Blackface mod?

[Mars-Hall]

Hello all, I have a 70 Super Reverb that I have already switched the bias "balance" to "adjust".  The amp sounds ok.  However, I like an amps natural OD when cranked.  This one sounds a little "harsh" or "raspy".  Will completeing the Blackface mod "smooth out" the OD?  Is the mod outined in the Library here?  I looked but could not find any thing other than the Bias mod.  Thanks...

[sluckey]

Which specific model Super Reverb do you have? Someone on this forum may have explicit instructions for your particular model.

The "Blackface mod" is not a single mod but several changes that have a goal of converting a later Fender amp back to the '60s AB763 model. Also the AB763 model covered several amps, ie, Deluxe, Super Reverb, Twin Reverb, Concert, Vibrolux, Vibroverb, to name a few. All these AB763 amps used a very similar schematic and layout, but there may be a few slight differences between all the AB763 amps. Mostly the differences were about iron, output tubes for different power levels, and speaker configurations.

Also a particular model amp, for example Super Reverb went through several changes thru the years. I have Super Reverb schematics for all these models (and there may be others too)...
  AA763
  AB763
  AB568
  AA1069
  AA270
  cbs 45w MstrVol
  cbs 70w MstrVol

What I'm getting at is there are so many different variations that to do a "Blackface mod" probably requires specific instructions for a given model, and all or some of those instructions may not apply to another model. I think the best thing to do would be locate the schematic/layout for the particular Super Reverb model. Compare to the AB763 model. Then make the particular/necessary changes to revert that model back to the AB763 model.

[Mars-Hall]

I'm fairly certain it the AB568 circuit.  I will confirm latter this evening.  From what I've read, there some resistor changes to the phase inverter and removing some from pin 8 of the power tubes.

[sluckey]

Take a look at this web page...
http://fenderguru.com/amps/super-reverb

Scroll way down to the section called "AB568 vs AB763". Looks like that covers most everything. Let us know if you have questions.

Lot of other good mods on that page too.

[SILVERGUN]

Nice posts sluckey 

That's a great link that will answer lots of questions in one place....very cool

[Mars-Hall]

Thank you!  It is the AB568 circuit.  As it turns out, I did more "blackfacing" than I remember.  The only thing left to do is change the 2 PI resistors.  Will this yield my desired results?  What affect on tone should I expect?  Thanks again!

[sluckey]

The only thing left to do is change the 2 PI resistors.  Will this yield my desired results?

I doubt it. I think you should consider different speakers. My hearing is shot, but there are others here that can advise.

[bigsbybender]

Is that a 5U4 rectifier model or a GZ34/5AR4?   

The GZ34/5AR4 is proper for the Blackface, but eventually the cheaper/more common (back then) 5U4 found itself into the Super Reverb.  Rumor has it that they bumped up the voltage in the transformer secondaries to compensate for the big voltage drop of 5U4... I really haven't noticed it much though.


j.

[Mars-Hall]

I think you should consider different speakers. My hearing is shot, but there are others here that can advise.

I have Jensen reissue speakers, pulled from a reissue Super Reverb.  I have heard they can be harsh until they break in.  The amount of play time before I purchased them is unknown but I doubt much.  This person sold me the cabinet with speakers, as he had his chassis in a head box.  Swapping speakers is not a viable option, at this point. 

Could the amp benefit from a better tube choice.  When I bought this amp it was a basket case, so I didn't afford expensive tubes, not knowing exactly what might happen.  However, the amp has proven itself reliable.  With Russian STR 440 6L6GC's in it now, a tube swap would be a more economical upgrade.  How about a set of JAN 6L6WGB's, would they get me closer?

[Mars-Hall]

Is that a 5U4 rectifier model or a GZ34/5AR4?   

The GZ34/5AR4 is proper for the Blackface, but eventually the cheaper/more common (back then) 5U4 found itself into the Super Reverb.  Rumor has it that they bumped up the voltage in the transformer secondaries to compensate for the big voltage drop of 5U4... I really haven't noticed it much though.


j.

The amp does have a GZ/34, also shown on the tube chart, as well.

[bigsbybender]

The amp does have a GZ/34, also shown on the tube chart, as well.

Ok good.  It could have been an issue tonally if you were getting 40-50 more volts B+, if it were a 5U4 model with GZ34 in it. I end up blackfacing a lot of Silverface amps... but like Steve said before, some you have to go about differently. I remember doing a very late Bassman 50 (probably 1977 model) and tried to take it to AA864 Bassman  by changing the PI resistors, bias circuit and Negative Feedback loop...  It was horrible, by then the changes to the Bassman were so many that an AA864 PI and power section didn't work with it.   

