What does this tube do? SF Twin tube questions

[Todd Brown]

O.K, so I don't read electronic circuit schematics. I have looked diligently on the web for a chart or listing of what the function/designation is of the 6 pre-amp tubes. I can't find it.

I know, looking at the amp from the back. Tube 1 is all the way to the right. 6 is closest to the power tubes. What I'm not exactly sure of is each ones function. I think I know a few, but would like to familiarize myself with them for sure. That way I fully understand what a tube change in each particular position would do. Can someone list each tube function for me?

Also, I know this has been discussed, but I would like some current, up to date info on this one. Where is the best place currently to buy tubes? The best tubes for the best prices? Who are you using? This includes the best matching service and everything. The web is full of places, but I want to use a reputable place that others are using. Where do you buy your tubes??


Thanks!

[Jack Stoner]

What is the chassis Model, such as "AA270", etc.

Looking at the AA270 chassis schematic (the latest one I have) from right to left the tubes are V1, V2, V3, V4, V5, V6.

V1 is a 7025 (or 12AX7) and is the input preamp tube for the Normal input.

V2 is a 7025 (or 12AX7) and is the input preamp tube for the Vibrato channel.

V3 is a 12AT7 and is the driver tube (output) to the reverb pan.

V4 is a 7025. The "a" section is the reverb pan return preamp. The "b" section is a "mixer" tube for the reverb, preamp and tremolo and feeds V6 (12AT7) which is the driver tube for the 6l6's.

V5 which is a 12AX7 is the Tremolo tube.

I also have schematics for AA768, AB768 and AC568 and they are identical.

[Stephen Cowell]

O.K, so I don't read electronic circuit schematics. I have looked diligently on the web for a chart or listing of what the function/designation is of the 6 pre-amp tubes. I can't find it.

Let's examine one example, the BF Twin, at Schematic Heaven:

http://www.webphix.com/schematic%20heav ... _schem.pdf

One thing it doesn't do, is show you which one is V1, V2 etc. Looking at the second page (layout), you count the tubes from the right to the left starting at V1.

V1 - normal channel gain and tone recovery
V2 - Reverb channel gain and tone recovery
V3 - reverb driver
V4 - reverb recovery and buffer
V5 - trem oscillator and neon driver
V6 - phase inverter



(snip)

Also, I know this has been discussed, but I would like some current, up to date info on this one. Where is the best place currently to buy tubes? The best tubes for the best prices? Who are you using? This includes the best matching service and everything. The web is full of places, but I want to use a reputable place that others are using. Where do you buy your tubes??

I normally use Antique Electronics for most stuff.

www.tubesandmore.com

For NOS tubes you can try Ned Carlson if you're a liberal, or Lord Valve if you're a conservative.

http://triodeelectronics.com/
http://www.merchantcircle.com/business/ ... 3-778-1156

His Highness of Thermionic Flatulence (otherwise known as LV) has never let me down... except for his rabid political views, that is.

[Todd Brown]

Not sure which circuit. It's a 73-74 MV. 100 watt. Partially Blackfaced(less reverb & phase inverter). So I've been told.

"V6 is the driver tube for the 6L6's". Is that the same thing as the phase inverter tube as Stephen has stated for V6? Just wanna be sure.

Stephen, thanks for the info. That is exactly what I needed.

Antique Electronics looks like a good place. I've heard about LV. Doesn't seem like an easy guy to do business with necessarily. No website?

Who are some tube sellers I should stay away from? Bad experiences? Anybody wanna take that one?

[Jack Stoner]

That is the same thing.

[Stephen Cowell]

Not sure which circuit. It's a 73-74 MV. 100 watt. Partially Blackfaced(less reverb & phase inverter). So I've been told.

"V6 is the driver tube for the 6L6's". Is that the same thing as the phase inverter tube as Stephen has stated for V6? Just wanna be sure.

Stephen, thanks for the info. That is exactly what I needed.

Antique Electronics looks like a good place. I've heard about LV. Doesn't seem like an easy guy to do business with necessarily. No website?

Who are some tube sellers I should stay away from? Bad experiences? Anybody wanna take that one?

