Bassman type amp users???

[Mike67]

Hi, I am new here!

I am between bands and have a really good audition coming up with some national artists. The band plays some huge stages, and the keyboard player and guitar player are running amps much bigger the I am used to. For whatever reason, the band leader is really into having me take over the spot of their frontman who recently moved to AZ.

I have a Bassman Ltd, and Kinder AFB. I am trying to come up with the best tone I can at moderate to high volumes. I really want to get 40w worth of power from the amp. I have a medium and small amp for those gigs, so the Bassman is for my "festival" stages. I've enjoyed the fat sound of the 4x10 when set up for 20-30w, but I don't know much about using it optimally set up. In fact, after having the amp put back to near stock (I was running a different rectifier and tubes to really cut back the wattage), it just doesn't do it for me.

Right now I have the original tubes. The only mod is lowered preamp gain. What tubes and mods do you guys use for Bassman type amps? I've heard of a Sonny Jr. mod, what's that? Do you guys do the Alnico/Ceramic mix of speakers?

I was thinking of getting some Ceramics for the bottom two speakers, but don't know what to get. They should be louder then the Jensen RI's.

I've found a lot of info on reducing the power of a Bassman via tubes and bias to get it to break up at low volumes for harp and reduce feedback. However, I haven't found much on how amps like the SJ410, Meteor, and HarpKing can get that tone at higher volumes. Right now I can get good volume with the Kinder, but the tone isn't there. I like my smaller amps better. It is bright and sterile while my other ones seem thick. Yes the 4x10 sounds big...it just doesn't sound as juicy.

Thanks!

Mike Fugazzi
www.myspace.com/mikefugazzi

[MWJB]

Hi Mike,

"However, I haven't found much on how amps like the SJ410, Meteor, and HarpKing can get that tone at higher volumes", those are 3 appreciably different amps and subsequently sound different. The SJ is closest to your amp and typically has quite a smooth tone with a bit of mid/hi end bite (check the clips on his site).

"Sonny Jr Mod" is a larger value grid load resistor at the input, it predates the SJ amps (and Sonny himself too). Otherwise his amps (SJ410 & Cruncher) are classic Western Electric (5F6A) circuits with his preference of caps, tubes & speakers, which obviously make a difference.

If I remember right the SJ410 comes with a 12AT7 in V1, 12AX7 in V2, and a 12AY7 or 12AU7 in v3 (counting from right to left) & a 5U4GB rectifier? Changing these tubes will get you closer to that sound but there are some circuit &, obviously, construction differences. You could also try a 100K treble slope resistor in parallel with the stock 100K on your amp (total 50K)? I don't like this value but you might? This resistor is R17 on your PCB. I would try the tube swaps & this resistor in the first instance.

The ceramics that Sonny uses are Legend 105s, they are punchy with a middy bite. I prefer the Fane AX10 but Fane appear to have gone to the wall...you may still be able to find some? Be aware that subbing out your Jensens with 6 or 7 oz plug magnets for ceramics (or even alnicos) with 20-35oz magnets is going to make your amp heavier (I know weight is an issue you have mentioned on another forum). For that reason I'd suggest the Legend 102 if you're looking for a speaker sub, same weight, thicker meatier mids & lows.

Your DT runs 6V6s, have you tried JJ6V6s (don't try this with NOS 6V6s) in your Bassman? These will give a hotter, tone than 6L6s with sweeter hi end & a little more compresssion (don't know if that meets your definition of Juicy?). IMPORTANT, you MUST rebias before fitting them, try 17-20mA per tube with the JJ6V6. Bias up the 6L6/5881 to 35mA or a little over (-45 to -50v at pin 5), then sub the 6V6s and you'll probably find they are biased on the cold side. Then fine tune.

It won't make your Bassman sound exactly like a DT but it's worth a try. Outright volume will be about the same as 5881/6L6 (with harp), before you use the AFB.

There is a slight impedance mismatch with JJ6V6, the tubes will take it, but if this concerns you disconnect one speaker.