Yours is a very early Silverface, and is very near BF specs. I know speakers cost many times more than a handful of resistors... but I don't see much more you can do circuit-wise to get more tonal changes, without radical mods.

Super is should have a big bright sound. If you listen to Rev. Horton Heat for example, he uses BF Super Reverb overdriven as his main tone, compare yours to clips of his.


j.

[SILVERGUN]

The only thing left to do is change the 2 PI resistors.  Will this yield my desired results?  What affect on tone should I expect?

What value resistors do you believe are in there now? (AB568 stock should be 47K+47K)....(AB763= 100K+100K)

If you have the stock AB568 values and you change them to the AB763 values, you will be slightly increasing gain through your 12AT7 phase inverter, which will result in a little more clipping through that stage,,,,which you may or may not like

If the amp sounds "harsh or raspy" cranked now, you are probably hearing some PI clipping and may not want to increase the gain there,,, because you might wind up with more of what you don't like about it...

A quick test would be to pop a 12AX7 in the PI, and it will either be an improvement to your ears, or you won't like the increased clipping, and you'll know you want to go in the other direction.....
This is all very fresh to me because I have an AB763 laid out on an experimental platform,,,and I've been running through every possible value in that spot,,,,because I was surprised at the amount of clipping in the stock circuit at higher volumes (but, I'm trying to build a super-clean amp, so any clipping is bad in my design)

Another tube to try in the PI would be a 12BZ7.....there is some more info on the subject here:
http://www.el34world.com/Forum/index.php?topic=14280

[ac427v]

My new blackface Fender clones always sound harsh or raspy at volume. My ears prefer the plate voltages on the preamp tubes to be at or below original specs. 180 volts sound really good so I adjust the power supply dropping resistors to get my sound. I also like to use 56k plate resistors on the phase inverter 12AT7. Happy tweaking!
Craig

[Ed_Chambley]

Best sounding SR I have is a 73 with the Circuit converted to Ab763, added dwell.  It has Weber speakers, 2 alnico 20 watts on top and 2 ceramic 30 watt on the bottom, no dope.  12AX7 in the PI.  Tube lineup are all RCA in the preamp except for the Reverb driver which is the original JAN 12AT7.

I removed the NFB, but it can be switchable if you wish.  This was the biggest change in how the breakup sounds.  Power Tubes are =C= since it is one of my go to amps and I wanted to get something I could get at a reasonable price.  I do have some RCA 6l6gc Blackplates I have tried, but not much difference.

I did add a 1 wire reverb, but this just adds reverb to the normal channel.  Basically I just put it together with the tubes I wanted to use and tweaked it to sound like I wanted.  It has Mallory coupling and bypass and Sprague filters with each one being a little higher than stock, but not much.

I have 3 other SR's which are Ab763 and using the speakers in the 73 cabinet, it is a great improvement.  Not that the others sound bad with Jensens, but I do not care for CTS.

[Mars-Hall]

Read through the fender guru site.  There's some very good information there.  The plan is to change my PI resistors to stock AB763 values and drop in the 6L6WGB's.  Depending on the results, will decide if I'm saving up for some new Webers.  

Also, plan trying a 12AU7 for the reverb driver.

[SILVERGUN]

Good luck M-H,
Please stop back and tell us how that works out for you.....

 

[Mars-Hall]

I have the PI resistors installed completing my blackface conversion.  6L6WGB tubes installed and biased.  Much, much happier with the tone.  It really smoothed out the OD when cranked.  Thinking this is more due to the tubes and less to do with the resistor swaps.

As for the speaker swap, I'm happy with the amp now, leaving well enough alone.  I felt all along the speakers were fine. The only bad reviews I've heard about these RI Jensens were they are "icepicky" until broken in.  This wasn't the case for me.

I want to thank everyone on this board for what is my "go to" on information about projects.  I feel I get facts not opinions, the average member here seems to have more knowledge than "gurus" on other boards I've visited.  I don't even bother with them anymore.  This is also why I buy the bulk of my parts from Hoffman, I want to support what goes on here.  Thanks again!

[Mars-Hall]

Just out of curiosity, what input voltage does your P/T ask for?  and what is the voltage you are feeding the amp?  What PI tube are you using?

