Blackface mod??- what to look for-PICS ADDED

Todd Brown · Post by **Todd Brown** » 16 May 2012 8:40 pm

Going to check out a 73-74 Twin Reverb this weekend. He says it's been Blackfaced by a previous owner. It does still have the Master Volume. Says he put in new JJ 6L6's last year, and it already had 2 THD 12's. A Longhorn and a Vintage. If I get it, I'll be replacing those with my Eminence EPS.

What are some key things I should look for when I pull the chassis that would tell me its been Blackfaced? Does this typically include the reverb mod(both channels)? If no reverb mod, should I be skeptical that it has even been Blackfaced? Certain values to look for on the caps?

Anybody got a pic of their SF that has been modded to a BF?? That would probably be a big help!

Thanks in advance!!

Tim Marcus · Post by **Tim Marcus** » 16 May 2012 9:00 pm

you can tell right away if you see ceramic caps on tube sockets or the reverb jacks - if they are there, it has not been converted all the way.

That said, the most important mod is the bias mod. If that has been done, you will gain the most.

Other changes are to the phase inverter and the power supply. I would look at this schematic and layout and compare it to what you see in your amp. It will always look close - but pay special attention to the areas mentioned above.

http://ampwares.com/schematics/twin_reverb_ab763.pdf

Rick Johnson · Post by **Rick Johnson** » 17 May 2012 4:02 am

I would think that if its been blackfaced,
the MV would not be in the circuit.

Rick

www.rickjohnsoncabinets.com

Jerome Hawkes · Post by **Jerome Hawkes** » 17 May 2012 5:41 am

i have always heard for steel - the 70's MV silverface was preferred.
guitar players like the BF because it breaks up earlier - exactly the opposite of what a steel player wants.

Todd Brown · Post by **Todd Brown** » 17 May 2012 7:26 am

I thought I've seen plenty of blackfaced twins that still had the MV? Some leave it, some get rid of it.

Jerome, seems like I've heard that about the SF twins as well. Better for psg than a BF.

Tim Marcus · Post by **Tim Marcus** » 17 May 2012 2:08 pm

Certainly the 135W silverface Twin is a monster amp for pedal steel, but terrible for regular guitar

however, the overall tone of the original Black Twins is much better for both guitar and steel. The amp has less power though - only 85W

The Master Volume might have been left in - however, I would remove it if I were you because its kind of unnecessary for steel. Ideally you would have it turned up to 10 anyway in order to keep the preamp as clean as possible.

Like I said before - the adjustable bias is the big one. Especially considering that modern tubes run much hotter than the tubes the amp originally had - if they are not biased correctly, they will be running cold and that is not a good sound at all.

Michael Brebes · Post by **Michael Brebes** » 18 May 2012 10:00 am

The biggest problem with the Master Volume is the capacitor that is across the top conductor and the wiper. It acts like a bright switch I cut those out and leave the pot in place.

Bill Terry · Post by **Bill Terry** » 18 May 2012 2:06 pm

I did the BF mod on a '69 Twin a few years ago, one step at a time (this was the 85W version). To my ears getting rid of those 2000pF caps on the output tubes gave the most bang for the buck.. and I had no oscillation problems with them gone.

Tim Marcus · Post by **Tim Marcus** » 18 May 2012 7:53 pm

Haha! We all think one thing is the most important

Imagine how great it will be when you do them all!

Bill Terry · Post by **Bill Terry** » 18 May 2012 10:22 pm

Imagine how great it will be when you do them all!

Haha.. Yeah, I did get around to all of them, even the dropping resistors on the PS. Those drip-edge Twins were a great value, at that time they were a lot cheaper than a BF, and virtually identical, i.e. transformer etc. Probably should have kept that one, but I traded it for a D-8 Stringmaster.

Tony Prior · Post by **Tony Prior** » 19 May 2012 3:12 am

I think the whole BF mod thing is totally overrated and most people don't even know what it is even when they pay for it. I sometimes read on other forums where people buy a SF amp..have it BF modded before they even use it...makes no sense to me....they had no idea what they had..and then changed it anyway...

SF Twins are great amps...as are BF Twins...

My take, the biggest thing about Twins is speaker selection...these amps can be real middy or even real bright , speaker selection is imperative.

My 71 , found it and purchased it fully stock, with the Utah's it was just not alive, real dull in the mids, limited bright...I put in a pair of Fender gold label Emmy's and it came alive...night and day... A pair of Jensen C series, they can really bring a Twin home..but they are not cheap...

JBL's can be excellent as well.

This in my opinion is the only MOD that should be done to a SF Twin early on as an owner and user... When having electronic modifications performed on any amp..the user should know exactly why and what they are gaining from the mod...

