Blackfacing ??

Ray DeVoe · From: Hudson, FL

For all of the "tube amp geeks" Smile

What is "blackfacing" and how does it affect sound when applied to steel amps.?

Im sure there must be threads about this topic but lets see if someone has an easy to understand answer.

Thanks
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Ken Fox · From: Nashville GA USA

From Machine Gun Amps:
Modding a silverface amp to blackface specs.

Silverface amps all sound better when modded back to blackface specs in my opinion. I will outline the mods below. However, some of the changes that Fender did in the silverface years are not easily changed back to blackface specs.

Don't go into the amp unless you know how to not get shocked! These amps will even shock you when unplugged. They store extremely harmful voltages that will jump out and grab you if you put your paws in the wrong place. I know this from experience! It hurts!

Suppresser caps: Fender added .002uf (or sometimes 1200pf) capacitors to the grids of the power tubes (pin 5). These bleed off frequencies that they thought were too high to be heard with guitar. The effect of these is to bleed off any frequencies that the amp will oscillate at. Oscillation is like feedback with a microphone. It feeds itself and runs away from you if you don't do something about it. Amps can do this internally, and it's a big problem. For you tech types, somebody emailed me and said that the effect of these caps is -18 dB at 6 kHz! Ouch! The caps are actually a good idea, but they tend to bleed of high end "sparkle" from the amp. These caps were added because of problems with the lead dress that was causing the amps to oscillate. It's unfortunate that Fender needed these. The best way to control oscillation is to design the amp not to oscillate in the first place! But for cost cutting's sake, it was cheaper to put these caps in than spend the extra labor to make the amp more stable. These caps can usually be removed and the amp will run fine. I haven't run across an amp yet that started oscillating without them. But, I have heard from some techs that have seen many amps that can't live without these caps. Oscillation suppression is nothing new in Fenders. Tweed bassmans had a cap across the plates of the phase inverter to help with this (47pf). If your amp plays fine after the mod and then all of a sudden acts like it looses most of it's power, it is probably oscillating. Try the 47pf cap like the tweed Bassman and see if that fixes it (look in schematics to see how it is done). There is also a much rarer oscillation suppression method Fender had, it involved a .02 cap and a 220k resistor going from one leg of the power section then held 100 ohms above ground via the feedback loop. This is rare and only occurred in the early 70's.

Phase inverter: Fender changed the phase inverter in a few ways. Starting from one end and going to the other: The coupling cap increased from .001 to .01. This has the effect of letting more bass through to the power section. This sounds like a good idea, but to my ear makes the bass get overbearing. The .001 cap sounds tighter with more defined bass to me. After that, Fender used 330k resistors on the grids of the phase inverter instead of 1 meg. The cathode resistor on the phase inverter was made smaller which ran this tube a little hotter. The plate load resistors were decreased from 82 and 100k to 47k. This reduces gain. Overall, the changes to the phase inverter look like they were designed to tame the amp and change the way the amp sounds to what Fender wanted at the time.

Reverb circuit: Fender tended to run the reverb driver tube very hot in the silverface years. Blackface amps came with 2.2k resistors bypassed with a 25uf-25v electrolytic cap. Sometime in the 70's, they started to change this value. I've seen 1.5k, 820 and 680 ohm resistors here without a bypass cap. Fender also added a cap from the plates of the reverb driver to the cathode. They added a cap to ground after the reverb tank as well. I've found that I sometimes like the silverface method for reverb better than blackface, but I do take out the added caps to ground. I will leave the amp otherwise stock if the reverb sounds good to the owner.

Bias supply: Fender changed the bias supply from a level to a balance control. The balance control allows the tech to match the tubes, but not set the bias level which is what can determine tone. Also, some extra filtering was added to the circuit (two 70uf-100v's? Don't remember exactly). I always change the bias supply to blackface specs because we use matched tubes these days! When replacing the bias supply filter caps, I usually just use one 100uf-100v.

There are a few other changes that I don't mod back to blackface specs because I don't feel they change tone all that much. The main ones have to do with the power supply.

Changes in the silverface years that can't easily be changed back to blackface specs: Sometime when Fender went to the 5U4 rectifier tube, they increased voltages on the high voltage secondary of the power transformer. The 5U4 has a higher loss, so the increase makes the voltage after the rectifier tube similar to what it was in the blackface years with a GZ34. When installing the GZ34 in these silverface amps, the voltages will be higher than those in a blackface amp sometimes. The only way this can be changed back to blackface is to change the power transformer. This is expensive. In the late silverface years, Fender changed the power supply and power section of the amp quite extensively. They do not look like the earlier blackface and silverface amps at all. These changes included new power and output transformers and solid state rectifiers for all of the larger amps. Voltage was greatly increased on the plates of the power tubes. These changes are not easily reversed. The way to tell if you have one of these amps is to look under the speaker jacks. If it says. 70 or 135 watts, you have the later model that cannot be easily or cheaply modded back to blackface specs. I'd recommend selling this amp if you are not happy with the tone before trying to do extensive and expensive mods to it. They actually do sound pretty good clean though. And they are extremely loud!

