Bassman 5b6

[Blackburn]

Yeah, I wish they were on there. I'm guessing Tino's are probably right where you wanna be anyway. I think that's what I'll end up getting. Initially, I used a 375-0-375 PT and wanted it lower.

[rp]

Having carefully mulled all the Fender schematics from the Late Pleistocene before settling on a 5C8, all those early 2x6L6 amps all seem to have run about 370-380V perfect for old metal 6L6s, 6L6Gs or 5881s. 390V is nice as at/below 370V you're really in 6V6GT territory and above 400V you're already into late '50s 6l6GB/C tubes. So if the Tino plans is that's what MF followed and got 390V that seems the sweet spot for authenticity and some kick. On my 5C8 clone I got ~380Vdc on the plates from an unloaded 335Vac PT.

As for headroom, I'm not sure I consider doing a huskier tube swap as really giving more headroom, just a harder tubeset to drive to distortion w/o the dynamics of an increase in headroom. To me more headroom means increasing the sound envelope then playing at the same dbs you were at before. So you'd have to up the voltages and dissipation to really get more headroom. Make that 25W 5B6 into a 40W amp with some 6L6GCs pushing 475-500V then play at 25Ws. Kind of an expensive experiment as you need a new PT and maybe an OT. You can also switch to fixed bias and more filtering but then it's not really a 5B6 anymore. Still, you might wind up with a simple, immediate, powerful, octal beast - or just a loud harsh microphonic monster.

[M Fowler]

RP I did all that used BF bassman iron, LTP PI, 6SC7 & 6SL7 then changed to 6SL7 & 6SL7, PTP PI 68k/68k bias resistors with 6550 tubes.

The amp sounds the best left alone as Fender intended.

The stock circuit with KT120's was very smooth using SS plug rather then 5U4 or 5AR4 recto. Keeping stock 270k/270k power tube bias resistors. Also, tried KT88's.

Mark

[rp]

The amp sounds the best left alone as Fender intended.

Words to live by.

[Blackburn]

Having carefully mulled all the Fender schematics from the Late Pleistocene before settling on a 5C8, all those early 2x6L6 amps all seem to have run about 370-380V perfect for old metal 6L6s, 6L6Gs or 5881s. 390V is nice as at/below 370V you're really in 6V6GT territory and above 400V you're already into late '50s 6l6GB/C tubes. So if the Tino plans is that's what MF followed and got 390V that seems the sweet spot for authenticity and some kick. On my 5C8 clone I got ~380Vdc on the plates from an unloaded 335Vac PT.

As for headroom, I'm not sure I consider doing a huskier tube swap as really giving more headroom, just a harder tubeset to drive to distortion w/o the dynamics of an increase in headroom. To me more headroom means increasing the sound envelope then playing at the same dbs you were at before. So you'd have to up the voltages and dissipation to really get more headroom. Make that 25W 5B6 into a 40W amp with some 6L6GCs pushing 475-500V then play at 25Ws. Kind of an expensive experiment as you need a new PT and maybe an OT. You can also switch to fixed bias and more filtering but then it's not really a 5B6 anymore. Still, you might wind up with a simple, immediate, powerful, octal beast - or just a loud harsh microphonic monster.

I think 335-0-335 PT sounds pretty good to me, RP. I tend to prefer lower voltages anyway. I don't need much headroom at all and tend to leave that to picking dynamics. My 5B6 stayed pretty clean up to around halfway with my Burstbuckers and LP. The plates were higher, but like I said, I don't really want much headroom with any tweed amp. In PTP, these octals and their microphony don't bother me too much, at least, not the ones I had in my 5B6.

[bgkyt1]

RP I did all that used BF bassman iron, LTP PI, 6SC7 & 6SL7 then changed to 6SL7 & 6SL7, PTP PI 68k/68k bias resistors with 6550 tubes.

The amp sounds the best left alone as Fender intended.
Mark

It sounds like getting the right 6SC7 tube is a pain. Is it worth trying a build using 6SL7 in both places, leaving everything else stock, or doesn't it sound good? Are those tubes more reliable/consistent?

thanks

[rp]

It sounds like getting the right 6SC7 tube is a pain.

Yes, I have about a dozen, metal and glass, and they are all microphonic, some are pulls, most are NOS. I built a 5C8 so I had 4 to deal with. The PI isn't a big worry, but I had a second gain stage. In the end it's not that big a deal though I wouldn't build a combo. I also built it as a house amp and I've yet to try it full on sitting top of a cab. I have a bad feeling about that, when I booted it up first time I had my bench speaker about 2 feet from it and at first I thought I had a howler.