A friend of mine who has a stock bassman, Kinder modded bassmans, Concerts & harpking testifies that he can dial in the same tone accross the Fender 4x10"s using the AFB box, even with the stock amp.

Subbing preamp tubes (unless you're fitting mega hi gain 12AX7 variants) & rebiasing for more breakup & reduced feedback does not reduce the power of your amp, that's mostly dictated by power tube plate voltage.

If you could expand a bit on what "Juicy" is, that may help (crunchier, smoother, brighter, thicker etc.)

Regards, Mark.

[Alex R]

For what it's worth, I play harp through a self-built Bassman-type amp with these little wrinkles (below). You can get it wide open without bad feedback, and up at those levels it can be good and fat, though I don't play all that distorted. Yes, at lower levels it is cleaner and brighter than a small SE amp, but crank it and see!

Preamp tubes in this order from the input: 12AU7, 12AT7, 12AT7. (But you will need to get a few different types and experiment). Loads of volume without feedback this way. But I use an old hi-z shure unidyne type of mic with a lot of output, and these swaps are quite mic-dependent, so... experiment.

These is a bigger resistor dropping the voltage to the preamp by about 40v, I forget the value, but there's a switch on the panel to take it in and out so I can get a good guitar sound too (with 2 x 12AX7 1 x 12AT7 of course)

My speakers are in fact 8 inch, but I think 10s would work the same way - two Eminence Alphas (which are kind of standard PA type speakers), and two Weber alnicos, not the sigs, the one up from that - one with corrugations and one without. I tried a few different combinations, including all 4 alnicos (bass not strong enough) and some celestion ceramics (too toppy and harsh). This way it has good loud tight bass as well as that kind of decorative thing that alnicos seem to do to the tops, sweet and chimy.

I like to turn the treble down (of course) - but the presence up a good way - 'juicy' is my word for how this sounds, but your juice may vary. What I think I might mean is it lets me hear the difference you can make with your mouth shape etc. There's a kind of 'mouthful of sound' effect with the presence up - maybe you know what I mean.

It has a bassman OT but with the one with a few different speaker taps - which can give you some more output tube options (not that I bother changing taps when I plug different tubes in). Most of the time I run it with 4 x 6V6, not an option open to you but I often pull two out and then get quite a lot of crunch at slightly lower volumes. I like the higher-wattage output as I play relatively clean for a harp player (ie really quite dirty but not insanely so). Sometimes I go 2 x 6V6, 2 x 6L6 and with my low-gain preamp I can still crank it without too much feedback (mind I have the amp the other side of the stage from me)

I have this belief that it is overdriving the mic more than the amp that gives the sound I want. 80% is mic overdrive. And if I plug into a PA through a line transformer I still like the sound. I don;t think you need a preamp which adds overdrive if you can find a mic you can drive that hard. Magnetics do it, ceramics and crystals don't so much, I find. I guess it's a physical compression and noise caused when the diaphragm is pushed to its limits. Tight cup helps.

There you go, that's what I know.

Good luck with the audition. I think I remember you on harp-L when I used to look at it a few years ago.

I'll attach some pics as I am proud of the little darling. Yes I know the 6V6 are too close together but it works fine and stays cool.

[Mike67]

Hi Mike,

Subbing preamp tubes (unless you're fitting mega hi gain 12AX7 variants) & rebiasing for more breakup & reduced feedback does not reduce the power of your amp, that's mostly dictated by power tube plate voltage.

If you could expand a bit on what "Juicy" is, that may help (crunchier, smoother, brighter, thicker etc.)

Regards, Mark.

Thanks, Mark! What do you suggest with preamp volatage? I had it lowered, but am thinking the tube subs might be better with the regular voltage. Not to sure how to approach that.

With the Kinder, I've found that too....but I prefer to use it in a manner that doesn't color my tone. Just my preference. A very handy tool!

[MWJB]

The critical issue is by how much you had it lowered, what are the colour bands on R39?

Have you tried a 5751 in V1 or V2?