*Disclaimer - My lack of electrical engineering knowledge means I don't fully understand what Fender was trying to accomplish with some of the changes in the silverface years. If you have something to add or a correction to make, please let me know! I'm always happy to hear from someone that knows more about this than I do.

Ray DeVoe · From: Hudson, FL

Well I asked and got a great answer.

Thanks Ken for all of the great info. !!!!

Its a shame I dont live close to you or you would be working on my new project amp.

Some of the info is over my head but then Im not the one that would be working on the chassis.

I already own one 135 watt Vibrosonic which I acquired from James Morehead this winter. I know the 135 watt model can sound great as its the best sound I have ever acheived. James set it up right and I beleive he had some tips from you and Brad.

It has all of the depth and sparkle that any one needs. I usually use this amp with a 69 Emmons PP, pot volume pedal and RV 3 direct into the amp. I had purchased one of the 65 reissue amps with the 15" several years ago and I can tell you that it would not "touch" the sound and performance of these restored amps.

Im in the process of restoring an identical Vibrosonic to make into a head cabinet unit. Both amps have the orange frame JBL D 130 F speaker.

I only use these all tube amps on certain gigs but when I do, they sound great.

The shop thats putting new caps and power tubes in my project amp asked if I wanted to do any "blackface work" to it and I was lost as to any advantage that might have.

You are definately right. A 135 watt Vibrosonic can "get loud" when pushed a bit. Tube tone all of the way to the top !!

Thanks
Ray D.
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Jon Light (deceased) · From: Saugerties, NY

To add to this and to try to put in less tech terms.....
and please note that most of what I know I really only think I know.....

blackfacing a siverface amp, NOT including the 135 UL amps, tends to soften them up a bit, tonally and headroom-wise---soften as in the SF amps may be perceived by some as 'hard' sounding. I'm not talking about loudness.

The BF'd amps I've done and played and heard have really pleased me.

If you love your 135W Vibrosonic Reverb then your thinking and hearing is leaning in the opposite direction and I sure wouldn't think that any sort of BF'ing makes sense on your amp except for utility stuff like bias adjustment...this does not relate to sound, it relates to servicing.

As thrilled as you are with your Vibrosonic, you would be nuts to depart from that as a model unless you seek another flavor. And as pointed out, those 135W amps are not as amenable to BF'ing.

Note, though, that identical amps will not necessarily sound the same. There are a lot of variables that can get you scratching your head as to why is this amp sweet, why is this one shrill?, etc...

David Doggett · Posted 25 Apr 2009 7:18 am

I agree with Jon. From a player's standpoint, BF means warmer, good crunch, and earlier breakup - what rock and blues guitar players love. SF means a colder, cleaner sound with more headroom before breakup. However, a SF Fender will be warmer and sparklier than most solid-state steel amps. For me, the SF Fenders are a great compromise for steel between the distortion of guitar tube amps and the cold, sterile sound of solid-state tube amps. You get some warm tube tone without the early breakup.

These are just generalities. Of course someone will come on here and say it's not that black and white, that you can setup a BF to play colder and cleaner, and a SF to play warmer with earlier breakup. Everyone will want to kill you if you mess up the tone of a BF - they go for huge money. As the post above says, apparently the first years of SF are easier to BF. There were few or no major changes in those first years, and some of the smaller amps (Champ, Princeton, Deluxe) never did change much. Many SF amps on the used markets have already had some BF changes by previous owners. It is so common that techs doing a tuneup will sometimes make BF mods even without asking you. The 135 watt models can't really be black-faced completely. But because of the extra headroom they make great pedal steel amps.

I have a mid-'70s SF Pro Reverb that was BFed without my asking. It's great for rock and blues, on guitar or steel. I use it for steel at home, but it doesn't have enough clean power to take to a gig. For recording, or if you mike the amp on stage, you can keep the volume of a BF in the clean range and have some beautiful warm tone. Lloyd Green does that. The only problem I have with that for steel is that you are carrying a big heavy amp for which you can only use maybe half the volume range. Lloyd has a BF Twin in a head cab. But it's still a heavy 80 watt amp with only maybe 30 or 40 watts of clean power, depending on how it is setup.