The JAN/Philips 6L6WGB's data sheet show 400v plates, rated at 26 watts.  There is some debate about biasing these tubes as if they were 30 watts.  I played it safe and went by the 26 watts.  These are robust tubes and many say you can run up to 470v on the plates.  My SR comes in at 424 @ 43ma bias.  Thats running them at 70% plate dissipation on the hottest tube.    This set has a 7-8ma mismatch, so the other obviously comes in quite a bit lower.  These are oddballs I had laying around.  If I like these, I have a matched set I will install later.  The real test will be this weekend at the gig.

[Mars-Hall]

The amp sounded great this weekend!  Played 2 sets and the amp yielded smooth, creamy tones.  Really delighted...  I would have to think it had more to do with the tubes than the remaining PI resistor swap.  Either way, I love it!

[SILVERGUN]

The amp sounded great this weekend!  Played 2 sets and the amp yielded smooth, creamy tones.  Really delighted...  I would have to think it had more to do with the tubes than the remaining PI resistor swap.  Either way, I love it!

OK, cool,,,write that down:
For smooth, creamy tones,,,go with a 7-8mA mismatch   

SO, just for the record,,,12AT7 PI, with 100K plate resistors?

Congrats, and thanks for letting us know.....my amp always sounds better when I work on it 

[dude]

I think you should consider different speakers. My hearing is shot, but there are others here that can advise.

I have Jensen reissue speakers, pulled from a reissue Super Reverb.  I have heard they can be harsh until they break in.  The amount of play time before I purchased them is unknown but I doubt much.  This person sold me the cabinet with speakers, as he had his chassis in a head box.  Swapping speakers is not a viable option, at this point. 

Could the amp benefit from a better tube choice.  When I bought this amp it was a basket case, so I didn't afford expensive tubes, not knowing exactly what might happen.  However, the amp has proven itself reliable.  With Russian STR 440 6L6GC's in it now, a tube swap would be a more economical upgrade.  How about a set of JAN 6L6WGB's, would they get me closer?

I have four reissue Jensen's, made in Italy. I bought them years ago when when they first came out. Yes, they are harsh till "well broken in" then very tone-full. Back then I talked to Ted Weber about the harshness, he told me a good cheap way to break them in fast (I think this is the way he did it). They're only 25 watts each, so get a Radio Shack Transformer # SEC 6.3-0-6.3  3V  3A  Don't know the model number but they didn't carry it in their stores, it's on line for $12 but I bought it through a RS store and had it sent to me, about three days. They even paid the shipping. You'll find the item number on there site, look up the spec's here. You can do two speakers at a time a 120 V PRI 60HZ and two sec. 6.3vac. Use two 1/4" jacks and just plug in two speakers at a time. It will hum and move the cone breaking them in fast but no too hard. Ted said run them for 24 hours at a time, rest them and do that for a week on and off. They will hum noisy but not too bad. I have a separate shop detached from my house so no problem for me but in your basemen in a closet or something and you shouldn't hear the hum. I just ran them straight for 72 hours, three days. The tone was great, made them sound like vintage jensens. I had them in an Allen old flame (his copy of a Super R). Well worth the $12. I've used this transformer on several new speakers and it sure opens them up without any cone damage. Some people put acetone on the cone too and do it but I'm not a fan of that, i think it softens the cone to much for premature wear.

If your interested I'll send you the RD part number, it's not on the Transformer.

Works well, perhaps someone else here might chime in about this.

al 

[Mars-Hall]

The amp sounded great this weekend!  Played 2 sets and the amp yielded smooth, creamy tones.  Really delighted...  I would have to think it had more to do with the tubes than the remaining PI resistor swap.  Either way, I love it!

OK, cool,,,write that down:
For smooth, creamy tones,,,go with a 7-8mA mismatch   

SO, just for the record,,,12AT7 PI, with 100K plate resistors?

Congrats, and thanks for letting us know.....my amp always sounds better when I work on it 

These tubes certainly sound better than the matched STR 440's that were in it.  The harsh grating to tones are gone.  Likely, a matched pair of WGB's can sound even better, but for what it is, I'm happy.  As for the PI, I installed the BF spec of 82k and 100k.

[Mars-Hall]

I think you should consider different speakers. My hearing is shot, but there are others here that can advise.

I have Jensen reissue speakers, pulled from a reissue Super Reverb.  I have heard they can be harsh until they break in.  The amount of play time before I purchased them is unknown but I doubt much.  This person sold me the cabinet with speakers, as he had his chassis in a head box.  Swapping speakers is not a viable option, at this point. 