I would agree with Tim above though, after using the amp for a while, perhaps the Bias circuit change would be a good consideration if any updates were in order...I have not done this to my 71, the amp offers a fine balance for guitars and Steel..

my take on the matter...

Brad Sarno · Post by **Brad Sarno** » 19 May 2012 6:16 am

One of the things that I think confuses the whole idea of blackfacing is because of some of that dreadful mess they did in the power section in '69 for a while that may have continued on into the next year or so as well. That included using 150 ohm cathode resistors on the 6L6's, adding snubber caps at the grids to the 6L6's, using 47k phase inverter tube plate resistors, etc. In these aspects, I prefer to revert to AB763 blackface with the 82k and 100k, no snubbers, grounded cathodes, etc. instead.

Then the whole ditching of the bias voltage control for a bias balance control, that's a big one when it comes to wanting to blackface it. With the ease of finding matched tubes these days, we need a bias voltage control. We always need a bias voltage control. It's stupid that CBS ever ditched that...

I'm a fan of completely ditching the master volume control on those '70s versions and using the original AB763 blackface circuit there too.

Basically, it seems like CBS mucked up a good thing in a handful of ways. The way they had it from '63 up till '68 or so seems best to my ears. I guess CBS was trying to squeeze out more loud and clean and trying to keep it stable, but they didn't really help the tone of the amp in practical use. And the master volume thing was always a joke to me. The Twin simply wasn't a good amp to try and overdrive the preamp and tame the loudness at the master volume knob. That's a failed idea for sure.

The later ultralinear thing is really awful as a guitar amp because ultralinear just doesn't seem to sound very good when driven hard, but as a clean steel amp if you don't overdrive the power section, it's pretty steel friendly, although I'd take a 85watt good old Twin over ultralinear in a heartbeat. Just a better, more musical tone.

I think that following the blackface AB763 schematic and ditching all that CBS crap is generally a great idea.

B

Steve Ahola · Post by **Steve Ahola** » 21 May 2012 12:38 am

Tony Prior wrote:I think the whole BF mod thing is totally overrated and most people don't even know what it is even when they pay for it. I sometimes read on other forums where people buy a SF amp..have it BF modded before they even use it...makes no sense to me....they had no idea what they had..and then changed it anyway...

SF Twins are great amps...as are BF Twins...

I agree with you, although I do believe that having an adjustable bias control is a big improvement for any amp as it will allow you to fine-tune the sound of the output tubes.

I think it is a good idea for an amp tech to inspect 35+ year old amps and get his recommendations on replacing the filter caps, etc.

Steve Ahola

P.S. I consider the 135W ultralinear amps to be an entirely different animal than a BF/SF Twin Reverb, along with the Twin II's and the Red Knob "Evil" Twins.

Donny Hinson · Post by **Donny Hinson** » 21 May 2012 5:31 am

When having electronic modifications performed on any amp..the user should know exactly why and what they are gaining from the mod...

My take was always that many did it just because it sounded so cool and "in"...sorta like "overclocking" CPUs. Many want to be able to have something different and non-standard so they can relate it instantly to anyone who shows a casual interest in their gear. $:\$

Bill Terry · Post by **Bill Terry** » 21 May 2012 5:12 pm

Yeah, it's kind of cool to say you've got a BF'd Twin or whatever, and as Donny says that may be why a lot of guys have it done.

But I'm old, and I do remember when those SF Twins started showing up. Guitar players in those days weren't necessarily hip to the details of what exactly changed, but a lot of them knew that something about the older Twins sounded better. Notice I said guitar players..

. The beginning of the whole BF mystique was definitely a 'tone thing'.

Todd Brown · Post by **Todd Brown** » 21 May 2012 9:59 pm

Well boys, here's what I got. I went and checked it out and I couldn't leave it! It sounded so warm and rich compared to my Session. It is a 73-74 according to the date code. It does not have the push/pull pot on the MV.

It checked out to my untrained eye. The guy I bought it off of is a Blues guitar player who bought it basically as is about 3 years ago. He had his former tech in Mass. check it out, install a new a/c chord, and 4 new 6l6's.

The speakers are my first obvious problem. The 2 THD's are 16 ohm wired parallel. That gives it 8 ohms when the TR needs 4 ohms.

So I'll either build splits or put in a baffle for a 15". Should I do that to this original cab? Seems in decent shape, I've seen alot worse! Probably shouldn't alter the original, huh?

The MV is disabled. I guess it was left in for aesthetic purposes. Reverb only on the Vibrato channel. He said he was told it was Blackfaced when he bought it. His tech in Mass. didn't tell him any different(I might be in trouble if this tech didn't notice the wrong speakers either). We'll see what you guys have to say. It's fairly quiet. All the pots are clean. Extremely loud and the reverb is super lush!

I pulled the chassis and took a look inside, but hell, I don't know what I'm looking at!

