B15/baxandall eq valves

[davidlovellbass]

I was looking at changing the valves in my valve pa head from the standard 12ax7 to a 6SL7 as it also has a baxandall eq. The only problem i've read about is the added noise. Has anyone tried this?

[6v6]

Maybe I'm stating the obvious, but arent 6SL7's octal, so you'll have to hack bigger holes into the chassis, rewire new bases etc - seems like a lot of work!

Also I expect you'd need to change the bias resistors.

Is there a specific reason why you want 6SL7s rather than some easier 9-pin substitution like a 12AT7 or 12AY7?

[Mr. Foxen]

What are you hoping to achieve?

[Musky]

Based on the thread title I'm guessing David is looking to end up with something sounding like a B15?

[Mr. Foxen]

Doing that is a whole new circuit sort of job, and won't make it sound like a B15, there is so much more going on. Pretty much all of the idea of a Baxandall eq is that it is flat in the middle, thus isn't a tone consideration unless you tell it to be.

[6v6]

[quote name='Musky' timestamp='1360867788' post='1977700'] Based on the thread title I'm guessing David is looking to end up with something sounding like a B15? [/quote]

If thats the case then I'd be checking out the transformers first, to make sure the power-amp voltages, power output and tube types are same/similar to a B15, and as Mr. Foxen has said, you'd then need to go through the whole amp changing components to match a B15 schematic.

Since some B15 models (B15-S and the current heritage reissue B15) used 12**7 tubes anyway, I personally wouldn't bother with changing out all the preamp tube sockets to octal unless the aim is a vintage-correct clone (which it won't be anyway since it's a modded PA amp and not a scratch-built clone)

[umph]

6sl7s sound much nicer anyway, they pull a bit more current than 12ax7s though

[davidlovellbass]

What i was hoping to achieve was more of a B15 type tone from one of the channels in the same way that some guitar amps have differently voiced preamp sections, being able to have one amp with 3 or 4 classic sounding preamps in would be ideal. What made me think of changing valves was the already present baxandall eq on 3 of the 4 channels, everything i'd read was said the 6SL7 valve sounded more musically pleasing and had been swapped using a secondry 9 pin to 8 pin converter. I'll the trying lower gain valves first tho.

I'm not looking for exact cloned tones as that'd be impossable to achieve in one valve amp without some form of modeling.

Edited February 15, 2013 by davidlovellbass

[6v6]

[quote name='davidlovellbass' timestamp='1360925005' post='1978340']
What i was hoping to achieve was more of a B15 type tone from one of the channels in the same way that some guitar amps have differently voiced preamp sections, being able to have one amp with 3 or 4 classic sounding preamps in would be ideal. What made me think of changing valves was the already present baxandall eq on 3 of the 4 channels, everything i'd read was said the 6SL7 valve sounded more musically pleasing and had been swapped using a secondry 9 pin to 8 pin converter. I'll the trying lower gain valves first tho.

I'm not looking for exact cloned tones as that'd be impossable to achieve in one valve amp without some form of modeling.
[/quote]

Interesting, I'd not considered using an adapter - do you have any links for suppliers? Sounds like it could be an interesting experiment, be interested to hear how you get on

Bear in mind with the other 9 pin tubes that you may still need to change the bias resistor as many won't work optimally with the values used for 12ax7's

[umph]

[quote name='6v6' timestamp='1360926712' post='1978374']
Interesting, I'd not considered using an adapter - do you have any links for suppliers? Sounds like it could be an interesting experiment, be interested to hear how you get on

Bear in mind with the other 9 pin tubes that you may still need to change the bias resistor as many won't work optimally with the values used for 12ax7's
[/quote]

Yeah was just about to say the loads will be all off!

[davidlovellbass]

http://stores.ebay.co.uk/Hanshare-Electronics/Convert-/_i.html?_fsub=2826040011

[6v6]

[quote name='davidlovellbass' timestamp='1361095320' post='1980850']
[url="http://stores.ebay.co.uk/Hanshare-Electronics/Convert-/_i.html?_fsub=2826040011"]http://stores.ebay.c...fsub=2826040011[/url]
[/quote]

Interesting, thanks!

I'm sure it's just the perspective of the photograph, but the picture makes it look like the bolt in the centre of the 9 pins is drilled off-centre and is about 0.5mm from pin 1 (which may have up to about 300v on it!)

http://www.ebay.co.uk/itm/2-x-convert-tube-socket-12AU7-12AX7-6SN7-6SL7-/320737763638?pt=US_Amplifier_Parts_Components&hash=item4aad75e136

[voxpop]

[quote name='davidlovellbass' timestamp='1361095320' post='1980850']
http://stores.ebay.co.uk/Hanshare-Electronics/Convert-/_i.html?_fsub=2826040011
[/quote]

I've bought the adaptors from that seller and they are a handy way of trying a 6sl7 tube in a mini socket. Worh giving it a go for a few pounds.