Sc20/sv20 Power Tubes...what Is The Deal Exactly?

[santiall]

To be extra clear....All these tubes will work with no changes to screen/grid resistors?
Just as long as there is enough range in the current bias?

no changes, pretty much the way to go go is to install the tubes and see if you like the result

 

[paul-e-mann]

I think the overwhelming majority like EL34 that's why Marshall took the trouble to fit them into these small watt amps, be happy they did and use it this way! You want 6L6 etc. buy a different amp.

 

[Jethro Rocker]

I think the overwhelming majority like EL34 that's why Marshall took the trouble to fit them into these small watt amps, be happy they did and use it this way! You want 6L6 etc. buy a different amp.

But nice that you can try a pair of 6L6s and run em to the top in 5 watt mode (or 20 ) and see.

 

[Georgiatec]

yeah, let us know!

Finally got around to slotting a KT66 into the SL-5. Tested it first to make sure it was a good valve.
Not only does it work but, it sounds magnificent. So good that I've left it in there. The valve retainer requires a bit of adjustment in order to stay on but the rear cover fits flush onto the valve retainer and holds it in place. The cover also acts as a heat sink for the bigger KT66.

 

[santiall]

that's like it should be

 

[Pistons&Petrol]

I just had KT88's fitted into a SC20 combo. It was a good pedal platform amp before but now it roars. It has more bottom end. The KT88's gave it a low end thump that just wasn't there with the EL34's. I'll be recording with it soon and I'll be sure to post clips.

I also dropped of an Origin 20 for a pair of KT66's which I suspect will be ready in about a week.Very excited about that one.

 

[askthedust]

Thanks for this message! Happy to know it works with KT88. I just got one and those were my favorite tubes 20 years ago when I was gigging with a 100w 2203 red head
Did you have to rebias it?
Thanks again

 

[Gene Ballzz]

Its quite possible and probable that using KT88s here will be problematic, down the road. The heater filament of both the KT88 & 6550 draws 1.6 Amps, while the heater of the EL34 (that the amp and transformer were designed for) draw 1.5 Amps. While it might not immediately seem to cause an issue, it may well be over stressing the power transformer's current capabilities. Marshall has not been recently known to "over spec" their transformers!

And while I completely respect and am confident of the comments/info from former Marshal designer @santiall , in posts #21 & #35, I'm a bit less confident that the corporate bean counters, with sharp pencils, at Marshall have not subsequently trimmed down specs to squeeze out a few of extra profit margin!

On the other hand, almost any other octal power tube should run fine and "self bias" themselves, due to the "cathode bias" design of these amps. I have run 6V6 in my DSL20 (also "cathode bias") and quite liked them!



Just My ,
Gene

 

[_Steve]

Its quite possible and probable that using KT88s here will be problematic, down the road. The heater filament of both the KT88 & 6550 draws 1.6 Amps, while the heater of the EL34 (that the amp and transformer were designed for) draw 1.5 Amps. While it might not immediately seem to cause an issue, it may well be over stressing the power transformer's current capabilities. Marshall has not been recently known to "over spec" their transformers!

On the other hand, almost any other octal power tube should run fine and "self bias" themselves, due to the "cathode bias" design of these amps. I have run 6V6 in my DSL20 (also "cathode bias") and quite liked them!

Just My ,
Gene

Do you need to mismatch the load to make the primary impedances in the correct ballpark?

 

[Dogs of Doom]

Thanks for this message! Happy to know it works with KT88. I just got one and those were my favorite tubes 20 years ago when I was gigging with a 100w 2203 red head
Did you have to rebias it?
Thanks again

to the forum...

the answer to your question, is no... There is no adjustable bias on the SC20/SV20 amp's...

 

[Dogs of Doom]

I just had KT88's fitted into a SC20 combo. It was a good pedal platform amp before but now it roars. It has more bottom end. The KT88's gave it a low end thump that just wasn't there with the EL34's. I'll be recording with it soon and I'll be sure to post clips.

I also dropped of an Origin 20 for a pair of KT66's which I suspect will be ready in about a week.Very excited about that one.

that looks sexy, too bad they put small speakers...

 

[Jethro Rocker]

Its quite possible and probable that using KT88s here will be problematic, down the road. The heater filament of both the KT88 & 6550 draws 1.6 Amps, while the heater of the EL34 (that the amp and transformer were designed for) draw 1.5 Amps. While it might not immediately seem to cause an issue, it may well be over stressing the power transformer's current capabilities. Marshall has not been recently known to "over spec" their transformers!

And while I completely respect and am confident of the comments/info from former Marshal designer @santiall , in posts #21 & #35, I'm a bit less confident that the corporate bean counters, with sharp pencils, at Marshall have not subsequently trimmed down specs to squeeze out a few of extra profit margin!

On the other hand, almost any other octal power tube should run fine and "self bias" themselves, due to the "cathode bias" design of these amps. I have run 6V6 in my DSL20 (also "cathode bias") and quite liked them!



Just My ,
Gene

I will try some in mine when I get it. I am also confident in Santiall and have no reserveations whatsoever. If it was designed that way, it will have stayed that way.

 

[Jethro Rocker]

that looks sexy, too bad they put small speakers...

Apparently sounds fantastic. Looks can be deceiving. Maybe it is because of that small cabinet.

 

[Dogs of Doom]

Apparently sounds fantastic. Looks can be deceiving. Maybe it is because of that small cabinet.

I would just rather a 12" speaker than a 10"...

 

[EndGame00]

Marshall user question: "Can I use any other octal tube on my Studio Series?"

Typical Marshall phone rep: "Sure, why not? If the amp blows up, then it is not compatible"

 

[_Steve]

Do you need to mismatch the load to make the primary impedances in the correct ballpark?

Just bumping this - i'd love to know the answer!? My assumption is that you'd need to plug an 8ohm cab into the 4ohm socket, or 16ohm into the 8ohm socket - is that correct?

 

[askthedust]

to the forum...

the answer to your question, is no... There is no adjustable bias on the SC20/SV20 amp's...

Thanks everyone for your help.
I just installed a pair of KT88 and...to be honest I didn’t think it would make such a difference! A big increase in low end makes the amp sound even more pleasing than before. I’m using it with a 2x12 jubilee cab and it sounds heavenly.
So happy I’ve done it. Thanks again!

 

[Madfinger]

.

 

[paul-e-mann]

A bit harsh of a comment after all tubes are cheaper amongst all other things to be original. There's sheppards & there's sheep imo. Not having a go at you but most seem to be trying to copy someone else these days. Sort of borrowing someone else's brain instead of exercising their own maybe.

Go for it, put whatever you want in it apparently its safe.

 

[_Steve]

FWIW I tried JJ KT66's in mine last week and wasn't impressed by it. To me it sounded lifeless and lost all it's bark.

BUT I tried the same KT66's in my Super Lead clone and it sounds absolutely immense. Both deeper and tighter lows and less fuzz.

Before the change, I felt the difference between the SL and the SV20h was minimal so I played the SV20 more often as it's more convenient. Now however it's night and day between the two with those KT66s in the SL. It's magic!