The other thing I like about SF Fenders is that the later ones have on-board spring reverb.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

I have found that I tend to like either blackface or earlier silverface Fender amps better than later ones, but it's not absolute. The first step of my algorithm to decide whether or not to mess with an amp is to play it at home and on gigs and see if it works or not. Sometimes something may not seem right at low volume, but then at gig volume sounds great - or vice versa. Only after thoroughly checking things out would I consider modding an amp.

I partly agree with the idea that blackfacing reduces headroom and increases distortion, but not completely. All amps distort, and to me, the character of the distortion is at least as important as the amount. I've had blackface amps that were really quite clean-sounding and silverface amps that weren't, even after cleaning up and rebiasing. There are tons of variables in these amps, as the Machine Gun Amps recommendations indicate, and they all interact with each other in complex ways. To me, some of the things done in the silverface era were kludges to address problems brought on by changes in manufacturing or parts.

For example, the lead dress issue mentioned above is critical to keep parasitic oscillations down without suppressor caps, which I hate - I think they tend to stifle the presence of the amp. A parasitic oscillation is a high audible or ultrasonic frequency oscillation caused by sloppily-wired long leads acting like an antenna at high frequencies, which couples the preamp and output sections. This creates a feedback loop and if the gain is high enough, results in an oscillation at high frequencies. The correct way to eliminate parasitics is to trim the offending long leads - this frequently allows those tone-sucking capacitors to be eliminated. That is not a saturation distortion issue at all. In principle, this problem can happen on any amp, but I think tends to happen much more on later silverface Fenders than blackface or earlier silverface ones - I think they just paid more attention to lead dress earlier.

I think a blackface or early silverface Twin Reverb, properly tweaked out and biased with a good set of tubes, and the right speakers, may well be the best pedal steel amp ever, to my tastes. Only problem is that they are relatively expensive to buy and maintain in tip-top condition, collectible (and hence tough to justify dragging out to bar gigs), and heavy as blazes with speakers that do the amp justice for steel like a set of EVM-12L's, JBL D/K-120 or maybe a set of 12" Black Widows. I guess that's why I prefer my well-worn but tweaked and blackfaced '69 Dual Showman Reverb head into a separate cab. Nobody has ever told me it ain't loud enough. Muttering

Bill Terry · From: Bastrop, TX

I went through this whole 'BF or not' thing several years ago with a '69 Twin I owned. This thread has a lot of good discussion and details about the topic, particularly from a good friend Bob Metzger, who doesn't seem to post much anymore.

http://bb.steelguitarforum.com/viewtopic.php?t=57826&highlight=
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Ray DeVoe · From: Hudson, FL

Hey guys.

Thanks for all of the great info.

I also checked out the link sent by Bill Terry and there is a lot that can be learned from everyones input.

I sincerely appreciate the effort of all who responded.

Thanks
Ray DeVoe
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Zum SD 10 Hybrid, Zum D 10 Hybrid, Emmons SD 10 P.P.
SMS: Revelation & Classic Preamps: Furlong 12" Splits.
Webb 15" Splits: Telonics 500 C: Head and 12" cabinet:

Jim Sliff · From: Lawndale California, USA

What Donny said is true - MOST steel -players would not want the BF conversion...at least what guitar players would call a conversion. OTOH, there are several items that WOULD benefit steel players as much as anyone else:

1. Converting to adjustable bias. This gets confusing to non-techs, as amps that can be set up for adjustable bias are called "fixed bias" amps (don't ask). The non-adjustable system was se5t up by Fender as in the 60's power tubes were pretty consistent. Nowadays they are all over the map, and an adjustable bias is a must (do NOT buy into the "just buy the ones graded 4-6"...or, "get the "blue" coded ones. Yikes, what a mess. but a bias conversion is simple, a bias tool is cheap and can really help you get more...or less...headroom.

2. Snipping the 2000pf caps running from the tube socket to ground - they were installed to prevent weird oscillation dues to lousy wiring - but in my experience 75% of the time they are NOT needed. Snip them right at the spot where they are soldered to the chassis, leave them in place, and just sick electrical tape on the ends to insulate them. If you don't get odd noises, you WILL probably pick up some clarity on the high end.

There are a few others but those come to mind right now.

However...

You can't blackface a 135-watt model. You CAN make some changes, but it's a different amp.

Also, paying someone to BF a Deluxe Reverb is silly. There are SO few changes that have any effect on the sound you are far better off just buying good tubes, making sure the amp has been properly serviced and maybe swapping out the speaker. I've been in a studio with about 20 BF and SF Deluxe Reverbs in the room, and 15 or so players could not tell what was what idf their back was turned!
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