As I stated earlier, he's never done me wrong... and he knows his stuff, and keeps all the old and new good stuff in stock. Phone is the way to go for him... but if you're not a super cork-sniffer you might just be happy with Antique... LV keeps the top-shelf stuff, and knows what it's worth.

My only bad experiences are buying old tubes from volume sellers at hamfests... caveat emptor there.
Some of my best finds are in old PA sets... don't neglect them, that's where the Mullards are hiding.

[Todd Brown]

Cool. What about The Tube Store or Tube Depot? Any experience with those guys?

[Steve Ahola]

As far as I know the tube numbering for Twin Reverbs has always been the same- V1 is the 12AX7/7025 closest to the Normal input jack and they go across in order. V1 and V2 pretty much determine the character of the sound of the Normal and Vibrato channels, respectively, so they are the ones that you would want to do some "tube rolling" to get the sounds that you are looking for.

Preamp tubes are not like spark plugs- its not like you necessarily want all of the 12AX7's to be a matched set. I love NOS tubes when I can afford them but they all have their own character so its not like you plug them in and like magic your amp will sound better. If you are looking for a brighter sound a dark sounding NOS tube may not be what you want to use (although that tube might be absolutely perfect in an amp that is too bright.)

V3(12AT7) drives the reverb tranformer so it pretty much either works or it doesn't work, although you might want a stronger tube. V4(12AX7)is more critical as it can determine the character of the reverb sound. It has no effect at all on the Normal channel. I personally prefer a more neutral sounding tube for V4, using V2 to set the character of the Vibrato channel.

If your tremelo works fine there is no need to replace V5(12AX7) as it isn't being used as an audio tube. If you are having problems with your tremelo you might want to try swapping in a different 12AX7 (like V1 from the Normal channel) although the problem is usually with the tremelo circuitry not the tube.

V6 is the driver/phase inverter tube and I prefer a strong clear 12AT7. Some guitarists like to replace the 12AT7 with a 12AX7 but the circuit was designed and biased for a 12AT7 so I would stick with that.

Just my thoughts on a Saturday morning...

Steve Ahola

P.S. Don't overlook the Normal channel- I think that it has a clearer sound than the Vibrato channel because the signal is routed around the reverb circuitry. If you are going to plug in a lot of pedals or a multi-processor I would recommend trying the Normal channel first.

[Todd Brown]

Thanks guys!! Got some good info on this thread.

[Patrick Rusert]

Here's a couple of links that've been very helpful for me, although I haven't bought anything from KCA (yet).

https://www.kcanostubes.com/content/fen ... mendations

http://www.watfordvalves.com/cgi-bin/do ... port_2.pdf

Forumite Orlando Colom has a stash of vintage tubes that he'll sell a few in the Amps & Accessories FS section from time to time. Here's his last post:

http://bb.steelguitarforum.com/viewtopi ... ight=12ax7

[Richard Rice]

Thanks for all the input here. I revisited a couple of my favorite amps (which recently fell out of favor) and tried some different things. Replacing V1 in my Dual Showman Reverb amp with a 12AT7 got a much more useful sound for me. That one went back to the rotation immediately. Then I tried the normal channel of my Vibrosonic Reverb (instead of the vibrato channel), tweaked the tone a bit, and it sounds great, too. I guess I'm back to that pair in stereo.

In the meantime, I just bought a Vegas 400 that needs some repairs. It hasn't arrived yet, but I'm hoping it will sound as good as these old Fenders, once it's fixed.. I've never played pedal steel through a Peavey combo amp, so it will be interesting to see how they compare...

Looks like the old BL pickups were just pushing the front end too hard, causing unwanted breakup when cranked.. The lower gain tube helped the Dual Showman clean up, with lots of headroom. I may do the same thing to the Vibrosonic and see if it improves, but it sounds way better through the normal channel. Since I hve a TC Hall of Fame reverb pedal, reverb is a non issue. I like the pedal better than the spring reverb, it sounds less "swooshy"- a tad cleaner on the decay. Nice and smooth now!

[William Hughes]

I just want to put my 2 cents in. When retubing an amp I would recommend having a tech check the bias and also an amp that old should have the filter caps replaced if they haven't been.