Could the amp benefit from a better tube choice.  When I bought this amp it was a basket case, so I didn't afford expensive tubes, not knowing exactly what might happen.  However, the amp has proven itself reliable.  With Russian STR 440 6L6GC's in it now, a tube swap would be a more economical upgrade.  How about a set of JAN 6L6WGB's, would they get me closer?

I have four reissue Jensen's, made in Italy. I bought them years ago when when they first came out. Yes, they are harsh till "well broken in" then very tone-full. Back then I talked to Ted Weber about the harshness, he told me a good cheap way to break them in fast (I think this is the way he did it). They're only 25 watts each, so get a Radio Shack Transformer # SEC 6.3-0-6.3  3V  3A  Don't know the model number but they didn't carry it in their stores, it's on line for $12 but I bought it through a RS store and had it sent to me, about three days. They even paid the shipping. You'll find the item number on there site, look up the spec's here. You can do two speakers at a time a 120 V PRI 60HZ and two sec. 6.3vac. Use two 1/4" jacks and just plug in two speakers at a time. It will hum and move the cone breaking them in fast but no too hard. Ted said run them for 24 hours at a time, rest them and do that for a week on and off. They will hum noisy but not too bad. I have a separate shop detached from my house so no problem for me but in your basemen in a closet or something and you shouldn't hear the hum. I just ran them straight for 72 hours, three days. The tone was great, made them sound like vintage jensens. I had them in an Allen old flame (his copy of a Super R). Well worth the $12. I've used this transformer on several new speakers and it sure opens them up without any cone damage. Some people put acetone on the cone too and do it but I'm not a fan of that, i think it softens the cone to much for premature wear.

If your interested I'll send you the RD part number, it's not on the Transformer.

Works well, perhaps someone else here might chime in about this.

al 

Thanks for the info!  I really like the tone so much, I'm leaving well enough alone.  Being used when I bought them, not sure how much the speakers were broken in.  I will certainly break them in some more the old fashioned way...  However, this is good to know for future projects.  Thanks for posting.

[SILVERGUN]

I hope you know I was kidding.....playing up our obsession with matching,,,,or "tone" in general

Is the PI an AT7...... did you ever try the AX7,, and if yes, what were your thoughts?

Is the Gibson in your avatar pic your main guitar used through this amp?.......I ask because single coils sound best to me in this circuit, and just wondering if you've experimented?

[Mars-Hall]

I hope you know I was kidding.....playing up our obsession with matching,,,,or "tone" in general

Is the PI an AT7...... did you ever try the AX7,, and if yes, what were your thoughts?

Is the Gibson in your avatar pic your main guitar used through this amp?.......I ask because single coils sound best to me in this circuit, and just wondering if you've experimented?

Thanks for the confirmation, sarcasm isn't always picked up on, in written form. 

Yes, I play the 345 and or a LP through this amp.  I use to play Strats through my 66 SR exclusively and still have several.  But it seems since SRV came along everybody and their brother is playing a Strat!  I like the 345 best, with the varitone engaged and can get some really funky tones going.

As for the PI, I have a 12AT7.  Have not experimented with a 12AX7.  Would it be more gain and or volume?  The amp is already so loud, I need an attenuator on most occasions.  Thanks Again!

[Ed_Chambley]

I like humbuckers using s SR myself.  Glad you got it like you wanted.  They really are great sounding amps, it is just a shame we don't get the opportunity to play the on 8 much.

Great deal, nothing like having a cool tone.  Sort of make you groove as well.

KEWL.

[Mars-Hall]

I like humbuckers using s SR myself.  Glad you got it like you wanted.  They really are great sounding amps, it is just a shame we don't get the opportunity to play the on 8 much.

Great deal, nothing like having a cool tone.  Sort of make you groove as well.

KEWL.

Yeah, it's why I use an attenuator to get those tubes humming!  Great tone inspires great playing...

[SILVERGUN]

As for the PI, I have a 12AT7.  Have not experimented with a 12AX7.  Would it be more gain and or volume?  The amp is already so loud, I need an attenuator on most occasions.

