6sl7 tubes for 12ax7

[alex_st-louis]

hi,

did somebody swap 6SL7 tubes for 12AX7 in his amp, i know you need a converter to do that. my amp is an old ampeg m-12 and i'd like to have a bit more gain.

thx
alex

[backline]

You have a REAL Mercury M-12.?
I have a clone. Those amps are awesome as they come. You sure you do not just need new tubes, and a pedal.?
best

[alex_st-louis]

yes it's a mercury, but i do not have the original speaker, i put a celestion gold in it and it's great...i might changed for a blue, just to get a bit more mid and highs. and yes it sounds good, but i'd like to have just a bit more gain. mabe as you say the tubes are dead.

[alex_st-louis]

Originally Posted by backline

You have a REAL Mercury M-12.?
I have a clone. Those amps are awesome as they come. You sure you do not just need new tubes, and a pedal.?
best

what are the tubes you are using in this amp?

[eugenedunn]

Hi Alex,
The 6SL7 is an octal twin triode with amplification factor (mu) of about 70. It's lower gain octal brother is the 6SN7 with amplification factor of about 20.

The nine-pin 12AX7 has a amplification factor of 100. So you aren't gonna get more gain out of substituting the 6SL7.....but you might get a really cool tone out of it.....those adaptors are cheap and probably work, but they won't fit on many 9-pin tube sockets if the sockets have a spring-loaded metal shield can. The bayonet ring will prevent the adaptor from plugging in all the way.
You'd have to remove that 9-pin socket and wire in a flush 9-pin socket first. From experience. (^_^)

[alex_st-louis]

thx folks,

alex

[eugenedunn]

It's too bad those 9-pin metal can shielded sockets are so ubiquitous. I bought one of those adaptors 'cause I wanted to experiment with swapping in an octal preamp tube in some of my amps and reverb tank.....

But as I said, I'd have to remove that bayonet mounting ring in order to allow the octal adaptor to be inserted all the way.... maybe someday, I'll do it...but it would mean that I'd lose the benefit of having the metal can shield when running a 9-pin twin triode.

[backline]

Originally Posted by alex_st-louis

what are the tubes you are using in this amp?

1 x 5Y3
3 x 6SL7
2 x 6V6

My amp is a one channel head.

http://i111.photobucket.com/albums/n...oore/ampeg.jpg
http://i111.photobucket.com/albums/n...Mercury003.jpg
http://i111.photobucket.com/albums/n...Mercury002.jpg
http://i111.photobucket.com/albums/n...Mercury001.jpg

[eugenedunn]

Oh dang sorry guys...... I just realized you are trying to do the opposite of what I thought. in your case, if you are already running octal preamp tubes and wanna convert to 12AX7 types....then you WILL get an increase in gain.......

[alex_st-louis]

Originally Posted by eugenedunn

Oh dang sorry guys...... I just realized you are trying to do the opposite of what I thought. in your case, if you are already running octal preamp tubes and wanna convert to 12AX7 types....then you WILL get an increase in gain.......

lol, that what's i thought, and will the amp need some tweaks?

[alex_st-louis]

Originally Posted by backline

1 x 5Y3
3 x 6SL7
2 x 6V6

My amp is a one channel head.

http://i111.photobucket.com/albums/n...oore/ampeg.jpg
http://i111.photobucket.com/albums/n...Mercury003.jpg
http://i111.photobucket.com/albums/n...Mercury002.jpg
http://i111.photobucket.com/albums/n...Mercury001.jpg

it looks so much like a old bogen PA amp, i use to have a little challenger 18. it's a cool looking ap you have

[eugenedunn]

Alex,
I gotta feeling you'd be better off keeping the amp as is.... if you need more gain, you might wanna use a clean boost pedal to hit your preamp front end with more signal.

Or just run with your amp wide open and control it all with your guitar volume knob. That's the best way to take advantage of the gain your amp has to give.

Is the amp just too clean for you? Or are you trying to get a dirtier tone at a lower volume?

