and Kettner Tubeman is tempting - though the
sound certainly is harsher than the Marble Max and I don't think I'd
use the full range of possibilities on the Tubeman. Haven't found any
Mesa V-Twin sound clips yet to listen to.

Gianandrea Pasquinelli's site at the following URL is a good one,
including Marble Max, Harp Commander, and Tubeman samples:
http://www.bluestime.it/harmonica_house/harp_gear_review/harp_gear.html

This may all sound like common knowledge to some of you - but it's all
new and fun to me. I've been playing harp for about 40 years, mostly
just along with records/CD's, and those clips I put on box.net for
this newsgroup a couple months back were the first time I'd heard
myself play.

Take a listen to my last upload with a backing track by Blues Tom
called Criyin at the following URL and let me know what you think
http://www.harmonicaboogie.com/artist/ericstahl.php

- Eric