I know I see some orange caps and some other caps that look new. Spague Atoms and whatever else. Has it been converted to the AB763 circuit? That's what you guys are for!

According to what Tim Marcus said, "you can tell right away if you see ceramic caps on tube sockets or the reverb jacks", it has not been converted completely. Right? Aren't those ceramic disc's on the reverb output and in line with preamp socket #3?

Doesn't really matter to me either way, the "Blackfacing" thing. As to what Tony Prior said, I don't know which is which. I might would like a more true early SF tone. Won't know 'till you try it, right? The seller stated in his ad it had been "Blackfaced", I was just trying to get a heads up on what to look for, other than letting common sense be a guide on whether to buy or not.

So take a look and tell me what you think. For $600 I don't think I did too bad. Sounds good to me. Will it catch fire on stage next week? We'll see...Maybe I should carry the Session just in case.

Here's the pics-

Steve Ahola · Post by **Steve Ahola** » 21 May 2012 11:07 pm

Todd Brown wrote:The speakers are my first obvious problem. The 2 THD's are 16 ohm wired parallel. That gives it 8 ohms when the TR needs 4 ohms.

Most amp techs will tell you that it is usually safe to go up or down by a factor of 2 with those old BF/SF amps, like using 2 to 8 ohms for a 4 ohm output transformer, or 4 to 16 ohms for an 8 ohm tap. So if I liked how the THD speakers sounded I would leave them in, at least for awhile.
There is one big advantage with using a pair of 8 ohm speakers in a Twin Reverb: to lower the output when necessary you can pull out one pair of tubes and disconnect one of the speakers and there will be no mismatch of the load.

Looks like a real deal for $600!

Steve Ahola

Tim Marcus · Post by **Tim Marcus** » 22 May 2012 7:25 am

Yeah - its been partially done but it looks like they did the bias and power supply part. The phase inverter still has SF values but who cares - if it sounds good I would leave it be!

Tim Marcus · Post by **Tim Marcus** » 22 May 2012 7:32 am

Oh also-

Many of the silver face amps do not have a removable front baffle

If you want to mount a 15" in there you will either need a good carpenter friend, or just get a new cabinet altogether. Or go head cabinet and 15" in a separate cab. Lots of options there.

Just keep in mind that some of the SF amps are a tad wider than their black faced brethren. You may need a custom box put together by someone like Mather

12's sound good too

Todd Brown · Post by **Todd Brown** » 22 May 2012 10:25 am

Is it normal for the "normal" channel to be a bit quieter than the "vibrato" channel. With the Vibrato at 3, the normal channel has to be around 5 or 6 to match the volume.

I've always played through 15's. What are some good option for 12's in this TR for psg. Eminence Deltalite's?? What else?

Tim Marcus · Post by **Tim Marcus** » 22 May 2012 10:34 am

the vibrato channel has an extra gain stage - so yeah, it might have a bit more pop to it

I had Weber D120 Types in my SF Twin back in the day - but I can not recommend their speakers anymore. The quality has gone down significantly. Kind of a bummer.

Are you using it just for steel - or for guitar as well?

Also - you should be able to see right away if the baffle is removable. If there are screws holding it on, then you should be good to go. If not - might be time to get creative

Todd Brown · Post by **Todd Brown** » 22 May 2012 10:43 am

Yeah, it's glued in. I see no screws holding the baffle. From the front or back.

So, I'm leaning towards 12's or just doing a split cab. Don't really wanna start cutting up this cab. Or is that something I shouldn't really care about? Like I said, it's decent shape. Original pop out casters!

Just pedal steel. I don't play any guitar in a band situation.

Tim Marcus · Post by **Tim Marcus** » 22 May 2012 11:07 am

if it were me, and I was just using it for steel, I would get a new cabinet with a 15" baffle and put the original one into a closet.

Just make sure you get a cabinet that will fit the Silverface chassis. Maybe they are the same - whomever you find (I suggest Mojotone) will know what to do.

Then you can put in a SICA or a JBL and you will be in tone heaven!

And you will still have a great steel amp for a very good price

Todd Brown · Post by **Todd Brown** » 22 May 2012 12:17 pm

Thanks for your help, Tim, and everyone else!!! Much appreciated.

I'll probably go with a new cab or a split and run it with the Eminence EPS that I put in my Session.

Steve Ahola · Post by **Steve Ahola** » 22 May 2012 1:56 pm

Todd:

It would be a lot easier to build a cabinet just for the chassis- I think that the hardest part would be covering it with tolex, although you could do like Mesa Boogie and just stain the wood...

Steve Ahola

P.S. I would try rewiring the phase inverter to BF specs to see if you like it better. It's easy enough to switch it back if you don't. I suggest that only because the BF phase inverter circuit has been used successfully in so many different amps. Have fun!