[Wally]

I have to ask....has this Ampeg been recapped. IF not, you are barking up an empty tree, ime. IF it has already been been recapped, there are other ways that are much simpler to get more gain out of it....biasing, preamp gain changes... IF you like the basic tone of the amp, I would not suggest changing to a different type of tube. You will change the gain, but you will also drastically change the tone.
to answer your question, though, I don't know of anyone who builds octal to noval converters for 6sl7 to 12A_7.

I just took a look at the schematic. One gain stage prior to the PI....I simply would get it healthy and turn it up to 10. That is when these types of amps go to work, ime.

[eugenedunn]

Wally and I practically offered the same type of advice, as far as turning up your amp to max and letting the amp's full available gain structure take over. You just "play the amp" with your guitar volume knob....which is how most cool touch-sensitive amps wanna be played.

Back off on your guitar volume knob to go clean, twist up for all the gain your amp can give. If that ain't dirty enough for you, or it's too loud.....use a great pedal to get you where ya wanna go.

Having an octal preamp amplifier is pretty unique and wonderful.

[alex_st-louis]

Originally Posted by eugenedunn

Wally and I practically offered the same type of advice, as far as turning up your amp to max and letting the amp's full available gain structure take over. You just "play the amp" with your guitar volume knob....which is how most cool touch-sensitive amps wanna be played.

Back off on your guitar volume knob to go clean, twist up for all the gain your amp can give. If that ain't dirty enough for you, or it's too loud.....use a great pedal to get you where ya wanna go.

Having an octal preamp amplifier is pretty unique and wonderful.

you were right my friends, i replaced the old russian 6v6, for the ones i had in an other amp, and it is a HUGE improvment. nice creamy distortion and gain is not an issue anymore. i will test the 6sl7 later. there's still a lot of bass when a roll back the volume knob, but i think if i had a speaker that matches this amp a bit better it would be ok. i think it's a really nice amp.

thx

[Wally]

Alex, you may or may not know this....but when you chagne power tubes in that amp, you are in effect rebiasing the output section. That is the way of a cathode biased amp. IF the tubes you have in there now are 'graded'...that is, if you have the boxes withthe performance specs...thenyou need to maintain the situation by using those tubes with those specs....or something that acts just like them. Youcoudl put a set of the saem make and model of 6V6 in there that would sound totally different. ONe needs to use the saem tube with the same sepcs to maintain the same sonics.
BAss....there is a 100mfd bypass cap on that 6sl7.....one might want to use a smaller cap there to control that low end. BAck then, they were trying to make the amp soudn'rich' at the lower voluems they expected the amp to be used at. They didn't think we would jack the volume up the way we do....adn that much bass early on can be a problem.

[backline]

Originally Posted by alex_st-louis

it looks so much like a old bogen PA amp, i use to have a little challenger 18. it's a cool looking ap you have

Yeah, this a conversion I did from an old, Rauland PA Head.
It is almost a clone of an Ampeg M-12.....but with just one channel. I was lucky the tranny set was in good shape. This amp has some real beautiful Trem
As always.....
if anybody lives near me and wants to plug in, just shoot me an E-Mail/PM.
best

[backline]

Per usual.....
Wally brings up some good points.
That amp is suffering from advanced youth.
Has it had maintenance (cap job) pot and jack cleaning/replacement, the afore-mentioned tubes, a check of the power tube cat resistor, etc. etc.?
I would love to see some pics of your amp.....
best

[Ringo]

here is a 6sl7 adaptor so you can use a 12ax7
http://www.ebay.com/itm/290526992444...84.m1423.l2649
How does that work? the 6SL7 is 6 volts and the 12AX7 is 12 volts correct?

[BobbyZ]

Ringo 12ax7s and such in most amps are 6 volts. If I rember right they'll run on 6 or 12 so thay'd work in car radios and such back in the day.
Groove tubes used to sell an adapter. (maybe still do?)