Is it worth trying a build using 6SL7 in both places, leaving everything else stock, or doesn't it sound good? Are those tubes more reliable/consistent? thanks

Can't definitely say, I'm a stickler for exact clones, at least at first - gotta know where you stand before you can head somewhere. It's only one 6SC7 here, I think you'll be fine, mount it on rubber grommets like Fender did, I did it, can't say it does much but it looks purposeful. 6SC7s are pricey but ANOS isn't bad. Not sure how much the 6SL7 sounds like a 6SC7, don't recall if the gain is the same. The bummer is that you can't split the cathodes on the 6SC7 so you can't play around with that.

I'd say layout for 1 and build it straight, you can then easily rewire for a 6SL7. Then you can tell us what you heard.

[M Fowler]

RP I did all that used BF bassman iron, LTP PI, 6SC7 & 6SL7 then changed to 6SL7 & 6SL7, PTP PI 68k/68k bias resistors with 6550 tubes.

The amp sounds the best left alone as Fender intended.
Mark

It sounds like getting the right 6SC7 tube is a pain. Is it worth trying a build using 6SL7 in both places, leaving everything else stock, or doesn't it sound good? Are those tubes more reliable/consistent?

thanks

I've built 3 5b6 amps so far with 6SC7 preamp, 6SL7 PI, 6L6GC, and 5u4 recto. I started off using NOS metal and glass but ended up relying on new Tungsol or Sovtek 6SL7 and Sovtek 6SC7 tubes as well as JJ 6L6GC power tubes/recto tube. Recto tubes from EH and Sovtek are fine as well.

http://www.parts-express.com/sovtek-6sc ... e--072-402

https://tubedepot.com/t/tubes/preamp-tubes/6sl7

The two tubes have different pin wiring and the 6SC7 does not have separate cathodes like the 6SL7 has. The 6SC7 has a higher gain then the 6SL7.

[M Fowler]

My latest project is a small fry version of the 5b6 using 6V6 power tubes, SS recto, 12AX7 PI and 6SL7 pre. https://tubeamparchive.com/viewtopic.ph ... highlight=

But I found out the used Fender Blues Jr PT is bad so getting a replacement or one from my stash of old audio chassis sitting around collecting dust.

The other version with Bassman size PT/OT I decided to just build a version of the Ampeg B15N using two 6SL7 and 6550 tubes. That amp sounds great and lots of power. Has a slight hum as you get louder but maybe I'll figure that out too. It is fixed bias and LTP PI.

[rp]

The two tubes have different pin wiring and the 6SC7 does not have separate cathodes like the 6SL7 has. The 6SC7 has a higher gain then the 6SL7.

Now I remember deciding the 6SL7 was like a 12AY7, which Fender used a lot of in Tweeds for a reason - the world wasn't yet ready for a Marshall. I think 5E3s sound better with a 12AY7. So, I figured they must have had a reason to use the higher gain 6SC7 wherever they used it. Don't mess w/ Leo, he had both good engineers and then those Bakersfield cats for test pilots. You might want to argue with the engineers but you'd have to have tin ears to go against the Bakersfield cats.

[Phil_S]

6SC7 Mu=70.225, 6SL7 Mu=70.4. I hope we can agree for discussion purposes this is the same.

The most notable difference is Ra. 6SC7 Ra=53K, 6SL7 Ra=44K and this probably will account for the 6SC7 offering a bit more gain.

I'm not convinced it will make a very noticeable difference.

Having said that, I built my 5B6 with a 6SC7. I think RP is right. Don't mess with a good design. Besides, you can find a used but still good 6SC7 for dirt cheap.

[bgkyt1]

thanks, everyone, for your opinions.

[RWood]

Both NOS 6sc7s I started with were problematic. The first(glass) was doa. The second NOS RCA metal (although I believe it was a cleaned up pull) went microphonic shortly after first use.
The two new Russians I replaced them with are now 6+ months with no problems whatsoever.
Both amps get used twice weekly for about 2hrs.

I recently built a third for a friend who didn't trust the availability of good octals, with a new EH 12AY7 which is tonally only slightly different (a little tighter, smoother, and looses some gain) but still very good. Although I must say I like the raw quality of the octals better. Also with different speakers who knows?

[matt h]

(deleted)

[M Fowler]

Gut shot of a Little Walter 80w combo chassis, reversed layout.