5F6A bias (and now feedback)

[Cliff Schecht]

I used one of my Stancor A3851's for now. These transformers sound great with whatever I put them in but I never figured out how to use the 10% inverse feedback windings on the primary side..

The '52 RI I used to use was a great amp because it was very versatile. I usually kept a low-mu tube somewhere in the mix for max headroom and had a good set of GE/Mullard 6L6GC clear tops in the mix too (were stolen with the amp ). I'm not necessarily trying to nail the sound of the RI I had, I'm just looking for something that is very versatile. I used to run a gamut of pedals (16 at one time) and just built sounds off of my board (using the amp as a clean slate) and I sort of miss that setup. The guitar-->amp approach is nice in that you get a consistently great sound but the versatility just isn't there. I'd like to get this Bassman build to a similar style of amp, one that is nice and clean at high volumes and takes pedals well (but can distort when pushed still).

I guess the real test will come when I get to try this amp out at practice. I'll tweak to taste after I test it there.

My only concern right now is that I really don't have a speaker that I think will go well with the Bassman. The 1x12 I use now is pretty dark and I don't ever really associate the classic Bassman sound with a closed back cab.. What should I be looking at for speakers/cab setups?

[Zippy]

My only concern right now is that I really don't have a speaker that I think will go well with the Bassman. The 1x12 I use now is pretty dark and I don't ever really associate the classic Bassman sound with a closed back cab.. What should I be looking at for speakers/cab setups?

Classic tweed Bassman had 4x10 alnico speakers in an open back cabinet.

For a lil' twist and enhanced bass (if your guitar needs it), I like to mix a pair of alnicos in the top slots with a pair of medium power ceramic 10s in the bottom.

[Cliff Schecht]

I was really wanting something more compact than a 4x10 or 4x12. Surely I could get a good sound with a compact 2x12. Maybe it won't be the classic Bassman sound but I'm really looking for a great clean and a smooth distortion. I'm not very knowledgeable when it comes to matching amps with speakers so again, any insight is more than welcome .

[rp]

Surely I could get a good sound with a compact 2x12. Maybe it won't be the classic Bassman sound but I'm really looking for a great clean and a smooth distortion.

2x12 will do fine.

[statorvane]

First amp I built was a 5F6-A clone in a narrow panel tweed style cab with 2 x 10" speakers, Sovtek 5881s, EH 12A_7s in the preamp/PI. Very loud - it didn't break up until around 6 out of 10 on the bright volume. I later jumpered both channels for more fun. Still very loud. Plenty of clean, but for my purposes too much so. I think with 6V6s it would have been fine.

The cab was the same size as a HRD 1 x 12", but with 2 x 10" Legend 105s.

[tubeswell]

I did a '5F6B+' with verb and trem running 2 x greenback 25Wers. This has been through several incarnations - latest one (see attachments) uses an Old Flame (2007 version) verb circuit inserted between the TS and the LTP. The V1 stage grids are permanently paralleled and can be blended independently. The LFO circuit utilises an AC coupled follower and has plenty of slam. At the mo' I am running 2 x el-cheapo Russkie 6P3S idling at 13.6W with 442V on the plates. They seem to be holding out okay. This amp is a surfin' monstrosity.

[FYL]

Surely I could get a good sound with a compact 2x12. Maybe it won't be the classic Bassman sound but I'm really looking for a great clean and a smooth distortion.

Fender shipped briefly in '02 a 2x12 version of the Bassman, called the Bass Breaker. Std '59 RI silly everything (PCB-based, too high voltage PT, 12AX7 for V1, etc.), 2x12 cab fitted with a pair of Celestion V30.

One is currently for sale at Elderly: http://www.elderly.com/vintage/items/130U-9202.htm

One of my fave amps is a custom build loosely based on the Hoffman 5F6A layo, with a vintage-style lopo Twin cab and a pair of Emi Red Fangs.

[Zippy]

I was really wanting something more compact than a 4x10 or 4x12. Surely I could get a good sound with a compact 2x12. Maybe it won't be the classic Bassman sound but I'm really looking for a great clean and a smooth distortion. I'm not very knowledgeable when it comes to matching amps with speakers so again, any insight is more than welcome .

Ah, that takes you to my favorite territory, the compact combo. Check out the tweed Super (5F4) cabinet - 2x10 on a slant. Same approach as before - mix alnico and ceramic for best of both worlds. I think there is something to be gained by going with a pair of 10s vs 1-12 or 2-12.