12AX7 can quickly get "stodgy" & overly thick sounding with too low voltages (but the crispness of the AFB should help a bit there). Generally as you go lower in mu on the preamp tubes, the chimey qualities come back in.

E.g. A 12AX7 much under 130v can sound quite dull in a bassman (though I have a customer who runs 90v on a 12AX, with his AFB), whereas a 12AY at 80-90v (i.e. in the same circuit) will have better fidelity, as will a 12AU that will still have good fidelity down to 40vdc or so. It all depends on how hot your mic signal is, whether you have enough gain to keep good dynamics & punch with a lo-z mic & transformer (I doubt that will be the case with a lo-z mic & a 12AU?) - usually I'd expect 3x12AX7 or 2x12AX and an AY or 5751? I would look at changing V1 OR V2 to start with. You'll have to experiment a bit, but my feeling is it wil be easy to end up with the amp sounding dull/sterile if you go too low on mu, with a lo-z mic.

If you find 3x12AX7 works best then you may only need a relatively subtle drop in preamp voltage, maybe 39-47K at R39. You could pop a suitably sized resistor (at 2-3W rating) in parallel with what's on there already to get to that value. E.g if you had 100K at R39, adding an 82K in parallel would give you 45K.

(Multiply the resistor that's on there by the additional value, then divide that by the sum of the 2 resistors so:
100K * 82K = 8200K
8200K/182K = 45.05K)

There are over 100 combinations of preamp tube set up, but only 2 or 3 may really work well with a particular mic.

Your presence control is very useful for getting some crispness, or "edge" on notes, that last bit of fidelity. With moderate output mics I often end up with this flat out or thereabouts?

Get it so you're happy before introducing the AFB (but it sounds like you have that sussed).

[Mike67]

I am pretty sure my preamp voltage is still over 100k...around 115-120k if I remember right. I am going to have to go back and do more A/Bing with my other amp. I wish I had a recording of the Bassman that you guys could judge. Actually, HideAway on my Myspace uses the Bassman....that was with the lowered preamp voltage, 5u4gb, and JJ 6l6g tubes...not I have the original GT6l6 tubes and 5AR4 and same preamp voltage....after using the 5u4gb at a huge festival, I thought the amp didn't have a pleasing breakup or enough cut. It was too distorted and mushy. Hence bringing the rest of the amp up to spec. Now it holds together longer, but it still doesn't inspire me.

Although my note selection/phrasing is very different, I really enjoy the sound of Jason Ricci's Bassman on his newest cd and on the YouTube clips from Terra Blues. I know my own tone is going to be quite different, but I like the distortion and compression. Having seen him live, he gets a lot of cut from the amp and can run it pretty loud. The notes don't get too blurry...they stay crisp without being too trebly.

I tend to not enjoy my current distortion with the Bassman. What I like about the DT is the way it breaks up and the point at which is does so.

With the Bassman, I need to be able to keep it loud and with a bit of headroom (for the last two years, I've had no use for it...but I need to be prepared for this audition. These guys are WAY legit and I want to be confident in using the amp). I am worried that rectifier tube and preamp voltage choices are going to take the volume away.

One of the guitar players uses a Super Reverb and a Marshall together (like I said before, they play some large stages!). I am probably making no sense.

[MWJB]

Hi Mike,

More than 100K sounds like a lot with a lo-z mic, even with a lo to hi-Z transformer. Solder a 56K or 82K (at 3W) in parallel with the resistor on there already. Typical hi-Z mics that most harp players use (crstal/CM/Hi-Z dynamic) have more output than a lo-Z mic (even with transformer), the bigger signals tend to have more highs & mids, so more aggressive voltage dropping can work fine with these, warming tone & increasing volume before feedback.

I wouldn't normally go over 82K or 100K at R39 even with a Hi-Z mic.

I wouldn't recommend a saggy rectifier like a 5U4 with dropped preamp voltage, or even with a stock bassman if headroom is what you are after. Use GZ34/5AR4 or SS, bias your JJ 6L6 tubes to 15 to 20mA (you might find 20mA with solid state gives you approx 15mA with GZ34?).