It will change the way the PI clips your signal......no real significant perceived change in volume, but could be icing on the cake for you, depending on what you're after.
If you wanted to continue to tweak it,,,,that area willl have a great affect...
By simply replacing the AT7 with an AX7 (and you can try that without damaging anything) you will notice a slightly different feel to the amp (and drive)
And I'm not suggesting one way or the other,,,just presenting the option  
You could alter bias and NFB for even more fun later,,,but if you're happy with it already, then you're probably "close enough for rock and roll"

Here's more brain food on the subject:
http://www.aikenamps.com/LongTailPair.htm

If you're not that technical about it, then you could just 'plug and play' an AX7 and tell us what you think.....
I think Ed would agree, it's worth a try  

[SILVERGUN]

OK, so I went out to the bench and tried it,,,and I was wrong about the change in volume...it was noticeable,,a slight boost
The amp has a more classic/balanced drive with the AT7 in there....and then with the AX7 it was more pushed/aggressive

I also tried increasing the NFB resistor value and right around 1.5K with the AX7 in there was a nice "sweetspot" in gain (but a little more volume)
The amp was a little easier to play and sustain was improved....also a tad brighter, which may work well with your attenuator 

Happy tweaking,,,, or just leave it and be happy the way it is....it's already better than it was
If you do wind up switching to an AX7 or just replacing the AT7, look for one with matched triodes (don't ask "how closely matched?"  )

I'd say there is a very noticeable difference in the way those 2 different tubes respond in that position
Better or worse is for you to decide 

[Ed_Chambley]

As for the PI, I have a 12AT7.  Have not experimented with a 12AX7.  Would it be more gain and or volume?  The amp is already so loud, I need an attenuator on most occasions.

It will change the way the PI clips your signal......no real significant perceived change in volume, but could be icing on the cake for you, depending on what you're after.
If you wanted to continue to tweak it,,,,that area willl have a great affect...
By simply replacing the AT7 with an AX7 (and you can try that without damaging anything) you will notice a slightly different feel to the amp (and drive)
And I'm not suggesting one way or the other,,,just presenting the option  
You could alter bias and NFB for even more fun later,,,but if you're happy with it already, then you're probably "close enough for rock and roll"

Here's more brain food on the subject:
http://www.aikenamps.com/LongTailPair.htm

If you're not that technical about it, then you could just 'plug and play' an AX7 and tell us what you think.....
I think Ed would agree, it's worth a try  

You dog gone right I would agree.  There are soooooooooooooooo many things you can do to a AB763 Super Reverb.  I have always felt it is the best platform for anything you can imagine.  The reason is the amp sounds great just as is and you can do anything with it to tweak it to your preference.  If I has only 10 minutes to tweak, I would use a nicely balanced 12AX7 in the PI, remove the NFB (simplest thing to add touch response).  This would allow to dial that attenuator back a little.  If I had a little more time I would put a switch pot on the tremolo intensity to turn it off.

If I had even more time I would look at V1a and b and ask myself if I would rather setup a marshall there or use the tube for overdrive.  I could not decide, so I added a tube and did both.  They are so versatile as it is the only amp I can get tones I am happy with when playing different styles.  It will do Jazz, Country, Blues and if you carefully choose slope and tonestack values it will grunt like a pig and give up the Classic Rock vibe, it will do surf and sound great playing Beatles.

I would post a photo of the inside of the chassis, but it would be dangerous.  All the fender lovers would have a cow.  All the mods can be returned to stock, hell I even have the original CTS (stands for Cancel Tone Source).  It may take me 4 or 5 hours to do it, but I can.  It has a LarMar Master and a VVR which is out of the circuit right now.  Just have never warmed up to a vvr.  That ground switch will hold a nice push pull pot.  The rca connectors for the tremolo hold 2 mini pots, Dwell and a Marshall style master switching pot.  Still has Tremolo as well, now it resides in holes on a replacement Dog House cover.  Soon I plan to move the Reverb there as well.  2 more holes.  Sounds like time for a little relay action.  Oh, it has a effects loop as well which replaced both speaker jacks.

I have never drilled the chassis and I still have the original Gibbs tank in it.  But remember, it is the amp I began learning on before the internet.  I have learned more here in a year than the 35 previous years of owning the amp.  Coolest thing is I have done all this stuff, built many fine amps and successfully designed a few and have never considered which way the excited electron flows.  I am probably not intelligent enough to understand it anyway.

Since I have 3 other Supers, 2 are BFace SR and another is a Drip edge, and 2 5F4's which is a very cool circuit a lot of people overlook.  I have never heard any guitar plugged into one that did not sound good.  This is not true of any other amp I a familiar.  Even at bedroom volume they still sound full.  God bless Thomas Edison and Leo Fender.

Sorry if i rambled.  I guess you can tell I am not very fond of the Super Reverb.