[Cliff Schecht]

Dayum! Finally got time to fire up the amp today and I was thoroughly happy with the sound. My tube compliment right now is a GE 5751 for V1, a Telefunken 12AT7 in V2 and a 12AX7 in V3. I probably need to play around with where I stick the lower gain tubes but I'm trying to avoid excessive preamp distortion (or any, really). I prefer to have a loud, shimmering clean and then throw on distortion/OD as I see fit with volume knob and pedals.

I think this amp will be great for the bar not only because it's more than loud enough (I'm running the 6L6GC's at 21W plate dissipation) but it's so small too! Plus it's kinda cool that I can jump between a high gain Marshall sound and a spanky clean Fender sound just with a retube.

Only goofy things I did in the amp are leaving off the standby switch, grid resistors and sticking with a SS rectifier only. The only thing worrying me about the lack of standby switch is I used 15uF for both of the fixed bias supply filter caps and the bias supply does take a bit to get to full voltage. But by the time the tubes see full plate voltage, the bias is well on it's way towards the -43V I have it set at so there shouldn't be any problems there.

The final plate voltage is around 417V (415V screen) which is great, I know a lot of people end up with ridiculously high plate voltages and I wanted to avoid that. I used a spare Antek 2T300 PT which the chassis was already drilled for and conveniently enough, with a wall voltage of 124V+, my heaters are actually within spec for once!

I probably don't need to post soundclips, it sounds like a Bassman. It sure doesn't look like one though!

Once again I appreciate all of your help guys. Who knows what kind of terrible advice I'd be getting if I had to go talk to the local amp techs about this stuff..

[Cliff Schecht]

I was really wanting something more compact than a 4x10 or 4x12. Surely I could get a good sound with a compact 2x12. Maybe it won't be the classic Bassman sound but I'm really looking for a great clean and a smooth distortion. I'm not very knowledgeable when it comes to matching amps with speakers so again, any insight is more than welcome .

Ah, that takes you to my favorite territory, the compact combo. Check out the tweed Super (5F4) cabinet - 2x10 on a slant. Same approach as before - mix alnico and ceramic for best of both worlds. I think there is something to be gained by going with a pair of 10s vs 1-12 or 2-12.

I like this idea myself. I'll talk to my cab builder guy and see if he has any 2x10 stuff I could test this through. He's also an Eminence dealer, so which Eminence speakers should I look at?

[Structo]

I never have warmed up to 10 inch speakers. Something about them for the frequency range of a guitar I don't care for.

There is probably one out there that I would like but I've gone through a few when I was trying to finish a Marshall combo I built and they just didn't do it for me.

It was an open back, or semi open depending how you define it.

But once I cut 12" holes and put in a G12H 30 and a CL80, the amp came alive.
I just love the low end punch I get from 12 inch speakers.

[Zippy]

I like this idea myself. I'll talk to my cab builder guy and see if he has any 2x10 stuff I could test this through. He's also an Eminence dealer, so which Eminence speakers should I look at?

I used a mismatched pair of Webers (10A125/10F125) - don't know the Eminence line that well.

https://taweber.powweb.com/weber/

[M Fowler]

Nice job Cliff I have never used those round transformers before but I hear they are good.

[Cliff Schecht]

Thanks! I love fitting new amps into old chassis. I also am digging this method of semi-PTP builds, i.e. all of the power components laid out neatly and the rest is point to point as needed. I think the real winner here is the ground bar which allows each stage to ground right at its decoupling capacitor. The only place that ground meets the chassis is at the input as per Merlin's advise. Seems to lead to some very low noise builds.

The Antek power transformers are great, very inexpensive but quite beefy and low noise to boot. You can usually add on about 20% more to a full load without any worry. I've heard some pretty bad things about their OT's though.

[Cliff Schecht]

Played on this amp a bunch today. Sounded surprisingly good on the closed back 1x12, definitely loud enough for practice and the bar. I think the darker nature of the cab plays well with the Bassman, especially because I insist on playing maple neck Tele's.

One thing I played around with a bunch was tube compliments. I tried an all 12AX7 setup with EL34's and got a nice early Marshall lead tone but I could never get the amp to clean up well. Instead I swapped out the preamps with (in order) a 5751, a Telefunken 12AT7 and a GE 12AT7 and the power amp got some clear top 6l6GC's (just labeled HP, don't know what they are). The first thing I noticed that freaked me out was that the Telefunken flashes on the first fire-up after resting for a while. I've used TF tubes before but I've never had one that flashes, pretty neat! Anywho, this tube compliment sounded killer, got a nice thick clean sound that sounded awesome with Jerry Reed/Chet Atkins type playing. When I crank the volume I can get a good amount of distortion but it's not a great sounding distortion, but then again I'm not so interested in that with this build. It also sounded really nice with an acoustic. I think we have another winner!